ABSTRACT
Background and Objectives: The foramen spinosum (FS) is an important opening on the greater wing of the sphenoid bone and transmits the middle meningeal artery to the middle cranial fossa. Because the presence of FS is important in microsurgery of this area, the anatomic and morphometric consideration for localizing the FS using external landmarks were studied. Methods: One hundred and three dry skulls were examined for the FS in the middle cranial fossa and at the extracranial view of the skull base. The type of FS was classified according to its shape. Its diameter and the distances to the zygomatic arch (ZA) and the external acoustic meatus (EAM) were also measured. Results: The FS in both views of the skull base was mostly round in shape (43.2% intracranially and 49.5% extracranially) and was present bilaterally 30.1% extracranially. The maximum and minimum diameters of the FS and the FS-ZA distance were greater in males than females and the ZA-EAM distance was greater on the right than the left sides significantly. (P<0.05) Conclusion: Although a great variation was found in the shapes of the FS, prior estimation of the location of FS was suggested using external landmarks as the point on the ZA 16.42 mm anterior to the EAM and 34.19 mm from that point medial and perpendicular to the ZA. These findings may help neurosurgeon to approach the middle cranial fossa more precisely and gain better preservation of surrounding neurovascular structures.