Retroperitoneal mesenchymal chondrosarcoma. Report of a case diagnosed by fine needle aspiration cytology.

An unusual case of retroperitoneal mesenchymal chondrosarcoma diagnosed by fine needle aspiration (FNA) biopsy is described. CT-guided FNA of a mass arising in retroperitoneal soft tissues yielded an amorphous, myxoid material containing two distinct and separate populations of tumor cells. One was an undifferentiated, monomorphic, small cell component with granular cytoplasm and round central nuclei. The second population was an overtly malignant chondroid component scattered within an abundant myxoid matrix showing foamy cytoplasm, marked nuclear pleomorphism and frequent multi-nucleation. These cytologic findings were distinctive and similar to the histologic findings. The differential diagnosis and the possible pitfalls in the FNA diagnosis of this relatively rare tumor are discussed.