Concomitant completely ossified trigeminal pore and Dorello's canal.

Commonly, the trigeminal and abducens nerve course to the middle cranial fossa, beneath the tentorial border (posterior petroclinoid dural ligament) and, respectively, beneath Grüber's petrosphenoidal ligament, in Dorello's canal. It is hereby reported a rare unilateral association of anatomic variants which was found when the brain computed tomography angiography of a 56-year-old male patient was observed. On the left side, the tentorial border was ossified above the petrous apex, resulting in a tentorial bar 1.96 cm long that transformed the trigeminal pore into a completely ossified one. On that side was also found an ossified petrosphenoidal ligament determining a completely ossified Dorello's canal. On the opposite side a 2.9 mm long clinoid bar extended from the posterior clinoid process to the anterior one. Although these bars are not common in humans they should be documented in computed tomography in cases with associated trigeminal neuralgia and abducens nerve palsy.

Bilateral absence of the transverse sinuses with fenestrated superior sagittal sinus draining through enlarged occipital and marginal sinuses.

The endothelial-lined dural venous sinuses collect blood from the brain, meninges, and calvaria and drain it to the internal jugular veins. The adult drainage pathway of the venous sinuses confluent is commonly via the transverse and sigmoid sinuses to the jugular bulb. The occipital (OS) and marginal (MS) sinuses are well-represented before birth, in most cases. During a retrospective study of the computed tomography angiograms of a 64-year-old female was found a rare combination of variants of the posterior fossa sinuses. The confluence of the dural venous sinuses was rhomboidal and drained superiorly the superior sagittal sinus, and inferiorly a well-represented OS. The transverse sinuses were aplastic, on the right side, and hypoplastic on the opposite side. The OS further drained into the MS which, on each side, emptied into the respective jugular bulb. On each side a condylar vein left the junction of the sigmoid sinus and jugular bulb. Such posterior fossa drainage, exclusively on the OS-MS pathway, should be kept in mind when transections of the venous sinuses are intended during neurosurgical approaches of the foramen magnum. The OS-MS drainage is rather a persisting foetal pattern. The bilateral anatomical exclusion of the transverse sinuses is an added condition to spare the OS and MS.