Endometriosis: clinical features, MR imaging findings and pathologic correlation
Insights into Imaging
Endometriosis: clinical features, MR imaging findings and pathologic correlation
Pietro Valerio Foti 0 1 2
Renato Farina 0 1 2
Stefano Palmucci 0 1 2
Ilenia Anna Agata Vizzini 0 1 2
Norma Libertini 0 1 2
Maria Coronella 0 1 2
Saveria Spadola 0 1 2
Rosario Caltabiano 0 1 2
Marco Iraci 0 1 2
Antonio Basile 0 1 2
Pietro Milone 0 1 2
Antonio Cianci 0 1 2
Giovanni Carlo Ettorre 0 1 2
0 Department of General Surgery and Medical-Surgical Specialties - Institute of Obstetrics and Ginecology, University of Catania , Catania , Italy
1 Department G.F. Ingrassia - Institute of Pathology, University of Catania , Catania , Italy
2 Radiodiagnostic and Radiotherapy Unit, University Hospital BPoliclinico-Vittorio Emanuele
3 Pietro Valerio Foti
4 , Via Santa Sofia 78, 95123 Catania , Italy
Objective We illustrate the magnetic resonance imaging (MRI) features of endometriosis. Background Endometriosis is a chronic gynaecological condition affecting women of reproductive age and may cause pelvic pain and infertility. It is characterized by the growth of functional ectopic endometrial glands and stroma outside the uterus and includes three different manifestations: ovarian endometriomas, peritoneal implants, deep pelvic endometriosis. The primary locations are in the pelvis; extrapelvic endometriosis may rarely occur. Diagnosis requires a combination of clinical history, invasive and non-invasive techniques. The definitive diagnosis is based on laparoscopy with histological confirmation. Diagnostic imaging is necessary for treatment planning. MRI is as a second-line technique after ultrasound. The MRI appearance of endometriotic lesions is variable and depends on the quantity and age of haemorrhage, the amount of endometrial cells, stroma, smooth muscle proliferation and fibrosis. The purpose of surgery is to achieve complete resection of all endometriotic lesions in the same operation. Conclusion Owing to the possibility to perform a complete assessment of all pelvic compartments at one time, MRI represents the best imaging technique for preoperative staging of endometriosis, in order to choose the more appropriate surgical approach and to plan a multidisciplinary team work. Teaching Points Endometriosis includes ovarian endometriomas, peritoneal implants and deep pelvic endometriosis. MRI is a second-line imaging technique after US. Deep pelvic endometriosis is associated with chronic pelvic pain and infertility. Endometriosis is characterized by considerable diagnostic delay. MRI is the best imaging technique for preoperative staging of endometriosis.
Endometriosis; Magnetic resonance imaging; Endometrioma; Deep infiltrating endometriosis; Pelvis; Pelvic pain
Endometriosis is a chronic multifocal gynecologic disease that
affects women of reproductive age and may cause pelvic pain
and infertility. The aetiology of endometriosis is unknown ;
the pathogenesis is complex, multifactorial and still debated.
The disease is characterized by the growth of functional
ectopic endometrial glands and stroma outside the uterus [1–3].
Its prevalence is of approximately 10% in women of
reproductive age, 20–50% in women with infertility and nearly
90% in women with chronic pelvic pain [1, 3]. It is thought
that the disease affects about 176 million women of
reproductive age worldwide , with a peak of incidence
between 24 and 29 years .
The disease includes three different manifestations, namely
ovarian endometriomas, superficial peritoneal implants, and
deep pelvic endometriosis. The latter is defined as
endometriotic lesions penetrating into the retroperitoneal
space or the wall of the pelvic organs to a depth of at least
5 mm; it has an estimated prevalence of 1% among women of
reproductive age  and affects up to 20% of women with
Although the definitive diagnosis is based on laparoscopy
or surgery with histological verification of endometrial glands
and/or stroma, imaging is necessary for treatment planning.
Among imaging modalities, magnetic resonance imaging
(MRI) is often used as a problem-solving additional
examination in complex cases and should be considered as a
secondline technique after ultrasound (US) . Currently, MRI is
considered the best imaging technique for mapping
endometriosis, since it provides a more reliable map of deep
infiltrating endometriosis than physical examination and transvaginal
ultrasound (TVUS) .
In this article we review clinical manifestations and
histological features of endometriosis. We describe MR imaging
appearances of the different manifestations of pelvic
endometriosis and some extrapelvic locations, using examples, many
of which pathologically proven, from our institution. Our MR
protocol is also included.
Locations and clinical features
The primary locations of endometriosis are in the pelvis: on
the ovaries, uterus, fallopian tubes, uterosacral ligaments
(USL), broad ligaments, round ligaments, cul-de-sac,
rectosigmoid colon, bladder, ureters, and rectovaginal septum
(RVS) (Fig. 1) . Endometriotic locations with
corresponding prevalence are listed in Table 1 [
3, 10, 11
Women with peritoneal endometriosis can be
asymptomatic; on the other hand deep pelvic endometriosis is frequently
associated with pelvic pain, dysmenorrhea, dyspareunia,
urinary tract symptoms, and infertility . Pelvic pain may be
chronic rather than cyclic.
The enriched sensory innervation of endometriotic lesions
may play a key role in hyperalgesia and pain generation. In
deep infiltrating lesions the nerve fibre density is higher than
in peritoneal and ovarian ones; in particular, deep infiltrating
lesions involving the bowel are the most densely innervated of
all lesion types, which correlates with the high incidence of
patient-reported pain . According to Koninckx the
intensity of the pain is proportional to the depth to which the lesions
penetrate ; nevertheless, in many cases the extent of
endometriotic lesions does not correlate with the severity of
Clinically, endometriosis should be considered in any
woman of reproductive age with pelvic pain or infertility.
However, since symptoms are often nonspecific, the disease
may be misdiagnosed as other clinical conditions
characterized by chronic pelvic pain (irritable bowel syndrome,
interstitial cystitis/painful bladder syndrome, recurrent
cystitisoveractive bladder), thus leading to inadequate treatment and
considerable diagnostic delay. The interval between the onset
of the first symptoms and the clinical diagnosis of
endometriosis may be of approximately 7–10 years .
Clinical manifestations depend on the anatomic locations
of the disease.
Bladder: dysuria, gross hematuria during menses, irritative
voiding symptoms, urgency, frequent urination, urinary
storage symptoms, tenesmus, burning sensation, suprapubic
discomfort and pain, urinary incontinence [2, 3, 15].
Ureters: dysmenorrhea, dyspareunia, urinary symptoms,
hydronephrosis, flank pain, decline of renal function [2, 3].
Round ligaments: painful, palpable inguinal mass
(extrapelvic portion of the ligaments); nonspecific pelvic pain
(intra-pelvic portion) .
Retrocervical region and uterosacral ligaments: severe
and painful symptoms, dyspareunia .
Vagina: dysmenorrhea, dyspareunia, postcoital spotting,
prolonged menstruation not responding to medical
therapy leading to anaemia [3, 16].
Rectosigmoid colon: cyclic pain during defecation,
dyschezia, cyclic hematochezia, bloating, constipation,
bowel cramping, catamenial diarrhoea, pencil-like stools,
bowel obstruction [2, 3, 12, 17].
