Case
A 66‑year‑old female was referred to the emergency department. She reported several days of fever, hypogastric pain, and skin erythema around the renal transplant surgical scar. A renal transplantation had been performed seven years earlier. Clinical examination confirmed the local erythema and mild tenderness on palpation.
Laboratory tests demonstrated impaired renal function and elevated inflammatory markers. Ultrasound of the kidney demonstrated a hypoechoic, hypervascular mass in the interpolar region, approximately 3 cm in diameter (Figure 1).
Figure 1
Ultrasound of malakoplakia in the transplanted kidney showing a hypoechoic (A), hypervascular (B) mass in the interpolar region.
Further assessment by MRI confirmed the presence of the mass and also identified two smaller lesions with identical imaging characteristics. The lesions appeared T2‑hypointense and T1FS‑hyperintense, and demonstrated restricted diffusion and contrast enhancement (Figure 2). Furthermore, the lesions were largely progressive compared with the ultrasound performed two weeks earlier, with infiltration of the abdominal wall.
Figure 2
MRI of the transplanted kidney showed a T2‑hypointense lesion (A) with enhancement after gadolinium contrast administration on the T1 fat‑saturated sequence (B) and restricted diffusion (C, D).
Based on these features, the differential diagnosis included renal cell carcinoma, post‑transplant lymphoproliferative disorder (PTLD), and chronic inflammatory disease. An ultrasound‑guided percutaneous biopsy of the dominant lesion confirmed the diagnosis of malakoplakia of the renal graft. Despite targeted intravenous antibiotic therapy, control of the infection was not achieved, and a transplantectomy was performed. Macroscopic examination showed multifocal, multinodular, yellowish renal masses with purulent and necrotic appearance (Figure 3).
Figure 3
Macroscopic appearance of malakoplakia in the transplanted kidney.
Comment
Malakoplakia is a rare granulomatous disease resulting from an abnormal response to infection, predominantly in immunocompromised patients. Although the bladder is most commonly affected, other organs (including renal grafts) may also be involved. Escherichia coli and other Gram‑negative bacilli are the primary pathogens in genitourinary malakoplakia. Histologically, the disease is characterized by histiocytic infiltrate containing cytoplasmic inclusions (Michaelis–Gutmann bodies).
On imaging, ultrasound typically shows a hypoechoic, poorly defined lesion. MRI demonstrates T2‑hypointensity, T1‑hyperintensity, heterogeneous contrast enhancement, and restricted diffusion. PET‑CT reveals pronounced FDG‑avidity. A definitive diagnosis generally requires a targeted biopsy.
The differential diagnosis includes PTLD and renal cell carcinoma. Rapid onset and progression favor malakoplakia. Accurate distinction between these entities is often not possible without histological confirmation.
First‑line management consists of broad‑spectrum intravenous antibiotics and supportive therapy. In refractory cases, surgical excision of the affected organ may be required to achieve disease control [1].
Competing Interests
The authors have no competing interests to declare.