A case of a 47-year-old male with a sacral spine mass was investigated by histology, immunohistochemistry (IHC), and electron microscopy (EM). The light microscopy of the first core biopsy revealed scant cellularity with spindle and round cells with eosinophilic cytoplasm within a fibromyxoid background. Immunostaining with pancytokeratin, cytokeratin 19, and S100 was nonspecific. Another biopsy was attempted to obtain a more definitive diagnosis. Light microscopy of the second core had scant cellular material. However, the tissue was specifically requested for ultrastructural evaluation and revealed features diagnostic of chordoma. After definitive diagnosis, radical resection of the mass was performed. This case illustrates how EM was instrumental in the definitive diagnosis before radical resection in a case that was not clear by hematoxylin and eosin (H&E) and IHC alone.
Keywords: Brachyury; chordoma; ultrastructure.