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

## TL;DR

A rare kidney tumor in a man was mistaken for hydronephrosis, highlighting the importance of considering unusual diagnoses in complex cystic kidney lesions.

## Contribution

This case highlights the atypical presentation of MESTK in men and emphasizes the need for careful evaluation of cystic renal lesions.

## Key findings

- MESTK can present with a cystic pattern mimicking hydronephrosis, especially in men.
- Histopathological analysis is crucial for accurate diagnosis when clinical and radiologic findings conflict.
- The patient had an uneventful recovery and remained well at six-month follow-up.

## Abstract

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.