When unusual locations outside the pelvis occur, the pain
may be site specific.
Thoracic-diaphragmatic endometriosis: chest pain
(diffuse or basithoracic) with right-sided predominance,
scapular or cervical pain associated with menses, sometimes
radiating to the arm, pneumothorax, dyspnea, hemoptysis
Sciatic nerve: cyclic sciatica, back pain, gluteal pain
radiating to the dorsal thigh and lateral lower leg, positive
Lasègue’s sign, sensory loss, reflex alterations, muscle
weakness, paresis [2, 21–23].
Our MR protocol
The MR imaging protocol we use at our institution to study
patients with pelvic endometriosis is summarized in Table 2.
MR imaging is performed with a closed-configuration
superconducting 1.5-T system (Signa HDxT; GE Healthcare,
Fig. 1 Drawings of the female
pelvis in the (a) ventral and (b)
lateral views illustrate the primary
locations of endometriotic lesions
Milwaukee, WI, USA), by using an eight-channel
high-resolution surface phased-array torso coil with array spatial
sensitivity technique (ASSET) parallel acquisition.
In preparation for imaging, it is recommended that patients
fast (4–6 h) before the examination. Bowel preparation
includes an enema administered approximately 2–3 h before
the examination. The study should not be conducted during
the menstrual cycle.
MR imaging is performed with moderate repletion of the
patient’s bladder, since an overfilled bladder may cause
detrusor contractions and may obliterate the adjacent recesses
thus compromising the identification of small parietal nodules
[1, 2]. On the other hand, an empty bladder prevents optimal
visualization of the ureters.
MR imaging is performed with the patient lying in the
supine position (entry position feet first). In patients who show
a dilatation of the excretory system, the urographic phase is
acquired in the prone position. In claustrophobic patients,
prone position may reduce anxiety and improve exam
When the clinical evaluation suggests a rectosigmoid
endometriosis, rectal opacification is performed before the
examination. Retrograde distension of the rectum and the
sigmoid colon is obtained inside the gantry with a rectal enema
of 750 mL of saline solution introduced through a Nelaton
catheter (20 Ch, 6.67 mm × 360 mm). Bowel cleansing is
performed through oral administration of a polyethylene
glycol solution (1000 mL) the day before the study. In these
patients the intravenous administration of an antispasmodic
agent, scopolamine-N-butyl bromide (Buscopan® 20 mg;
Boehringer Ingelheim, Milano, Italy) just before image
acquisition is mandatory to reduce motion artefacts caused by
bowel peristalsis. Even if rectal opacification is not strictly
necessary to detect endometriotic lesions of the intestinal
wall, rectal distension may be useful to evaluate the degree
of bowel stenosis.
Primary locations of endometriosis, their prevalence in patients with endometriosis, clinical features and differential diagnosis [
3, 10, 11
dysmenorrhea, dyspareunia, postcoital spotting
dyschezia, cyclic pain, rectal bleeding
MR differential diagnosis
urachal remnant, epithelial and mesenchymal
obstruction by cervical cancer
dermoids, hemorrhagic cysts, endometrioid
and clear cell tumours
cervical and vaginal carcinoma
colorectal cancer, metastatic implants
Section thickness (mm)
Interslice gap (mm)
Field of view (cm)
N. of averages
N. of images
longitudinal axis of the uterus identified on the previous axial
T2weighted SSFSE sequence. Oblique coronal and oblique axial
T2weighted FRFSE sequences are oriented respectively parallel or
perpendicular to the longitudinal axis of the uterus
Axial T2 W
320 × 288
Right to left
Sagittal T2 W
Sagittal, oblique coronal and oblique axial T1-weighted 3D gradient-echo liver acquisition with volume acceleration (LAVA) sequences with fat
suppression are acquired before and after intravenous administration of paramagnetic contrast agent (0.1 mmol/kg at a flow rate of 2 mL/s, followed
by 20 mL of saline solution at the same flow rate); in particular, the sagittal sequence is acquired at 60 and 120 s after contrast administration. About 10
min after contrast administration, T1-weighted 3D gradient-echo LAVA sequences are acquired in the sagittal, coronal and axial planes, to obtain an
T2-weighted FRFSE, T2* and DW sequences are acquired with patient breathing freely, T1-weighted 3D gradient-echo LAVA sequences are acquired in
breath hold. T2* and DW sequences are not routinely performed and represents optional sequences
T2 W T2-weighted, T1 W T1-weighted, SSFSE single-shot fast spin-echo, FRFSE fast relaxation fast spin-echo, DWI diffusion-weighted imaging, SE
spin-echo, EPI echoplanar imaging, GRE gradient-echo, LAVA liver acquisition with volume acceleration
The state-of-the-art MR imaging protocol for the diagnosis
of endometriosis includes T2- and fat suppressed T1-weighted
T2-weighted sequences without fat-suppression are the best
sequences for detecting pelvic endometriosis , in particular
for the evaluation of fibrotic lesions .
Fat-suppressed T1-weighted 3D gradient-echo LAVA
sequence. This pulse sequence improves the sensitivity of
MR imaging in the detection of small lesions. It is the most
sensitive for the detection of bloody foci and peritoneal
endometriosis, since fat suppression narrows the dynamic signal
range, thus accentuating the differences in tissue signal. It also
increases MRI specificity, since fat-containing lesions such as
dermoids are ruled out from the differential diagnosis of
endometriomas . LAVA is a fast MR imaging sequence
(acquisition time about 22 s), thus, when possible (cooperating
patients), acquisition in the three spatial planes allows
achieving better anatomical localization of small peritoneal implants,
without prolonging too much the examination time.
Contrast-enhanced fat-suppressed T1-weighted 3D
gradient-echo LAVA sequence is useful in the following
detection of enhancing mural nodules within adnexal
masses, when atypical features on US or T2-weighted
MR sequences suggest potential malignancy ;
in our experience the major benefit of intravenous
gadolinium is ureter visualization. The anatomical
relationship between the ureters and endometrial cysts or
implants is important for the surgeon even when
endometriotic lesions do not involve directly the
ureters (Fig. 2). Indeed, because of their position from the
lateral edge of the cervix, the ureters are particularly
v u l n e r a b l e t o d e t a c h m e n t o r l i g a t i o n d u r i n g
gynaecological surgery. Injury to the ureters is the most
common urologic complication of pelvic surgery, with
an incidence that ranges from 1% to 10%, most cases
related to gynecologic procedures .
Some optional sequences, such as diffusion-weighted and
susceptibility-weighted, may be acquired in selected cases
according to the authors’ experience.
