Neuropathological spectrum of pilocytic astrocytoma - an Indian series of 120 cases

Pilocytic astrocytomas (PAs) are generally well circumscribed, slowly growing, cystic tumors, occurring in the pediatric age group. Our aims were to retrospectively analyze the neuropathological spectrum of PA, and correlate it with various clinicopathological features. A total of 120 PAs, diagnosed and managed at this center during a 5-year period, were included. The study population had a mean age of 18.9 years, with male predominance (68.3%), and demonstrated predilection for posterior fossa (61.7%). On histopathology, biphasic pattern (89.2%) along with Rosenthal fibers (66.7%) and eosinophilic granular bodies (60%) were present in the majority of cases. Vascular features were characterized by perivascular hyalinization (51.7%), angiomatous proliferation (21.7%) and glomeruloid changes ( 21.7%). Hemosiderin-laden macrophages were noted in 37.1% of cases. Further, 60.8% showed lymphoplasmacytic infiltration, while atypia and necrosis were present in 25.8% and 1.7% of cases, respectively. Statistical evaluation revealed significant correlation of angiomatous proliferation with age (<= 12 and > 12-year age groups) (p=0.011); and of hemosiderin deposition with angiomatous proliferation (p=0.006), perivascular hyalinization (p=0.035), and age (<= 12 and > 12-year age groups) (p=0.028). This study emphasizes that though PAs generally display classical histomorphology, diagnosis may be challenging in patients with unusual clinicopathological features, e. g. in older patients, uncommon location, absence of biphasic pattern, or presence of nuclear atypia, mitotic figures and necrosis, and also in cases of small biopsies. In the absence of diagnostic histology enumerated above, vascular features like angiomatous proliferation, glomeruloid changes and perivascular hyalinization, along with hemosiderin-laden macrophages and perivascular lymphocytic infiltration should be considered as surrogate histological markers of PA.