Pineal parenchymal tumours and pineal cysts.

BACKGROUND AND PURPOSE

Pineal parenchymal tumours (PPTs) and pineal cysts represent one third of the pineal region lesions. PPTs are subdivided into pineocytoma (PC), pineoblastoma (PB) and PPT with intermediate differentiation (PPTID). We report morphological and immunochemical features which permit to grade these tumours.

METHODS

The description of histopathological features and grading is based on a large cooperative series and on the WHO 2007 classification.

RESULTS

PCs occur in adults between the third and the sixth decade of life. PBs typically occur in children. PPTIDs have a peak incidence in young adults between 20 and 40 years of age. There is no sex preference. PC is characterized by a uniform cell proliferation with large fibrillary pineocytomatous rosettes. PB is a high-density tumour composed of small blue cells with hyper-chromatic, round or carrot shaped nuclei. PPTIDs have lobulated or diffuse patterns. Grading is based on morphological features, count of mitoses and neurofilament protein (NFP) expression. PCs (grade I) have no mitosis and NFP is highly expressed in pineocytomatous rosettes. PBs (grade IV) are high mitotic tumours and present low or no expression of NFPs. PPTIDs are grade II when mitoses are fewer than 6 for 10 high-power fields and NFPs are expressed, and are grade III when mitoses are greater or equal to 6 or are fewer than 6 with NFPs lowly expressed. Pineal cysts may be differentiated from PPTs by the high expression of NFPs and no expression of Ki-67.