We report a rare instance of primary pulmonary angiosarcoma presenting as a large solitary mass in the left upper lobe with mediastinal invasion. In particular, we emphasize the magnetic resonance (MR) imaging features, which included a markedly heterogeneous pattern consisting of hyperintense areas scattered throughout a background of intermediate signal intensity, rendering the lesion a cauliflower-like appearance especially on T2-weighted images. Being unreported so far in primary pulmonary angiosarcomas, these distinct MR imaging findings may be helpful in the differentiation of these neoplasms from lung cancers.