A complex dural-venous variation in the posterior cranial fossa: a triplicate falx cerebelli and an aberrant venous sinus.

Variations of the dural folds and the dural venous sinuses are seldom reported in the extant medical literature. Such variations in the posterior cranial fossa may be problematic in various diagnostic and operative procedures of this region. We report our observation of an extremely rare variation of the falx cerebelli and posterior cranial fossa venous sinuses encountered upon dissection of a young male cadaver. In this specimen the falx cerebelli was duplicated with dimensions of 45.3x5.1 mm and 49.8x5.3 mm for the right and left falces respectively. The distance between the two falces was 3.2, 4.5 and 7.8 mm at their proximal, middle and distal thirds. An accessory small falx (31.8x2 mm) was also found approximately 3.4 mm lateral to the right falx cerebelli and blended with the lateral surface of the right falx cerebelli. There was only one occipital venous sinus (diameter, 2.5 mm) and no marginal sinus was detected. At the right floor of the posterior cranial fossa (posterolateral to the foramen magnum) an additional dural venous sinus was found, which connected the terminal portion of the right sigmoid sinus to the occipital and right transverse sinuses via one medial and two lateral branches respectively. We believe that such a complex dural-venous variation in the posterior cranial fossa has not previously been reported. Neurosurgeons and neuroradiologists should be aware of such variations, as these could be potential sources of haemorrhage during suboccipital approaches or may lead to erroneous interpretations of imaging of the posterior cranial fossa.