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Radiologic Findings: Large 2.1 x 2.7 x 2.9 cm (AP, lateral, c-c) mass in the pineal region. Abnormal signal is seen extending into the dorsal medial thalamus and into the tectum of the midbrain. Following contrast administration there is slight heterogeneity of this mass.
Diagnosis: Pineoblastoma.
Discussion: The pineal gland lies just posterior to the third ventricle. Pineal region masses account for 1-2% of all brain tumors. Pineoblastoma is a malignant neoplasm composed of undifferentiated pineal cells. This tumor is considered to be a type of PNET. Typically this lesion exhibits calcifications along the periphery of the mass as opposed to germinoma (typically central) or teratoma (dispersed). Following contrast administration on MR studies, this lesion typically exhibits dense enhancement. Additionally CSF dissemination is common with this lesion. Pineal region tumors often occur in children and young adults. Patients with pineal region tumors may present with Parinaud syndrome. This syndrome involves the inability to gaze upward due to compression of the tectal plate. Other patients may present with hydrocephalus due to compression of the cerebral aqueduct.
50% of pineal region tumors are germ cell tumors. These include germinoma (most common tumor), teratoma, embryonal cell carcinoma, and choriocarcinoma. Pineoblastoma is in the category of pineal cell tumors. This category comprises approximately 25% of pineal region tumors. The benign counterpart to the malignant pineoblastoma is the pineocytoma. Other differential considerations of a pineal region mass include meningioma, metastases, arachnoid cyst, or epidermoid/dermoid lesions.
References:
Osborn A. Diagnostic Neuroradiology. Mosby 1994.
Weissleder R, et al. Primer of Diagnostic Imaging, 2nd edition. Mosby 1997.
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