Answer: Gliomatosis peritoneii

Histology: The omentum contains multiple nodules of variably cellular glial tissue. No significant pleomorphism is identified. Many of the nodules are covered by a benign mesothelial surface.

Discussion: This histology is classic for gliomatosis peritoneii. This patient had a primary ovarian teratoma which was both solid and cystic. The ovarian teratoma contained various structures such as hair, teeth, intestinal type tissue etc. However the majority of the ovarian teratoma consisted of mature glial tissue. As with the peritoneal implants, the primary contained several areas with increased glial cellularity yet these areas lack characteristic findings of immature neuronal tissue. Immature neuronal tissue resembles neuroblastic tissue often making rosettes or pseudorosettes. In contrast to immature neuronal tissue, the cellular glial tissue seen in the current case lacks atypia and lacks mitotic figures in addition to lacking the architectural pattern of immature neuronal rosettes. Given that all of the peritoneal nodules were mature and lacked other teratomatous elements, the presence of peritoneal nodules of glial tissue is associated with a benign clinical course.