Granulomatous encephalitis, intracranial arteritis, and mycotic aneurysm due to a free-living ameba.

Primary amebic meningoencephalitis and granulomatous amebic encephalitis are well recognized clinicopathological entities caused by free-living amebas. Associated arteritis and "mycotic aneurysms" with infiltration of intracranial arteries by lymphocytes, amebic trophozoites and cysts have not been previously reported. A 26-month-old girl had a 3-week history of encephalitis, characterized, initially, by vomiting and low-grade fever. Subsequently, she developed ataxia, generalized weakness, lethargy, and esotropia. The first CSF showed 490 RBC/microliters, 705 WBC/microliters with 90% mononuclears. Her pupils reacted briskly to light. Moderate nuchal rigidity, nystagmus, fixed downward gaze, anisocoria, bilateral 6th nerve palsy, left arm monoparesis and left Babinski were present. CAT scan revealed slight symmetrical dilatation of anterior horns of lateral ventricles and an area of abnormal enhancement above the 3rd ventricle. She died 14 days after admission, 5 weeks after onset of symptoms. The brain showed focal necrotizing encephalopathy, involving thalami, cerebellum, brain stem, and cervical and upper thoracic spinal cord. Numerous free-living amebic trophozoites and cysts were present within a chronic granulomatous encephalitis. There were trombosis of basilar, posterior cerebral, and vertebral arteries with profuse chronic panarteritis, fibrinoid necrosis, and mycotic aneurysms.