The odontoid process in children--is it hypoplastic?

Atlanto-Axial Instability in People with Down's Syndrome and its Impact on the Ability to Perform Sports Activities - A Review

Atlanto-axial instability (AAI) is a developmental anomaly often occurring in persons with Down’s syndrome (DS). According to various reports, AAI affects from 6.8 to 27% of the population with DS. The aim of this review was to illustrate the issue of AAI with regard to the progressively changing state of scientific knowledge. The extended distance between the rear surface of the frontal arcus of the C1 cervical vertebra and the anterior surface of C2 cervical vertebra dens (anterior atlanto-odontoid distance, AAOD) indicates the occurrence of AAI and is detectable through X-ray examination. Hypoplasia of the C2 dens, also detectable through X-ray examination, is another suggested risk factor for AAI. According to current data, the methodology of taking measurements is inconsistent, which leads to errors in interpretation. As research focusing on AAI was progressing, new data emerged from other studies on persons with DS, suggesting that neurological symptoms in persons with DS that indicated the occurrence of spinal cord compression were an important factor in medical imaging detection of AAI. One of the main arguments supporting this thesis is that in isolated cases spinal cord (SC) damage was noted during screening examinations conducted on a large population of subjects. Moreover, cases in which the neurological symptoms indicate spinal cord compression existed long before the occurrence of the actual damage also remain of significant importance. Therefore, it is necessary to promote neurological studies on persons with DS to enable early diagnosis of spinal cord compression and, at the same time, reduce the use of medical imaging in cases of neurological symptoms.

Developmental anatomy of the atlas and axis in childhood by computed tomography

OBJECT

The CT modality plays a central role in the diagnosis of cervical spine fractures. In childhood, radiolucent synchondroses between ossification centers can resemble fractures, and they can be the sites of fractures as well. Recognition of cervical spine fractures in children requires familiarity with normal developmental anatomy and common variants as they appear on CT scans.

METHODS

A convenience sample of 932 CT scans of the cervical spine accessible on the picture archiving and communications system (known as PACS) at a single children's hospital was examined. Scans were excluded from further analysis if they did not include the atlantoaxial region or were otherwise technically unsatisfactory; if the patient carried the diagnosis of a skeletal dysplasia; or if there were developmental lesions noted at other levels of the spine. No more than 1 scan per patient was analyzed. Synchondroses were graded as radiolucent, not totally radiolucent but still visible, or no longer visible. Their locations and symmetries were noted. The presence or absence of the tubercles of the transverse ligament was noted as well.

RESULTS

After exclusions, 841 studies of the atlas and 835 studies of the axis were analyzed. The 3 common ossification centers of the atlas arose in the paired neural arches and the anterior arch, but in as many as 20% of cases the anterior arch developed from paired symmetrical ossification centers. The 5 common ossification centers of the axis arose in the paired neural arches, in the basal center, in the dentate center (from which most of the dentate process develops), and in the very apex of the dentate process. The appearance of each synchondrosis was noted at sequential ages. The tubercles for the transverse ligament generally did not appear until the ossification of the synchondroses of the atlas was far advanced. Anomalies of the atlas included anterior and posterior spina bifida, absence of sectors of the posterior arch, and anomalous ossification centers and synchondroses. Anomalies of the axis were much less common. What appeared possibly to be chronic, incompletely healed fractures of the atlas were discovered on review for this analysis in 6 cases. No fractures of the axis were discovered.

CONCLUSIONS

There is substantial variation in the time course and pattern of development of the atlas, and anomalies are common. Some fractures of the atlas may escape recognition without manifest sequelae. Variation in the time course of the development of the axis is notable as well, but anomalies seem much less common.

