Chiari malformation associated with vitamin D-resistant rickets: case report

Chiari Type 1 Malformation and Syringomyelia in Children: Classification and Treatment Options

Chiari type 1 malformation (CIM) is defined as tonsillar ectopia of >5 mm, while syringomyelia (SM) is defined as a cerebrospinal fluid (CSF)-filled cavity larger than 3 mm dissecting the spinal cord. Over the last decades, our understanding of these pathologies has grown; however, many controversies still exist almost in every aspect of CIM and SM, including etiology, indication for treatment, timing of treatment, surgical technique, follow-up regime, and outcome. This chapter provides a comprehensive overview on different aspects of CIM and SM and on the still existing controversies, based on the evidence presently available. Future directions for clinical research concerning CIM and SM treatment and outcome are elaborated and discussed as well.

Chiari malformation type I: what information from the genetics?

PURPOSE

Chiari malformation type I (CMI), a rare disorder of the craniocerebral junction with an estimated incidence of 1 in 1280, is characterized by the downward herniation of the cerebellar tonsils of at least 5 mm through the foramen magnum, resulting in significant neurologic morbidity. Classical CMI is thought to be caused by an underdeveloped occipital bone, resulting in a posterior cranial fossa which is too small to accommodate the normal-sized cerebellum. In this review, we dissect the lines of evidence supporting a genetic contribution for this disorder.

METHODS

We present the results of two types of approaches: animal models and human studies encompassing different study designs such as whole genome linkage analysis, case-control association studies, and expression studies. The update of the literature also includes the most recent findings emerged by whole exome sequencing strategy.

RESULTS

Despite evidence for a genetic component, no major genes have been identified and the genetics of CMI is still very much unknown. One major challenge is the variability of clinical presentation within CMI patient population that reflects an underlying genetic heterogeneity.

CONCLUSIONS

The identification of the genes that contribute to the etiology of CMI will provide an important step to the understanding of the underlying pathology. The finding of a predisposing gene may lead to the development of simple and accurate diagnostic tests for better prognosis, counseling, and clinical management of patients and their relatives.

The Role of Vitamin D in the Pathogenesis of Adolescent Idiopathic Scoliosis

Several theories have been proposed to explain the etiology of adolescent idiopathic scoliosis (AIS) until present. However, limited data are available regarding the impact of vitamin D insufficiency or deficiency on scoliosis. Previous studies have shown that vitamin D deficiency and insufficiency are prevalent in adolescents, including AIS patients. A series of studies conducted in Hong Kong have shown that as many as 30% of these patients have osteopenia. The 25-hydroxyvitamin D3 level has been found to positively correlate with bone mineral density (BMD) in healthy adolescents and negatively with Cobb angle in AIS patients; therefore, vitamin D deficiency is believed to play a role in AIS pathogenesis. This study attempts to review the relevant literature on AIS etiology to examine the association of vitamin D and various current theories. Our review suggested that vitamin D deficiency is associated with several current etiological theories of AIS. We postulate that vitamin D deficiency and/or insufficiency affects AIS development by its effect on the regulation of fibrosis, postural control, and BMD. Subclinical deficiency of vitamin K2, a fat-soluble vitamin, is also prevalent in adolescents; therefore, it is possible that the high prevalence of vitamin D deficiency is related to decreased fat intake. Further studies are required to elucidate the possible role of vitamin D in the pathogenesis and clinical management of AIS.

Diameters and bone thickness at the margin of the foramen magnum in dry skulls from pediatric population: a cross-sectional anatomical study

PURPOSE

The purpose of the study was to estimate the size and bone thickness at the margin of the foramen magnum in a pediatric population.

METHODS

Sixty occipital bone specimens from the collection of macerated skulls at the Department of Anatomy, University of Zagreb, were examined and measured using a vernier scale/caliper. For the purpose of analysis, specimens were divided into two age groups: 1-6 years and 7-18 years of age (before and after the fusion of ossification centers in the occipital bone). We measured the following: antero-posterior and transverse diameters of the foramen magnum, bone thicknesses at the basion, opisthion, two paramedial points on the anterior and posterior margins, and at the occipito-squamous junction.

RESULTS

Data presented in this study show that diameters of the foramen magnum increase with age, whereas bone thickness shows variable behavior depending on the measured area.

CONCLUSIONS

Increases in diameters in specimens from the younger age group and their absence in specimens from older subjects reflect the growth pattern of the basilar part of occipital bone. Variability of bone thickness at the margin of the foramen magnum and lack of its association with age of the subjects may be attributed to various factors and may potentially affect the clinical presentation of compression syndromes at the level of foramen magnum.

Histological study of the occipital bone from patients with Chiari I malformation

BACKGROUND

This study is focused on the histologic characteristics of occipital bone removed during Chiari I decompression in the hope of discovering unique features that may be related to the pathogenesis of this condition.

METHODS

Ten consecutive pediatric patients with Chiari I malformation underwent standard posterior fossa decompression surgery. Bone that was removed from the posterior fossa was sent for histological examination. Bone from age-matched controls also underwent histological analysis.

RESULTS

For all study and control specimens, bony samples were found to be made up of dense lamellar bone without marrow elements. In all aspects, histologically, the bone tissue had a normal appearance compared to control samples.

CONCLUSIONS

Although many authors have mentioned that the occipital bone in patients with Chiari I malformation is abnormal on imaging or at operation (e.g., thinned, thickened), based on our study, there is no histological difference between the occipital bone removed at operation and controls.

