Steroid-Responsive Retroperitoneal Fibrosis and Sclerosing Mesenteritis as the Initial Manifestation of an Occult Neuroendocrine Tumor

Retroperitoneal fibrosis (RPF) and sclerosing mesenteritis (SM) are rare entities characterized by fibrous inflammatory tissue that can surround and compress adjacent abdominal structures, leading to organ damage. RPF and SM have rarely been reported to present simultaneously. Idiopathic forms of RPF and SM are typically treated with immunosuppression, whereas treatment of RPF and SM secondary to malignancy relies on treating the underlying malignancy. We present a patient with steroid-responsive RPF and SM ultimately found to be secondary to an occult small intestinal neuroendocrine tumor who responded to octreotide therapy for the underlying neuroendocrine tumor.