Unusual primary central nervous system lymphoma location involving the fourth ventricle and hypothalamus.

A previously healthy 65-year-old man presented with a two-week history of weight loss, headaches, blurred vision, asthenia and quickly worsening walking impairment. He denied photophobia, neck stiffness, fever, nausea or vomiting.Neurological examination showed global motor slowing, tendency to fall asleep during the clinical examination, generalized weakness against resistance to head and limbs, and osteotendon reflexes present in the upper limbs, but not evoked in the lower limbs. No sensitive deficit or focal neurologic sign was recognizable.Non-contrast multislice computed tomography (MSCT) of the head was performed in the emergency department, showing diffuse periventricular white matter and thalamic mild hyperdensity.Lumbar puncture, blood tests, including serology for HIV and other infections, were negative.On the third day the patient, showing decreased consciousness, underwent magnetic resonance imaging (MRI) with contrast medium injection. MRI revealed the presence of multiple pseudonodular avidly enhancing lesions, supra and infratentorial, crossing the midline, involving the ventricular system, including the fourth ventricle, with extension into the surrounding white matter, the corpus callosum, the thalamus and the hypothamalus.A stereotactic biopsy led to a diagnosis of diffuse large B-cell lymphoma, primarily located in the central nervous system (PCNSL).After the completion of the first phase of treatment (immunotherapy with intravenous Rituximab and corticosteroid), the MRI showed a marked regression of tumor masses.