Middle Cranial Fossa Dehiscence as an Incidental Finding on CT

Objectives:

This retrospective chart review demonstrates that the prevalence of middle cranial fossa (MCF) dehiscence on computed tomography (CT) scans increases with age.

Methods:

High-resolution temporal bone CT scans, which had been obtained for any otologic complaint, were reviewed independent of all clinical history. Scans showing soft tissue, fluid, trauma, or previous operations were excluded. The CTs from 183 patients (296 ears) were reviewed, blinded for age and body mass index (BMI). The MCF floor was divided into 7 regions and systematically inspected. Ages and BMIs of the patients were subsequently extracted from the medical record.

Results:

Logistic regression analysis confirmed increasing MCF dehiscence with age (P < .05, odds ratio [OR] = 1.07, R = .584). Over all ages (range, 1-88 years; average, 38.5), 32% of MCF floors were dehiscent at any 1 site. For age 60 and over, 55% were dehiscent. The most common sites of MCF dehisence were directly above the malleus head and above the additus ad antrum (35% and 28%, respectively). Superior canal dehiscence (SCD) was seen in 7% of all patients and only in the context of MCF dehiscence. The prevalence of MCF dehiscence increased with age when patients were analyzed by BMI <25, BMI = 25-30, and BMI >30 (P < .003, P < .04, P = .03).

Conclusion:

The increase of middle cranial fossa dehiscence with respect to age is statistically significant. Over all ages, approximately 32% of ears show dehiscence. Over 60 years, approximately 55% show dehiscence. The odds of having dehiscence double with a 10-year difference in age. The most common sites along the MCF floor are in the epitympanum over the malleus head and the additus ad antrum. There was a statistically significant increase in MCF dehiscence with age when patients with equivalent BMIs are compared.

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