Mesenteric Fibromatosis Mimicking Metastasis of Neuroendocrine Tumor on 18F-AlF-NOTA-Octreotide PET/CT and Contrast-Enhanced MRI

A 52-year-old man with a prior history of resected G2 pancreatic neuroendocrine tumor presented with a newly identified abdominal mass during 17-month follow-up. Contrast-enhanced MRI depicted a heterogeneously hyper-enhancing jejunal mesenteric lesion, highly suggestive of metastatic disease. ¹⁸F-AlF-NOTA-Octreotide PET/CT revealed mild tracer accumulation within the lesion, which was initially interpreted as NET metastasis. Surgical pathology ultimately confirmed mesenteric fibromatosis. This case emphasizes an important diagnostic trap, as benign fibromatosis can mimic NET metastasis on both anatomic and SSTR-targeted PET imaging, alerting clinicians to avoid misdiagnosis and unnecessary treatment.