A 39-year-old woman first noticed episodic paresthesias involving her left trunk and left leg in January 1998. Neurologic examination was normal at the time, and she was able to continue all activities without limitations. Electrophysiologic studies and magnetic resonance images (MRIs) of the cervical, thoracic, and lumbosacral spine failed to show a cause for these paresthesias. In October 2000, she developed vertigo, gait ataxia, bilateral arm paresthesias, and bilateral facial numbness. Her symptoms were gradually improving, when in midNovember, she had progressive left-sided weakness and dysphagia. She received 3 days of intravenous methylprednisolone for presumed demyelinating disease and was transferred to our hospital for further evaluation. Medical history was remarkable for hypothyroidism following partial thyroidectomy, and duodenal ulcer. She had no history of tobacco, alcohol, or illicit drug use. She had two normal pregnancies without complications. Examination showed an obese woman, in acute distress secondary to hematemesis. She was mildly tachycardic, with normal ENT, dermatologic, cardiac, lung, and musculoskeletal findings. Neurologic examination showed a scanning type of dysarthria. Extraocular movements were normal, except for nystagmus on extreme lateral gaze. The remainder of the cranial-nerve examination was normal. She had a spastic left hemiparesis with predominant upper-extremity involvement. Muscle stretch reflexes were 2 and symmetric. Plantar responses were flexor. Initial ancillary studies during this admission are summarized in Table 1. MRI of the brain showed infarctions of varying ages involving multiple vascular territories (Fig 1). Magnetic resonance angiography showed mild tortuosity of the left vertebral artery. Catheter cerebral angiography was unremarkable. Five months later, she presented with a 2-week history of progressive right-sided weakness and dysarthria. She had no headaches, visual complaints, seizures, or syncope. She had no fevers, chills, nausea, vomiting, chest pain, shortness of breath, cough, upper-respiratory symptoms, lower-extremity edema, abdominal pain, change in bowel or bladder habits, or skin rashes. On examination, blood pressure was 126/55 mm Hg, pulse was 70 pm, respiratory rate was 20 pm, and temperature was 37.9C°. There was flaccid right-arm paralysis and right-leg spasticity. Strength was graded 1/5 on the right lower and upper extremities. There was decreased sensation to light touch and pinprick on the right leg and arm. She received a combination of aspirin/modifiedrelease dipyridamole (Aggrenox), and intensive rehabilitation with some improvement. Repeat MRI of the brain showed an area of restricted diffusion involving the left fronto-parietal cortex with no associated enhancement (Fig 2). Areas of old infarctions were seen as previously described. Results of cerebrospinal fluid (CSF) studies are shown in Table 2. A follow-up cerebral angiogram was unremarkable. Computed tomography (CT) scan of the abdomen and pelvis showed the presence of renal cysts and a right ovarian cyst. Chest CT scan showed no lymphadenopathy or arteriovenous fistula. Spine MRI showed only mild degenerative changes. Admission laboratory data showed a normal white blood cell count, normal serum chemistries and normal serum lactate dehydrogenase (LDH) levels. Repeat autoimmune and prothrombotic studies were completely unremarkable. Leptomeningeal and left posterior parietal and occipital open brain biopsy showed intravascular malignant lymphocytes in the capillaries, veins, and small arterioles of the meninges and cortex (Fig 3). The neoplastic cells were pleomorphic and mononuclear with high nuclear/ cytoplasmic ratio, prominent nucleoli, and occasional miFrom the Department of Neurology, Section of Neuropathology, and Section of Neurological Surgery, Indiana University School of Medicine, Indianapolis, IN. Address reprint requests to Alfredo Lopez-Yunez, MD, Department of Neurology, Indiana University School of Medicine, Indianapolis, IN 46202. Reprinted from Seminars in Cerebrovascular Diseases and Stroke 2002;2(1), copyright 2002 by Elsevier Science (USA). All rights reserved. 1052-3057/02/1105-00013$35.00/0 doi:10.1053/jscd.2002.129619