The patient underwent urgent cardiac surgery and the lesion was resected. The lesion was thought to be intracardiac myxoma. Initial histology suggest atypical appearance for myxoma. Further testing suggested most likely diagnosis is a left atrial spindle cell sarcoma - pathology proven.

Primary cardiac tumors are 100 - 1000 times rarer than secondary cardiac neoplasms. About 75% of primary cardiac tumors are benign and 25% malignant. Primary cardiac spindle cell sarcoma of the heart is extremely rare and only a handful of cases reported in the literature; they are aggressive and associated with poor prognosis.

The rarity of spindle cell sarcoma and its similarities to benign cardiac myxoma and thrombi on echocardiography and CMR imaging present a diagnostic challenge when evaluating patients pre-operatively. Therefore, a malignant spindle cell sarcoma may only be diagnosed during surgery, after histological examination.