A primary melanocytic lesion arising from the pineal gland is very rare. The authors report a case of primary pineal melanocytic
tumor with dissemination to the right hippocampus in a 50-year-old woman who presented with memory disturbance. Magnetic resonance (MR) imaging revealed a mass that was hyperintense on T1-weighted and hypointense on T2-weighted MR images. The
pineal tumor was removed subtotally via the occipital transtentorial approach, and the patient underwent whole-brain irradiation. Results of histological examination revealed that the
tumor predominantly consisted of atypical cells with scanty
melanin pigment and some necrotic foci. The strongly pigmented areas of the
tumor contained well-differentiated cells similar to those of melanocytoma. An ultrastructural study demonstrated evidence of a mature type of melanosome. The patient died 11 months after surgery and
radiotherapy (1.7 years after the onset of symptoms). The autopsy findings demonstrated
tumor invasion into the parenchyma through the leptomeningeal space and the ventricular wall. The
tumor was diagnosed as being malignant, and it was finally concluded that the atypical cells in the
tumor were probably responsible. This pineal melanocytic
tumor exhibited a wide spectrum of differentiation, ranging from highly
malignant melanoma to well-differentiated melanocytoma, which may have contributed to the patient's relatively long survival period. The biological behavior and morphological characteristics of this
tumor appear to be similar to those of other pineal parenchymal lesions.