Renal Cyst's Dark Secret: A Rare Case of Fungal-Infested Necrotizing Granulomatous Inflammation in a Renal Cyst.

Fungal infections of renal cysts are exceptionally rare, particularly in immunocompetent individuals, and are often misdiagnosed due to nonspecific clinical and radiological findings. This report presents the first documented case of necrotizing granulomatous inflammation caused by Candida species within a renal cyst in an immunocompetent host. Here we present a 49-year-old immunocompetent male who presented with right loin pain and fever. He had a prior episode of renal cyst infection managed with percutaneous catheter drainage (PCD) three months earlier. Laboratory investigations revealed leukocytosis and marginally elevated serum creatinine. Imaging showed a thick-walled lower pole renal cyst (247 cc) with internal echoes, parenchymal thinning, and features suggestive of chronic obstruction. Initial management involved the use of empirical broad-spectrum antibiotics and ultrasound-guided aspiration with a 12 Fr pigtail catheter placement, yielding 180 mL of turbid fluid. Microbiological cultures, including bacterial and fungal, were negative. Due to persistent drainage and residual cavity on follow-up imaging, the patient underwent open cyst decortication with DJ stent removal. Histopathological analysis confirmed necrotizing granulomatous inflammation with fungal hyphae, consistent with Candida infection. Postoperatively, the patient was treated with oral fluconazole for six weeks. At two-month follow-up, he remained asymptomatic with no signs of recurrence. This case underscores the importance of considering fungal etiologies in persistent or recurrent renal cyst infections, even in immunocompetent patients. Histopathological confirmation is essential when cultures are inconclusive. Combined surgical and antifungal management remains key to achieving definitive resolution.