The craniocervical junction following successful haematopoietic stem cell transplantation for mucopolysaccharidosis type I H (Hurler syndrome)

Mucopolysaccharidosis I Hurler (MPS IH) is a progressive multisystemic disorder caused by alpha-L-iduronidase deficiency. First choice of treatment in MPS IH children is haematopoietic stem cell transplantation (HSCT). The effect of HSCT has been shown to have limited influence on skeletal manifestations by poor penetration of musculoskeletal tissues by the enzyme derived from donor leucocytes. Aim of this study was to investigate the effect of HSCT on the craniocervical junction (CCJ) in Hurler patients. We analysed retrospectively sequential magnetic resonance imaging (MRI) scans of 30 patients with Hurler disease treated by HSCT since 1982 at the Royal Manchester Children's Hospital, UK, in order to determine whether the patients suffer from dens hypoplasia. Results were compared with biochemical and clinical characteristics: Enzyme activity (EA), chimerism, urinary glycosaminoglycan (GAG) excretion and neurological status. Investigations were part of standard clinical procedures. Results are descriptive in presentation. In 26/30 patients a determination of odontoid hypoplasia was feasible. The majority showed a normal dens length and an increase with age. Only 3/26 revealed a dens hypoplasia. One of them had only partial donor engraftment (DE) with reduced EA, one of them suffered from chronic graft versus host disease (GVHD). One patient with only partial DE and reduced EA presented with initial dens hypoplasia until preadolescence but normalized later on. There may be a trend towards lower EA and the occurrence of DH in transplanted MPS patients - perhaps the dosage of enzyme plays a role in the correction of skeletal complications in this patient group. HSCT patients with incomplete DE and therefore lower EAs may require special attention and care.

Chiari I malformation associated with atlanto-axial dislocation: focussing on the anterior cervico-medullary compression

BACKGROUND

Chiari I malformation with atlantoaxial dislocation may cause both posterior and anterior cervicomedullary compression. We studied the clinicoradiological features and surgical outcome in patients having Chiari I malformation with atlantoaxial dislocation.

METHOD

Thirty-nine patients with Chiari I malformation with atlanto-axial dislocation underwent preoperative and follow-up neurological status assessment. In Chiari I malformation with reducible atlanto-axial dislocation (n = 11), a direct posterior stabilization was done. In Chiari I malformation with irreducible atlanto-axial dislocation (n = 28), a single stage transoral decompression with posterior stabilization and/or posterior decompression and duraplasty were done in 18 patients. In 10 patients, only posterior decompression and/or posterior stabilization was performed. Seven among the latter patients subsequently deteriorated and required transoral decompression. Comparison of mean neurological status scores of patients with Chiari I malformation with irreducible atlanto-axial dislocation who underwent single stage transoral decompression with posterior stabilization versus the posterior procedure alone was done using T-test and proportional significance also calculated.

FINDINGS

Patients with Chiari I malformation with atlanto-axial dislocation have a high incidence of long tract signs and sphincteric disturbances with a decrease in the mean foramen magnum diameter. The mean neurological status scores of patients with Chiari I malformation with irreducible atlanto-axial dislocation who underwent single stage transoral decompression with posterior stabilization were significantly better than those patients who underwent the posterior procedure alone. The latter patients also showed significant clinical improvement following transoral decompression. In the presence of Chiari I malformation with reducible atlanto-axial dislocation, reduction and stabilization of atlanto-axial dislocation resulted in neurological improvement. The follow up neurological status scores of these patients improved after surgical intervention even in the presence of poor preoperative grades.

CONCLUSIONS

Patients with Chiari I malformation should be investigated for the presence of atlanto-axial dislocation. In case atlantoaxial dislocation coexists, priority must be given to relieving anterior cervicomedullary compression.

Pediatric congenital atlantoaxial dislocation: differences between the irreducible and reducible varieties

OBJECT

Clinicoradiological differences and outcome following surgery in pediatric patients (< or = 16 years of age) with congenital irreducible atlantoaxial dislocation (IAAD) and reducible atlantoaxial dislocation (RAAD) were analyzed.

