Perihepatic dedifferentiated liposarcoma mimicking IgG4-related disease

Dedifferentiated liposarcoma (DDLPS) may originate in perihepatic adipose tissue, but can radiologically present as a hepatic mass. Moreover, dense Immunoglobulin G4 (IgG4)-positive plasma cell infiltration may mimic IgG4-related disease (IgG4-RD) and delay curative-intent resection. We herein describe a unique case that exemplifies this diagnostic pitfall.

A 67-year-old woman was incidentally found to harbor a hepatic mass in segment 6 along with small mesenteric nodules. Cross-sectional imaging showed heterogeneous non-fat containing lesions, while needle biopsy revealed abundant IgG4-positive plasma cells. Prednisolone treatment was commenced for presumed IgG4-related inflammatory pseudotumor. Although the lesions initially shrank slightly, they both enlarged during steroid tapering. Segment 6 hepatectomy with limited bowel resection was subsequently performed. Pathohistological examination revealed atypical stromal cells arising in perihepatic adipose tissue, and Mouse double minute protein 2 (MDM2) amplification confirmed liposarcoma infiltration into the liver and mesentery. Following the discontinuation of steroids, the patient has remained recurrence-free for fourteen months after surgery.

DDLPS can masquerade as IgG4-RD and even show temporary steroid responsiveness. When clinical or imaging treatment findings are atypical, comprehensive tissue evaluation with molecular analysis is essential to prevent diagnostic delay.