Rare bone tumour arising from ectopic notochordal tissue. The most common sites are the sacrum, base of skull and spine. They are locally invasive, but indolent, and in patients unfit for radical surgery, conservative treatment is reasonable.
Characterised by physaliferous cells (cells with bubbly/vacuolated/pale cytoplasm), but other myxoid lesions should be considered as differentials. Immunohistochemically positive for S100 and brachury.