Periventricular white-matter cysts in a murine model of gram-negative ventriculitis.

Hydrocephalic patients with shunt infections frequently develop multiple cerebrospinal-fluid-density cysts that cause midline shift and life-threatening intracranial hypertension and respond poorly, if at all, to shunt diversion of cerebrospinal fluid. These cysts have been considered to represent multiloculation of the ventricular system by ependymal adhesions and veils resulting from ventriculitis. Studies using an experimental model of E. coli meningitis/ventriculitis in the hy-3 mouse suggest these cysts: (1) develop by the coalescence of lakes of white-matter edema, (2) grow to large size entirely within the periventricular white matter, and (3) cause pseudoloculation of the ventricle by compression from without. The so-called intraventricular septa or "veils" are the ependyma displaced inward by subependymal cysts or sheets of residual pericystic white matter. This finding permits better interpretation of computed tomographic images depicting persistent enlargement of the so-called multiloculations despite functioning ventricular shunt catheters, the multiplicity of cysts, and the white-matter location of these cysts.