Imaging in otosclerosis: A pictorial review

Insights Imaging (2014) 5:245–252 DOI 10.1007/s13244-014-0313-9 PICTORIAL REVIEW Imaging in otosclerosis: A pictorial review Bela Purohit & Robert Hermans & Katya Op de beeck Received: 11 November 2013 / Revised: 5 January 2014 / Accepted: 13 January 2014 / Published online: 9 February 2014 # The Author(s) 2014. This article is published with open access at Springerlink.com Abstract Otosclerosis is an otodystrophy of the otic capsule and is a cause of conductive, mixed or sensorineural hearing loss in the 2nd to 4th decades of life. Otosclerosis is categorised into two types, fenestral and retrofenestral. Imaging plays an important role in the diagnosis and management of otosclerosis. High-resolution CT (HRCT) of the temporal bone using 1-mm (or less) thick sections is the modality of choice for assessment of the labyrinthine windows and cochlear capsules. MRI has limited application in the evaluation of the labyrinthine capsules but is useful for assessment of the cochlear lumen prior to cochlear implantation in patients with profound hearing loss. The treatment of fenestral otosclerosis is primarily surgical with stapedectomy and prosthesis insertion. Patients with retrofenestral otosclerosis and profound hearing loss are treated medically using fluorides, but may derive significant benefit from cochlear implantation. This pictorial review aims to acquaint the reader with the pathology and clinical features of otosclerosis, the classical imaging appearances on CT and MRI, a radiological checklist for preoperative CT evaluation of otosclerosis, imaging mimics and a few examples of post-stapedectomy imaging and complications. Teaching points • Otosclerosis causes conductive, sensorineural and mixed hearing loss in adults. • HRCT of the temporal bone is the diagnostic imaging modality of choice. • Stapedectomy is used to treat fenestral otosclerosis. • Fluorides and cochlear implantation are used to treat retrofenestral otosclerosis. Keywords Otosclerosis . Fenestral . Retrofenestral . HRCT temporal bone . Stapedectomy Abbreviations HRCT high-resolution CT CHL conductive hearing loss SNHL sensorineural hearing loss MHL mixed hearing loss CI cochlear implantation Introduction Otosclerosis is a unique autosomal dominant otodystrophy of the otic capsule. It is also called ‘otospongiosis’ as it is characterised by replacement of the normal ivory-like enchondral bone by spongy vascular bone. The decalcified foci tend to recalcify, becoming less vascular and more solid. Patients typically present in the 2nd- 4th decades of life with conductive hearing loss (CHL), sensorineural hearing loss (SNHL) or mixed hearing loss (MHL) and/or tinnitus. Otosclerosis is commoner in Caucasians as compared to blacks, Native Americans and Asians. The disease is more common in women and commonly bilateral (85 %). Otosclerosis is categorised into two types, fenestral and retrofenestral/ cochlear. Retrofenestral otosclerosis rarely occurs without fenestral involvement; hence these manifestations are considered to be a continuum rather than two separate entities [1–4]. Fenestral Otosclerosis B. Purohit (*) : R. Hermans : K. Op de beeck Department of Radiology, University Hospitals Leuven, 3000 Leuven, Belgium e-mail: Pathology, clinical findings and imaging The more common fenestral type of otosclerosis involves the lateral wall of the bony labyrinth. Histologically, 246 Insights Imaging (2014) 5:245–252 Fig. 1 Axial (a) and coronal (b) HRCT images of the right temporal bone in an adult patient with right-sided CHL. A hypodense demineralised plaque (arrow) is noted in the region of the fissula ante fenestram in keeping with fenestral otosclerosis demineralised foci of spongy new bone typically occur in the region of the embryonic fissula ante fenestram, which is a cleft of fibrocartilagenous tissue between the inner and middle ear, just anterior to the oval window (Fig. 1). Bilateral involvement is common (Fig. 2). The promontory, round window Fig. 2 Axial HRCT images of the right (a) and left (b) temporal bone in an adult patient with bilateral CHL. Hypodense demineralised plaques (arrows) are noted in bilateral fissula ante fenestram regions in keeping with bilateral fenestral otosclerosis Fig. 3 Axial (a,b) and coronal (c,d) HRCT images of the right and left temporal bone in an adult patient with bilateral severe CHL. Heaped-up bony otosclerotic plaques are noted causing severe bilateral oval window narrowing (arrows) niche and tympanic segment of the facial nerve canal can also be involved [1–3]. The disease gradually extends to involve the entire footplate of the stapes and may subsequently involve the cochlea. Heaped-up bony plaques formed in the healing phase typically cause narrowing of the oval and round Insights Imaging (2014) 5:245–252 247 Fig. 4 Axial HRCT images of the right (a) and left (b) temporal bone in a patient with bilateral fenestral otosclerosis. Otosclerotic plaques are noted causing bilateral round window narrowing (arrows), right more than left windows. Involvement of the annular ligament leads to mechanical fixation of the stapedo-vestibular joint, which is responsible for the typical CHL/audiometric air-bone gap (Carhart’s notch) [1–5]. Complete obliteration of the oval window may occur in 2 % cases (Fig. 3). This rarely is associated with secondary torsional subluxation of the incus [2]. Otosclerosis can sometimes present as isolated round window involvement without pericochlear or oval window involvement [6]. The classical clinical findings include progressive CHL up to about 50–60 dB, absent stapedial reflexes, a normal tympanic membrane and no evidence of middle ear inflammation [1–5]. Imaging is usually not pursued in patients with uncomplicated CHL and characteristic clinical findings. The treatment of fenestral otosclerosis is primarily surgical with stapedectomy and stapes prosthesis insertion [1–5]. Fig. 5 a Axial HRCT image of the right temporal bone in an adult patient with progressive right-sided CHL and remote history of ipsilateral head injury. A hypodense demineralised otosclerotic plaque (arrow) is noted in the fissula ante fenestram. b Axial HRCT image of the same patient as (a) at a slightly higher level. There is also evidence of malleo-incudal dislocation (arrow) Fig. 6 Axial (a) and coronal (b) HRCT images of the left temporal bone in an adult patient with left-sided CHL and previous history of left-sided otitis media. The soft-tissue density noted in the attic (asterisk) causing blunting of the scutum (arrow) is in favour of a cholesteatoma. In addition, a tiny hypodense fenestral otosclerotic focus (arrowheads) is noted anterior to the oval window 248 Insights Imaging (2014) 5:245–252 Table 1 Reporting checklist for preoperative HRCT of the temporal bone in otosclerosis 1. 2. 3. 4. 5. 6. 7. 8. 9. Reporting points Clinical and surgical relevance Size and location of plaques Status of oval window Status of round w (...truncated)