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Background: Melanocytomas are rare neoplasms derived from leptomeningeal melanocytes. Cerebellopontine localisation has rarely been reported. Presenting manifestations include cranial nerve involvement such as sensory disturbances in the face, diplopia and deafness. We report a patient with a posterior fossa melanocytoma revealed by a Bell's type facial palsy. Clinical details: A14-year-old boy developed a rightsided facial palsy diagnosed as a Bell's type palsy. A blood examination including serology for Mycoplasma and Borrelia was normal. Two months later he was admitted because of increasing facial weakness, diplopia, right-sided hearing loss and dysphagia. Clinical evaluation confirmed the involvement of cranial nerves VI, VII, VIII, IX, X and XI on the right side. Brain MRI revealed a circumscribed, polylobular, enhancing tumour in the right cerebellopontine angle extending in the foramen jugulare. The tumour was hyperintense on the T1- and hypointense on the T2-weighted images. A subtotal resection was performed. Pathological examination revealed a melanocytoma. Radiotherapy was given. Pathology: Light microscopical examination revealed a collagen-rich, heavily pigmented, poorly cellular tumour composed of islands of spindle and epitheloid cells, with minor nuclear atypia, small nucleoli and no mitotic figures. There were no necroses. Most cells were positive for protein S100, vimentin and HMB-45. They were negative for EMA. The Ki-67 labeling index was low (Conclusions: This is the first report of a patient with a cerebellopontine angle melanocytoma revealed by a Bell's type facial palsy. Although MRI may suggest melanin content, pathological examination is essential for diagnosis of this rare lesion and for differentiation from other pigmented tumours found in this location such as melanomas, melanotic schwannomas and melanotic meningiomas.

Summary: The differential diagnosis between intracerebral necrotic tumors and cerebral abscesses is frequently impossible with conventional MR imaging. We report two cases of cerebral abscesses that showed high signal on diffusion-weighted echo planar imaging and a strongly reduced apparent diffusion coefficient. This appearance was not present in our cases of necrotic/cystic gliomas (eight cases) and necrotic metastases (two cases). We believe that diffusion-weighted MR imaging may be a diagnostic clue in cases of cerebral “ring-enhancing” masses.