Unilateral Duplication of the Foramen Spinosum With Unusual Bilateral Variation of Hypoglossal Canals in a Dry Human Skull: Their Clinical Implications

The foramen spinosum is one of the foramina of the skull that lies bilaterally close to the spine of the sphenoid in the middle cranial fossa. The recurrent meningeal branch of the mandibular nerve, middle meningeal artery, and vein usually passes through it. The hypoglossal canal, situated superior to the occipital condyles at the skull base, is a paired bony canal directed anterolaterally and serves as a conduit for the hypoglossal nerve, meningeal branch of the ascending pharyngeal artery, and emissary veins communicating with the basilar venous plexus. Duplication of the foramen spinosum along with duplication and triplication of the hypoglossal canal in the same skull is a rare osteological variant that may lead to variation in the course of contents. Recognition of such variations is of considerable clinical importance for neurosurgeons, skull base surgeons, and radiologists, as these anomalies may influence surgical planning and increase the risk of inadvertent neurovascular injury during procedures involving the middle and posterior cranial fossae. We report a case with duplication of the left foramen spinosum having a maximum diameter of 3.3 mm and 2.7 mm located just medial to the spine of the sphenoid. The same skull showed duplication of the left hypoglossal canal with a maximum extracranial diameter of 6.5 mm and triplication of the right hypoglossal canal with a maximum diameter of 7.6 mm located lateral to the occipital condyles. Coexistence of variation in the two types of foramina would certainly make it much clinically significant during skull base surgery to approach the middle meningeal artery and hypoglossal nerve in the middle and posterior cranial fossae, respectively. Surgeons should be cognizant about these variants while doing surgical procedures involving the middle meningeal artery and the transcondylar approach for the hypoglossal nerve to avoid further complications.