Neuropathological and ultrastructural features of amebic encephalitis caused by Sappinia diploidea

Here we present the neuropathological, ultrastructural, and radiological features of Sappinia diploidea, a newly recognized human pathogen. The patient was a 38-year-old man with visual disturbances, headache, and a seizure. Brain images showed a solitary mass in the posterior left temporal lobe. The mass was composed of necrotizing hemorrhagic inflammation that contained free-living amebae. Immunofluorescence microscopy showed that the organism was not a species of ameba previously known to cause encephalitis. Trophozoites had a highly distinctive double nucleus, and transmission electron microscopy confirmed that they contained 2 nuclei closely apposed along a flattened surface. The 2 nuclei were attached to each other by distinctive connecting perpendicular filaments. This and several other unique structural features led to the diagnosis of S. diploidea encephalitis. The patient was treated postoperatively with a sequential regimen of anti-amebic drugs (azithromycin, pentamidine, itraconazole, and flucytosine) and is alive after 5 years. Guidelines to recognize future cases of S. diploidea encephalitis are as follows. 1) It presented as a tumor-like cerebral mass without an abscess wall. 2) It had central necrotic and hemorrhagic inflammation that contained acute and chronic inflammatory cells without granulomas or eosinophils. 3) It contained trophozoites (40-70 μm diameter) that contained a distinctive double nucleus. 4) Cyst forms in the host were not excluded or definitely evident. 5) Trophozoites engulfed host blood cells and were stained brightly with Giemsa and periodic acid-Schiff. 6) Trophozoites often were present in viable brain parenchyma on the periphery of the mass without inflammatory response. 7) The prognosis after surgical excision and medical treatment was favorable in this instance.