Unilateral vestibular schwannomas (VS) differ from those in patients with neurofibromatosis 2 (NF-2) clinically and by in situ appearance. To determine whether there are histopathologic differences, the presence of each of 16 histologic features was compared in first surgical resection specimens of 48 VS from 39 NF-2 patients and 293 unilateral VS. Antoni A and B areas, nuclear atypia, whorls, scarring, chronic inflammation, and sheets of macrophages were found equally in both groups. Vestibular schwannomas in NF-2 had more Verocay bodies, foci of high cellularity, and lobular growth patterns, the latter possibly correlating with in situ appearance. Ten NF-2 VS specimens had either meningiomas or microscopic meningeal cell proliferations removed with the VS from the same area, whereas none of the patients with a unilateral VS had these findings. Unilateral VS had more hyalinized and malformed vessels, recent and old thromboses and hemosiderin deposits. The differences could not be attributed to patient ages because there were similar differences between the VS in NF-2 and the unilateral VS of 40 patients age-matched to the NF-2 patients. There were more female patients in both groups, but gender did not influence the occurrence of any histologic features. There were nine additional patients with apparently unilateral VS but in whom the diagnosis of NF-2 was suggested by additional findings; six of the VS from these patients had lobular patterns.(ABSTRACT TRUNCATED AT 250 WORDS)