Pseudomyxoma retroperitonei secondary to appendiceal mucinous adenocarcinoma disguised as psoas abscess – A case report

Introduction and importance: Appendiceal cancers are rare tumors, with mucinous cystadenocarcinoma accounting for 58 % of malignant appendiceal tumors. Mucinous cystadenocarcinomas are typically low grade but may lead to pseudomyxoma peritonei, causing accumulation of gelatinous material in the abdomen, often referred to as ‘jelly belly’. In rare instances, the tumor may perforate into the retroperitoneal cavity leading to the phenomenon described as pseudomyxoma retroperitonei or extraperitonei. Case presentation: We describe the case of a young man presenting with a psoas abscess, initially treated with antibiotics. When the abscess failed to resolve, further testing was undertaken and revealed a diagnosis of mucinous adenocarcinoma with pseudomyxoma retroperitonei. The patient underwent a right hemicolectomy with debridement of the psoas abscess cavity. This case illustrates the need for a high index of suspicion for malignancy in the setting of recurrent or atypical psoas abscess. Clinical discussion: Appendiceal mucinous neoplasms are found in <2 % of appendectomy cases. Due to the rarity of the pathology, they are often misdiagnosed as was in this scenario as a psoas abscess. Being in a tuberculosis-endemic area further complicated the diagnosis. Imaging and colonoscopy play a crucial in the proper, early diagnosis of these neoplasms that may present as a psoas abscess. Conclusion: Appendiceal tumors initially presenting as psoas abscess can be misguiding, leading to dismissal of the underlying diagnosis. An appropriate diagnostic workup should be considered early in the disease course for prompt treatment of the condition.