T2*-weighted sequences depict magnetic susceptibility
effects as signal voids . Because of its sensitivity to
Fig. 2 Ureter visualization with
intravenous gadolinium and
variability of the ureteral course in
two different patients with
27-yearold woman (a, b). (a) Axial
T1-weighted image (acquired
about 10 min after contrast
administration) and (b)
corresponding coronal MIP
image. The right ureter (white
arrows) courses along the lateral
margin of the right endometrial
cyst (white arrowhead) and the
uterus (white *), the left ureter
(white arrows) courses along the
posterior margin of the left
arrowheads). 35-year-old woman
(b, c). (c) Axial contrast-enhanced
image (acquired about 10 min
after contrast administration) and
(d) corresponding coronal MIP
image. The right ureter (white
arrows) courses medially to the
omolateral endometrial cyst
(white arrowheads), the left ureter
(white arrows) courses laterally to
the omolateral endometrioma
(white arrowheads). Preoperative
knowledge of ureteral course is
important in order to prevent
iatrogenic injuries to the ureters
hemosiderin, this pulse sequence is useful in the detection of
old hemorrhagic content of endometriomas and endometriotic
implants. Nevertheless, because of the susceptibility artefacts
caused by intestinal gas, it is not routinely used in the standard
MR protocol and represents an optional sequence.
The potential role of diffusion-weighted sequences is
described from time to time in the specific subsections of BMR
Types of endometriotic lesions: MR imaging appearance with pathologic correlation
The main different types of endometriotic lesions are as
endometrial ovarian cysts (endometriomas);
small superficial peritoneal implants;
deep infiltrating endometriosis—solid deep lesions
involving round ligaments, parametrium, retrocervical region,
deep infiltrating endometriosis—visceral solid
endometriosis involving the bladder and rectal wall.
In order to understand signal intensity features of
endometriotic lesions is mandatory to correlate MR imaging
findings with histologic appearance. Pathologic appearance
of endometriosis depends on the duration of the disease and
depth of penetration of the lesions . The ectopic
endometrium responds to hormonal stimulation with cyclic
haemorrhage that induce an inflammatory response and fibrous
reaction; therefore, at histologic examination endometriotic
lesions are characterized by endometrial glands and stroma
with various amounts of inflammation and fibrosis. At MR
imaging the signal intensity of endometriotic lesions is a
function of the quantity and age of the haemorrhage on the
one hand and the proportion of endometrial cells and stroma
on the other .
Endometrial ovarian cysts (endometriomas) are discussed
in the specific section.
Small superficial peritoneal implants (<1 cm in
diameter) are the first grossly recognizable lesions on the surface
of pelvic organs or pelvic peritoneum. The lesions have a
micronodular or microcystic appearance; however, cysts
do not enlarge except in the ovary. Only pigmented lesions
can be detected at non-contrast-enhanced MR imaging
because of the presence of haemorrhage . At MR imaging
these small implants manifest as multiple round (cystic or
nodular) lesions homogeneously hyperintense on
fatsuppressed T1-weighted images, due to old hemorrhagic
content, regardless of their signal intensity on
T2weighted images .
Involvement of peritoneal reflections over the cul-de-sac
and the uterus may also manifest on contrast-enhanced
fatsaturated T1-weighted images as diffuse peritoneal
enhancement secondary to the inflammatory reaction induced by
endometrial implants .
Over time a fibrotic reaction may occur, thus leading to
adhesions formation between pelvic structures .
Adhesions represent a common complication of
endometriosis. Histologically, they are seen as bands of dense
connective tissue mainly composed of type I collagen and
poor cellular component represented by fibroblasts and
macrophages. At MR imaging, especially on T2-weighted
images, retractile adhesions may be observed as spiculated
hypointense peritoneal strands arranged in confluent
angles (Figs. 3 and 4). Tethering of pelvic structures and loss
of the corresponding cleavage planes, without appreciable
nodular lesions, may be another imaging finding
suggestive of adhesions . Extensive adhesions may distort
pelvic anatomy, compartmentalize the pelvis and obliterate
Douglas pouch. Posterior displacement of uterus and
ovaries, angulation of rectosigmoid colon and bowel loops,
elevation of the posterior vaginal fornix, loculated fluid
collections, and a hydrosalpinx may be indirect signs of
adhesions . Free fluid in the pelvis on Banti-declive
position^ rather than in the cul-the-sac may be another
indirect sign of adhesions (Fig. 5).
In deep infiltrating endometriosis endometrial glands and
stroma infiltrate the peritoneum and then the adjacent tissues
and induce smooth muscle proliferation and fibrous reaction,
thus causing the formation of solid nodules.
In visceral solid endometriosis, implants adhere to the
serosal surface of the bladder or intestinal wall and may invade
the underlying muscular layers, inducing smooth muscle
proliferation and fibrosis, and eventually the submucosa.
At MR imaging both fibrous tissue and smooth muscle
show intermediate signal intensity on T1-weighted images
and low signal intensity on T2-weighted images. Therefore,
on T2-weighted images, solid endometriotic lesions appear as
hypointense nodular structures with irregular or stellate
margins due to fibrous tissue and smooth muscle proliferation. In
certain cases, deep endometriotic lesions may also appear as
irregular and hypointense soft-tissue nodular thickening on
T2-weighted sequences, as it occurs when the disease involves
the USL or the vaginal or rectal wall. Within solid
endometriotic masses, hyperintense foci on T2-weighted
images may be seen, representing dilated ectopic endometrial
Usually, endometrial glands without haemorrhage are not
detectable on fat-suppressed T1-weighted images; so deep
lesions may show homogeneous intermediate signal intensity
on T1-weighted images (Fig. 6). When red cell extravasation
outside the glandular ducts into the surrounding stroma
occurs, these small haemorrhages become visible as small
hyperintense spots on fat saturated T1-weighted images (Fig. 7).
However, unlike endometriomas and superficial
peritoneal implants, deep infiltrating visceral solid
endometriosis (especially of the rectal wall) is less likely to contain
hyperintense foci on fat saturated T1-weighted images,
probably because surrounding fibrous reaction and
smooth muscle proliferation minimize cyclical bleeding
within ectopic endometrial glandular ducts .
Fig. 3 Adhesions in a 40-year-old woman with dysmenorrhea, who
underwent two previous surgical interventions for endometriosis. (a)
Sagittal, (b) oblique axial, and (c) oblique coronal T2-weighted images
show spiculated hypointense strands arranged in confluent angles (white
arrows) with loss of the cleavage planes among the anterior surface of the
sigma, the posterior uterine serosa and bilateral endometriomas (white
Fig. 4 Adhesions in a 43-year-old
woman. (a) Sagittal, and (b)
oblique axial T2-weighted images
display spiculated hypointense
strands (white arrows) between
the anterior surface of the sigma
and the posterior uterine serosa
with angulation of rectosigmoid
In certain locations (i.e. round ligaments) the absence of the
hyperintense hemorrhagic foci on T1-weighted images may
be due to the effect of hormonal treatment .
After the intravenous administration of gadolinium, lesion
enhancement may occur due to inflammatory reaction,
glandular and fibrous tissue.
MR imaging findings
Because of the multifocal nature of the disease, often foci of
endometriosis are simultaneously observed at different sites.
Owing to the possibility to perform a complete assessment of
all pelvic compartments at one time , MRI represents the
best imaging technique for preoperative staging of
Endometriotic lesions may affect the urinary tract in up to
20% of cases; these implants are associated with lesions
in other pelvic locations in up to 50–75% of cases [2, 14].
The bladder is the most frequently involved organ (85%),
followed by ureter (9%), kidney (4%), and urethra (2%)
. Different locations of urinary tract endometriosis
may coexist, especially the bladder and ureters. Bladder
endometriosis is often multifocal, the trigone and the
dome being the most frequently affected sites . The
distal ureter, 3–4 cm above the vesico-ureteral junction, is
the most common ureteral segment involved [14, 30].
