Pulmonary tumor thrombotic microangiopathy with pulmonary hypertension.

Pulmonary tumor thrombotic microangiopathy is characterized by fibrocellular intimal proliferation of small pulmonary arteries and arterioles in patients with metastatic carcinoma. Its morphologic features, including precursor lesions, were studied in 21 patients diagnosed in 630 consecutive autopsy cases with carcinoma (3.3%). Nineteen of 21 patients had adenocarcinoma and 11 of these 19 patients had gastric carcinoma. The pathogenetic events start with microscopic tumor cell embolism. Tumor emboli do not occlude affected vessels but induce both local activation of coagulation and fibrocellular intimal proliferation, which lead into stenosis or occlusion. Hemodynamically, an increase in vascular resistance results in pulmonary hypertension. In three patients, metastatic carcinoma was unknown before death, and the condition was diagnosed as pulmonary hypertension of unknown origin. Thus, pulmonary tumor thrombotic microangiopathy should be considered in the differential diagnosis of primary pulmonary hypertension, particularly in patients with well-known carcinoma who develop acute or subacute cor pulmonale.