CUTANEOUS PARACHORDOMA - A LIGHT-MICROSCOPIC AND IMMUNOHISTOCHEMICAL REPORT OF 2 CASES AND REVIEW OF THE LITERATURE

Parachordomas are rare cutaneous tumors that show virtually identical histologic findings to chordomas. Therefore, the major differential di agnosis in a case of parchordoma is metastatic chordoma. Parachordomas are benign neoplasms and most often develop on the extremities adjace nt to tendons, synovium or osseous structures, as opposed to chordomas , which are malignant tumors located along the craniospinal axis. Whil e recurrences may occur in cases of parachordoma, metastases have not been reported. In this report, two cases of parachordomas are reported and the literature reviewed. By light microscopy parachordomas show e osinophilic bands of fibrous tissue separating lobules of cells with v ariably vacuolated cytoplasm (physaliphorous cells) admired with more epithelioid cells in a myxoid stroma. Parachordomas and chordomas shar e immunohistochemical and ultrastructural features. Both stain with S- 100 protein and vimentin, and ultrastructurally both demonstrate cytop lasmic vacuoles, intermediate filaments, pinocytotic vesicles, cell ju nctions, and cytoplasmic membranes with microvillous processes. Chordo mas more frequently express cytokeratin (98% vs. 66% in parachordomas) and epithelial membrane antigen (90% vs. 20% in parachordomas) and ch ordomas have a larger number of rough endoplasmic reticulum-mitochondr ial complexes. Thus, positive staining with epithelial membrane antige n and the identification of a large number of rough endoplasmic reticu lum-mitochondrial complexes are suggestive of metastatic chordoma. How ever, the definitive distinction remains a clinical one after appropri ate radiologic studies of the skull and spinal chord.