According to the degree of wall infiltration, bladder
and ureteral involvement may be classified as extrinsic
or intrinsic. In extrinsic involvement, the most common
form, implants are confined to the serosal surface (or
the ureteral adventitia) or the surrounding connective
tissue; it can be treated by bladder or ureteral shaving.
In intrinsic involvement lesions infiltrate the muscular
layer manifesting as mural masses; rarely implants
infiltrate and ulcerate the mucosal layer. Preoperative
differentiation between intrinsic and extrinsic ureteral
endometriosis is not always easy; furthermore, the two types
Fig. 5 Indirect sign of adhesions
in a 36-year-old woman with
bilateral endometriomas. (a)
Sagittal and (b) oblique coronal
T2-weighted images show free
fluid in the pelvis on Banti-declive
position^ (white arrows), due to
the presence of adhesions and
bilateral endometriomas (white
arrowheads). Both ovaries are
joined together involved in
adhesions (kissing ovaries)
Fig. 6 Deep infiltrating
endometriosis in a 34-year-old
woman. (a) Sagittal
fatsuppressed T1-weighted image
shows an endometriotic nodule
(white arrows) infiltrating the
muscular layer of the anterior
rectal wall. The lesion displays
homogeneous intermediate signal
intensity due to fibrous tissue and
smooth muscle. (b)
Photomicrograph (H&E 250X).
Focus of endometriosis without
Regards to its origin, bladder endometriosis may be
classified as primary when it occurs spontaneously, or as secondary
when it is related to iatrogenic lesions due to pelvic surgery
(caesarean delivery, hysterectomy) .
At MR imaging bladder endometriosis may manifest as
localized or diffuse wall thickening and signal intensity
abnormalities . The appearance is of low signal
intensity on T2-weighted and intermediate signal intensity on
T1-weighted images, with or without spots of high signal
intensity on T1-weighted images, representing
hemorrhagic content  (Figs. 8 and 9). Implants minimally enhance
after injection of a gadolinium-based contrast material. The
maximum lesion diameter varies between 1 and 5 cm. MRI
reaches sensitivity up to 88%, specificity up to 99% and
diagnostic accuracy of about 98% for the diagnosis of
bladder endometriosis .
Clinical management of bladder endometriosis may be
conservative, using hormonal therapies, or surgical. For
planning a correct surgical treatment, it is important: to ascertain
the precise location of bladder nodule (distance between the
ureteral meatus and the caudal border of the endometriotic
lesion) and to define the ureteral status .
The differential diagnosis of bladder endometriosis
includes urachal remnant, epithelial tumours (bladder
carcinoma) and mesenchymal tumours (angiomas, leiomyoma) [3,
15]. Malignant transformation of bladder endometriosis is
extremely rare .
Ureteral endometriosis may be defined as any situation
where endometriosis or surrounding associated fibrosis causes
compression or distortion of the normal ureteral anatomy,
even when hydroureteronephrosis is not yet present [33, 34].
All patients with urinary tract endometriosis should be
Fig. 7 Deep infiltrating endometriosis in a 48-year-old woman. (a)
Sagittal fat-suppressed T1-weighted image displays an endometriotic
nodule (white arrows) infiltrating the muscular layer of the anterior rectal
wall. Within the lesion hyperintense foci are detectable (white
arrowheads), representing hemorrhagic content. (b) Photomicrograph
(H&E 200×). Focus of endometriosis with marked haemorrhage. On (c)
sagittal T2-weighted image the solid endometriotic lesion appears mainly
hypointense (white arrows), with small hyperintense cystic foci inside
representing dilated ectopic endometrial glands (white arrowheads)
serosal surface of the bladder representing a small peritoneal implant with
hemorrhagic content (white arrows). Note the endometrioma in the left
ovary (white arrowhead in a). On (c) sagittal T2-weighted image the
implant (white arrow) is hardly detectable because it is partly masked
by the hypointense signal of the bladder wall
assessed for renal function by blood creatinine measurements,
since when endometriosis involves the ureters a silent loss of
renal function may occur [15, 29]. Ureteral endometriosis is
most often unilateral, with a left predisposition; bilateral
involvement is present in approximately 10–20% of cases .
Ureteral involvement is often associated with an ipsilateral
Fig. 9 Bladder endometriosis with intrinsic involvement in a 35-year-old
woman with dysuria, hematuria and urinary incontinence during menses.
(a) Sagittal and (b) oblique axial T2-weighted images show a mural mass
with low signal intensity infiltrating the posterior bladder wall (white
arrows). On (c) axial T2* image punctate signal voids due to hemosiderin
deposition can be seen along the borders of the lesion (white arrow). On
(d) sagittal and (e) oblique axial fat-suppressed T1-weighted images the
implant displays intermediate signal intensity with spots of high signal
intensity, representing hemorrhagic content (white arrows). (f) Oblique
axial MIP image (acquired about 10 min after contrast administration)
demonstrates the relationship between the lesion and the ureters (white
coronal T2-weighted images demonstrate dilatation of the ureter
upstream and of the contralateral ureter (white arrowheads). On (e)
sagittal, (f) coronal and (g) axial contrast-enhanced fat-suppressed
T1weighted images the lesion displays enhancement (white arrows)
Fig. 11 Ovarian endometriotic cysts in a 36-year-old woman. The same
patient as in Fig. 5. (a, b) Sagittal, (c) oblique axial and (d) oblique
coronal T2-weighted images show bilateral endometriomas with
intermediate to low signal intensity (white arrows). The ovaries are joined
together behind the uterus (kissing ovaries). Note the low signal intensity
in the declivous portion of the left cyst (Bshading^ sign, white arrowhead
in c). On (e, f) sagittal and (g) oblique axial fat-suppressed T1-weighted
images the cysts demonstrate high signal intensity (white arrows). (h)
Photomicrograph (H&E 20X). Ovarian endometriotic cyst
endometrioma or with a recto-vaginal nodule larger than 3 cm
[29, 30]. Even if ureteral endometriosis is now increasingly
recognized because of the improvement in diagnostic tools
, preoperative diagnosis is challenging mostly when it is
not complicated by obstruction and proximal dilatation .
MR is the best imaging technique for ureteral evaluation.
On T2-weighted MR images ureteral implants appear as solid
nodules with spiculated margins, showing low signal
intensity, that envelop the ureter, causing dilatation of the ureter
upstream  (Fig. 10).
In a retrospective series including 77 patients affected by
ureteral endometriosis Seracchioli et al.  described two
different histological pattern of ureteral involvement:
endometriotic ureteral endometriosis characterized by
endometrial glands and/or stroma cells within the wall of the ureter
or within periureteral tissue, and fibrotic ureteral
endometriosis where only fibrosis tissue was observed. They found that
the endometriotic pattern (77% of patients) was significantly
associated with hydroureteronephrosis at pre-operative
uroCT scan, whereas the fibrotic pattern (23% of patients) was
significantly associated with concomitant endometriosis in the
recto-vaginal septum. According to author’s point of view this
new classification of ureteral endometriosis based on tissue
composition and histological pattern could be useful in both
diagnostic and therapeutic fields. Indeed, fibrotic tissue
typically does not respond to hormonal therapy .
