A Report of a Rare Case of Rapidly Progressing Immature Teratoma With Associated Splenic Metastasis and Gliomatosis Peritonei.

Gliomatosis peritonei (GP) is a rare condition of mature glial tissue within the peritoneum often associated with immature teratomas. This was a case of rapid progression of immature teratoma with splenic lesions and associated GP. The patient was a 21-year-old female who presented with abdominal pain and CT imaging showing suspected malignant teratoma. The patient underwent exploratory laparotomy with fertility-sparing debulking surgery and was diagnosed with stage IIIC grade 3 immature teratoma. She then received adjuvant chemotherapy with bleomycin, etoposide, and cisplatin. Surveillance imaging demonstrated a non-avid splenic lesion. The tumor markers remained normal. She underwent robotic splenectomy and partial peritonectomy with intra-operative findings revealing numerous peritoneal nodules. Follow-up surveillance imaging showed no further lesions. The final histopathology examination demonstrated mature and mesenchymal neural tissue consistent with residual teratoma and no immature elements. The specimens were largely composed of nodules of mature glial tissue and focal areas of mature neuronal tissue. Immunohistochemistry demonstrated glial fibrillary acidic protein (GFAP) and S100 expression, confirming neural origin tissue. Octamer-binding transcription factor 4 (OCT-4) immunostain was negative which confirmed the absence of immature neural tissue. We report a rare case of rapid progression of immature teratoma with splenic metastasis and peritoneal nodules found ultimately to be mature teratoma and associated GP. Recognition of rapidly growing teratoma with new lesions as potential GP is imperative to prevent misdiagnosis as recurrence or progression of disease. This case was treated with secondary debulking surgery which should be a consideration of management if surgically feasible.