Pilocytic astrocytomas: well-demarcated magnetic resonance appearance despite frequent infiltration histologically.

Abstract

OBJECTIVE: To determine the magnetic resonance imaging (MRI) characteristics of pilocytic astrocytomas and to correlate them with the histopathologic findings. MATERIAL AND METHODS: MRI examinations and histopathologic findings in 56 patients with pilocytic astrocytomas were retrospectively reviewed. In 38 patients, findings on MRI were compared with those on computed tomography. RESULTS: The tumors occurred at all levels of the central nervous system, including the spinal cord. The intracranial tumors were periventricular (73%) or periaqueductal (9%). All tumors were typical pilocytic astrocytomas and were grade 1 on the basis of the World Health Organization classification. At operation, they were often circumscribed and cystic. Radiologically, the tumors were well demarcated (96%), had benign morphologic features, and almost always showed enhancement (94%). CONCLUSION: MRI of pilocytic astrocytomas typically demonstrated a relatively large, sharply demarcated periventricular mass with pronounced contrast enhancement but minimal or no associated edema. Often, the tumors were cystic on MRI. Despite the well-demarcated appearance grossly and on MRI, pathologic review showed that many of these tumors (64%) infiltrated the surrounding parenchyma, particularly the white matter.