8.23\ Vestibular Nerve Section

8.23.1\ Discussion

Vestibular nerve sectioning (neurotomy) is another treatment option for intractable Meniere’s disease if preservation of residual hearing is a consideration. Vestibular neurotomy consists of delicately severing the vestibular nerve fibers just

a

distal to the division between cochlear and vestibular nerves. This procedure can be performed via a retrosigmoid, retrolabyrinthine, or middle cranial fossa approach, and changes associated with these surgical approaches can be identified on radiologic images (Fig. 8.95). In particular, thin-section steady state MRI sequences, can evaluate for residual vestibular nerve fibers that could be responsible for recurrent vertigo attacks.

b

Fig. 8.95  Vestibular neurotomy. Sagittal CISS MRI image (a) shows the absence of the vestibular and cochlear nerves in the internal auditory canal. The remaining seventh cranial nerve (arrow) sags posteriorly in the internal

auditory canal. Sagittal CISS of the normal contralateral side (b) shows intact internal auditory canal nerves for comparison

8.24\ Superior Semicircular Canal

Dehiscence Repair

8.24.1\ Discussion

Repair of superior semicircular canal dehiscence is an option to treat associated vestibular and audiological symptoms. The procedure can be performed via a transmastoid or middle cranial fossa approach. Repair can be achieved via several techniques that aim to plug the dehiscent canal and/or resurface and repair the adjacent middle cranial floor. Materials used to accom-

plish this include bone pate, fascia, and bone wax (plugging), bone graft, cartilage graft, and hydroxyapatite cement (resurfacing and skull base repair). It is very common that these patients have diffuse thinning of the middle cranial fossa floor on both sides and sometimes cerebrospinal fluid leak or encephalocele may also be present. On CT, bone graft, hydroxyapatite, and bone putty are high attenuation (Fig. 8.96), while temporalis fascia and bone wax are generally imperceptible since they are used in small quantities and have imaging characterization that blend in with the surrounding soft tissues.

8.25\ Tube Drainage of Petrous

Apex Cholesterol Granuloma

8.25.1\ Discussion

Drainage tube insertion can be performed for treating symptomatic petrous apex cholesterol cysts (granulomas). Silastic drainage tubes can be inserted into the lesion after drilling of the temporal bone and creating a drainage tract into the middle ear. Alternatively, the tube can be inserted into

a

c

the cysts via the middle cranial fossa with drainage into the sphenoid sinus via sphenoidotomy (Fig. 8.97). The desired end result of treatment is permanent ventilation of the cyst cavity (Fig. 8.98). Potential complications of drainage include tube obstruction with cyst recurrence and damage to the labyrinthine structures and surrounding cranial nerves, particularly the facial and trigeminal nerves depending on the approach. Lesions that are not amenable to tube drainage can be treated by complete surgical resection.

b

d

Fig. 8.97  Transsphenoidal tube drainage of cholesterol cyst. Axial (a) and coronal (b) CT images and axial T2-weighted (c) and T1-weighted (d) MR images show a

Silastic drainage tube (arrows) that extends from the right petrous apex to the sphenoid sinus (Courtesy of Hugh Curtin, M.D.)