Developmental anomalies of the lateral portion of the cervical neural arch: Multimodal imaging and clinical implications

Abstract

Objective

This study aimed to describe the imaging spectrum of developmental anomalies of the lateral portion of the cervical neural arch.

Method

This was a five-year retrospective review of consecutive computed tomography (CT) scans of the cervical spine for structural anomalies of the cervical vertebral pedicle and facets. CT, radiographs and, when available, magnetic resonance imaging studies were independently reviewed. Anomalies were grouped into the following three categories: the absence of a pedicle, clefts in the vertebral arch or isolated dysmorphism of the facet. Clinical data on demographics and neurological outcomes were documented.

Results

Among 9134 consecutive patients undergoing a CT scan of the cervical spine, 18 (0.2%) patients were found to have developmental anomalies of the pedicle and facets. Findings included 7/18 (39%) with congenital absence of a pedicle, 8/18 (44%) with clefts in the vertebral arch and 3/18 (17%) with isolated dysmorphism of the articular facets. No acute neurological deficits or spinal cord injuries were reported. Associated chronic symptoms included neck pain 10/18 (56%), radiculopathy 7/18 (39%) and myelopathy 1/18 (6%).

Conclusion

Developmental anomalies of the pedicle and facet may mimic traumatic spinal pathologies. Recognising a diverse spectrum of imaging findings is vital to prevent misdiagnosis and unnecessary intervention.

Introduction

The constituents of the vertebral neural arch include a pair of pedicles, laminae and facets. Midline spinal dysraphism is a well-recognised congenital disorder. However, developmental anomalies of the lateral portion of the neural arch are less well understood. The spectrum of anomalies includes the absence of a pedicle, clefts in the vertebral arches (neurocentral, pedicular, pars interarticularis, retroisthmic and paraspinous) and isolated dysmorphism of the articular facets.^1–5 Anomalies of the lateral portion of the neural arch are extremely rare and have a predilection for the cervical spine.^1–5 These anomalies can easily mimic acute fracture or facet joint subluxation/dislocation on imaging. An in-depth understanding of the embryology and postnatal development of the spine and pattern recognition is necessary to avoid misdiagnosis and avoid unnecessary treatment. We performed a five-year retrospective review of trauma computed tomography (CT) scans of the cervical spine to determine the incidence, imaging characteristics and clinical outcomes in patients with developmental anomalies of the lateral portion of the neural arch.

Methods

Case selection

A five-year retrospective review of trauma CT scans of the cervical spine performed at a tertiary institution from December 2012 to December 2017 was undertaken. The institutional ethics board approved the study, and informed consent was waived. Eighteen cases of developmental anomalies of the cervical pedicle and articular facet were identified from a review of 9134 consecutive emergency patients who underwent a CT scan of the cervical spine. Imaging studies and medical records were retrospectively reviewed. Clinical data collected included demographics, clinical presentation, neurological status and final clinical outcome.

Imaging acquisition

All studies were performed using a standardised trauma CT cervical spine protocol performed on the Definition Flash scanner (Siemens, Erlangen, Germany). The acquisition parameters were 120 kV (peak), Eff. mAs 230 auto-mA modulation case dose 4D, 0.8 pitch, 128 × 0.6 mm, slice thickness of 0.75 mm. The source axial data were reconstructed into 1 and 5 mm sections in the axial, sagittal and coronal planes using a predetermined soft-tissue and bone-kernel algorithm for image interpretation. Volume rendered 3D images were created on a Philips CT Brilliance Workstation (Amsterdam, The Netherlands) with right–left rotation. The exclusion criteria included non-diagnostic quality imaging degraded by motion artefact. Cervical spine magnetic resonance imaging (MRI) studies were performed on either a 1.5 T Magnetom Avanto (Siemens) or a 3 T Skyra (Siemens) scanner utilising a standard spine trauma protocol. Sequences included sagittal T1 weighted, sagittal T2 weighted, sagittal STIR, axial T2* gradient echo and axial T2 weighted.

