Subduodenal Retroperitoneal Paraganglioma Mimicking a GIST: A Case Report

Abstract

Retroperitoneal paragangliomas, which are rare (<3% of pheochromocytomas/paragangliomas), are non-secreting in 40–60% of cases and are often discovered incidentally due to mass effect. We report the exceptional case of a 66-year-old woman (outside the peak incidence age of 40–50 years) presenting with chronic low back pain and a history of major surgery (gastrectomy, cholecystectomy, thyroidectomy). Ultrasound revealed a 47 mm hypoechoic cystic paraumbilical mass, confirmed on CT scan by a hypervascularised necrotic subduodenal lesion suggestive of a GIST (Gastrointestinal Stromal Tumour). A midline laparotomy allowed for complete R0 resection of a 58 mm multilobulated mass, with early ligation of the vascular pedicles. Histology confirmed a benign paraganglioma (chromogranin+, synaptophysin+, S100+, Ki-67 <3%, succinate dehydrogenase subunit B [SDHB] preserved). The postoperative course included a wall infection treated with IV antibiotics, with discharge on day 10 and follow-up at 1 year without recurrence (negative PET scan). This case highlights the diagnostic pitfall of a paraganglioma mimicking a GIST (an error seen in 20–25% of incidentalomas >4 cm), the critical lack of preoperative metanephrine measurement (sensitivity >96%, grade IA recommendation from the European Network for the Study of Adrenal Tumours / European Society for Medical Oncology (ESMO/ENSAT), and the superiority of laparotomy for vascularised lesions >5 cm (recurrence 3–5% vs 15–20% with laparoscopy). Despite a benign phenotype, genetic sequencing is recommended (hereditary in 30–40% of cases). A multidisciplinary approach is essential for these rare presentations.