Malakoplakia Presenting as a Peri-Kidney Allograft Mass

Introduction: Malakoplakia is a granulomatous inflammatory condition in immunosuppressed individuals that is frequently associated with urinary tract and pulmonary infections. It can present as a mass in the urinary system and can mimic a renal abscess. Case Description: A 47-year-old woman with a history of recurrent E. coli UTIs and kidney transplantation 6 months prior presented with a 3-week history of right flank/leg pain and an acute hemoglobin drop to 5.7 g/dL. Vital signs were unremarkable. Beyond anemia, labs were significant for leukopenia and AKI (serum creatinine peak 1.85 mg/dL from a baseline of 0.9 mg/dL). Abdominal CT revealed a right psoas hematoma and a perinephric mass (star on image A). Upon aspiration, the hematoma was found to be infected with E. coli. Despite drain placement and antibiotics, the perinephric mass remained unchanged. Biopsy revealed malakoplakia [Image C, H&E, 400X, showing Michaelis-Gutmann bodies (arrows)]. Her symptoms improved with escalation of antibiotics. Follow-up CT scan after 10 weeks of antibiotic treatment (image B) showed complete resolution of the perinephric mass. At 2-year follow-up, she is doing well with a new baseline creatinine of 1.3 mg/dL. Discussion: This patient’s recurrent E. coli UTIs likely seeded her hematoma, leading to chronic infection and pseudotumor formation due to malakoplakia. Malakoplakia should be considered in the evaluation of perinephric masses in immunosuppressed patients.H&E, 400X shows Michaelis-Gutmann bodies (arrows)