When deep pelvic endometriosis involves the uterosacral
ligaments and rectovaginal septum, ureteral involvement may
occur even if not suggested preoperatively. Hence these patients
should undergo retroperitoneal laparoscopic inspection and
isolation of both ureters in order to avoid complications .
The differential diagnosis of ureteral endometriosis
includes ureteral invasion by cervical cancer.
The ovaries are the most common site of endometriosis (20–
40% of cases) .
Ovarian endometriosis may show the following patterns :
superficial implants associated with fibrous adhesions;
micro intra-ovarian endometriomas;
deep implants with repeated cyclic haemorrhage resulting
in endometriotic cysts (endometriomas).
Fig. 12 Endometriosis of the
uterine serosa in a 46-year-old
woman, who underwent a
previous surgical intervention for
endometrioma of the right ovary.
(a) Sagittal and (b) oblique axial
T2-weighted images show
endometriotic implants involving
the uterine serosa. The lesions
demonstrate indistinct margins
and low signal intensity (white
arrows). On (c) sagittal and (d)
T1weighted images the lesions
display high signal intensity
Peritoneal implants confined to the ovarian surface are
often underdiagnosed at imaging due to their small size (<
5 mm) .
Micro intra-ovarian endometriomas are small size (<
1 cm) implants within the ovaries. They show hyperintense
signal on T1-weighted images and variable signal intensity
on T2-weighted images. Often multiple and bilateral, these
endometriotic foci may be overlooked at laparoscopy .
Endometriomas are pseudocysts with hemorrhagic content,
formed by the invagination of endometriosis within the
ovarian cortex ; they are frequently multilocular and bilateral
(50% of cases).
Even though in the differential diagnosis of ovarian
endometriosis, transvaginal US is highly sensitive and specific, MR
imaging is considered by some authors as the best imaging
modality for diagnosing endometriomas . At MR imaging
the pathognomonic feature of endometriomas is the Bshading^
sign, which can be seen on T2-weighted images. It reflects the
chronic nature of endometriomas and is the result of cyclic
bleeding occurring over time. Old blood products contain high
iron and protein concentrations which determine a decrease in
T2-relaxation time. Therefore, on T2-weighted images
endometriomas will show a gradual loss of signal within the
lesion with low signal intensity till complete signal void in the
declivous portion (Bshading^). Endometriotic cysts show high
signal intensity on T1-weighted images. Fluid-fluid levels may
also be observed within the lesion [3, 14, 38, 39] (Fig. 11).
The most specific pathologic feature of endometrioma is
the thick fibrous capsule containing a cluster of
hemosiderinladen macrophages due to repeated haemorrhage. Takeuchi
et al.  evaluated hemosiderin deposition within the walls
of endometriomas on susceptibility-weighted MR images at
both 3.0 T and 1.5 T. They found punctate or curved linear
signal voids due to hemosiderin deposition along the cyst
wall in 92.9% of the endometriomas of their series, thus
concluding that this imaging sign may be diagnostic of
endometrioma and that susceptibility-weighted imaging can
contribute to its diagnosis.
In certain cases, the ovaries may be joined together behind
the uterus in the pouch of Douglas due to adhesion formation
between the adjacent peritoneal surfaces, a sign described at
US as Bkissing ovaries^ and suggestive of severe pelvic
In a recently published meta-analysis the sensitivity and
specificity of MRI for the diagnosis of endometrial cysts were
95% and 91% respectively .
The differential diagnosis of endometriomas includes lesions
with high signal intensity on T1-weighted images: dermoids,
mucinous cystic neoplasms, and hemorrhagic masses.
Fat saturated T1-weighted sequences are helpful to rule out
a fat-containing lesion (such as dermoids) and to confirm the
presence of blood .
Mucinous lesions may show hyperintensity on T1-weighted
images, but signal intensity is lower than that of blood.
Fig. 13 Endometriosis of the round ligaments in a 45-year-old woman
with dysmenorrhea, urinary symptoms and chronic pelvic pain, who
underwent a previous surgical intervention for endometrioma of the left
ovary. (a-c) Oblique coronal and (d, e) oblique axial T2-weighted images.
Both round ligaments (white arrows) appear thickened, nodular and
shortened. (f) Oblique coronal fat-suppressed T1-weighted image reveals
small intralesional high signal-intensity foci within the right ligament
(white arrowheads) that represent hemorrhagic component
Hence, the most challenging differential diagnosis is with
other hemorrhagic masses. To differentiate endometriomas
from functional hemorrhagic cysts is important in order to
prevent unnecessary surgical interventions. Functional
hemorrhagic cysts (i.e. hemorrhagic follicular cysts and
hemorrhagic corpus luteum cysts) are usually unilocular and
unilateral, do not display shading on T2-weighted images, and
mostly disappear on follow-up examinations (generally in 4–
6 weeks) .
The role of DWI sequences in differentiating endometriomas from
functional hemorrhagic ovarian cysts is still debated. Balaban et al.
 found significantly lower ADC values in endometriomas
compared with functional hemorrhagic ovarian cysts in all b values. On
the other hand, in a retrospective study by Lee et al.  the mean
ADC values of endometriomas (1.06 ± 0.38 × 10−3 mm2/s) was
significantly higher than that of functional hemorrhagic cysts (0.73 ±
0.29 × 10−3 mm2/s).
Endometrioid and clear cell tumours may be associated
with endometriosis. Large lesions with wall nodularity, thick
septations and enhancing solid components may be suggestive
Surgical excision of an ovarian endometrioma is effective
in managing pain. Nevertheless, operative treatment of
endometriomas is controversial in women desiring future
fertility since it may lead to reduced ovarian reserve in the short
term and premature ovarian insufficiency; bilateral and
recurrent endometrioma excision may further reduce ovarian
Uterine serosa, round ligaments, broad ligaments, fallopian tube
The vesicouterine pouch or anterior cul-de-sac is a common
site of endometriotic involvement . Either peritoneal or
deep endometriotic implants involving the serosal surface of
the uterus often determine adhesions between the peritoneal
folds of the bladder dome and the uterus with anteflexion of
the uterus and obliteration of the anterior cul-de-sac.
At MR imaging deep endometriotic implants involving the
anterior uterine serosa demonstrate infiltrative pattern with
indistinct margins and show low signal intensity on
T2weighted images, with small cystic areas (Fig. 12) .
Fig. 14 Hematosalpinx in a
46year-old woman with
endometriosis. The same patient
as in Fig. 12. (a) Sagittal and (b)
axial T2-weighted images show a
tortuous, tubular structure with
internal fluid-fluid level in the left
adnexa (white arrows). On (c)
sagittal and (d) axial
fatsuppressed T1-weighted images
endoluminal content displays
high signal intensity (white
arrows), a finding consistent with
hematosalpinx. Note the
incomplete mucosal and
submucosal plicae along the tubal
wall (white arrowheads)
At MRI the round ligaments can be identified as thin
structures with hypointense fibrous signal on T1- and T2-weighted
images, extending from the uterine horns to the pelvic
sidewall, passing anteriorly to the external iliac vessels. They have
an intra- and an extra-pelvic portion, the latter being the distal
part of the ligament in the canal of Nuck .
