Sections show a fragments of tissue in which there is a diffuse sheeted arrangement of epithelioid cells. These have small hyperchromatic nuclei, a large amount of cytoplasm containing
myxoid/mucinous material and well-defined cell borders and are set within a myxoid stroma. No well formed cords or solid aggregates of these cells are seen. There are no mitoses and no necrosis is identified. There is a background inflammatory cell component comprising CD3 positive T cells, CD20 positive B cells and CD68 positive macrophages and neutrophils. Fragments of mature lamellar bone are present with no bone destruction identified.
Immunohistochemistry shows the epithelioid cells to be CAM 5.2+, EMA+, S100 focal +
Double-labelling immunohistochemistry shows positive staining for topoisomerase in a moderate number of the background inflammatory cells. Only scattered lesional epithelioid cells show nuclear staining (proliferation index approximately 1%).
DIAGNOSIS: The histological and immunohistochemical features are those of a
notochordal lesion favouring ecchordosis physaliphora. However, chordoma cannot be absolutely excluded and close patient follow-up is recommended.