Calcified Amorphous Tumor in a Patient with Severe, Unremitting Hyperphosphatemia Receiving Peritoneal Dialysis

Introduction: Calcified amorphous tumors (CATs) are rare, non-neoplastic intracardiac masses. CATs have been reported in multiple case studies, however the exact pathogenesis remains unclear. They are frequently misdiagnosed as vegetations, cardiac myxomas, or osteosarcomas. Current theories suggest derangements in mineral metabolism or hypercoagulability. We present a case of CAT formation in a patient receiving peritoneal dialysis who had severe, refractory hyperphosphatemia. Case Description: A 47-year-old woman with type 2 diabetes mellitus, hypertension, heart failure with reduced ejection fraction, and end stage kidney disease on peritoneal dialysis had severe unremitting hyperphosphatemia (>10 mg/dL during more than half of monthly laboratory reports). She presented to the emergency department with left leg pain; imaging raised concern for a possible psoas abscess. An echocardiogram performed to evaluate for possible bacterial or non-bacterial (marantic) endocarditis revealed a mobile mass and mitral valve dysfunction. Urgent surgical resection was performed; histopathology confirmed CAT. Discussion: CATs are typically accompanied by signs or symptoms related to obstruction or embolization. Imaging modalities provide nonspecific findings, making histopathologic examination essential. Grossly, CATs appear as firm, yellow-white masses with partial calcification. Microscopically, they consist of nodular calcium deposits embedded within degenerating blood elements and chronic inflammatory cells. Resection remains the mainstay of treatment, with recurrence being rare. Although CATs can arise from any cardiac valve, most reported cases involve the mitral valve and annulus. Although further research is needed to establish optimal guidelines for management, maintaining serum phosphate concentrations within or near the population reference range may help reduce the risk of CAT in patients receiving maintenance dialysis.