Superior Canal and Posterior Canal Dehiscence: Case

Timothy C. Hain, MD   • Return to Main SCD page. • Page last modified: March 8, 2021

A 45 year old man developed dizziness provoked by exercise.

Audiometry revealed a mixed hearing loss on the left side

An ENG revealed normal calorics and Valsalva, but there was vibration induced nystagmus on the left side alone.


VEMP testing showed an enlarged VEMP on the left.


CT scan of the temporal bone showed both SCD and PCD on the left side.


(Direct coronal view)


Reformatted oblique sagittal to image the entire PC.


The major clue here that this man had a dehiscence was the larger VEMP on the side of the conductive hearing loss. "True" conductive hearing loss obliterates VEMP's. The larger VEMP was strong evidence for a dehiscence. This case illustrates the high value of VEMP testing as a clinical tool combined with audiometry and clinical exam.

This case also illustrates that patients with SCD may also have dehiscence of other canals. Although we are generally unenthused about doing axials and coronals of the temporal bone both, as this doubles the radiation exposure (and cost), this case shows the value of having a reformatted oblique sagittal image. Perhaps the "best" practice here would be to do direct coronals (for the most common SCD), along with reformatted axials (for the LC), and oblique sagittals (for the PC). This would reduce radiation exposure to a minimum.

In this case, the radiologist suggested that the PCD was due to an "aggressive arachnoid granulation". One would think instead that this highly unlikely jutaxposition of dehiscences in two different canals would be due to a congenital maldevelopment of the inner ear.