Case of the week Details

• Confluent arc like hypodense plaques are seen in the fissula ante fenestram with demineralisation around the basal, middle and apical turns of cochlea.
• There is also partial demineralisation around the around the round window niche which appears obliterated.
• There is also partial demineralisation around the basal turn of cochlea with involvement of the round window niche.

DIAGNOSIS:

• Bilateral otosclerosis - Grade 3 (Fenestral and retrofenestral type).

DISCUSSION:

• 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.
• It is an 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.
• CLINICAL PRESENTATION: 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 categorised into two types:

1) fenestral (stapedial): ~80

• involves the oval window and the stapes footplate.
• hearing loss is often conductive, due to stapes thickening and fixation.

2) retrofenestral (cochlear): ~20%

• cochlear involvement with demineralization of the cochlear capsule.
• hearing loss is often sensorineural, but the mechanism by which this occurs is uncertain.

Pathology and clinical findings:

• The more common fenestral type of otosclerosis involves the lateral wall of the bony labyrinth.
• Histologically, 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.
• Bilateral involvement is common.
• The promontory, round window niche and tympanic segment of the facial nerve canal can also be involved.
• 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 windows.
• Otosclerosis can sometimes present as isolated round window involvement without pericochlear or oval window involvement

CT grading system (Symons and Fanning):

grade 1

• solely fenestral, either spongiotic or sclerotic lesions, evident as a thickened stapes footplate, and/or decalcified, narrowed or enlarged round or oval windows

grade 2

• patchy localized cochlear disease (with or without fenestral involvement)
• grade 2A: basal cochlear turn involvement
• grade 2B: middle / apical turns involvement
• grade 2C: both the basal turn and the middle / apical turns involvement

grade 3

• diffuse confluent cochlear involvement of the otic capsule (with or without fenestral involvement)

Management:

• A stapedectomy with stapes prosthesis is the treatment of choice for fenestral otosclerosis.

References:

• Purohit, B., Hermans, R. & Op de beeck, K. Imaging in otosclerosis: A pictorial review. Insights Imaging 5, 245–252 (2014).
• https://doi?org/10?1007/s13244-014-0313-9
• T.C. Lee, R.I. Aviv, J.M. Chen, J.M. Nedzelski, A.J. Fox and S.P. Symons.
• American Journal of Neuroradiology August 2009, 30 (7) 1435-1439; DOI: https://doi.org/10.3174/ajnr.A1558

Dr ANITA NAGADI
Consultant Radiologist
Manipal Hospital, Yeshwanthpur, Bengaluru.

Dr NEHA SATHYANARAYANA
Radiology resident
Manipal Hospital, Yeshwanthpur, Bengaluru.