The tumor was pseudoencapsulated, was circumscribed, and had multiple septa (Figure 2). Microscopically, the capsule and septa exhibited features typical of SFT.2,4 There were bland spindle cells haphazardly arranged, without a tendency to form bundles. Some regions were highly cellular, while other regions were hypocellular with abundant matrix and deposition of thick collagen fibers (Figure 2). There was characteristic perivascular fibrosis, particularly in hypocellular areas. Vascularity was rich with dilated vessels and small capillary-sized vessels. Pleomorphism, tumor giant cells, and mitotic activity were absent. The tumor cells formed and lined the septa, indicating that the tumor was really a pseudocyst. The tumor cells also invaded through the pseudocapsule, reaching the resection margin multifocally. The tumor cells stained positively for immunoreactive vimentin, CD99, CD34, and Bcl-2 (Figure 2). Fibroblasts, including those forming the pseudocapsule, did not stain with CD99, CD34, or Bcl-2. Tumor cells showed no S-100 protein, glial fibrillary acidic protein, epithelial membrane antigen, neurofilament, smooth muscle–specific actin, or desmin immunoreactivity.