Prepared by: Jacobo Kirsch, MD
Solved by: Juan C. Batlle, MD
A 51-year-old female marathon runner presented with a complaint of not being able to tolerate her usual exercise load. Her PCP treated her for bronchial pneumonia without success.
Her dyspnea on exertion progressed significantly. Over the next 18 months, the patient underwent extensive work-up with x-ray (Fig 1), echocardiogram, TEE, and CT scans. It was then found that she had a left atrial myxoma and was referred to open-heart surgery for removal.
Transesophageal Echocardiogram showed a mildly dilated left atrium with a large heterogeneous mass with evidence of calcification that extended posteriorly towards the pulmonary veins and did not appear to go towards the inter-atrial septum nor to be mobile. There was spongy appearance of the mitral valve due to probable myxomatous changes with very mild bi-leaflet prolapse with moderate mitral regurgitation. The left ventricle was normal in size and function.
Fig 1. Lateral CXR shows dense calcifications in the hilar regions.
Fig 2. ECG-gated contrast enhanced cardiac CT examination and coronal reconstructions reveal tumor infiltration of the walls of the left atrium, sparing only the inferior surface. There is soft tissue within the mediastinum extending posteriorly from the left atrium into the subcarinal area. Additional soft tissue irregularly shaped extension of the tumor is present in the right side and into the right superior pulmonary vein. The mass has soft tissue density as well as extensive calcification, particularly the portion involving the RSPV. There is irregular thickening of the anterior, posterior, and superior walls of the left atrium as well as the interatrial septum and anterior mitral leaflet likely secondary to tumor involvement.
The patient underwent open-heart surgery, but it was aborted when a calcified and densely adhered mass involving the left atrium extensively and the superior right pulmonary vein was found. Sections of the mass obtained at that time showed circumscribed nodules of histologically benign hypercellular cartilage with focal mineralization and small fragments of bone. No epicardial soft tissue, mesothelial lining, cardiac muscle or vascular smooth muscle was present in this sample.
Continuous close follow-ups with imaging of the chest were performed which consistently showed a calcified mass in the right side of the left atrium extending into the right upper lobe pulmonary vein. Myxoma was given as the most likely diagnostic consideration, although other unusual etiologies could not be excluded.
A dedicated ECG-gated cardiac CT was performed (Fig 2) and was described as revealing a partially calcified left atrial tumor involving the majority of the left atrial walls, with protuberant polypoid partially calcified soft tissue occluding the right superior pulmonary vein without obvious invasion into extra-cardiac structures. The appearance is most consistent with a malignant neoplasm. The differential diagnosis is broad and includes sarcomas, lymphomas, etc.
The process had a slow progression and it was not until there was definite mitral valve involvement and significant clinical worsening that the patient underwent surgical debulking with partial resection of the left atrial tumor, endarterectomy of the pulmonary veins, reconstruction of the right atrium and interatrial septum with a Periguard patch and mitral valve replacement.
The pathology report from the surgical specimen reveals sections of the mass with spindle cell proliferation with bony trabeculae. The tumor forms osseous matrix with extensive bone component and also contains cartilage. Mitoses are up to 7 per 10 high power fields in the most mitotically active area. The tumor invades myocardial tissue and is also noted focally present growing over valvular tissue. An adequate assessment of surgical margins however is not possible due to the fragmentation of the tumor. While the classification of this tumor as an osteosarcoma is straight forward, determination of histologic grade and prediction of its biological behavior are difficult because of the very unusual occurrence of primary osteosarcomas in the heart. There are no specific guidelines and standardized criteria for the grading of cardiac sarcomas given its low frequency. In the simplified grading scheme by Burke and Virmani, the absence of necrosis and mitoses of less than 10 per high power field were associated with increased survival rate irrespective of histologic type.
The patient tolerated the procedure and improved clinically. She then underwent 6 cycles of chemotherapy but unfortunately expired approximately a year after surgery.
DISCUSSION:
The most common cardiac neoplasms are metastatic lesions, estimated to be 20-40 times more common than primary tumors. The prevalence of primary cardiac malignancies is estimated at approximately 0.002-0.28%. One of most uncommon primary cardiac neoplasms is the primary cardiac osteosarcoma, which represents approximately 3% to 9% of all cardiac sarcomas. So far, only approximately 40 cases have been reported in the literature.
The age of patients at diagnosis ranges from 14 to 77 years old, and the median age is in the 4th decade. Females are more frequently affected than males.
Primary cardiac osteosarcomas can occur in any heart chamber, but most cases occur in the left atrium. In contrast, osteosarcomas metastatic to the heart most commonly involve the right cardiac chambers.
The cellular mechanisms involved in the development of primary cardiac osteosarcoma includes the existence of a pluripotent precursor cell (mesenchymal stem cell) in the heart which may be activated and transformed into active osteoblasts.
The imaging manifestations of primary cardiac osteosarcomas are very non-specific. On echocardiography they often show asymmetrical internal echoes.
Computed tomography has shown the calcification of cardiac osteosarcomas. Other features (e.g., a broad base of attachment or origin at a site other than the atrial septum) may help differentiate these tumors from left atrial myxomas.
The final diagnosis of a cardiac osteosarcoma is established on histological and immunohistochemical examinations. The tumor cells are positive for alpha-smooth muscle actin, as observed in cases of non- cardiac osteosarcomas and chondroid differentiation is a valuable clue for the differential diagnosis.
When feasible, complete surgical resection is the optimal treatment for the tumors. Recurrence and metastasis are common and the survival time varies greatly; five cases in the previous reports died within one month of the operation, while the longest survival time recorded was 131 months postoperatively.
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