Gastric duplication cyst mimicking an adrenal-region cyst: a diagnostic challenge.

Introduction and importance: Gastric duplication cysts (GDCs) are rare congenital malformations that may mimic adrenal or retroperitoneal cysts. Misdiagnosis can delay proper management. We report a unique case of a GDC that was misdiagnosed as a left adrenal cyst, with reversible hyperreninemia and indirect hyperbilirubinemia. Presentation of case: A 28-year-old asymptomatic man was incidentally found to have a left adrenal cyst on ultrasound. CT revealed a 4.1 × 5.5 cm non-enhancing unilocular cyst with preserved adrenal structure. Laboratory tests showed elevated upright plasma renin concentration (63.3 pg/mL) and indirect bilirubin (57.6 μmol/L). During laparoscopic excision, a cyst arising from the gastric fundus was identified. Pathology confirmed a non-communicating GDC lined by gastric mucosa and smooth muscle. Three months postoperatively, renin and bilirubin levels normalized. Clinical discussion: Ectopic GDCs in the adrenal region are extremely rare and often misinterpreted radiologically. The postoperative normalization of renin and bilirubin raises a possible association, but the mechanisms remain speculative, and causality cannot be established from this single case. Intraoperative cyst-fluid analysis and multidisciplinary evaluation assist in accurate diagnosis. Complete resection provided definitive diagnosis and a favorable short-term outcome in the present case; however, longer follow-up is required to assess recurrence and sustained biochemical remission. Conclusion: GDC should be considered in adrenal-region cystic lesions with atypical features. Total excision provides both definitive diagnosis and a favorable short-term outcome, although longer surveillance is required.