Prepared by Rahul Gupta, MD and James Lally, MD of the Department of Radiology, Christiana Care Health Services, Newark, DE.

CASE SUMMARY:

A 50-year-old Asian man with no significant past medical history fell while working on a ladder and was brought to the emergency room with weakness of all four extremities. The lower extremities were weaker than the upper extremities, with minimal sensory deficits. The reflexes were brisk in all four limbs. Figures 1-3 are images performed after admission.

DIAGNOSIS:

Ossification of posterior longitudinal ligament with spinal canal stenosis and cervical myelopathy.

IMAGING FINDINGS:

The cervical spine radiograph (figure 1) shows ossification along the posterior vertebral column. Axial and sagittal reconstruction CT scans of the cervical spine (figure 2) reveal ossification along the vertebral column with a lucent space between it and the vertebral column and encroachment of the spinal canal by the ossification. There is evidence of spinal canal stenosis on a congenital basis. MR imaging (figure 3) show low signal intensity along the vertebral column compressing on the thecal sac with no evidence of spinal cord contusion.

The patient showed signs of spontaneous neurological recovery during the hospital course and underwent prophylactic decompressive laminectomy from C1 to C7.

DISCUSSION:

Ossification of the posterior longitudinal ligament (OPLL) usually involves the cervical spine. The prevalence of OPLL among the Japanese is the highest of any nation and is, therefore, called "Japanese disease." ¹ While its etiology remains unknown, there have been many theories proposed. It is associated with diffuse idiopathic skeletal hyperostosis in about 50% of cases. ² It is also associated with other forms of spinal hyperostosis, such as the ossification of the ligamenta flava and ankylosing spondylitis. To date, no infectious agent has been isolated in this condition.

Although compromise of the spinal canal due to an ossified posterior longitudinal ligament was reported by Key in 1839, the recognition of a distinct clinical entity related to such ossification was first recorded by Tsukimoto ³ in 1960. Tereyama and his colleagues ⁴ introduced the term ossification of the posterior longitudinal ligament in 1964.

OPLL is more common in men than in women, occurring in a ratio of 2:1. The diagnosis is usually made in the fifth to seventh decade of life. Most individuals with OPLL are entirely asymptomatic; however, a variety of symptoms and signs have reportedly been associated with this disorder. Ono and coworkers ⁵ have divided the principal neurologic symptoms into three groups: cord signs, manifested by dominant motor and sensory disturbances in the lower extremity (56%); segmental signs, manifested by dominate motor and sensory disturbances in the upper extremity (16%); and cervico-brachialgia, causing no obvious neurologic deficits but associated with pain in the neck, the shoulder, and the arm (28%). These investigators and others have found a probable correlation between the thickness of the ossified ligament that is detectable on roentgenogram and the presence of neurologic manifestations. Symptoms are initiated by trauma in approximately 20% of reported cases.

Radiographically, the diagnosis of OPLL is established by its characteristic appearance of a dense, ossified stripe or plaque of variable thickness (1 to 5 mm) evident along the posterior margins of the vertebral bodies and the intervertebral discs. It is common in the mid-cervical region (C3-C5). OPLL is classified as (a) continuous type, defined as ossification that extends along the posterior edge of vertebral column and at the disc level either continuously or discontinuously; or (b) segmental type, defined as ossification confined to posterior edge of vertebral column. In the thoracic spine, OPLL is most common in the fourth to seventh thoracic vertebral levels and in lumbar spine along L1 to L2 region. The extent of OPLL can be evaluated further by CT scan since it is more effective in the detection of minute ossification or assessment of spinal canal stenosis. On MR imaging, OPLL is seen as low-intensity signal on T1- and T2-weighted images, and differential diagnosis for this includes areas of low proton density such as calcification and ossification, flowing blood, or the presence of paramagnetic substances as (hemosiderin). ⁶ If high signal is observed within the low-signal intensity on T1- and T2-weighted images, this reflects marrow and OPLL should be considered. MR imaging can demonstrate directly and noninvasively location and the degree of cord compression as well as pathological changes in the cervical cord including edema, demyelination, myelomalacia cavitation, and necrosis as high-signal intensity on T2-weighted images. ^7,8 The diagnosis of ossified ligament is important because the spinal cord can be damaged by slight injury, and X-rays, CT, and MR are all required to establish a diagnosis of OPLL.

References

1. Breidahl P: Ossification of the posterior longitudinal ligament in the cervical spine: The Japanese disease occurring in patients of British descent. Austral Radiol 13:311-313, 1969.

2. Resnick D, Guerra J Jr, Robinson CA, Vint C: Association of diffuse idiopathic skeletal hyperostosis and calcification and ossification of the posterior longitudinal ligament. Am J Roent 131:1049-1053, 1978.

3. Tsukimoto H: An autopsy report of syndrome of compression of spinal cord owing to ossification within spinal canal of cervical spine. Arch Jpn Chir 29:1003, 1960. Letter.

4. Tereyama K, Maruyama S: Ossification of the posterior longitudinal ligament in the cervical spine. Orthoped Surg 15;1083, 1964.

5. Ono M, Russel WJ, et al: Ossification of the
thoracic posterior longitudinal ligament in a fixed population: Radiological and neurological manifestations. Radiology 143;469-474, 1982.

6. Luetkehans TJ: Ossification of the posterior longitudinal ligament diagnosis by MR. AJNR 8:924-925, 1978.

7. Hashizume Y, Iijima S, Kishimoto H, Yanagi T: Pathology of spinal cord lesions caused by ossification of the posterior longitudinal ligament. Acta Neuropathol 63:123-130, 1984.

8. Resnick D: Calcification and ossification of posterior spinal ligaments and tissues, pp 1603-1615. In: Resnick D, Niwayama G (eds): Diagnosis of Bone and Joint Disorders, ed 2. Philadelphia, WB Saunders, 1986.