1. Sclerosing mesenteritis
Chronic mesenteric inflammation, usually involving the mesentery of the small bowel (rarely peripancreatic, omentum, and retroperitoneum)
Cause
Unknown cause, but often associated with other idiopathic inflammatory disorders like retroperitoneal fibrosis, sclerosing cholangitis, Riedel thyroiditis, orbital pseudotumor
May be related to prior abdominal surgery
Coexist with malignancy (69%) (lymphoma, breast, lung, colon cancer, melanoma)
3 subtypes, based on predominant tissue type within mass
Mesenteric panniculitis: acute inflammation with/without fat necrosis
Mesenteric lipodystrophy: fat necrosis > inflammation or fibrosis
Retractile mesenteritis: fibrosis/retraction > inflammation or fat necrosis

2. Imaging Findings of Sclerosing Mesenteritis
Acute mesenteritis
“Misty mesentery”: non-specific sign, increased attenuation of jejunal mesentery, without discrete soft tissue mass
Thin pseudocapsule encasing inflamed mesentery
Cluster of mesenteric lymphadenopathy
Mesenteric vessel and node have “halo” of uninflamed fat (“fat ring” sign)
Chronic phase
Solid soft tissue mass in mesentery root (fibrous tissue)
Often has stellate appearance
Encasement of mesenteric and collateral vessels
With or without calcification
Fatty necrotic cystic mass may be seen
Fat ring sign

3. Differential Diagnosis
Lymphoma
Usually multiple large discrete or confluent mesenteric nodes
No calcification unless treated (treated mesenteric lymphoma can look identical to mesenteritis)
Preservation of fat-ring sign favors sclerosing mesenteritis
Carcinoid tumor
Usually involves ileal mesentery
Primary hypervascular tumor with/without liver metastasis
Mesenteric edema
Seen in conditions like cirrhosis, heart failure, vasculitis, etc.
Desmoid tumor (fibromatosis)
Usually discrete solid mass
Others: carcinomatosis (metastasis), amyloidosis, inflammatory pseudotumor, IgG4-related disease