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Neuroradiology

Pineoblastoma

primary pineal tumour arising along with pineocytoma from neuroepithelial cells of the pineal gland. As compared to pineocytoma it is composed of less differentiated cells but the two entities may coexist in the same lesions. This tumour is classified as one of the primitive neuroectodermal tumours (PNET), since it appears histopathologically identical to other primitive, undifferentiated neoplasms, e.g. cerebellar medulloblastoma, and exhibits similar biological behaviour. Although it can be found at all ages it predominates in the paediatric population. Unlike germinoma, females are equally affected as males. Pathologically it is a highly cellular tumour composed of poorly differentiated, immature cells with very scant cytoplasm. It tends to disseminate early through the subarachnoid pathways, with leptomeningeal and subependymal seeding often found at the time of initial diagnosis. The prognosis in children with these tumours is generally poor.

Pineoblastoma appears usually as a lobulated mass with irregular margins. Imaging features, shared with other PNET tumours are consistent with the paucity of cytoplasm and overlall dense cellularity, i.e. low water content, and are not very distinctive as compared to germinoma. On CT pineoblastoma is most commonly iso- to hyperdense and on MR it displays essentially isointensity to grey matter on both T1- and T2-weighted spin echo images. Enhancemenet is marked and uniform after contrast infusion. Focal haemorrhage and microscopic necrosis may occur and in this case the tumour appearance is less homogeneous. Calcification is common in the tumour tissue.

Pineoblastoma may coexist with bilateral retinoblastoma in the so-called "trilateral retinoblastoma" syndrome (see retinoblastoma).

FS