Morphological Study of Stylomastoid Foramen at the Base of Skull and its Role in Facial Nerve Palsy

The facial nerve emerges out of skull through the stylomastoid foramen located between styloid process and mastoid process. Unilateral paralysis of facial nerve is known as Bell's palsy and is reported to be caused most frequently by herpes simplex virus. The herpes infection is comparatively common but Bell's palsy is not very common. So, other causes of Bell's palsy like variation in morphological forms of stylomastoid cannot be ruled. There is paucity of literature elucidating morphological shapes of this foramen and correlating these forms of foramen with Bell's palsy. Hence the study was carried out. The aim of this study is to expound varied forms of stylomastoid foramen and to bring out clinical implications. The study was conducted in the department of anatomy using undamaged 70 adult dry human skulls of unknown age and sex. The morphological shapes were observed, interpretated and compared with available literature and their clinical implications were brought out. Most common shapes observed were round and oval followed by square shapes. Round shaped foramina were observed in 40 skulls on right sides constituting 57.1% and in 36 skulls on left side constituting 51.4%. While oval shapes were found in 16 skulls on right side (22.6%) and in 12 skulls on left side (17.1%). Rare variants of the foramen include triangular, serrated and closely applied to styloid process. The rare morphological forms were mostly observed to be unilateral in occurrence. Unilateral Bell's palsy is common, so, the rare morphological forms might be responsible for Bell's palsy.