METHODS

Ninety-six patients (57 with IAAD and 39 with RAAD) were categorized as follows: Grade I, no deficits except hyperreflexia or neck pain (six patients); Grade II, minor deficits but independent for activities of daily living (25); Grade III, partially dependent (30); and Grade IV, totally dependent (35). Patients with RAAD underwent direct posterior fusion, and those with IAAD were treated with transoral decompression and posterior fusion. Patients with good outcomes included those who could walk unaided, with improvement in spasticity and weakness, and those who maintained Grade I status. The category of poor outcome included patients with the following conditions: postoperative deterioration or lack of improvement; inability to ambulate regardless of neurological improvement at a minimum follow-up duration of 3 months; or perioperative death. A significantly higher incidence of C-1 assimilation, C2-3 fusion, asymmetrical occiput-C2 facet joints, and basilar invagination were seen in patients with IAAD, and os odontoideum was noted in those with RAAD (p < 0.05). A good outcome was recorded in 35 patients with IAAD and 22 with RAAD, whereas 14 with IAAD and nine with RAAD had a poor outcome (eight patients in each category were lost to follow up).

CONCLUSIONS

Radiological differences in the anatomy of patients with IAAD and those with RAAD may be due to improper segmentation of the occipital and upper cervical sclerotomes in the former and dysfunction of the transverse ligament in the latter. A significantly better outcome was noted in completely dependent patients with IAAD compared with those with RAAD. Respiratory compromise was an important prognostic factor.

Odontoid hypoplasia presenting as torticollis: a discussion of its significance

Odontoid dysplasias are considered rare but are becoming increasingly recognized. Patients may have no symptoms, localized neck pain, or neurologic symptoms. Because patients with odontoid anomalies have the potential for craniovertebral instability, recognition of the entity is essential. A discussion of the axis, its development and anomalies follows.

Craniovertebral junction anomalies in inherited disorders: part of the syndrome or caused by the disorder?

Patterns of skeletal abnormality at the craniovertebral junction in the normal population and in syndromes such as Down, Morquio etc, are compared and the recent embryological data and comparative anatomy reviewed. The authors' view based on their own clinical and radiological experience is that the os odontoideum is the product of excessive movement at the time of ossification of the cartilaginous dens and is exactly analogous to the unfused Type II odontoid fracture. True hypoplasia of the odontoid peg is part of a wider segmentation defect associated with Klippel Feil, occipitalised atlas and/or basilar invagination; it is hardly ever associated with instability.

Atlantoaxial instability in Down's syndrome: a five year follow up study

In 1986 all 90 children aged 4-19 years with Down's syndrome attending school in the area served by the Southern Derbyshire Health Authority underwent radiography to identify atlantoaxial instability (AAI). This study details repeat observations five years later. Full results were available on 67 (74%), information on health status was available on the remaining 19 (21%); four (4%) were untraced. There was an overall significant reduction in the atlanto-axial gap over five years. No one developed AAI on repeat testing who had not had it earlier. One child who had previously had normal neck radiography developed acute symptomatic AAI after ear, nose, and throat surgery. Radiographs were done on three occasions on the same day in 49 individuals, ensuring full flexion of the upper neck. There were no significant differences between the radiographs, even in five subjects with AAI. Management of AAI in Down's syndrome is discussed in the light of these findings. Radiography can reliably detect children with chronic AAI who may be at risk of gradually developing symptoms; this may justify a screening programme. This must be distinguished from those who develop symptoms after acute trauma or anaesthesia, for which specific precautions are needed, and previous screening radiographs are unhelpful.

Atlantoaxial instability and abnormalities of the odontoid in Down's syndrome

Radiography of the lateral neck was performed on all children with Down's syndrome aged 4-15 in the Southern Derbyshire health district (n = 67) and a random selection of adults (n = 94). Atlantoaxial instability, defined as a gap of over 4 mm, was present in seven (10%) children and two (2%) adults. Odontoid hypoplasia, defined as an odontoid peg two standard deviations below the mean in an age matched population, was present in 15 (22%) children and 14 (15%) adults, with accessory odontoid ossicles present in two (2%) and two (3%) respectively. No one was found to have symptoms or clinical signs of spinal cord compression. Atlantoaxial instability was therefore found to be commoner in children than adults. Different programmes of management are suggested, in terms of regular clinical examination for signs and symptoms and by radiographic screening. Particular care should be taken with those who have both atlantoaxial instability and odontoid hypoplasia or accessory ossicles as they are at particular risk of spinal cord damage.