When involved by endometriosis, round ligaments appear
thickened (more than 1 cm), nodular, shortened and irregular
(Fig. 13). Usually endometriotic implants are a mixture of
fibrous tissue and haemorrhage. Fibrous tissue shows
hypointense signal on T1- and T2-weighted images; small
hemorrhagic foci displays hyperintense signal on
fatsuppressed T1-weighted images . The presence of free
fluid around the intra-pelvic portion of the round ligaments
may represent an indirect sign of endometriosis .
Endometriosis of the broad ligaments usually manifests as
thickening and nodularity of these peritoneal folds extending
between the uterus and the lateral walls of the pelvis .
Asymmetry of the morphology or signal intensity at MR
imaging of the parametrium may represent a sign of
endometriotic involvement .
Endometriosis is the most common cause of hematosalpinx
and peritubal adhesions in women of reproductive age.
Endometriotic involvement of the fallopian tubes is strongly
associated with infertility. Serosal or subserosal implants
involves the peritoneal surface of the fallopian tubes, where
repeated haemorrhages lead to fibrosis and retraction of the
tube with hydrosalpinx. Intraluminal implants determine
cyclic haemorrhage thus causing hematosalpinx.
At MR imaging hematosalpinx appears as a tortuous
enlarged tubular adnexal structure filled with hemorrhagic fluid.
Endoluminal content shows high signal intensity on
fatsuppressed T1-weighted images and intermediate signal
intensity, with or without internal fluid-fluid level, on T2-weighted
images  (Fig. 14). According to Siegelman the presence of
T1-weighted hyperintensity within a dilated fallopian tube is
suggestive of endometriosis .
Nevertheless, more rarely hematosalpinx can be associated
with other pathologic conditions such as tubal torsion, tubal
ectopic pregnancy or malignancy.
Retrocervical region, uterosacral ligaments
The retrocervical area is a virtual extraperitoneal space behind
the cervix, located above the rectovaginal septum . It is a
common site of deep pelvic endometriosis.
Retrocervical implants are often associated with USL
involvement and may extend inferiorly to the posterior vaginal
Fig. 15 Endometriosis of the
retrocervical region in a
39-yearold woman with dysmenorrhea,
catamenial dyschezia and dysuria.
(a, b) Sagittal, (c) oblique coronal
and (d) oblique axial T2-weighted
images show a retrocervical
implant (white arrows) infiltrating
the posterior uterine serosa and
the anterior rectal wall, extending
to the left vaginal fornix (black
arrowheads in b and c) and to the
left uterosacral ligament (white
arrowhead in d)
Fig. 16 Endometriosis of the
retrocervical region in a
41-yearold woman with dysmenorrhea
and dyspareunia, who underwent
adhesiolysis. (a) Sagittal and (b)
oblique axial T2-weighted images
show a hypointense ill-defined
infiltrative tissue (white arrows)
involving the posterior portion of
the cervix, the retrocervical region
and the anterior rectal wall. Small
cystic cavities are seen within the
lesion. On (c) sagittal and (d)
axial fat-suppressed T1-weighted
images the lesion exhibits
intermediate signal intensity
(white arrows) with small
hyperintense foci reflecting
haemorrhage. Note the small left
hemorrhagic cyst (white
arrowheads in b and d) showing a
fluid-fluid level on T2-weighted
image; it disappeared in the
follow-up US examinations and
was likely a hemorrhagic
fornix or posteriorly to the anterior rectal wall (Fig. 15).
Usually such lesions determine obliteration of the pouch of
Douglas and uterine retroflexion. In more severe cases,
endometriosis of this anatomical region may determine multiple
adhesions and distortion of pelvic anatomy resulting in a
frozen pelvis .
Deep endometriotic lesions of the retrocervical area
frequently appear as ill-defined infiltrative tissue, hypointense
on T2-weighted images, extending from the posterior uterine
serosa to the retrocervical region [2, 3]. Nevertheless, some
lesions may contain abundant glandular component and little
fibrotic reaction, thus showing high signal intensity on
T1weighted images and variable signal intensity on
T2weighted images [2, 12]. Small cystic areas, hyperintense on
T2-weighted images may also be seen (Fig. 16) . The solid
glandular component enhances after intravenous
administration of contrast material [2, 12].
In a recently published meta-analysis the sensitivity and
specificity of MRI for the diagnosis of endometriosis of the
pouch of Douglas were 89% and 94%, respectively .
The differential diagnosis of retrocervical lesions includes
peritoneal metastases from intraperitoneal malignancies (i.e.
gastrointestinal and ovarian neoplasms). Peritoneal metastases
usually show intermediate to high signal intensity on
T2weighted images and, as the primary cancer site, high signal
intensity on DWI ; moreover, ascites and a tumour mass
into the abdominal cavity may be identified. On the other
hand, solid endometriosis shows low signal intensity on
USL are the most frequent location of deep endometriosis.
Bilateral USL involvement is often associated with other
posterior deep endometriotic locations, mostly the rectosigmoid
At MR imaging normal USL are not visible  or are
depicted as thin, regular, semicircular hypointense cords
that originate from the lateral aspect of the uterine cervix
and the vaginal vault and course dorsocranially toward the
sacrum . USL endometriosis is depicted as nodularity
within the ligament or as unilateral or bilateral hypointense
thickening of the ligament, with regular or irregular
margins [2, 48]. Hyperintense spot on fat-suppressed
T1weighted images, representing punctate foci of
haemorrhage, may also be observed  (Figs. 17 and 18). The
proximal medial portion of the USL is most commonly
Fig. 18 Endometriosis of the right uterosacral ligament in a 28-year-old
woman with dyspareunia. (a) Oblique axial, (b) sagittal and (c) oblique
coronal T2-weighted images show a low-signal-intensity endometriotic
lesion with spiculated margins involving the right uterosacral ligament
(white arrows). The lesion extends to the iliococcygeus muscle (white
arrowheads). (d) Photomicrograph (H&E 250X). Endometriosis in the
affected by endometriosis . According to Bazot et al.
 thin-section oblique axial T2-weighted sequences
(3 mm thick, perpendicular to the long axis of the cervix)
can improve the capability of conventional MRI to assess
USL endometriosis. Left uterosacral endometriosis may be
more difficult to diagnose than the right one, because of the
frequent location of the rectosigmoid colon in the left part
of the pelvic cavity .
In a recently published meta-analysis the sensitivity and
specificity of MRI for the diagnosis of endometriosis of
USL were 85% and 80%, respectively .
In patients undergoing surgery, to establish whether USL
endometriosis is unilateral or bilateral is particularly relevant.
Indeed, the risk of urinary dysfunction and dysuria is
significantly higher in patients after bilateral than unilateral USL
resection . Other potential complications of the resection
of USL are bleeding, ureteral lesions, and pelvic support
The rectovaginal space is the anatomical region located
between the posterior vaginal wall and the anterior rectal
wall. It extends from the deepest part of the pouch of
Douglas to the top of the perineal body. The inferior two
thirds of this space constitute the rectovaginal septum, a
thin membranous partition usually filled with fat [2, 3].
Usually rectovaginal implants represent extensions
from retrocervical or posterior vaginal lesions, but may
also involve the rectovaginal septum alone, without any
link to the cervix. These latter implants usually manifest
as small nodular lesions palpable at vaginal examination.
