Pathology of Pineal Parenchymal Tumors Seunggu J. Han, MD a , Aaron J. Clark, MD, PhD a , Michael E. Ivan, MD a , Andrew T. Parsa, MD, PhD a, *, Arie Perry, MD a,b Neoplasms of the pineal region are a rare group of tumors accounting for less than 1% of all intracranial tumors, 1–3 and represent a very clinically and path- ologically heterogeneous group of tumors including pineal parenchymal tumors, germ cell tumors, as- trocytomas, ependymomas, and papillary pineal tumors. Many investigators have therefore stressed the importance of a tissue-based diagnosis for pa- tient management. 2 Tumors thought to arise from the parenchymal cells of the pineal gland, also referred to as pineal parenchymal tumors, consist of approximately one-third of all tumors of the pineal region. 1,4 The latest World Health Organization (WHO) classification scheme, released in 2007, cat- egorizes pineal parenchymal tumors into 3 sub- types with up to 4 different grade categories: (1) WHO Grade I pineocytomas, (2) WHO Grade II or III pineal parenchymal tumors of intermediate differ- entiation, and (3) WHO Grade IV pineoblastomas. 5 This review focuses on the spectrum of pathologic features found in these pineal parenchymal tumors. PINEOCYTOMAS Pineocytomas are the lowest grade (WHO Grade I) tumors with the most favorable prognosis. 6,7 The 5-year survival has been reported to range from 64% to 91%, 1,8–10 although the latter figure is prob- ably more accurate when strictly defined using the most current criteria. These tumors are found most commonly in the adult population, and clinically appear to progress slowly, although symptomatic recurrences have commonly been reported even after aggressive resection. 11–13 Pineocytomas grossly are well circumscribed and cause symp- toms by local growth with local compressive mass effect. 1,8,14 The histologic features of pineocytomas include their cellular resemblance to mature pine- ocytes, and they are primarily composed of well- differentiated cells. 4 However, in contrast to the normal pineal gland’s lobular architecture created by gliovascular septae (Fig. 1A), pineocytomas are arranged in sheets of rounded tumor cells with variable oligodendroglioma-like clear haloes (Fig. 1B). Portions of the tumor are occasionally found to have focal ganglionic and/or astrocytic differentiation, and at times cells displaying fea- tures of ganglion cells and astrocytes can be found within the same tumor. 11,15 Early studies have sug- gested a more benign clinical course for pineocyto- mas with neuronal or neuronal and astrocytic differentiation, with a greater tendency to remain localized as compared with pineocytomas with as- trocytic differentiation. 15 More recent studies, how- ever, have failed to establish this correlation. 16 Pineocytomatous rosettes (Fig. 1C), also referred to as pineocytic rosettes, are frequently observed, and are believed to be a distinct feature of pine- ocytomas. 8,11 These rosettes consist of tumor cells surrounding pink neuropil (collections of neuronal processes) and are similar in appearance to a Department of Neurological Surgery, University of California, San Francisco, 505 Parnassus Avenue, M779, Box 0112, San Francisco, CA 94117, USA b Department of Pathology, University of California, San Francisco, 505 Parnassus Avenue, San Francisco, CA 94117, USA * Corresponding author. E-mail address: ParsaA@neurosurg.ucsf.edu KEYWORDS  Pineal parenchymal tumors  Pineocytomas  Pineoblastomas  Pineal parenchymal tumors of intermediate determination Neurosurg Clin N Am 22 (2011) 335–340 doi:10.1016/j.nec.2011.05.006 1042-3680/11/$ – see front matter Ó 2011 Published by Elsevier Inc. neurosurgery.theclinics.com