Xanthogranulomatous cholecystitis with histologic features suggestive of IgG4 related cholecystitis - A morphologic overlap with IgG4 related disease

Both xanthogranulomatous cholecystitis (XGC) and IgG4-related cholecystitis (IgG4-CC) are rare chronic fibroinflammatory tumefactive diseases of the gallbladder, which cause a strong confusion with resectable malignancy in view of their mass forming tendency with extension into the liver. We aim to study the histopathologic features of xanthogranulomatous cholecystitis with regard to IgG4-related cholecystitis in extended cholecystectomy specimens. Sixty cases of extended cholecystectomy with liver wedge resection, diagnosed as XGC on histopathology from January 2018 to December 2021 were retrieved from the archives. Representative sections were reviewed by two pathologists independently. Immunohistochemistry was performed for IgG4 and IgG4/IgG was derived. The cases were dichotomized in two groups on the basis of IgG4 positive plasma cells. Six cases with >50 IgG4 positive plasma cells had storiform fibrosis, IgG4/IgG ratio >0.40 and extra-cholecystic extension. Of these, 50 % had obliterative phlebitis and 66.7 % had perineural plasma cell wrapping. A small subset of XGC cases (~10 %) had morphologic overlap with IgG4-CC, but should not be overcalled as the diagnosis of IgG4-RD requires an integrative approach based on clinical, serologic and imaging criteria and not solely on histopathology. •Diagnosis of IgG4-RD relies on comprehensive assessment of clinical, serological, radiological and pathological correlations•IgG4 positive plasma cells >50/hpf (10%), IgG4/IgG >0.4 (10%), storiform fibrosis (10%), perineural plasma cell wrapping (6.6%) & OP (5%) can be seen in a subset of XGC•Pathologists should be wary of the morphologic overlap of XGC with IgG4-CC and should not overcall IgG4-RD solely on histology