Case of the week Details

• Lucencies around bilateral cochlea, representing demineralization (yellow arrow) – double ring sign.
• Foci of lucencies involving the fissula ante fenestrum on both sides.

Diagnosis:

• Bilateral fenestral and retrofenestral otosclerosis.

Discussion:

• Otosclerosis is a misnomer, as it is characterised by lucent rather than sclerotic bony changes and hence more appropriate term is otospongiosis.
• Female predilection is present with a F:M ratio of ~2:1.
• Most commonly presents with hearing loss, often conductive, but can also be sensorineural or mixed and is frequently bilateral.
• Hearing loss may be exacerbated by pregnancy.
• Pure-tone audiometry shows characteristic decrease in bone conduction at 2000 Hz (Carhart notch).

2 Subtypes:

• Fenestral (stapedial)
  • anterior to the oval window, involving a small cleft known as the fissula ante fenestram
  • conductive hearing loss due to stapes thickening and fixation
• Retrofenestral(cochlear)
  • demineralisation of the cochlear capsule
  • hearing loss is often sensorineural

Grading of otosclerosis (Symons and Fanning)

• Grade 0: normal.
• Grade 1: small lucent lesion at the fissula ante fenestram.
• Grade 2A: sclerosis and narrowing of the basal turn.
• Grade 2B: lucent lesion extending from the fissula ante fenestram to the middle turn of the cochlea. 
• Grade 2C: patchy lucency around the lateral aspect of basal, middle, and apical turns of the cochlea, the medial aspect of the cochlea appears spared.
• Grade 3: severe, confluent lucency around the cochlea.

References:

• Lee TC, Aviv RI, Chen JM, Nedzelski JM, Fox AJ, Symons SP. CT grading of otosclerosis. American journal of neuroradiology. 2009 Aug 1;30(7):1435-9.
• Purohit B, Hermans R, Op de Beeck K. Imaging in otosclerosis: a pictorial review. Insights into imaging. 2014 Apr;5:245-52.

Dr Anita Nagadi
Senior Consultant Radiologist
Manipal  Hospital, Yeshwanthpur, Bengaluru

Dr Rashmi Jayakar Poojary
Radiology Resident
Manipal  Hospital, Yeshwanthpur, Bengaluru