At MR imaging they show low signal intensity on
T2weighted images [2, 3].
In a recently published meta-analysis the sensitivity and
specificity of MRI for the diagnosis of rectovaginal septum
endometriosis were 82% and 77%, respectively .
Vaginal endometriosis is usually associated with implants
in other pelvic locations, mostly retrocervical and rectal
lesions; seldom isolated involvement of the vagina may
occur. The upper one-third of the vagina and the posterior
fornix are the most commonly affected sites.
Fig. 19 Endometriosis of the vagina and cervix in a 46-year-old woman.
(a) Sagittal, (b) oblique axial, (c) oblique coronal fat-suppressed
T1weighted images, and (d) sagittal, (e) oblique axial and (f) oblique coronal
T2-weighted images show small endometriotic implants involving the
posterior vaginal fornix and the cervix, with multiloculated appearance
(white arrows) characterized by cystic areas with hyperintense content,
better depicted on fat-suppressed T1-weighted images due to subacute
Generally, the vaginal wall implants show a thickened or
nodular appearance [2, 3], but may also have a polypoid
structure. Distention of the vaginal lumen with gel may
facilitate the identification of the lesion . At MR imaging
vaginal endometriotic implants show low signal intensity on
T2-weighted images. They often have a multiloculated
internal appearance because of the presence of cystic areas.
These locules can show hyperintense content on
T1weighted images due to subacute blood products 
(Fig. 19). Polypoid variant may have a T2 hypointense rim
corresponding to surrounding fibrous tissue associated with
endometriosis . Rectovaginal fistulation represents a
complication of vaginal endometriosis.
In a recently published meta-analysis the sensitivity and
specificity of MRI for the diagnosis of vaginal and posterior vaginal
fornix endometriosis were 82% and 82%, respectively .
Differential diagnosis includes epithelial neoplasms
arising from the uterine cervix or vaginal wall. DWI may
be useful in this setting demonstrating no restricted
diffusion within the endometriotic mass, thus avoiding invasive
surgery . On the other hand, vaginal carcinoma
displays restricted diffusion on DWI.
Among the bowel segments the rectosigmoid is the most
commonly involved by endometriosis (65.7%) , followed by
vermiform appendix, terminal ileum, cecum and descending
colon, in order of frequency . Rectosigmoid endometriosis
is often associated with other pelvic locations and with a
second intestinal lesion in 55% of cases .
Anatomically the rectosigmoid wall is characterized by
four intraperitoneal layers: serosa, outer longitudinal
muscularis, inner circular muscularis and mucosa . The
implants generally involve the serosal surface but may invade
the underlying muscular and submucosal layers; only rarely
implants erode the mucosa causing cyclic rectal bleeding.
Typically, endometriotic lesions infiltrating the anterior rectal
wall have a characteristic Bfan shaped^ configuration (or a
pyramidal shape, with the base adhering to the rectal wall
and the apex oriented anteriorly toward the retrocervical
region). The core of the lesion shows isointense signal
compared to muscle on T2-weighted and T1-weighted sequences
and at histopathology corresponds to thickening and distortion
of the muscularis propria and smooth muscle hyperplasia. The
Fig. 20 Endometriosis of the anterior rectal wall in a 48-year-old woman
with dysmenorrhea, chronic pelvic pain and catamenial diarrhoea. (a)
Sagittal and (b) oblique coronal T2-weighted images, and (c) sagittal
and (d) oblique coronal contrast-enhanced fat-suppressed T1-weighted
images show an endometriotic nodule (white arrows) infiltrating the
muscular layer of the anterior rectal wall. The lesion has a Bfan shaped^
configuration with the base adhering to the rectal wall and the apex
oriented toward the retrocervical region. The implant demonstrates
isointense signal compared to muscle on T2-weighted and T1-weighted
sequences; the slightly high signal at the luminal side (white arrowheads
in a and b) corresponds to (sub)mucosal thickening and enhances after
intravenous administration of contrast material (white arrowheads in c
and d). (e) Photomicrograph (H&E 40X). Endometriosis in the
muscularis propria (black arrows)
overlying layer, hyperintense on T2-weighted images, at the
luminal side of the bowel wall corresponds to (sub)mucosal
thickening, as a consequence of Bnon-specific inflammation^
with or without infiltration of endometriosis (Figs. 20 and 21)
. When the longitudinal extent of the parietal lesion along
the bowel wall is short, a pattern of intraluminal endophytic
growth, called Bmushroom cap^, may be observed .
In a recently published meta-analysis the sensitivity and
specificity of MRI for the diagnosis of rectosigmoid colon
endometriosis were 83% and 88%, respectively .
MR imaging is useful to predict infiltration of the
muscular layer of the bowel with a sensitivity of 100% and
specificity of 75%. On the other hand, it is of limited value in
diagnosing (sub)mucosal infiltration, as (sub)mucosal
thickening may be caused by edema without infiltration of
endometriosis. Nevertheless, extensive irregularities of the
(sub)mucosal layer may raise suspicion of (sub)mucosal
involvement . Transvaginal US after bowel preparation is
the best imaging modality for determining which bowel wall
layers are affected .
Adhesions, strictures, and bowel obstruction may occur
representing complications of intestinal endometriosis.
The surgical procedure depends on the lesion size
(>2 cm or 3 cm), degree of infiltration (muscularis
invasion), percentage of circumference involvement, number
and location of intestinal lesions [3, 17, 51, 53]. The
distance between the inferior margin of the nodule and the
anal border in another important information for surgical
planning and can be easily estimated at MRI on sagittal
T2weighted sequences .
The multilayer structure of the rectosigmoid wall lead to
several possibilities of intestinal resection depending on the
degree of invasion (Table 3) . Regarding clinical
symptoms, segmental bowel resection is performed when patients
do not respond to hormonal therapy and/or there is suspicion
of a clinically relevant stenosis of the bowel .
Fig. 21 Endometriosis of the rectal wall in a 45-year-old woman with
cyclic hematochezia, constipation, pencil-like stools and episodes of
intestinal subocclusion, who underwent previous right ureteral stenting.
(a) Sagittal and (b) oblique coronal T2-weighted images, and (c) sagittal
and (d) oblique coronal contrast-enhanced fat-suppressed T1-weighted
images show an endometriotic lesion (white arrows) infiltrating the
muscular and submucosal layers of the rectal wall. The lesion extends
longitudinally for about 7 cm and determines severe stenosis. Note the
hyperintense signal of the (sub)mucosal layer protruding into the rectal
lumen (black arrowheads in a and b). (e) Photomicrograph (H&E 25X).
Endometriosis in submucosa (black *) and in muscularis propria (white *)
Removal of the lesion only, followed by primary suture
Lesions <1 cm
Removal of both muscular layers followed by interrupted
Full thickness resection of the anterior bowel wall followed
by two-layer suture
Bowel resection followed by end-to-end anastomosis with
sparing of mesenteric nerves
Plaques located on the anterior rectosigmoid wall
Single lesions <3 cm involving less than one third
of the circumference
Multiple or bigger lesions determining bowel
Differential diagnosis includes rectal cancer and metastatic
implants to the bowel.
