Inflammatory angiomyolipoma of the liver: an unusual case suggesting relationship to IgG4-related pseudotumor

Abstract

Hepatic angiomyolipoma (AML) is rare. Based on its wide histomorphological range, several distinctive histological variants have been delineated. However, hepatic AML displaying predominantly or exclusively inflammatory pattern closely mimicking inflammatory pseudotumor (IPT) is exceptionally rare with only 7 cases reported so far. We herein describe a new case of hepatic inflammatory AML in a 51-year-old woman who presented with unexplained constitutional symptoms suggesting an infectious disease. A liver mass was detected during imaging examination and resected (4.3 cm in maximum diameter). The patient's symptoms resolved completely after surgery. Currently, she is alive and well 7 years after surgery. She has no evidence of other organ manifestations of IgG4-related systemic disease. The tumor displayed a pure IPT-like histological pattern with dense infiltrates of plasma cells, lymphocytes and histiocytes admixed with scattered few adipocytes, irregularly distributed thick-walled vessels (some of them showed obliterative phlebitis) as well as aggregates and fascicles of histiocytoid and spindle-shaped myoid cells that were immunoreactive for HMB45 and Melan A with focal expression of alpha smooth muscle actin. Lesional cells were negative for desmin, protein S100, CD21, CD23, CD15, CD30, HepPar-1, pankeratin (KL-1), ALK1, and EBV in situ hybridization (EBER). The surrounding liver parenchyma showed striking lymphoplasmacytic non-destructive pericholangitis. Numerous scattered and aggregated IgG4 positive plasma cells were seen within the mass and in the peritumoral inflammatory lesions (mean, 37 cells/HPF; IgG4: IgG ratio = 28%). To our knowledge, this is the first report of hepatic inflammatory AML closely resembling IgG4-related IPT of the liver. A possible role for IgG4 seems likely to explain the peculiar histological features and the unusual clinical presentation in this case.

Keywords: Angiomyolipoma; IgG4; cholangitis; inflammatory; inflammatory pseudotumor; liver.

Figure 1

Representative images of IPT-like hepatic angiomyolipoma. A. The tumor was partially sharply circumscribed from adjacent liver parenchyma but non-encapsulated. B. prominent fine-reticular storiform sclerosis is seen at this magnification. C. Obliterative phlebitis with prominent plasmacytic perivascular infiltrates. D. Small clusters of histiocytoid cells with voluminous granular eosinophilic cytoplasm. E. Occasional reed-Sternberg-like binucleated cells were seen (note scattered fat vacuoles). F. Another binucleated giant cell showed slender dendritic-like cytoplasmic processes.

Figure 2

Peritumoral changes within adjacent liver. A. Dense inflammatory infiltrates entrapping sheets of hepatocytes. B. A thick-walled vessel within adjacent liver showed prominent angiitis obliterating its lumen. C. Concentric fibrosis around a small bile duct associated with lymphoplasmacytic infiltrates but no evidence of epithelial destruction was seen. D. Another portal area showed both pericholangitis and obliterative angiitis. Isolated cells within perivascular/peribiliary aggregates strongly expressed HMB45 (D: inset).

Figure 3

Immunohistochemical findings in hepatic inflammatory angiomyolipoma. A. Large mono-, bi- and multinucleated histiocytoid myoid cells strongly expressed HMB45 (Note dendritic features of the larger cells on the right). B. Another area with several slender dendritic spindled cells with over all reticulum-like morphology highlighted by HMB45 immunostaining (note prominent sinusoidal vessels). C. several plasma cells expressed IgG4. D. IgG4-positive plasma cells formed dense aggregates at the interphase between tumor (upper left) and liver tissue (lower right).