Unilateral ossified ligamentum flavum in the high cervical spine causing myelopathy

High cervical ossified ligamentum flavum (OLF) is rare and may cause progressive quadriparesis and respiratory failure. Our two patients had unilateral OLF between C1 and C4 levels. MR showed a unilateral, triangular bony excrescence with low signal and a central, intermediate or high signal on all pulse sequences due to bone marrow within. There was Type I thecal compression (partial deficit of contrast media ring). The first patient had a linear and nodular OLF with calcification within tectorial membrane, C2-3 fusion and unilateral C2-facetal hypertrophy; and the second patient, a lateral, linear OLF with loss of lordosis and C3-6 spondylotic changes. A decompressive laminectomy using "posterior floating and enbloc resection" brought significant relief in myelopathy. Histopathology showed mature bony trabeculae, bone marrow and ligament tissue. The coexisting mobile cervical vertebral segment above and congenitally fused or spondylotic rigid segment below the level of LF may have led to abnormal strain patterns within resulting in its unilateral ossification. In dealing with cervical OLF, carefully preserving facets during laminectomy or laminoplasty helps in maintaining normal cervical spinal curvature.