Pancreatic Pseudocyst Masquerading as Right Atrial Thrombus: An Unusual Intracardiac Extension

Pancreatic pseudocysts are encapsulated collections of enzyme-rich pancreatic secretions that may extend beyond the peripancreatic region. Extension into the mediastinum and heart is uncommon and may mimic other thoracic or intracardiac pathologies. A 36-year-old man with chronic alcohol use presented with abdominal pain, fever, dyspnoea and palpitations on a background of recurrent alcohol-related pancreatitis. Contrast-enhanced CT demonstrated acute-on-chronic pancreatitis with multiple pancreatic pseudocysts and a right atrial filling defect initially interpreted as thrombus. Focused ultrasound, including a subxiphoid four-chamber view, demonstrated an avascular anechoic lesion within the right atrium, continuous inferiorly with an abdominal pseudocyst along the course of the inferior vena cava. A retrospective review of the CT confirmed this continuity. The findings indicated cranial extension of the collection along the periadventitial plane of the retrohepatic cava, with full-thickness breach of the caval wall at the caval-atrial junction and herniation of the collection into the lumen enclosed by its own fibrous capsule, without communication between the cyst cavity and the circulating blood. Cyst fluid was markedly amylase- and lipase-rich. Ultrasound-guided percutaneous drainage of the abdominal component produced regression of both components without embolic or hemorrhagic complications. Misinterpretation carries substantial consequence. A right atrial filling defect attributed to thrombus commits the patient to therapeutic anticoagulation at a time when acute pancreatitis independently predisposes to retroperitoneal and peripancreatic hemorrhage, arterial pseudoaneurysm formation and vascular erosion, and may additionally prompt consideration of thrombolysis or cardiac surgical thrombectomy. Correct characterisation therefore alters management directly and immediately.