Duplication of falx cerebelli, occipital sinus, and internal occipital crest.

The incidence of variations of falx cerebelli was studied in 52 adult cadavers of south Indian origin, at Kasturba Medical College Mangalore, after removal of calvaria. In eight (15.4%) cases, we observed duplicated falx cerebelli along with duplicated occipital sinus and internal occipital crest. The length and the distance between each of the falces were measured. The mean length of the right falces cerebelli was 38 mm and the left was 41 mm. The mean distance between these two falces was 20 mm. No marginal sinus was detected. Each of the falces cerebelli had distinct base and apex and possessed a distinct occipital venous sinus on each attached border. These sinuses were noted to drain into the left and right transverse sinus respectively. After detaching the dura mater from inner bony surface of the occipital bone, it was noted that there were two distinct internal occipital crests arising and diverging inferiorly near the posterolateral borders of foramen magnum. The brain from these cadavers appeared grossly normal with no defect of the vermis. Neurosurgeons and neuroradiologists should be aware of such variations, as these could be potential sources of hemorrhage during suboccipital approaches or may lead to erroneous interpretations of imaging of the posterior cranial fossa.