Solitary Primary Central Nervous System Lymphoma Mimicking Third Ventricular Colloid Cyst-Case Report and Review of Literature.

Primary central nervous system lymphoma is a rare malignant tumor of the central nervous system. It is associated with poor prognosis and accounts for 0.7%-0.9% of all lymphomas and only 0.3%-1.5% of intracranial tumors. Typically, these lesions are in the cerebral white matter near the corpus callosum, the central gray matter, the basal ganglia-thalamus-hypothalamic region, the posterior fossa and the periventricular region. Only 2 cases with pure third ventricular lymphoma have been reported in the literature.A 72-year-old female patient known to have type II diabetes mellitus treated with insulin, hypertension, chronic kidney disease, dyslipidemia, and obesity presented with a history of acute confusion and urinary incontinence. No headache was reported on admission, but previously she had intermittent mild headaches and generalized body aches. She had no history of visual symptoms. Her family said she was mildly confused and had memory difficulties that started acutely 2 days before presentation to the hospital. The patient had urgent computed tomography of the brain, which showed a hyperdense lesion in the region of the foramen of Monro. Pre-operative images diagnosed the case as colloid cyst, but post-operative histopathology proved the lesion to be primary CNS lymphoma.Eleven months after surgery, the patient is fully consciousness and oriented, with no memory issues or neurologic deficit. She is back to her baseline activities. We are reporting this case for the rarity of the disease and the unusual location of it.