The middle cranial fossa: morphometric study and surgical considerations

Abstract

The anatomical features of the temporal bone can vary significantly among different individuals. These variations affect the operative view in middle cranial fossa surgery. We performed 18 middle fossa approaches in 9 cadaveric heads, with detailed morphological analysis, to identify unfavorable situations and reliable systems to avoid complications during surgery. We recorded linear, angular measurements and calculated areas. We performed a computed tomography (CT) scan with analysis of the amount of bone to remove in two temporal bones. We found that the location of the internal auditory canal (IAC) is the keystone of bone removal. We also found accuracy in the system suggested by E. and J. L. Garcia-Ibanez for its identification and that there is a smaller surgical window in female patients (statistically significant) that can be predicted on preoperative imaging studies. Our study also confirms significant individual variability in the mutual relationships of different surgical landmarks. We concluded that surgery of the middle fossa requires detailed understanding of the complex temporal bone anatomy. The surgeon has to be aware of extreme variability of the more commonly used anatomical landmarks. The method to identify the position of the IAC described by E. and J. L. Garcia-Ibanez seems to be the simplest and most reliable. When the surgical strategy includes an anterior petrosectomy, interindividual variability can critically affect the working area, particularly in females. The working area can be estimated on preoperative CT scans through the petrous bone.

Keywords: Middle fossa approach; landmarks; measurements; microsurgical anatomy; temporal bone; transpetrous approach.

Figure 1

Computed tomography (CT) of the right temporal bone: (A) Internal auditory canal (straight arrow), cochlea (double straight arrow), and internal carotid artery (curved arrow). (B) The area of bone anterior to the internal auditory canal (IAC), which can be removed through the extended middle fossa approach, is delimited. This area is schematically divided into triangles. Applying Carnot's theorem, the triangles' area can be calculated from linear measurements.

Figure 2

Surgical view (A) and line drawing (B) of the floor of left middle fossa after dural elevation. Significant landmarks are labeled: gspn, greater superficial petrosal nerve (lateral); V₃, third branch of trigeminal nerve (anterior); Po, porus trigeminus (antero-medial); AE, arcuate eminence (posterior).

Figure 3

Surgical view (A) and line drawing (B) of the left middle fossa floor after complete bone removal. GG, geniculate ganglion; gspn, greater superficial petrosal nerve; ICA, internal carotid artery; V₃, third branch of trigeminal nerve; ssc, superior semicircular canal; Co, cochlea; IAC, internal auditory canal; ips, inferior petrosal sinus. (C,D) Areas of bone removal. A, anterior area; P, posterior area.

Figure 4

Graph showing extension of anterior bone removal area in male and female populations.