Unusual cause of high cervical myelopathy-C1 arch stenosis.

INTRODUCTION: High cervical myelopathy can be rarely caused by the developmental anomalies of atlas. Patients with C1 arch stenosis can present in early childhood or later in life. In symptomatic patients, posterior decompression at atlas is mandatory. We report the first clinical series of 20 patients of C1 arch stenosis in the English literature.
MATERIALS AND METHODS: This is retrospective case series having a cohort of 20 patients with congenital C1 arch stenosis.
RESULTS: There were 12 pediatric (age <18 years) and 8 adult patients. Mean age was 22.85 years. Syndromic association was seen in four patients. Following decompressive surgery, these patients noticed a symptomatic improvement.
CONCLUSIONS: Isolated C1 arch stenosis is a surgically curable rare cause of high cervical myelopathy and responds well to surgery.

INTRODUCTION

Developmental anomalies of the anterior and posterior arch of atlas can be a rare cause of high cervical myelopathy. The most common anomaly is a failure of posterior midline fusion of the two hemi-arches (Currarino classification Type A).[1] It may be seen with certain conditions such as achondroplasia,[2] Turner's syndrome, and various storage disorders, e.g., mucopolysaccharidosis.[3] Patients with C1 arch stenosis can present in early childhood or later in life. Many a times, the C1 arch stenosis is not diagnosed and may be missed and labeled as “no cause found.” Some of these patients may present later in life with degenerative cervical spine and managed accordingly even though the C1 shows stenosis.

Earlier, we had reported five children with C1 arch stenosis managed by senior author.[4] Over the past 20 years, we managed a total of 20 cases with C1 arch stenosis. We report the first clinical series of 20 patients with C1 arch stenosis in the English literature.

MATERIALS AND METHODS

This present cohort includes 20 patients with congenital C1 arch stenosis. Patients with spinal canal compromise due to atlantoaxial dislocation at atlas were excluded. All patients were evaluated with dynamic radiography, computed tomography (CT) cervical spine, and magnetic resonance imaging (MRI) cervical spine. Following evaluation, all patients underwent posterior cervical decompression.

RESULTS

The study cohort includes 14 male and 6 female patients, aged 4–60 years (mean age 22.85 years). This study had 12 pediatric patients (age <18 years). Four patients had a syndromic association; two children and one adult with mucopolysaccharidosis Type 4 Morquio disease, adult, with neglected turricephaly. One adult patient had ankylosing spondylitis.

The progressive spastic weakness of all four limbs (95%) was the most common clinical feature followed by a history of trivial fall (55%), neck pain (45%), dysmorphic features (20%) [Table 1]. Only two patients required surgery on emergent basis due to respiratory distress and recent neurological worsening. Clinical details, radiological features, and surgical findings are summarized in Table 2. At surgery inward, the inclination of the bifid C1 arch was seen.

Table 1

Common clinical features (n=20)

Table 2

Clinical details, radiological features, and management

DISCUSSION

Posterior arch of the atlas develops from the lateral dense zone of the first cervical sclerotome, while anterior arch of the atlas develops from hypochordal bow of the first cervical sclerotome ventral to the notochord.[5] Partial or complete agenesis of the posterior atlantal arch results from varying degrees of aplasia of the lateral sclerotome.[5]

The normal cervical vertebrae have a triangular spinal canal and are of a similar size to the vertebral body. The atlas has a ring-shaped spinal canal and lacks a vertebral body and a spinous process. Spinal canal diameter is maximum at the level of atlas and has the highest cord surface area-to-canal ratio. In C1 stenosis, canal becomes ellipsoid with reduced anteroposterior diameter, thus reducing the canal-to-cord ratio [Figure 1].

Figure 1

C1: (a) Normal ring-shaped atlas lacking vertebral body having maximum canal diameter. (b) In C1 stenosis: canal is ellipsoid with reduced anteroposterior diameter, thus reducing the canal-to-cord ratio. (c) Bifid posterior arch with inward inclination

Pediatric: Pediatric patient with C1 arch stenosis. (a) Midsagittal computed tomography showing absent posterior arch in midline. (b) Inturned posterior arch causing canal narrowing with absent arch in midline and anterior arch midline cleft. (c and d): No evidence of instability on Dynamic X-ray. (e) Preoperative magnetic resonance imaging showing cord thinning at C1 with cord signal changes. (f) Postoperative magnetic resonance imaging showing expansion of cord with cerebrospinal fluid around

Syndromic: Morquio syndrome patient (a and b) computed tomography showing absent anterior and posterior arch in midline. (c) Magnetic resonance imaging cord thinning due to posterior soft tissue at C1

Adult: Adult patient of cervical spondylosis with C1 stenosis. (a) Computed tomography spine showing anteriorly placed posterior arch of C1 with canal narrowing. (b) Magnetic resonance imaging showing canal narrowing at C1 with cord signal changes

