Posterior arch defects of the cervical spine: a comparison between absent pedicle syndrome and spondylolysis

Background contextAbnormalities of the posterior arch are rare entities that are usually found incidentally on neck radiographs. Their radiographic appearance may cause them to be confused with more serious entities such as fractures, locked facets, and tumor-induced bony erosions. It is important to distinguish these posterior arch abnormalities from the other entities because the treatment is very different.PurposePosterior arch defects of the cervical spine, including cervical spondylolysis and absent pedicle syndrome, occur rarely. In this case report, we describe three cases of posterior arch defects and present a review of the literature concerning the distinguishing features between spondylolysis and absent pedicle syndrome.Study designA case report and literature review of the posterior arch defects.MethodsTwo patients are presented who developed posterior neck pain after trauma. They had no neurologic deficits, but cervical radiographs suggested that they had a traumatic injury. Cervical spine computed tomography (CT) revealed absent pedicle syndrome and they were treated conservatively. Another patient is presented who developed worsening posterior neck pain and left shoulder pain. She had no history of significant neck injury. Cervical radiographs and CT showed bilateral spondylolysis of C6 vertebra and subluxation of C6 on C7. Because her symptoms were not relieved by conservative measures, we performed anterior cervical discectomy and fusion.ResultsWe treated two patients with absent pedicle syndrome by conservative measures and one patient with cervical spondylolyis by surgical treatment.ConclusionsPosterior arch defects were often confused with other disease entities. But, they have some distinctive features and such distinctive features may be helpful in confirming diagnosis and planning treatment. Furthermore, three-dimensional CT scan reconstruction provides comprehensive anatomic evaluation of the structures with an absent pedicle and the associated bony abnormalities.