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 :
- 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
Epidemiology
It is the most common cause of X-linked deafness, accounting for 50% of families with nonsyndromic X-linked deafness . In turn, this entity is 1-5% of all nonsyndromic genetic deafness .
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) :
- present interscalar septa, lending a "corkscrew" appearance to the cochlea
- 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 :
- 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 .
See also
