Answer: IgG4-related tumefactive sclerosing lesion

Histology: Sections show nodular dense fibrosis with entrapped hypertrophic nerves, small-medium arteries and lymphoid aggregates with scattered plasma cells. There are small adjacent benign lymph nodes. The fibrotic area has a round pushing border and an associated patchy peripheral lymphoid infiltrate is present. No granulomas, venulitis, mitoses or cytologic atypia is noted. Immunostains demonstrate patchy loose aggregates of IgG positive plasma cells with an increased proportion of IgG4 plasma cells (up to 20 IgG4 positive cells per high power field).

Discussion: The term “sclerosing mesenteritis” was proposed to include lesions previously reported under such names as mesenteric lipodystrophy, mesenteric panniculitis and retractile mesenteritis/mesenteric fibrosis. These entities share overlapping histologic and clinical features that include variable fibrosis, chronic inflammation and fat necrosis. In a recent study Chen et al. found that a subset of these cases contains an increased number of IgG4 positive plasma cells similar to lymphoplasmacytic sclerosing pancreatitis. Similar sclerosing lesions have been also described at other sites including the lung.

Reference(s):
– Chen TS, Montgomery AE. J Clin Pathol 2008; 61:1093-97.