Case report: retroperitoneal aspergilloma in a patient with rheumatoid arthritis presenting as malignant tumor

Background Aspergillosis in patients with impaired immunity usually presents with invasive pulmonary infection and dissemination to a variety of organs via hematogenous spread. Aspergilloma in the retroperitoneal cavity is a rare disease with only a few cases reported in the literature. To the best of our knowledge, the present case of a retroperitoneal aspergilloma with no surgical history is only the second report in the literature. Case presentation A 65 year-old man, who had been receiving immunosuppressive treatment for rheumatoid arthritis with vasculitis for 9 years, was referred to the Urology Department with a retroperitoneal mass. This was confirmed by computed tomography performed during treatment for pulmonary aspergilloma. Because it was not possible to rule out malignant disease (e.g., liposarcoma), surgical exploration was performed. Pathological examination revealed aspergillus hyphae with fat necrosis, and retroperitoneal aspergilloma was diagnosed and appropriately treated. The tumor did not recur subsequently. Conclusion Our present case emphasizes that pharmacological treatments for aspergilloma in the retroperitoneal cavity have poor drug transitivity, so the relative effectiveness of pharmacological response is not useful for differentiating retroperitoneal aspergilloma from malignant disease.