Primary amoebic (Naegleria) meningoencephalitis.

The computed tomographic (CT) appearance of a case of primary meningoencephalitis due to the free living amoeba Naegleria fowleri is presented. The cisterns around and above the midbrain and the subarachnoid spaces were obliterated on precontrast CT. Marked enhancement in these regions was seen after intravenous contrast medium administration. The sulci and adjacent grey matter were also strongly enhanced. The ventricular size was normal. Pathological findings were those of arachnoiditis and invasion of the leptomeninges and brain substance by amoebae, especially at the base of the brain and cerebellum.