Endoscopic Visualization of an Iatrogenic Valve Mechanism: Elucidating the Pathogenesis of Postoperative Tumor Bed Cysts.

Space-occupying tumor bed cysts have been reported after resection of intracranial tumors, although the exact mechanism of their pathogenesis is unclear. Opening of the ventricular system during the tumor resection appears to be a risk factor. Occlusion of the surgical opening of the ventricle using fibrinogen-coated collagen fleece has been suggested to restore the integrity of the ventricular system. Here we present a clinical image depicting an iatrogenic valve mechanism caused by a fleece intended to seal a surgical opening of the lateral ventricle, leading to development of a space-occupying tumor bed cyst and cerebrospinal fluid fistula.