The other morphologic pattern is that of undifferentiated ‘small blue cell’ or round cell sarcomas. Mesenchymal chondrosarcoma, with its intermixed mature chondroid nodules and primitive-appearing small round cells is one common example, often presenting as a dural-based mass in a child or young adult (Scheithauer and Rubenstein, 1978; Rushing et al., 1996; Bingaman et al., 2000; La Spina et al., 2003) (Fig. 36.1b). The tumor can present either intracranially or in the spinal region. Mesenchymal chondrosarcoma is also important to note, since it features a prominent hemangiopericytoma-like vascular pattern, leading to the potential confusion with HPC when the cartilage is less conspicuous. These tumors are often highly aggressive and the prognosis depends on the completeness of resection. Little is known about their genetics, though a
13;21 translocation has been recently reported in two extracranial cases (Naumann et al., 2002). Furthermore, Wehrli and colleagues have shown that mesenchymal chondrosarcoma may be differentiated from other small round
factor implicated in early cartilaginous development (Wehrli et al., 2003). Ewing sarcoma-peripheral primitive neuroectodermal tumor (EWS-pPNET) is a considerably rarer small blue cell tumor as a primary dural neoplasm (Stechschulte
et al., 2001; Dedeurwaerdere et al., 2002), though direct extension from a contiguous bony or soft tissue site (e.g. skull, vertebra, paraspinal soft tissue) is not uncommon (Fig. 36.1c). One cautionary note is that CD99, the so-called Ewing sarcoma antigen, is also expressed by many other tumor types, including hemangiopericytoma. Therefore, in an unusual site such as the dura, it is advisable to obtain genetic confirmation of EWS-pPNET via the 11;22 translocation or the EWS-FLI-1 (or other EWS variant) fusion transcript (Fig. 36.1d).