Stenosis at C1 can be congenital or acquired. Anomalies causing cervical myelopathy at the level of atlas are reported rarely in the literature and include clefts or aplasias of anterior and posterior arches of atlas, os odontoideum, ossification of the transverse atlantal ligament, and hypertrophy of the dens either alone or in combination.[6] Congenital stenosis of the cervical spinal canal most commonly occurs between C3 and C5 vertebrae.[5] Developmental stenosis of the cervical spine rarely occurs above C2.[7] The stenosis at the level of C1 may be due to excessive or disordered ossification. The posterior arch defects of C1 are uncommonly reported and the clinical significance is unknown. Generally asymptomatic, symptoms may be precipitated by head or neck trauma while playing. Eleven patients had a history of neck trauma secondary to fall or road traffic accident. Dynamic lateral cervical spine X-ray was done to look for instability. CT cervical spine is useful to demonstrate bony abnormality. MRI is useful in demonstrating site of compression and soft tissue anomalies. Table 3 highlights clinical and radiological details of previously reported cases of C1 arch stenosis in the literature.

Table 3

Clinical, radiological features and management of reported cases of C1 arch stenosis in the literature

The importance of congenital stenosis of the spinal canal was first recognized by Payne and Spillane, suggesting that the development of myelopathy may also be related to the initial size of canal.[14] If the spinal canal is small by nature relatively little encroachment by osteophyte, vertebral subluxation or hypertrophied ligament flavum can be tolerated without causing spinal cord compression. There have been a few reports as to the relative diameters of C1. According to Hinck et al., the sagittal diameter of the spinal canal at the level of C1 ranges between 15 mm and 20 mm.[15] A radiographic study of 300 normal Indians performed by Gupta et al. reported that the mean space available for the cord at C1 was 21.43 mm in male and 20.13 mm in female.[16] In our series, C1 canal diameter was 10.3 mm (range 0.5–16 mm).

The usually reported incidence of posterior arch anomalies of C1 is 4% and 0.1% for anterior arch.[17] The anomalies of posterior arch range from median clefts or hypoplasia. A failure of local chondrogenesis rather than subsequent ossification is thought as a cause for the development of defects of the posterior arch. The etiological hypothesis remains unclear; it may be due to the failure of local chondrogenesis or even hereditary factors.[1819] Sharma et al. showed the inward mobility of the posterior fragment during extension of the cervical spine in two patients as a possible reason for a patient with trivial trauma.[13] The presence of connective tissue bridging the bony defect is supported by autopsies and intraoperative findings.[20] Five different types of C1 arch deficiencies are described by Currarino et al.[21] In this series, one patient had absent posterior arch (Currarino classification Type E). In this patient, fibrous band was seen compressing the cord. In two patients, failure of posterior midline fusion of posterior C1 arch was seen (Type A).

C1 arch stenosis may occur as part of a syndrome. It may be associated with Arnold–Chiari malformation, Klippel–Feil syndrome, gonadal dysgenesis, Down's syndrome, and Turner's syndrome. Three patients had mucopolysaccharidosis, Morquio syndrome. In mucopolysaccharidoses, the cord at the C1–C2 level is at particular risk for stenosis, ventrally by localized thickening of the peri-odontoid tissue and transverse atlantoaxial ligament and dorsally due to a short narrow C1 posterior arch or anterior translation of the posterior arch of C1.[22] C1 arch stenosis in Morquio syndrome is due to narrow posterior arch with odontoid hypoplasia, soft tissue mass, or incomplete fusion of C1 arch. These patients require a preoperative evaluation of the airway and of cardiac, respiratory, and neurological function. Anesthetic management must focus on protection of the airway without compromising the integrity of the spinal cord.[23]

In addition to C1 arch stenosis, craniosynostosis was also seen in one of our patients. We think that impaired skull base cartilaginous ossification mechanism may be responsible for C1 arch stenosis since craniovertebral–vertebral junction is also part of the central skull base. Six patients in this series had Klippel–Feil syndrome.

All patients were managed with C1 arch excision. Only two patients required emergent surgery due to associated recent neurological deterioration and respiratory distress. Both these patients required ventilator support postoperatively and were gradually weaned off the ventilator. During surgery inturned, knob-like bifid posterior arch was seen compressing cord in most of the patients. One patient with deficient posterior arch, the fibrous band, was seen compressing cord. After excision of a posterior arch, fibrous band cord was lax and pulsatile. On follow-up, we have not found any instability in patients managed with C1 arch excision.[24] One patient with Morquio syndrome with associated odontoid hypoplasia underwent fusion after excision of C1 arch excision.

Our series on C1 arch stenosis is largest in the published literature till date and compromises the cohort with different age groups. Awareness of C1 arch stenosis will improve with the published literature. Previously, asymptomatic C1 arch stenosis can present in the later life and needs to be managed with decompression since surgical treatment may prevent neurological deterioration.

CONCLUSIONS

Isolated C1 arch stenosis is a surgically curable rare cause of high cervical stenosis and responds well to surgery. It can be managed with C1 arch excision alone without subsequent development of instability. Unless surgically treated, minor trauma may cause the serious neurologic deficit.

Informed consent

Informed consent was obtained from all individual participants included in the study.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patients have given his their consent for their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.