Pancreatic pseudocyst extending into psoas muscle mimicking acute complicated diverticulitis: A case report

Introduction and importance: Pancreatic pseudocysts (PP) are known sequelae of pancreatitis. In this case, we present a patient with a pancreatic pseudocyst extending to the left psoas muscle, initially masquerading as acute complicated diverticulitis. Case presentation: A 43-year-old male with previous episode of pancreatitis presented with a one-week history of abdominal pain. Physical examination revealed left lower quadrant tenderness. A computed tomography (CT) showed a large intraperitoneal fluid collection extending to the left psoas muscle with segmental inflammation of the descending colon. The patient was managed medically with empiric antibiotic therapy for concern of complicated diverticulitis. Ultrasound-guided percutaneous drainage was performed and fluid analysis showed lipase >20,000 U/L. The patient was discharged home with the drain. At one month follow up a repeat CT showed resolution of the left psoas fluid collection. The drain was removed and the patient remained asymptomatic at two month follow-up. Clinical discussion: Pancreatic pseudocysts are well-known complications of pancreatitis. In this case, we describe extension of a pseudocyst to the left psoas muscle. We identified twelve previously reported patients diagnosed with PP involving the psoas muscles. Our case is unique as there is no previously published case in which a pseudocyst masqueraded as complicated diverticulitis. In analysis of the literature, most patients were managed with percutaneous drainage. Only 50% had documented complete resolution on follow up; of those 75% had undergone percutaneous drainage. Conclusion: Pancreatic pseudocysts that extend to the psoas muscle can mimic acute complicated diverticulitis upon presentation. These may be effectively managed with percutaneous drainage.