The clinical conundrum of convexal subarachnoid hemorrhage

Nontraumatic subarachnoid hemorrhage (SAH) classically involves the subarachnoid space of the basal cisterns and the cerebral convexity, with ruptured aneurysms of the circle of Willis accounting for about 80% of the cases. The remainder, nonaneurysmal forms of SAH, are a heterogeneous group, in which about one-third (5% of total SAH) are limited to the cisterns that surround the brainstem, and are thought to be due to rupture of venous structures in the perimesencephalic region,^1,2 although other potential mechanisms have been postulated.³

A much less well-characterized form of SAH is the variety that occurs in the cerebral convexity as a localized focus of bleeding in one or several adjacent sulci, without associated SAH at the base of the brain or elsewhere. This form of “convexal” SAH (cSAH) is frequently encountered in clinical practice, and presents at times with acute headache suggestive of SAH, but often it is an unexpected finding on imaging in patients evaluated for a variety of symptoms, including change in mental status, transient focal neurologic deficits, or partial …