Localization
on the extremities adjacent to tendons, synovium or osseous structures
as opposed to chordomas, which are malignant tumors located along the craniospinal axis
Prognosius
recurrences may occur
metastases have not been reported
Microscopy
eosinophilic bands of fibrous tissue separating lobules of cells with variably vacuolated cytoplasm (physaliphorous cells) admixed with more epithelioid cells in a myxoid stroma.
Immunochemistry
S-100+ protein
vimentin+
Ultrastructure
cytoplasmic vacuoles
intermediate filaments
pinocytotic vesicles
celljunctions
cytoplasmic membranes with microvillous processes.
Differential diagnosis
metastatic chordoma
Chordomas more frequently express cytokeratin (98% vs. 66% in parachordomas) and epithelial membrane antigen (90% vs. 20% in parachordomas) and chordomas have a larger number of rough endoplasmic reticulum-mitochondrial complexes.
Thus, positive staining with epithelial membrane antigen and the identification of a large number of rough endoplasmic reticulum-mitochondrial complexes are suggestive of metastatic chordoma.
References
Imlay SP, Argenyi ZB, Stone MS, McCollough ML, Henghold WB. Cutaneous parachordoma. A light microscopic and immunohistochemical report of two cases and review of the literature. J Cutan Pathol. 1998 May;25(5):279-84. PMID: #9696295#