Extra-axial chordoma. Modern pathology. Clinical presentation of two cases

The very existence of extra-axial chordoma has been questioned since its initial description, and in fact, similar tumor is described in soft tissue in part of a morphological spectrum that includes mixes tumor and myoepithelioma. in bone, the entity has been described as extra-axial chordoma. in any case, only 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. the very existence of extra-axial chordoma has been questioned since its initial description, and in fact, similar tumor is described in soft tissue in part of a morphological spectrum that includes mixes tumor and myoepithelioma. in bone, the entity has been described as extra-axial chordoma. in any case, only 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, EACh), are now diagnosed with more accuracy and distinguished from parachordoma, which resembles chordoma on histology. the differential diagnosis between EAC and parachordoma is clinically important, EACh positive for brachyury tends to grow and recur with local bone destruction. Prior the specific marker brachyury, the diagnosis of EACh was challenging and therefore the imaging features of EACh have not been comprehensively described. now, there are only a few cases reporting the cytogenetics of the entity: trisomy 15 and loss of chromosome 1, 16 and 17 in one case with chromosomal studies, a loss of chromosomes 9, 10, 20 and 22, a loss of chromosome 17 and a structural rearrangement of chromosome 3 [del (3q)] and chromosomes 2 and 4 [t (2p; 4q)] in a recurrent tumor. Because studies about cytogenetics of parachordoma are rare, the characteristic need to be further explored. we report two cases of recurrent EAC confirmed by the expression of brachyury arising from the distal femur and proximal tibia and describe the imaging findings from radiography and mri at initial diagnosis and at recurrence.