Ossification of the Posterior Longitudinal Ligament

Diffuse Idiopathic Skeletal Hyperostosis

Diffuse idiopathic skeletal hyperostosis is a syndrome that involves ossification of the soft tissue and ligaments, commonly occurring near the ventral aspect of the cervical or thoracic spine (Figs. 1 and 2).^[38,45,59] This syndrome is quite common. The incidence of DISH in patients older than 65 years of age has been estimated to be between 15% and 30%.^[36,54] In sharp contrast to OPLL, this syndrome is uncommon in Asian populations and more common in North American or other Caucasian populations.^[34,35] Most individuals with DISH are asymptomatic. However, several cases of dysphagia have been noted. These can occur when significant bony overgrowth of the anterior longitudinal ligament leads to compression of the esophagus.^[38,45] The coexistence of OPLL and DISH has been previously reported. Ehara et al.^[10] found DISH to be indentified in 25% of 109 patients they studied with OPLL. Others have reported this rate of association to be as high as 50%.^[44] Given this association between OPLL and DISH, an awareness of the pathogenesis and treatment of OPLL may be of particular importance in North American populations. It should additionally be noted that recent studies have shown an increased prevalence of OPLL in patients with various metabolic disorders, including hypoparathyroidism, acromegaly, and diabetes^[30] as well as an association between DISH and ankylosing spondylitis.^[52]

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Figure 1.

Findings of DISH and OPLL can commonly be found in the same patient as seen on this preoperative CT scan. A: Sagittal midline CT demonstrates ossification of both the ligaments and soft-tissue ventral to the vertebral bodies (black arrow); double white arrows indicate the first layer of ossification and the single white arrow indicates the second layer. B and C: Axial images showing the 2 layers of bone formation as well as ossification ventral to the C-3 body consistent with DISH (arrows, B).

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Figure 2.

Postoperative nonenhanced T2-weighted MR image showing decompression 1 year after C3–7 laminoplasty in the patient in Fig. 1. Preoperative images showed 10° of lordosis, which was enough to allow dorsal migration of the cord away from the ventral bony bar. Left: Magnetic resonance imaging evidence of DISH (double arrows) as well as extent of decompression (single arrow) is shown. Right: Axial MR image at this level following decompression.

Neurosurg Focus. 2011;30(3):e10 © 2011 American Association of Neurological Surgeons