Flowing Ossifications, Syndesmophytes, and Parasyndesmophytes

• Flowing ossifications: Seen in diffuse idiopathic skeletal hyperostosis (DISH). The ossifications involve the anterior longitudinal ligament, paraspinal connective tissues, and annulus fibrosus of at least four contiguous vertebral bodies. Lateral radiographs of the spine may show radiolucencies between the anterior aspect of the vertebral bodies and the flowing ossifications of the anterior longitudinal ligament. The radiolucencies end at the level of the vertebral endplates.
• Syndesmophytes: Seen in ankylosing spondylitis. Vertically orientated outgrowths of trabecular bone forming in the outer margins of the annulus fibrosus. Related to repeated episodes of inflammation and repair. Arise at the discovertebral junction (in contrast to claw osteophytes, which arise several millimeters from the discovertebral junction).
• Parasyndesmophytes: Paravertebral ossifications seen in psoriatic arthritis and reactive arthritis. Begin at a distance from the vertebral body and intervertebral disc. Initially thick and fluffy or thin and curvilinear densities on one side of the spine that parallel the lateral surface of the vertebral body and intervertebral disc. Eventually become large and bulky and merge with the underlying bone and disc. Unilateral or asymmetric in distribution. Unlike syndesmophytes, they arise farther away from the vertebral column.

References

• Dihlmann W. Current radiodiagnostic concept of ankylosing spondylitis. Skeletal Radiol. 1979;4(4):179-88.
• Jones MD, Pais MJ, Omiya B. Bony overgrowths and abnormal calcifications about the spine. Radiol Clin North Am. 1988 Nov;26(6):1213-34.
• Taljanovic MS, Hunter TB, Wisneski RJ, Seeger JF, Friend CJ, Schwartz SA, Rogers LF. Imaging characteristics of diffuse idiopathic skeletal hyperostosis with an emphasis on acute spinal fractures: review. AJR Am J Roentgenol. 2009 Sep;193(3 Suppl):S10-9.