In this case, congenital ACSP of C5 with associated osseous spinal abnormalities in a male patient who has had a motor vehicle accident was misdiagnosed as a cervical fracture on plain radiographs. The correct diagnosis could only be established by the means of CT. In their study from 2005 Holmes et al. found a pooled sensitivity for cervical spine injuries on plain radiography of 52% (95% CI 47, 56%) and for CT of 98% (95% CI 96, 99%) . Despite the absence of randomized controlled trials, evidence exists that CT significantly outperforms plain radiography as a screening test for patients at very high risk of cervical spine injury. There is not sufficient evidence though to suggest that cervical spine CT should replace plain radiography as the initial screening test for less injured patients who are at low to moderate risk for cervical spine injury but still require a screening radiographic examination, as in our case. Although arguably primary CT-scan of the spine would have been the first choice in this setting, antero-posterior and lateral radiographs as well as 45° oblique views of the cervical spine were taken as a first imaging study (Figure 1).
ACSP is a very rare congenital abnormality of the spine. Any level of the cervical spine can be affected, though ACSP has been seen most frequently at the level C6 followed by the level C5 and C7 [1–5]. Although the exact pathogenesis of ACSP is unclear, it probably relates to in-utero defects in the formation of the chondrification and/or ossification centers of the spine.
In our case, ACSP was associated with several congenital osseous abnormalities. In previous reports, associations of ACSP with hypoplasia of the pedicles, hypoplasia of the vertebral body, sagittal vertebral body clefts, vertebral body and arch fusions or spina bifida occulta at the absent pedicle level have been described in up to 51% of all cases . Interestingly, hyperplasia of the contralateral pedicle at the involved level has not been encountered in the literature, as is commonly seen in absent or hypoplastic lumbar pedicle . In our patient, ACSP of C5 in association with spina bifida occulta at the same level resulted in a right vertebral hemi-arch with no osseous attachment to the adjacent vertebral bones. This has, to the best of our knowledge, not been reported in the radiologic literature so far. Ligaments of the spine and neck muscles might have maintained the anomalous fragment in its position, but deviation upon movement may inevitably have provoked the chronic symptoms of the patients [2, 4, 9]. Degenerative osseous changes of the involved or adjacent vertebral segment are frequently seen and a result of abnormal forces on the bones and articulations .
Antero-posterior and lateral-view radiographs of the cervical spine as a first imaging work-up give valuable information on the gross anatomy and the alignement of the vertebral structures, although subtle pathologies, e.g. fracture, of the vertebral pedicles cannot always be sufficiently ruled out . Therefore many centers add oblique-view projections to their standard-views of the spine to better depict the intervertebral neuroforamina and their surrounding structures, especially in a setting of acute trauma [11, 12]. Even with that extra-information it is sometimes difficult to distinguish congenital abnormalities of the spine, e.g. ACSP or spina bifida occulta, from acute traumatic injuries such as fractured pedicles or vertebral arch fractures [13–15]. CT as a three-dimensional imaging modality with the possibility of multiplanar reconstructions allows for the exact diagnosis of acute traumatic lesions of the cervical spine. It also permits to reliably identify congenital osseous abnormalities such as ACSP as well as to narrow the differential diagnosis of pathologies that might cause similar appearances on radiographs (e.g. neurofibroma which can also cause an enlarged intervertebral neuroforamen) . Thereby any unwarranted surgery or inadequate conservative therapy can be avoided.