Pineal parenchymal tumors of intermediate differentiation

Abstract

Pineal tumors arising from the gland parenchyma are a rare and heterogeneous group of neoplasms, representing less than 0.3% of all intracranial neoplasms. Among those tumors arising from the pineal region, approximately one quarter, will originate from pinealocytes, the principal cells of the pineal parenchyma. Given their rarity, our understanding of pineal parenchymal tumors continues to evolve; this has been reflected by changes to the World Health Organization (WHO) classification of the tumors of the central nervous system. Pineal parenchymal tumors represent a continuum of disease, ranging from the benign pineocytoma [WHO grade I] to the highly aggressive, small round cell tumor, pineoblastoma [WHO grade IV]. In between these two ends of cellular differentiation exists the pineal parenchymal tumor of intermediate differentiation [WHO grades II-III]. Pineal parenchymal tumors of intermediate differentiation are a recently defined disease; its first formal recognition by the WHO occurred in 2007. These tumors were first identified as having mixed elements of both pineocytomas and pineoblastomas, carrying an intermediate clinical prognosis. The number of available studies regarding pineal parenchymal tumors of intermediate differentiation is currently limited. The reported incidence of these tumors is variable within the literature, reflecting the difficulties in establishing clinically relevant and reproducible classification criteria. Management of this disease has been highly individualized, without any consensus treatment guidelines. This review aims to summarize the current understanding of tumor epidemiology, defining morphologic features, relevant subtyping schema, molecular and genetic features, clinical management, and expected prognosis.