Case 106. Naegleria meningoencephaliitis (26 y-o M)
Lethal acute meningoencephalitis menifesting 1 week after diving into fresh water
Key words : Naegleria fowleri, meningoencephaliitis, free-living ameba
Macrophage-like trophozoites of Naegleria fowleri are clustered around small vessels in the Virchow-Robin space (HE). The lesion extends in a centripetal fashion from the subarachnoid space into the cerebral cortex.   Numbers of macrophage-like trophozoites with eosinophilic vacuolated cytoplasm are clustered around small vessels near the brain surface (HE). Cysts are not formed in the lesion.
Oil immersion observation of the trophozoites in the Virchow-Robin space discloses the vacuolated cytoplasm and a single nucleus with centally located (target-like) karyosome.   Reference case 106A
Another case (35 y-o F) of fulminant amebic meningoencephalitis (HE). The free-living ameba trophozoites invade the subarachnoid space via the nasal cavity. The necrohemorrhagic lesion is thus prominent in the olfactory bulb.
Reference case 106A
Fulminant amebic meningoencephalitis with PAS-negative trophozoites. In contrast to anerobic Entamoeba histolytica, PAS reactivity is not observed in aerobic Naegleria fowleri.