Perimesencephalic nonaneurysmal subarachnoid hemorrhage in the pediatric population: case report and review of the literature.

In approximately 15% of children with atraumatic subarachnoid hemorrhage (SAH), the cause of the hemorrhage cannot be determined despite detailed imaging studies. Perimesencephalic nonaneurysmal subarachnoid hemorrhage (PNSH) is well recognized as a distinct type of SAH in the adult population and may account for up to two thirds of these SAHs of unknown cause. PNSH in the pediatric population, however, is not well recognized. In this report, we confirm the existence of PNSH in the pediatric population by describing a 4-year-old boy who presented with acute SAH in the perimesencephalic cisterns and subsequently had two negative angiograms with a benign clinical course. Recognition of PNSH in the pediatric population is important, especially in view of its benign nature.