[Myelopathy caused by hypertrophy of the posterior longitudinal ligament (HPLL): case report].

A case of myelopathy caused by hypertrophy of the posterior longitudinal ligament at the cervical spine is reported. A 71-year-old man was hospitalized with myelopathy with progressed during the last two months. Plain X-ray of the cervical spine revealed only mild spondylotic change. Myelography demonstrated completely blocked contrast medium at C4 to C5 vertebral height due to epidural mass. This epidural mass was localized ventral to the spinal cord from C3 to C5. CT scan revealed slightly high density area behind the vertebral body. On surgery, no evidence of disc fragment but only hypertrophied posterior longitudinal ligament which was removed was found to be a cause of cord compression. Excellent recovery of neurological symptoms after operation was obtained. On histological study, remarkable hypertrophy, edema, hyalinoid degeneration and a little calcification of the ligament was found, which did not show any evidence of new bone formation. HPLL was characterized by thickened and broad epidural mass in the ventral side of cervical cord with Hounsfield number of 90-156 on CT scan, which is not very easy to differentiate from metastatic epidural tumor. The cause of HPLL is not well elucidated, though, this may be a new category of compression myelopathy.