The microsurgical anatomy of the hypoglossal canal.

BACKGROUND: The hypoglossal canal (HC) is a region of the skull base whose involvement in many pathological entities is often ignored. Adequate knowledge of the anatomy of the HC and its related bony, neural, and vascular structures is essential for surgery of lesions involving this area.

METHODS: Ten adult human cadaver heads from a US source fixed by formalin (20 sides) and 20 dry human skulls from Indian sources (40 sides) were used in this study. Various aspects of the anatomy of this region including the size, course and variation of the hypoglossal nerve and its relationship to the adjacent and canalicular course were recorded.

RESULTS: The left HC was located at 10 o'clock and the right HC at the 2 o'clock position with respect to the foramen magnum. The canal was surrounded superiorly by the jugular tubercle, superolaterally by the jugular foramen, laterally by the sigmoid sinus and inferiorly by the occipital condyle. All dry skulls were drilled in the horizontal plane at an axis of about 45 degrees and directed slightly upwards.

CONCLUSIONS: Detailed knowledge of the microsurgical anatomy of the region of the HC is crucial when performing surgery for lesions of the condylar region, the lower clivus, and ventral brain stem. This study provides the knowledge required to achieve accurate orientation and effective maneuvers during surgical procedures for treatment of the patient without injuring the vital neural and bony structures.