Imaging analysis

All acquired images (CT and, when available, MRI) were reviewed on the PACS workstations (AGA IMPAX 6, reconstructions with AGFA IMPAX Volume Viewing 2.2 Cinapps 4.2; AGFA Healthcare, Mortsel, Belgium). Patients’ identities on the final images for interpretation were removed to facilitate blinded analysis. Two fellowship certified neuroradiologists (C.C.-T.H and T.W.W with four and eight years of experience, respectively) and one interventional radiologist (L.M with four years of experience) independently evaluated each study, with a final agreement by consensus. Inclusion criteria included non-traumatic anomalies of the cervical pedicle and articular facets. These were grouped into the following categories: congenital absence of a pedicle, congenital clefts (neurocentral, retrosomatic, pars and paraspinous) or dysmorphic articular facets. Studies with poor image quality or midline spinal dysraphism (spina bifida) were excluded. Analysis of results involved descriptive statistics. Specific parameters recorded included the abnormal vertebral level, vertebral element involved (pedicle, lamina or facets), morphologic description and relevant ancillary findings.

Results

Among 9134 consecutive patients undergoing CT scans of the cervical spine, 18 (0.2%) patients (10 males) were found to have congenital anomalies of the pedicle and facets (M_age = 41 years; range 23–67 years). Radiological findings included 7/18 (39%) patients with congenital absence of a pedicle, 8/18 (44%) patients with clefts in the vertebral arch (neurocentral, pedicular, pars interarticularis, retroisthmic and paraspinous) and 3/18 (17%) patients with isolated dysmorphism of the articular facets. No acute neurological deficits or spinal cord injuries were reported. Associated chronic symptoms included neck pain 10/18 (56%), radiculopathy 7/18 (39%) and myelopathy 1/18 (6%). Table 1 outlines the imaging and clinical findings.

Table 1.

Patient demographics, clinical and imaging findings.

	Number affected, n (%)	Unilateral (n)	Bilateral (n)	Affected vertebral level (n)		Neck pain (n)	Radiculopathy (n)	Myelopathy (n)
Absent pedicle	7/18 (39%)	7	0	C5	1	3	3 (ipsilateral)	0
				C6	4
				C7	2
Congenital cleft	8/18 (44%)	6	2	C2	1	4	3 (1 ipsilateral and 2 bilateral)	1
				C4	2
				C5	3
				C6	2
Isolated dysmorphic facet	3/18 (17%)	3	0	C4	1	3	1 (ipsilateral)	0
				C5	2

Seven (7/18; 39%) patients with absent pedicles were unilateral, with the majority occurring in the lower cervical vertebral levels (C5, n = 1; C6, n = 4; C7, n = 2). Characteristic findings common in all unilateral absent cervical pedicle cases include the absence of the ipsilateral posterior tubercle of the transverse process, widening of the neural foramen and posteriorly rotated ipsilateral lamina, giving rise to rudimentary/dysplastic articular facets which articulated with the adjoining levels (Figures 1 and 2). There were variable degrees of articular facet dysmorphism, ranging from subtle hypoplasia to a truncated appearance. Either or both superior and inferior articular facets can be involved. Invariably, the immediate adjoining level demonstrates dysmorphism of the articular facets. No vertebral segmentation anomalies were evident. Herniation of the nerve root dural sheath through the widened neural foramen was a uniform feature on MRI, and exiting nerve roots demonstrated no inter-level conjoinment. Cervical MRI in four patients did not demonstrate imaging features of osseous oedema, ligamentous injury or spinal cord injury. Three patients with absent cervical pedicle suffered from chronic neck pain and reported radicular symptoms of ipsilateral hand paraesthesia.

Figure 1.

Computed tomography (CT) cervical spine axial image (a) of the C6 vertebrae demonstrates an absent left pedicle and posterior tubercle of the transverse process with the widening of the left C6–C7 neural foramen (*). Magnetic resonance imaging (MRI) of the cervical spine in the axial (b) and sagittal (c) planes show a nerve root dural sheath diverticulum protruding through the widened neural foramen (*). The left C6 facet is dysplastic (arrow), and there is remodelling of the adjoining facets at the vertebral level above and below.

Figure 2.

Plain radiograph of the lower cervical spine ((a) and (d)) showing an absent right C7 pedicle (dotted circle) and a posteriorly positioned lamina with well-formed facets (arrows) and an ipsilateral cervical rib (arrowhead). A CT scan of the cervical spine in the sagittal (b) and axial (e) plane confirms the plain radiograph finding of the absent right pedicle and posterior tubercle of the transverse process at C7 with the secondary widening of the neural foramen (asterisk). 3D volume-rendered images ((c) and (f)) show the posteriorly rotated right C7 lamina giving rise to a shortened superior facet and morphological normal inferior facet (arrows).

