Cochlear incomplete partition type III

Cochlear incomplete partition type III (IP-III) is the type of cochlear incomplete partition present in X-linked deafness, a rare, nonsyndromic, genetic cochlear anomaly associated with mixed conductive and sensorineural hearing loss.

Terminology

The genetic disorder goes by many names ⁸:

• X-linked deafness type 2 (DFNX2)
• deafness type 3 (DFN3)
• conductive deafness with stapes fixation
• Nance deafness
• X-linked mixed conductive and sensorineural hearing loss
• X-linked progressive mixed deafness with perilymphatic gusher during stapes surgery
• X-linked stapes gusher ¹

Epidemiology

It is the most common cause of X-linked deafness, accounting for 50% of families with nonsyndromic X-linked deafness ¹⁰. In turn, this entity is 1-5% of all nonsyndromic genetic deafness ¹⁰.

Pathology

It is caused by a mutation in the POU3F4 gene located on the X chromosome.

Clinical presentation

Male patients present with profound hearing loss (can be progressive) that is predominantly sensorineural +/- conductive. Female carriers have normal hearing or only mild hearing loss. Vestibular function is impaired in affected males, however normal in females.

Radiographic features

The key findings of IP-III concern the cochlea, which is nearly normal in size but has internal abnormalities (incomplete partition) ^6,7:

• present interscalar septa, lending a "corkscrew" appearance to the cochlea ⁹
• absent modiolus
• absent cribriform plate (lamina cribrosa) between the basal turn of cochlea and internal auditory canal fundus

Additional findings are seen outside the cochlea ¹⁰:

• otic capsule: thin (always)
• internal auditory canal: bilateral and symmetrical widening of the fundus of the internal auditory canal (always; may be mild in female carriers)
• vestibule: irregular shape with small cystic bulges (90%)
• superior vestibular nerve canal: enlarged (majority)
• oval and round windows: dysplastic (majority)
• semicircular canals: irregular shape with small cystic bulges (minority), possible ossification
• vestibular aqueduct: dilated (minority)
• facial nerve canal: dilated labyrinthine segment (majority)
• singular canal: dilated (minority)
• stapes: abnormal (minority)

Practical points

Because of the abnormal communication between the subarachnoid and perilymphatic spaces, there is a high risk of gushing during stapes manipulation, and so recognition of the X-linked deformity is essential, precluding stapes surgery.

History and etymology

The term incomplete partition III was coined in 2006 by L Sennaroglu ⁶.

See also

• cochlear anomalies (classification)