Recurrent skeletal extra-axial chordoma confirmed with brachyury: imaging features and review of the literature.

A small number of tumors bearing histological resemblance to axial chordoma arising from the bone or soft tissue outside the axial skeleton have been reported. These lesions have historically been referred to as parachordoma, chordoma periphericum (CP), or extra-axial chordoma (EAC). With the introduction of the immunohistochemical stain brachyury, a sensitive and specific marker for notochordal origin, chordomas arising in extra-axial locations (i.e., CP, EAC), are now diagnosed with more accuracy and distinguished from parachordoma, which resembles chordoma on histology. The distinction between EAC and parachordoma is clinically important because EAC confirmed by immunoreactivity for brachyury tends to grow and recur with local bone destruction. Prior to the introduction of brachyury, the diagnosis of EAC was challenging and therefore the imaging features of EAC have not been comprehensively described. We report two cases of recurrent EAC confirmed by the expression of brachyury arising from the distal femur and distal tibia and describe the imaging findings from radiography and MRI at initial diagnosis and at recurrence.