Abdominal Tuberculosis Masquerading as Retroperitoneal Malignancy: A Diagnostic Dilemma in a Large Iliopsoas Mass

Abstract

Abdominal tuberculosis may present atypically and resemble retroperitoneal malignancy, particularly when the iliopsoas muscle is involved. A 75-year-old woman presented with a painful left iliac fossa lump that had developed over two weeks. Examination revealed a 12 × 13 cm retroperitoneal mass with an external extension above the left anterior superior iliac spine. Ultrasonography and contrast-enhanced computed tomography demonstrated a heterogeneous, lobulated lesion centred on the left iliopsoas muscle, with necrotic components, extension towards the left groin, and involvement of the left sacroiliac joint. Fluorodeoxyglucose positron emission tomography-computed tomography showed increased metabolic activity, with an SUVmax of approximately 8.5, raising suspicion of soft-tissue sarcoma. Diagnostic laparoscopy identified a 12 × 11 cm solid-cystic retroperitoneal mass adherent to the sigmoid colon, left fallopian tube, and external iliac vessels, with compression of the left ureter. Controlled aspiration yielded approximately 600 mL of thick, yellowish-white caseous material. Frozen-section examination demonstrated granulomatous inflammation without malignancy. Final histopathological examination and GeneXpert testing confirmed Mycobacterium tuberculosis. The patient received six months of antituberculous therapy and remained free of recurrence during two years of follow-up. This case demonstrates that retroperitoneal tuberculosis should be considered when a metabolically active iliopsoas mass has necrotic and infiltrative features, even in the absence of constitutional symptoms. Histopathological and molecular confirmation can guide appropriate treatment and help avoid unnecessary radical surgery.