Perineural spread-susceptible structures: a non-pathological evaluation of the skull base.

Perineural spread adenoid cystic carcinoma can alter the dimension of foramina and canals of the skull base. The objective of this study was to determine the range of normal variation of the foramina and canals of both hemicranium. We analyzed 200 individuals with no alterations of the skull base in a retrospective manner using high-resolution computed tomography. We measured the short and long axis diameters of the foramen rotundum (FR), foramen ovale (FO), stylomastoid foramen (SMF), pterygoid canal (PTC), internal auditory canal (IAC), and the facial nerve canal in its labyrinthine portion (LPFC) to calculate the area in each hemicranium, compare them and obtain the normal range of asymmetry. Parametric and non-parametric comparison tests were realized. The structures that had the lowest range of asymmetry were the LPFC (0.00-0.79 mm) and the FR (0.00-2.12 mm). The one that had the highest asymmetry range was the FO (0.00-9.16 mm). Significant differences were found in the FO (p = 0.01) and the IAC (p = 0.00) in the gender comparison. We determined a normal asymmetry range of the susceptible foramina and canals of the skull base. This study reports a useful and objective measure to differentiate anatomical from pathological variations of the foramina and canals of the skull base by age and gender. Our results establish a basis for future studies that evaluate this range as a diagnostic tool of metastasis in the skull base as a complement of other imaging techniques.