H & E sections showed a malignant neoplasm, in large part, confined to the main pulmonary artery and its segmental branches (Figs. 3 and 4). The neoplasm was composed of pleomorphic epithelioid and spindle cells arranged in a myxoid matrix (Figs. 5, 6, 7 and 8). Many cells showed an eccentric nucleus and brightly eosinophilic cytoplasm (Fig. 9). Multiple abnormal mitoses were identified. Pulmonary vessels distal to the hilar mass showed extensive involvement by the neoplasm (Fig. 10). An infarct was present in the lower lobe, corresponding to the grossly visible mass in lower lobe.
The neoplastic cells were strongly immunoreactive for vimentin (Fig. 11). Focal positive staining for smooth muscle actin (Fig. 12), desmin, myogenin (Fig. 13), myoglobin (Fig. 14) and c-kit (Fig. 15) was identified. Cytokeratin stain showed rare positive cells. CD31 and elastic tissue stains confirmed the primary intravascular location of this neoplasm (Fig. 16). The neoplastic cells were negative for CD31, S100, chromogranin and synaptophysin.