Know your notochord: A pictorial review of notochord remnants

Notochord formation begins between the third and fourth weeks of embryonic develop-ment. As the axial skeleton develops, the notochord regresses and eventually contributes to the formation of the nucleus pulposus of the intervertebral disks. Notochord regression can be variable, especially at the 2 poles of the skeleton, which results in the persistence of ectopic notochordal remnants. These remnants include benign entities (eg, ecchordosis physaliphora, benign notochordal cell tumor, Tornwaldt cyst, canalis basilaris medianus, fossa navicularis) or malignant lesions (eg, chordoma). We present a review of these lesions, their clinical presentations, and their typical radiographic appearances. Notochord remnants may have overlapping features in terms of their location and appearance; however, differen-tiation is crucial because the proper treatment and management may differ drastically. Familiarity with notochord development aids in understanding the characteristic locations of notochordal remnants. Noting the unique imaging findings of notochordal remnants can often help narrow the differential diagnoses. Learning Objective: To describe notochord development, normal regression during fetal life, and notochord remnants that give rise to anatomic variants, including benign and malignant lesions.