Purpose or Case Report: Peritoneal disease in the pediatric population is exceedingly rare. When encountered, differential diagnoses typically include infection, inflammation, and metastatic disease. However, we report a case of malignant epithelial peritoneal mesothelioma to emphasize that this primary malignancy should also be considered.

A 14 year old male with a history of growth hormone deficiency, gastroesophageal reflux disease, and asthma presented to his primary care physician with chronic abdominal pain, mild anemia, and over 20 pound weight loss in a 9 month period. Outpatient workup by gastroenterology showed elevated ESR and CRP and a single hyperplastic polyp on endoscopy. MRI enterography of the abdomen and pelvis with intravenous contrast was completed to evaluate for inflammatory bowel disease. This exam revealed a thickened omentum, hyperenhancement of the peritoneum and omentum, peritoneal nodularity, a moderate to large volume of ascites, and enhancing nodules along the superior surface of the diaphragm. The nodules were further evaluated with a dedicated CT chest, abdomen, and pelvis, which confirmed the above findings.

Differential diagnosis of an abdominal mesothelial process as above includes familial mediterreanean fever, malignancy, and infection. Laparoscopic omental and peritoneal biopsies showed mesothelial hyperplasia. Genetic testing returned positive for a CDKN2A homozygous and heterozygous deletion, confirming the diagnosis of diffuse malignant peritoneal mesothelioma.

The patient is currently under treatment with a cisplatin-based chemotherapy regimen and is being closely followed. Our case exemplifies the symptoms, imaging findings, diagnosis, and treatment associated with malignant epithelial peritoneal mesothelioma.
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