Diagnosis and surgery of ossification of posterior longitudinal ligament associated with dural ossification in the cervical spine.

Direct removal of the ossified mass via anterior approach carries good decompression to ossification of the posterior longitudinal ligament (OPLL) in the cervical spine. Ossification occasionally involves not only the posterior longitudinal ligament but also the underlying dura mater, which increased the opportunity of the cerebrospinal fluid (CSF) leakage or neurological damage. The surgeon was required to recognize the dural ossification (DO) and need more cautious manipulation. Hida et al. first described the computed tomography (CT) findings that indicated the association with DO, and suggest the double-layer sign appeared more specific for DO. This study reviewed 138 patients who received anterior cervical corpectomy and fusion (ACCF) for OPLL, and 40 patients were found in the association with DO during anterior procedure. Radiological studies revealed that the patients with severe OPLL (higher occupying rate and larger extent) have increasing opportunity of association with DO. The double-layer sign, as a specific indicator for association with DO was sensitive in the patients with mild OPLL, but less frequent in those with severe OPLL with DO. Two surgical techniques were used for the patients with DO in anterior decompression procedure. When the double-layer sign was observed on CT scans, the OPLL could be separated from DO through a thin layer consisting a nonossified degenerated PLL to avoid CSF leakage. Otherwise, the entire ossified mass including OPLL and DO was removed completely. In this technique, the arachnoid membrane needed to be persevered with the aid of microscope to avoid a large area of membrane defect, resulting in uncontrolled CSF leakage. There was no significant difference in clinical results between the patients with DO and those without DO. Therefore, ACCF is meritorious for the patient with OPLL associated with DO, although more difficult manipulation and higher risk of CSF leakage.