Histopathological patterns of papillary tumour of the pineal region

Papillary tumour of the pineal region (PTPR) is a rare neoplasm that has been formally included in the 2007 WHO classification of central nervous system tumours. The critical diagnosis of this neoplasm is often difficult because of its similarity to other primary or secondary papillary lesions of the pineal region, including parenchymal pineal tumours, papillary ependymoma, papillary meningioma, choroid plexus papilloma and metastatic papillary carcinoma. We present the variability of the histopathological pattern in three cases of PTPR. All cases showed predominant epithelial-like morphology but with various degrees of papillary formation and intensity of cellular pleomorphism. One tumour was highly cystic and exhibited cellular sheets containing vessels covered by several layers of uniform columnar to cuboidal tumour cells. The second tumour showed distinct papillae covered by layers of polymorphous cells with atypical, often hyperchromatic nuclei. Numerous cells displayed foamy, eosinophilic or clear, sometimes vacuolated cytoplasm. The third case consisted of solid cellular areas composed of pseudostratified columnar cells, most often arranged in perivascular pseudorosette formations. The cells lining papillary structures exhibited marked polymorphism with atypical, often plump nuclei. Mitotic figures were rare and areas of necrosis were observed only in one case. Immunohistochemical staining showed diffuse immunoreactivity for neuron-specific enolase, S-100 protein, cyto-keratin and vimentin. Focal reaction for synaptophysin and chromogranin A and epithelial membrane antigen (EMA) were observed. The tumours lacked expression of GFAP. The Ki-67 labelling index was relatively low but its focal increase was noted in two cases. The final diagnosis of PTPR was based on both predominant papillary morphology and immunohistochemical results. PTPR should be considered in diagnosis of pineal tumours but their natural history, therapeutic strategy and prognosis remain controversial.