Oncocytic choroid plexus carcinoma: case report.

: Herein, we report an unusual choroid plexus carcinoma with extensive oncocytic transformation. A 13-month-old girl presented with acute lethargy which quickly progressed to coma. A CT scan of the head revealed impending herniation due to hemorrhage within an intracranial tumor. An MRI scan showed a large, partly cystic and highly vascular left lateral ventricular mass. A near total resection was achieved. Microsections revealed a WHO Grade III choroid plexus carcinoma with extensive oncocyti c transformation. A minor portion of the moderately to poorly differentiated tumor exhibited classical microscopic features of choroid plexus carcinoma, including marked nuclear atypia, brisk mitotic activity (78/10 HPF), a high MIB-1 labeling index (44%) and zones of necrosis. In contrast, the large, eosinophilic, cytologically malignant but granular-appearing oncocytes comprising the majority of the lesion showed scant (1/10 HPF) mitotic activity and only a low MIB-1 labeling index (5%). A subsequent recurrence at 1 year consisted entirely of non-oncocytic tumor. Choroid plexus carcinoma with oncocytic transformation has not been previously reported. The remarkable extent of this alteration and its clinical significance remains to be determined.