Eight (8/18; 44%) patients with cervical vertebral clefts were identified at the lower cervical vertebral levels (C2, n = 1; C4, n = 2; C5, n = 3; C6, n = 2). Six patients had unilateral clefts, and two patients had bilateral clefts without associated anterolisthesis. The range of clefts identified were pedicular (n = 2), pars interarticularis (n = 2), retroisthmic (n = 1) and paraspinous (n = 3). Clefts in the vertebral arches are frequently associated with dysmorphic facets and shortened pedicles (n = 5; Figure 3). Four patients suffered from chronic neck pain, one patient had ipsilateral symptoms and two patients had bilateral radicular symptoms. One patient with bilateral C2 vertebral arch clefts had severe central canal stenosis and clinical features of cervical myelopathy.

Figure 3.

A CT scan of the cervical spine in the axial (a) and sagittal ((b) and (c)) plane showing a small pedicular cleft at the right C6 vertebra. The right C6 superior facet (arrowhead) is well formed which is derived from the remnant pedicle anterior to the cleft, whereas the dysmorphic inferior facet (arrow) is short and rounded deriving from the lamina. MRI of the cervical spine in the axial (d), sagittal (e) and coronal (f) planes confirms the structural findings and shows no associated neural foraminal narrowing.

Only three (3/18; 17%) patients were found to have isolated dysmorphic facets identified at the mid-cervical levels (C4, n = 1; C5, n = 2), and all were unilateral. CT features can be subtle, including a shortened pedicle, hypoplasia or truncated appearance of the superior and/or inferior articular process. Two patients underwent MRI of the cervical spine for suspected injuries to the facet based on the initial CT findings, but no bone-marrow oedema, ligamentous injury or periarticular soft-tissue abnormality was found. Three patients suffered from chronic neck pain, and one patient had ipsilateral radicular symptoms (Figure 4).

Figure 4.

A CT scan of the cervical spine in the left parasagittal planes (a) demonstrating a short right pedicle (asterisks) and hypoplastic dysmorphic facet of the C4 vertebrae. 3D CT volume-rendered images (b) provide better anatomic spatial relations of the described anomalies. MRI of the cervical spine (c) shows severe left C4–C5 neural foraminal stenoses.

Discussion

Developmental anomalies of the lateral portion of the cervical neural arch are not well recognised. The absent cervical pedicle was first recognised in 1946 by Hadley, but its anatomical description was more clearly detailed by Wiener in 1990, encompassing an enlarged neural foramen, dorsally orientated ipsilateral lamina and dysplastic-appearing ipsilateral transverse process.^1–6 A literature review of absent cervical pedicles between 1946 and 2010 described a total of 48 cases in 46 patients.^1–18 The most common reported vertebral level of involvement was the mid to lower cervical spine with C6, followed by C5 and C7 without right- or left-side predilection; which were similar to our findings. Literature data on clefts of the neural arch and dysmorphic facets in the cervical spine are limited to small case series and case reports, but there is also a predilection for the lower cervical levels.^1–18 Although the majority of cases were incidental findings on imaging in the context of trauma, clinical history revealed just over half of the patients in our cohort experienced chronic neck pain and a third experienced radicular symptoms mostly commonly due to stenosis of the ipsilateral neural foramen. Symptomatic cases were likely due to degenerative changes from altered biomechanics.^1–18 There were more symptomatic cases in our study cohort than there were in the literature review, as our patient cohort was older.

Developmental anomalies of the lateral portion of the cervical neural arch are likely the result of insults at different stages of spinal development. During the embryonic development, the vertebral column is derived from somites, the primary segments of the embryonic paroxysmal mesoderm. Ventral cells of the formed somites undergo epithelio-mesenchymal transition to form the sclerotome, signalling the commencement of vertebral development. Sclerotome derivatives form different parts of the vertebra, namely central, ventral and dorsal sclerotome (Figure 5).¹⁸ Each vertebra has six chondrification centres: two form the vertebral bodies; two the pedicles, lateral masses and transverse processes; and two form the lamina and spinous processes.^2,5,18 During the 10th gestational week, four chondrification centres coalesce to form two posterior ossification centres on either side of the vertebral midline. Endochondral ossification starts in the vertebral bodies and, with a slight delay, in the vertebral arches at the roots of the transverse processes.¹⁸ All anatomical constituents, including half lamina, pedicle and lateral mass, are formed by each of these ossification centres, with the ossification occurring via posterior fusion of lamina at two years of age and complete osseous fusion of the posterior arch with vertebral bodies occurring between three and six years of age.^2,18 An absent cervical pedicle is likely to be the result of developmental failure during the early ventral chondrification centres between seven and eight weeks of gestation.¹ On the contrary, insults during the endochondral ossification of the vertebral constituents can result in failure of fusion or hypoplasia, leading to clefts in the neural arch and dysmorphic appearance of the articular facets. This can occur in utero or in the early years (one to two years of age) before complete osseous fusion of the neural arch.^2,18

Figure 5.

