A case of pancreatic pseudocyst as a rare cause of a cystic lesion within the psoas muscle

Acute pancreatitis is highly prevalent in Australia (Nesvaderani et al. Acute pancreatitis: update on management. Med J Aust 2015;202:420–3). Pancreatic pseudocysts, although typically occurring in the peripancreatic tissues, can in up to 25% be extra-pancreatic (Rasch et al. Management of pancreatic pseudocysts—a retrospective analysis. PLoS One 2017;12:e0184374). Extension of pseudocysts into the psoas muscle is highly unusual, with only 13 previously recorded cases (Gupta et al. Retroperitoneal cystic malignant fibromas mimicking a psoas abscess. Iran J Radiol 2015;12:e17507). This article presents the case of a 45-year-old man presenting with progressive left hip pain. He was known to have a history of chronic alcohol misuse. He presented with symptoms and signs typical of psoas pathology and was found to have a large pancreatic pseudocyst extending into his left psoas muscle. In this case, management was via both computed tomography guided percutaneous drainage and endoscopic ultrasound guided drainage. Because of the rarity of psoas pseudocysts and their propensity to mimic other pathology, diagnosis can be extremely challenging. Cystic lesions within the psoas muscle have several differentials, ranging from the more common psoas abscess to extremely rare neoplastic lesions.