TRAUMATIC INCUDOMALLEOLAR DISRUPTION

The common serious consequences of the trauma to the temporal bone are hearing loss and/or facial nerve paralysis (4). Hearing loss can be conductive which is usually associated with longitudinal fractures of the temporal bone and sensorineural hearing loss is seen with transverse fractures (1).

Trauma related conductive hearing loss can be due to injury to the Ossicular chain, hematotympanum or laceration to the tympanic membrane. Sensorineural hearing loss is caused due to injury to the cochlea or organ of Corti. (5)

HRCT is the method of choice of evaluation of the Ossicular trauma (5). Ossicular injury usually occurs as a dislocation, of which there are five types: incudostapedial joint separation, incudomalleolar joint separation, dislocation of the incus, dislocation of the malleoincudal complex, and stapediovestibular dislocation (5).

The incudostapedial joint is the most commonly demonstrated disrupted articulation, but is associated with incudomalleolar joint disruption. Clinically, there is persistent conductive hearing loss following blunt trauma (3). Incudomalleolar disarticulation is the injury most frequently seen. The incudomalleolar joint is a saddle shaped diarthrodial joint which is seen as an ‘ice cream cone’ on axial CT planes. Head of malleus resembles the scoop and the body and short process of the incus resembles the cone. The malleus is the most stable ossicle, secured by

three ligaments (anterior, lateral and superior malleal ligament), attachment to the tensor tympani muscle and to tympanic membrane. 

Incus, on the other hand, is vulnerable to the traumatic dislocation as it is heaviest of all ossicles, has no muscular anchor and is secured by single posterior incudal ligament (2,5).

Incus can get dislocated owing to the inertia. It may remain in the epitympanic recess or prolapsed into the lower part of the tympanic cavity or in the external auditory meatus or may disappear as seen in this case (5).

Ossicular injury is the cause of unresolved hearing loss and may require surgical intervention. If the conductive hearing loss is more than 30dB and persists for more than 6 months, reconstruction of the Ossicular chain is to be considered. (1)