Tuesday, August 30, 2011

Primary Pulmonary Artery Sarcomas

Primary pulmonary artery sarcomas are rare tumors that always arise from the central pulmonary arteries. The natural history of the disease consists of local tumor growth with superimposed thrombosis and distal tumor emboli, resulting in progressive pulmonary artery obstruction. Clinical symptoms are therefore insidious and often nonspecific, making early diagnosis difficult. Untreated patients progress to decompensated heart failure, with a median survival of as short as 1.5 months.

Histologically, the most common primary pulmonary artery sarcomas are fibrosarcoma and leiomyosarcoma (shown above), but malignant mesenchymoma, angiosarcoma, anaplastic sarcoma, rhabdomyosarcoma, chondrosarcoma, and myxosarcoma have also been reported.

The main differential considerations are bland pulmonary embolus, tumor embolus, and lung cancer.

Pulmonary artery sarcomas can be polypoid intraluminal masses or sessile lesions spreading along the intima. Intimal spread, when extensive, can result in the characteristic appearance of a "lobulated, unilateral hilar mass projecting into the lung parenchyma in an arterial distribution."

In about 50% of cases, there is transmural spread into the adjacent lung, bronchial wall, or lymph nodes, in which case the imaging findings can mimic lung cancer.

CT angiography reveals a low-attenuation filling defect occupying the entire lumen of the proximal or main pulmonary artery with distension of the vessel. However, it can be difficult to distinguish pulmonary emboli from pulmonary artery sarcomas, unless there is extension beyond the lumen. MR imaging can be helpful by revealing enhancement in the tumor.

Pedunculated lesions can move with the cardiac cycle, which may help differentiate these tumors from emboli on conventional angiography.

Pulmonary artery sarcomas can have increased FDG activity, a feature that can be seen with tumor emboli and bland pulmonary emboli (likely due to local inflammation).

The mainstay of treatment is radical resection and distal pulmonary embolectomy. Without the latter, superimposed thrombosis and metastasized emboli in the distal pulmonary arteries can lead to decreased survival. Pneumonectomy, studied in a small retrospective series, has not shown a survival benefit; however, adjuvant chemotherapy and radiation therapy have been shown to increase survival. Endarterectomy techniques, tried earlier, have an unacceptably high local recurrence rate due to incomplete resection.

The images above are from a patient with slowly progressive cough and dyspnea. The CT image shows a low-attenuation filling defect within the left lower lobe pulmonary artery that extended distally into the subsegmental branches (not shown). The FDG-PET image, more caudad to the CT, shows intense activity in the left lung.


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