Derivatives of the sclerotomal compartments of a vertebra. The ventral dermomyotome (red) forms the vertebral body, central sclerotome forms the pedicles and vertebral arch including the transverse processes (yellow) and the dorsal sclerotome (blue) forms the lamina and spinous process of the vertebral arch. *La: lamina; Pe: pedicle; Sp: spinous process; Tp: transverse process; Vb: vertebral body.

Radiological clues to aid the recognition of developmental anomalies of the lateral portion of the cervical neural arch involve both pattern recognition (Figure 6) and analysis of the bone morphology and cortical margin. On plain radiographs, a unilateral absent pedicle would be best appreciated on the anteroposterior projection, and the widening of the ipsilateral neural foramen would be demonstrated on the sagittal or oblique sagittal projections. A cervical spine CT would be useful to demonstrate the ancillary findings of posteriorly rotated ipsilateral lamina giving rise to rudimentary/dysplastic articular facets which can be difficult to appreciate on plain radiographs. Cervical vertebral clefts and isolated dysmorphic facets are more difficult to appreciate on plain radiographs and are better depicted on CT. Utilisation of 3D volume-rendered images can assist in the classification of the location of the vertebral clefts (neurocentral, pedicular, pars interarticularis, retroisthmic and paraspinous) or better characterisation of a dysmorphic facet. Cervical vertebral clefts can closely resemble acute fracture, but findings of corticated margin, associated bony remodelling, and subchondral sclerosis would all suggest chronicity. Although CT remains the mainstay for the correct diagnosis, there may be a role for cervical spine MRI for further assessment of the ligaments and spinal cord, especially in the clinical context of trauma or investigation of chronic neck pain or radicular symptoms due to altered biomechanics.

Figure 6.

(a) Normal cervical vertebrae. (b) Unilateral absent pedicle with widened neural foramen (orange dashed line) and absent posterior tubercle of the transverse process (green asterisk). (c) Neurocentral cleft (yellow arrow), pedicular/retrosomatic cleft (green arrow), retroisthmic cleft (red arrow), spinous cleft (blue arrow), paraspinous cleft (white arrow). (d) Pars interarticularis/isthmic cleft (orange arrow).

Misdiagnosis can result in unnecessary hospitalisation and treatment. From the literature review, these anomalies are frequently misdiagnosed as unilateral facet fracture and dislocation, which can subject patients to unnecessary spinal precaution or even neck traction.^1–18 Interestingly, from the literature review and our patient cohort, these rare developmental anomalies do not appear to predispose patients to ligamentous or spinal cord injury in the setting of trauma.^1–18

Our study has some limitations. Given the low prevalence (0.2%) of developmental anomalies of the lateral portion of the cervical neural arch, there were only 18 cases included in the study, thus limiting detailed statistical analysis. Although we classified anomalies of the lateral portion of the cervical neural arch into three broad categories, we must emphasise that developmentally these represent different stages of insult which can be either pre- or postnatal. Lastly, our tertiary institution only provides adult service. Hence, we did not provide the paediatric imaging spectrum of these anomalies, which would be interesting to explore, especially in the age group before completion of vertebral ossification.

Developmental anomalies of the lateral portion of the cervical neural arch are very rare and have a propensity for the mid-to-lower cervical level. These are likely to be detected incidentally, but in the setting of acute trauma, they can closely mimic vertebral injuries. Therefore, it is crucial to recognise a diverse spectrum of imaging findings in order to prevent misdiagnosis and unnecessary investigation and intervention.

Conflict of interest

The authors declared no potential conflicts of interest with respect to the research, authorship and/or publication of this article.

Funding

The authors received no financial support for the research, authorship and/or publication of this article.

ORCID iDs

Charlie Chia-Tsong Hsu https://orcid.org/0000-0003-0803-593X

Timo Krings https://orcid.org/0000-0001-6321-5787