Prepatellar Morel-Lavallée effusion
Noushin Yahyavi-Firouz-Abadi
0
1
Jennifer L. Demertzis
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1
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J. L. Demertzis Division of Musculoskeletal Radiology, Mallinckrodt Institute of Radiology
, 510 South Kingshighway Boulevard, Campus Box 8131,
St Louis, MO 63110, USA
1
N. Yahyavi-Firouz-Abadi (
2
) Mallinckrodt Institute of Radiology
, 510 South Kingshighway Boulevard, Campus Box 8131,
St Louis, MO 63110, USA
The case presentation can be found at doi:10.1007/s00256-012-1399-0.
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Prepatellar Morel-Lavallee effusion (closed degloving injury)
Lateral radiograph of the left knee shows prepatellar soft
tissue swelling. MR images demonstrate a T2-hyperintense
unilocular prepatellar fluid collection located between the
subcutaneous fat and underlying fascia. The collection
extends beyond the transverse and craniocaudal boundaries
of the prepatellar bursa, with the medial and lateral margins
reaching the level of the femoral epicondyles at the
midcoronal plane, and the superior and inferior margins
extending from the mid-thigh to beyond the tibial tubercle. These
findings are indicative of a prepatellar Morel-Lavalle
effusion and are distinguished from prepatellar bursitis by
location beyond the anatomic confines of the prepatellar
bursa. Quadriceps muscle signal intensity is normal,
excluding muscle contusion as the cause of the patients pain.
Other post-traumatic subcutaneous lesions in the differential
diagnosis such as fat necrosis, pseudolipoma, and
coagulopathy-related hematoma are unlikely given the
anatomic location, imaging characteristics, and clinical history
[1]. The patient was successfully treated with activity
restriction, ice, and compression wraps.
Maurice Morel-Lavalle first described closed degloving
injuries of the hip and pelvis in 1853 [2]. Excessive shearing
force or repetitive compressive trauma causes separation of
the skin and subcutaneous fat from underlying deep fascia
resulting in disruption of perforating vessels and formation
of fluid collections containing blood, fat, and lymph [13].
Morel-Lavalle lesions adjacent to the greater trochanter,
proximal femur, buttock, and lower back are well known
[4, 5], and MR imaging has an established role in their
diagnosis. The appearance of Morel-Lavalle effusions on
MRI depends on lesion acuity and the amount of blood
product, fat, and lymph tissue within it [1]. Mellado et al.
described six types of Morel-Lavalle effusions ranging
from seroma to infected collections, with a unilocular T2
hyperintense fluid collection being the most common
finding of the basic subtypes [1]. Neither blood product, fat, nor
a fibrous pseudocapsule was identified in this particular
case. Of these findings, the presence of an enhancing
pseudocapsule has prognostic value, suggesting possible benefit
of therapeutic aspiration or debridement to facilitate
resolution of the lesion [1, 2].
Despite the established diagnosis of Morel-Lavalle
effusion in the pelvis and hips, its occurrence in the prepatellar
region has only recently been described in the orthopedic [6,
7] and radiology literature [8, 9]. A recent case series of 24
national football league players revealed a shearing blow
from the playing field as the most common cause of a
prepatellar degloving injury, with successful treatment with
compression wrap and cryotherapy in most cases and recurrent
aspiration and occasionally sclerotherapy in refractory cases
[6]. In this study, most cases of Morel-Lavalle effusion were
diagnosed clinically by identification of a fluctuant
suprapatellar fluid collection often extending medially and laterally at
the mid- to distal thigh, a location distinct from the prepatellar
bursa. Cadaveric studies have demonstrated that the normal
prepatellar bursa does not extend beyond the mid-coronal
plane medially or laterally or to the mid-thigh proximally
[10]. A more recent study evaluated MR imaging features of
prepatellar Morel-Lavalle injuries in four young wrestlers
with emphasis on differentiating prepatellar bursitis from
Morel-Lavalle effusion [8]. The authors found MR a valuable
diagnostic addition to size criteria and physical examination
used in the orthopedic literature by demonstrating the extent of
the fluid collection beyond the boundaries of a normal or
slightly swollen bursa. While follow-up imaging and clinical
response to steroid injection may also be useful in
distinguishing between these two entities [8], the distinction may not be
clinically necessary as treatment strategies and outcomes are
often the same. However, in cases where a fibrous
pseudocapsule has developed, or where there are clinical or imaging
findings suggestive of infection such as pseudocapsule
enhancement, internal septations, and inflammation of the
adjacent fatty tissue and fascia, this distinction has therapeutic
value, suggesting possible benefit of aspiration or debridement
of the collection [1, 2].
Relatively recent descriptions of prepatellar Morel-Lavalle
effusions in the radiology literature and a few published
imaging (...truncated)