The vascular layers on the rostral ventrolateral medulla.

There has been a keen interest in assessing the neurovascular anatomy of the rostral ventrolateral medulla oblongata (RVLM). The present study was aimed at documenting the complete neurovascular anatomy of the RVLM, in order to offer a general picture of the possible offending vessels of this area, which seems to be involved in the pathogeny of the essential hypertension. Noteworthy, syndromes of the last cranial nerves could be due to vascular contacts or compressions. The present study was performed on 20 human adult brainstem-cerebellum blocks, dissected out of the posterior cerebral fossa at autopsies. The origins of the inferior cerebellar arteries (anterior--AICA and posterior--PICA) were traced bilaterally (n=40 sides). When present (26/40) AICA most frequently left the basilar artery and PICA (28/40) most frequently left the vertebral artery. At the level of the RVLM, a quadrilateral space delimited by the vertebral artery (VA) and the vertebrobasilar junction, the AICA and the PICA, was defined. Within that space, three vascular layers were identified: a superficial one, formed by the inferior cerebellar arteries, a middle one, consisting of perforating arteries, and a deep, venous one. The RVLM perforating arteries left the VA (31/40), basilar artery (BA) (3/40), anterior spinal artery (ASA) (34/40), PICA (28/40) and AICA (24/40). These perforators had a transverse or oblique course if given off by the VA, BA or ASA, were descendant if given off by the AICA or BA, and were ascending if given off by the VA or PICA. Microanatomical studies of the vascular relations of the RVLM are able to complete the somewhat limited findings of studies based on imaging techniques. The offending vessels of the RVLM could be any of the vessels inside the quadrilateral space. Major vessels, such as the VA, AICA or PICA should not be viewed as the only possible offending vessels at this level. The perforators and the venous layers in the quadrilateral space should also be better evaluated from this perspective.