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cutaneous parachordoma

 
Parachordomas are rare cutaneous tumors that show virtually identical histologic findings to chordomas. Parachordomas are benign neoplasms and most often develop on the extremities adjacent to tendons, synovium or osseous structures

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#


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