Benign Notochordal Cell Tumor: An Entity Distinct from Ecchordosis Physaliphora and Chordoma

We read with interest “Ecchordosis Physaliphora: Does It Even Exist?” by Stevens et al.¹ This is a laudable effort in addressing the growing recognition that histologically and immunohistochemically, there is no pathologic distinction between ecchordosis physaliphora (EP) and chordoma. EP has a relative lack of abnormal mitotic activity, cytologic atypia, and necrosis; rather, it is the degree to which these features are present or absent that may influence the diagnosis for one or the other. Thus, radiology input has been used to suggest features more characteristic of EP or chordoma. As excellently noted in the article, findings on MR overlap because they can both demonstrate marked T2 hyperintensity and appear primarily intradural. In addition, the degree of enhancement is quite variable, with some chordomas demonstrating little-to-no enhancement, making the lack of enhancement an unsuitable differentiator. EP was initially described as an incidental finding and has been described as a benign lesion. Moreover, there is limited literature that critically evaluates the long-term outcome of these patients to support EP indeed having a different natural history than chordoma.²

However, benign notochordal cell tumors (BNCTs) are intraosseous lesions that have histologic features distinct from EP and chordoma. While there are more studies demonstrating BNCT in the spine than in the clivus, there has also been a recent report of BNCT and clival chordoma occurring concomitantly.³ In addition, the coexistence of BNCT and chordoma in the lumbar and sacrococcygeal regions has been well-documented. Indeed, multiple studies focusing on BNCT in the spine seem to indicate that in some situations, chordomas arise from BNCT.³

BNCTs are histologically composed of bland vacuolated cells with a portion of less-vacuolated cells with eosinophilic cytoplasm. These fill the medullary space between bony trabeculae without bony destruction.⁴ In contrast, EP and chordoma have multivacuolated epithelioid cells arranged as cords and clusters within the myxoid matrix. Immunohistochemistry cannot distinguish these entities because they all are immunoreactive for brachyury, cytokeratin, epithelial membrane antigen, and, variably, S-100. Genetic, environmental, or individual demographics may influence the disease severity and rate of progression seen with chordomas.⁵

The literature at times will discuss BNCT with EP as if they were a single entity. While EP is thought of as a benign lesion and it is a notochordal remnant, using the terms interchangeably has caused confusion with the terminology of these rare entities. Most important, a key differentiator, EP is nearly identical histologically to chordoma, while BNCT has its own unique histology. These terms should not be used interchangeably. In the future, research evaluating the genomic profiling of BNCT, EP, and chordoma may help elucidate what differences exist, if indeed EP is distinct from chordoma.