Rectal endometriosis may be difficult to differentiate
from colorectal carcinoma when presenting with
nonspecific clinical and imaging features or in cases of
incidental bowel wall thickening on MR imaging . In this
regard it is important to remember that endometriosis is an
extrinsic lesion which starts at the serosa, infiltrates the
muscular layer and only rarely invades the mucosa ,
whereas colorectal carcinoma is an intrinsic lesion starting
at the mucosa. Busard et al.  have proposed qualitative
assessment of high b-value diffusion-weighted images as a
valuable, non-invasive tool to facilitate differentiation
between endometriosis infiltrating the bowel and
colorectal carcinoma. Both colorectal carcinoma and
endometriosis infiltrating the bowel demonstrate low ADC values;
nevertheless, colorectal carcinoma shows high signal
intensity on DWI images due to high cellularity, whereas
endometriosis displays hypointense signal intensity on
DWI images. The low signal intensity of endometriosis
infiltrating the bowel on DW images could be due to the
BT2-blackout effect^ of these lesions, that are very
hypointense on T2-weighted imaging because of smooth
muscle hyperplasia and fibrous tissue; their restricted
diffusion (low ADC) might be explained by low water content
and fibres blocking diffusion.
Fig. 22 Diaphragmatic endometriosis in a 28-year-old woman with
rightsided basithoracic chest pain associated with menses, who underwent a
previous surgical intervention for endometrioma of the left ovary. (a)
Axial, (b) coronal, (c) sagittal T2-weighted images, and (d) axial, (e)
coronal and (f) sagittal fat-suppressed T1-weighted images show
rightsided hyperintense nodular diaphragmatic implants (white arrows). The
lesions are better depicted on fat-suppressed T1-weighted sequences
An estimated 12% of patients with pelvic endometriosis have
extragenital/extrapelvic endometriosis . This clinical
condition is often associated with considerable diagnostic delay
and morbidity. Among atypical locations, diaphragmatic and
sciatic nerve endometriosis are probably the most relevant for
both clinical and therapeutic implications.
Diaphragmatic endometriosis is thought to be rare, accounting
for about 1.5% in gynaecological surgical series . It is
symptomatic in up to 47% of cases , nevertheless it is also largely
under-diagnosed resulting in delayed diagnosis of up to 10 years
from the onset of symptoms . Association with pelvic
endometriosis is almost constant, thus confirming the Sampson’s
transplantation theory of retrograde menstruation through the
fallopian tubes as an etiological mechanism and the endometrial
cells clockwise peritoneal circulation through the right paracolic
gutter toward the ipsilateral subdiaphragmatic region.
MRI allows the diagnosis of diaphragmatic endometriotic
implants with a sensitivity of 78–83% . Lesions are right-sided
and predominantly posterior. Their structure is non-purely cystic;
the morphological appearance can be of nodule, micronodule
clustering (< 5 mm) or plaque lesion. Focal liver herniation,
corresponding to diaphragmatic defects, may also occur .
Typically, diaphragmatic implants are hyperintense on both
fatsuppressed T1-weighted sequences (consistent with blood
products) and T2-weighted sequences, and are better depicted on
fatsuppressed T1-weighted sequences  (Fig. 22).
However, MRI may fail to detect small superficial
diaphragmatic nodules; hence a negative MR examination does not
exclude the diagnosis of diaphragmatic endometriosis in women
with suggestive symptoms and would not eliminate the need to
surgically investigate the upper abdomen and diaphragm .
Suppressive hormonal treatment can lead to resolution or
significant relief of symptoms. Thoracic surgery is usually
only performed in cases of recurrent catamenial
Endometriosis of the sciatic nerve
Regarding peripheral nervous system endometriosis, the most
frequently involved site is the sacral plexus (57%), followed
by the sciatic nerve (39%) . Extrapelvic sciatic
endometriosis is due to implantation of endometrial tissue in the
sciatic nerve, usually in the region of the sciatic notch .
MRI is the diagnostic method of choice to demonstrate
endometriosis lesions along nerve pathways and to precisely
Fig. 23 Extrapelvic sciatic nerve endometriosis in a 31-year-old woman
who has been suffering from cyclic sciatica for about 2 years. (a) Sagittal,
(b) axial and (c) coronal T2-weighted images show hypointense
spiculated soft-tissue thickening centred around the right sciatic nerve at
the sciatic notch (white arrows). (d) Sagittal, (e) axial and (f) coronal
contrast-enhanced fat-suppressed T1-weighted images display
enhancement of the mass (white arrows). Note the sciatic nerve cephalad
to the lesion (white arrowheads in c) and within the lesion (white
arrowhead in e)
identify the site of the lesion . The appearance of
neurotropic endometriotic lesions can be variable as solid or
complex cystic masses with thick or thin walls . At MR
imaging they usually manifest as hypointense irregular spiculated
soft-tissue thickening centred around the sciatic nerve at the
sciatic notch on T2-weighted images; small intermingled
hyperintense foci, indicating bloody content, may frequently be
observed on fat-suppressed T1-weighted images  (Fig. 23).
Indirect MR findings may also be found as atrophy in
corresponding target muscles of the sciatic nerve and the
lumbosacral plexus (gluteal muscles, obturator internus muscle,
quadratus femoris muscle)  (Fig. 24).
Electromyography can demonstrate signs of denervation
and slowing of conduction speed. It can be useful to
differentiate between root and peripheral nerve involvement .
This clinical condition is often associated with considerable
diagnostic delay and morbidity. Since the prognosis depends on
the interval between the onset of symptoms and diagnosis, early
diagnosis and treatment are important in order to prevent
irreversible damage to the sciatic nerve . Therapeutic options
include pharmacologic treatment and surgical therapy. The
differential diagnosis includes benign neurogenic tumours .
(white arrows and white arrowhead in a). (c) Axial and (d) coronal
T2weighted images display atrophy of right piriformis muscle compared
with the contralateral one (white arrows)
Endometriosis is a chronic condition affecting women during
the reproductive lifespan. Diagnosis of endometriosis must
take into account clinical symptoms, physical examination,
laboratory tests and different imaging techniques. Since pelvic
anatomy is complex and may vary with distortion by invasive
endometriosis, the radiologist must be aware of both normal
and deranged anatomy.
The ideal purpose of surgery is a therapeutic and effective
intervention based on a careful preoperative evaluation. From
this point of view, the role of MR imaging to help diagnose and
plan surgical strategy is critical in the management of the
disease. Preoperative detection of all endometriotic lesions is
recommended to choose the surgical approach and to plan a
multidisciplinary team work . This multidisciplinary approach
including radiologists, gynaecologists, urologists,
gastrointestinal surgeons, and (in selected cases) neurosurgeons, is
recommended to improve diagnostic imaging accuracy and patients’
outcome, and to reduce postoperative complication rates. The
recent awareness that endometriosis may be medically treated
based on strong clinical suspicion  and that laparoscopy
should be intended for surgical treatment, not for diagnostic
purposes , furtherly enhance the role of non-invasive
diagnostic procedures and particularly of MR imaging.
In any case, due to the complexity of the disease, it is
appropriate to centralize the overall care of endometriosis patients
to reference centres in order to pursue a patient-centred
approach tailored to the patient’s specific condition and desires.
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