Clinical course of nontraumatic, nonaneurysmal subarachnoid hemorrhage: a single-institution experience.

Object: Angiogram-negative subarachnoid hemorrhage (SAH) accounts for 15% of nontraumatic SAH and has been reported with low morbidity and mortality rates. We report on a large series of patients with angiogram-negative SAH who experienced an atypical nonbenign clinical course.

Methods: Between December 2001 and November 2006, 95 patients with spontaneous nonaneurysmal SAH and negative initial angiographic evaluation were treated at the University of Florida. The authors retrospectively reviewed the patients' medical records and radiological images to determine associated morbidity and mortality.

Results: Aneurysms were found in 6 of the 95 patients on follow-up imaging after an initial negative angiogram (6.3% false negative rate); these patients were excluded leaving 89 patients as the study group. Hydrocephalus necessitating temporary CSF diversion developed in 22 of these patients (25%); 12 (13%) ultimately required permanent CSF diversion. Clinically significant vasospasm developed in 4 patients (4%), and 2 (2%) had cerebral infarctions. Three patients (3%) died.

Conclusions: The authors' experience with a large series of angiogram-negative SAH patients who had an atypical nonbenign clinical course associated with hydrocephalus, vasospasm, stroke, and mortality differs significantly from previously published case series of angiogram-negative SAH.