JOURNEY OF THE NOTOCHORD: LINKING EMBRYOLOGY TO RADIOLOGIC INTERPRETATION OF THE CRANIOCERVICAL JUNCTION

Abstract

<h3>Background</h3> The notochord is a mesoderm-derived cylindrical midline structure and a defining feature found in all chordates. In vertebrates, the notochordal process represents the initial embryologic axial skeleton and plays important structural and signaling roles in the development of the vertebral column, nervous system, and skull base. Besides persisting postnatally as the nucleus pulposus of the intervertebral disks, the remaining notochord typically regresses during fetal development after completion of its principal tasks. However, remnants of the notochord can persist along its developmental path within the craniocervical region. These remnants present as a spectrum of entities, ranging from anatomic variants, benign tumors, and malignant neoplasms of notochordal origin. Radiologists who interpret imaging in the area along the embryologic path of the notochord should be knowledgeable about its development and be able to recognize its wide array of potential pathologies. <h3>Discussion</h3> This presentation will review notochord embryology and the anatomic and pathologic relevance of notochordal remnants and demonstrate the vast range of imaging features and behavioral properties of these postnatal remnants in the area of the posterior cranial base and cervical spine. We present 3 cases of inferior median clival canal, a notochordal anatomic variant typically discovered as an incidental finding. Also known as <i>canalis basilaris medianus</i>, this notochord remnant manifests as a narrow, well-defined corticated canal passing through the sagittal plane of the clivus. Depending on its course and extent, 2 groups with 6 subtypes have been described. We also present imaging features of pathologic abnormalities, including Tornwaldt cyst, benign remnant ecchordosis physaliphora, and chordoma, a notochord malignancy. Awareness of the full spectrum of pathologic consequences of persistent notochord tissue, recognition of their imaging features, and directing appropriate referral add to the value provided by an oral and maxillofacial radiologist.