Histologic features of the tumor. A. The tumor is well-demarcated and situated transmurally. There are alternating light and dark areas within the tumor (H&E, ×20). B. The light area consists of haphazardly arranged, interweaving fascicles of plump, myoid-appearing spindle cells with elongated nuclei and abundant eosinophilic cytoplasm (H&E, ×400). C. The dark, more cellular area consists of primitive-appearing polygonal cells arranged in a hemangiopericytomatous pattern (H&E, ×400). D. Intravascular proliferation of tumor cells is noted at the periphery of the lesion (H&E, ×200).