Posterior bladder-associated pelvic cystic lesion with histologic features consistent with mesenteric cyst in an infant with a functionally solitary kidney: a diagnostic uncertainty case report.

Background: Posterior bladder-associated pelvic cystic lesions in male infants are diagnostically challenging, particularly when congenital anomalies of the kidney and urinary tract coexist. Deep pelvic cystic lesions may mimic mesenteric cyst, bladder duplication, bladder diverticulum, ectopic ureter-related pathology, seminal vesicle cyst, or Zinner-spectrum malformation. Case presentation: We report a male infant born at 39 weeks' gestation with severe right kidney atrophy, a functionally solitary left kidney with hydroureteronephrosis, a posterior bladder-associated pelvic cystic lesion, and bilateral undescended testes. Initial micturating cystourethrogram showed no vesicoureteral reflux, but posterior urethral valves could not be definitively excluded. No preoperative or intraoperative cystourethroscopy was performed. During follow-up, he had a culture-positive suspected urinary infection with extended-spectrum beta-lactamase-producing Discussion: After accidental drain removal, urine passage from the abdominal tract was reported, and ultrasound later demonstrated a supravesical tract. Postoperative cystoscopy reportedly excluded posterior urethral valves, bladder duplication, bladder diverticulum, ectopic ureteric opening, and internal bladder fistula, but the detailed report, intraoperative media, pathology images, and additional postoperative tract imaging were unavailable. Conclusion: This case is best interpreted as a posterior bladder-associated pelvic cystic lesion with histologic features consistent with mesenteric cyst, rather than a definitively proven mesenteric cyst. It highlights the need for cystourethroscopic evaluation, broad genitourinary differential diagnosis, clinicopathological correlation, and transparent reporting of diagnostic uncertainty.