Hidden in Hydronephrosis: Mixed Epithelial and Stromal Tumor of the Kidney (MESTK) Mimicking Hydronephrosis

Mixed epithelial and stromal tumor of the kidney is an uncommon renal lesion characterized by cystic architecture and hormonally responsive stromal components, which explains its predominance in women, particularly those with prolonged or fluctuating estrogen exposure. Its occurrence in men is unusual and can make diagnosis challenging. We present a case of a 43-year-old male who presented with vague abdominal discomfort and was found to have a markedly enlarged, non-functioning right kidney on imaging. Initial investigations suggested obstruction of the distal ureter and a non-functioning right kidney. The patient underwent laparoscopic nephrectomy, and histopathological evaluation of the tissue demonstrated features compatible with mixed epithelial and stromal tumor of the kidney (MESTK). The patient recovered uneventfully and remained well at the six-month follow-up. This case demonstrates how the tumor can present with an extreme cystic pattern that mimics chronic obstructive pathology, leading to a radiologic impression that differs from the underlying pathology. Recognizing such atypical imaging appearances may assist clinicians in considering this entity when evaluating complex cystic renal lesions, particularly in situations where clinical and radiologic findings do not align.