A rare case of primary retroperitoneal mucinous cystadenocarcinoma presenting with recurrent infected psoas abscess

Introduction and significance: Retroperitoneal mucinous adenocarcinoma is a rare malignancy, typically presenting with nonspecific symptoms leading to delay in diagnosis and treatment. Case presentation: A 53-year-old man patient was seen with debilitating pain in the right thigh and reduced mobility, following 1 year of recurrent psoas abscesses. The physical exam revealed a mass in the right flank and a positive psoas sign. The laboratory work revealed elevated alkaline phosphatase and carcinoembryonic antigen (CEA), with decreased hemoglobin and creatine phosphokinase. Imaging revealed a large heterogeneous retroperitoneal mass (25.88 × 17.44 × 17.26 cm) compressing adjacent structures. Drainage was mucinous in nature; histopathology revealed well-differentiated mucinous adenocarcinoma with cytokeratin positivity. Escherichia coli infection proved secondary contamination from gastrointestinal sources. Antibiotics, analgesics, and interval drainage were administered to the patient. Chemotherapy was considered but later contraindicated with the onset of renal failure. The patient was placed on palliative care with symptomatic improvement. Clinical discussion: This case highlights the diagnostic difficulty of retroperitoneal mucinous adenocarcinoma, especially when occulted by infection and nonspecific presentation. The secondary infection and massive size of the tumor contribute to the difficulty in diagnosis and treatment. Conclusion: Early detection through thorough assessment is paramount. Multidisciplinary management is indicated, although such complications as renal failure may interfere with treatment and decrease prognosis.