It seems quite possible that this patient may have acquired Acanthamoeba at the same time he acquired Legionella. Smoldering amoebic infection could account for much of the illness he experienced in the 28 months following transplantation. Acanthamoeba may have caused his facial abscess, his sinusitis and possibly even his diarrheal illness and urinary tract infection. The meninges overlying these foci may be cloudy. There may be uncal or cerebellar tonsillar herniation.
Lesions occur in the cerebral hemispheres, the basal ganglia, the brainstem and the cerebellum.
Microscopically, the characteristic lesion is a necrotizing subacute or chronic granulomatous encephalitis with lymphocytes, macrophages and multinucleated giant cells, associated with variable numbers of organisms. There may be thrombosis of small blood vessels associated with necrosis and hemorrhage. The cysts of Balamuthia are larger, 15-30 microns in diameter and have a thicker wall and more globular refractile contents than the cysts of Acanthamoebae. The trophozoites of all the amoebae have an irregular amoeboid shape. The trophozoites of Acanthamoebae tend to be 8-12 microns in greatest dimension in tissue sections.