Chiari malformation, syringomyelia and bulbar palsy in X linked hypophosphataemia

X linked hypophosphataemia (XLH) is a rare condition with numerous musculoskeletal complications. It may mimic other more familiar conditions, such as vitamin D deficiency, ankylosing spondylitis or diffuse idiopathic skeletal hyperostosis. We describe two cases with Chiari type 1 malformations and syringomyelia, neither of which is well recognised in XLH. The first presented late with the additional complications of spinal cord compression, pseudofracture, renal stones and gross femoroacetabular impingement requiring hip replacement. The second also had bulbar palsy; the first case to be described in this condition, to the best of our knowledge. We wish to raise awareness of the important neurological complications of syringomyelia, Chiari malformation, spinal cord compression and bulbar palsy when treating these patients. We also wish to draw attention to the utility of family history and genetic testing when making the diagnosis of this rare but potentially treatable condition.

Upward Translation of Cerebellar Tonsils following Surgical Expansion of Supratentorial Cranial Vault: A Unified Biomechanical Explanation of Chiari Type I

Cerebellar tonsils moved significantly upward in 3 patients with Chiari type I who underwent supratentorial cranial vault expansion to alleviate intracranial pressure related to multisutural craniosynostosis. The Chiari type I deformities in these patients were the biomechanical consequence of posterior fossa-cerebellar disproportion caused by supratentorial craniocerebral disproportion secondary to multisutural craniosynostosis. The authors postulate that all cases of Chiari type I deformity share the sine qua non feature of posterior fossa-cerebellar disproportion.

What differences exist in the appropriate treatment of congenital versus acquired adult Chiari type I malformation?

Chiari type I malformation is found in 1 out of 20 magnetic resonance imaging (MRI) studies. Isolated tonsillar herniation is of limited utility and should be considered within the clinical context because these patients can be asymptomatic. Cine MRI showing compression of the cerebrospinal fluid (CSF) spaces in the foramen magnum area is a crucial technique for making treatment decisions. Congenital malformation is thought to be due to a volumetric small posterior fossa. The most common symptom in these patients is cough headache. Posterior fossa reconstruction is mandatory in patients with progressive symptoms/signs, hydrocephalus, or syringomyelia, but not in patients who are asymptomatic or those with stable and tolerable symptoms. Acquired tonsillar descent can be secondary to a variety of disorders conditioning disproportion between the volume of the cranial cavity and that of the intracranial contents, or to CSF hypovolemia, which is the most common cause for acquired herniation. CSF hypovolemia can be spontaneous or secondary to CSF removal. Treatment of acquired tonsillar herniation depends on the responsible etiology.

Associated disorders of Chiari Type I malformations: a review

A single pathophysiological mechanism of Chiari Type I malformations (CM-I) has been a topic of debate. To help better understand CM-I, the authors review disorders known to be associated with CM-I. The primary methodology found among most of them is deformation of the posterior cranial fossa, usually with subsequent decrease in volume. Other mechanisms exist as well, which can be categorized as either congenital or acquired. In understanding the relationship of such disorders with CM-I, we may gain further insight into the process by which cerebellar tonsillar herniation occurs. Some of these pathologies appear to be true associations, but many appear to be spurious.

Chiari I malformation after cranial radiation therapy in childhood: a dynamic process associated with changes in clival growth

OBJECT

The small posterior fossa is believed to be relevant to the development of Chiari I malformation (CMI). In this study, we evaluated children with supratentorial tumors developing CMI after radiation therapy (RT) that involved the skull base. Changes in clivus and supraocciput growth rate were correlated with tonsillar herniation.

METHODS

Ten children who underwent RT for supratentorial tumors at St. Jude Children's Research Hospital (1994-2008) developed CMI on follow-up magnetic resonance imaging (MRI). Four other patients with supratentorial tumor and CMI who did not receive RT were identified. Length of the supraocciput, basisphenoid, and basichondrium and extent of tonsillar herniation were measured on serial midsagittal MRI.

RESULTS

Over the median follow-up of 85.5 months, basisphenoid annual growth rate was significantly lower in children receiving RT for suprasellar tumor (n=8) than those who did not (p=0.04). Growth of clivus and basisphenoid was significantly lower in the first 12 months after RT in children who received RT for suprasellar tumor (p=0.03 and p=0.04, respectively). In these patients, tonsillar herniation increased over 24 months after RT, reaching maximal descent at a mean of 20.2 months; this resolved as clival growth returned to normal. No patient was symptomatic.

CONCLUSIONS

In these children, restriction of clival growth occurred after RT for suprasellar tumors. Changes in clival growth were associated with changes in the extent of tonsillar herniation. This supports the importance of the small posterior fossa and reduced clival length in the etiology of CMI.

Posterior fossa arachnoid cyst, tonsillar herniation, and syringomyelia in trichorhinophalangeal syndrome Type I

The authors report the case of a patient with Chiari malformation Type I (CM-I) and syringomyelia probably caused by a retrocerebellar arachnoid cyst. The patient's phenotype corresponded to trichorhinophalangeal syndrome Type I. The authors attributed the origin of both the retrocerebellar cyst and the abnormal posterior fossa to endochondral ossification anomalies that occur in this syndrome. The patient's spinal pain was most likely a result of the combination of CM-I and syringomyelia. To the best of the authors' knowledge, this is the first report on the association of CM-I and syringomyelia with a retrocerebellar arachnoid cyst occurring in a patient with trichorhinophalangeal syndrome Type I. The authors discuss the pathogenetic mechanisms involved in the production of tonsillar descent and syringomyelia in this patient, and review the current literature on related conditions that can result in this association.

The role of cranial expansion for craniocephalic disproportion

The appropriate treatment for craniocephalic disproportion, such as caused by slit ventricle syndrome, is uncertain. We have reviewed the treatment and outcomes of 4 children who underwent cranial expansion over a period of 5 years. The ages at cranial expansion were 16 months, 3 years 6 months and 2 at 6 years. Two children had slit ventricle syndrome and were treated with bilateral parietal expansions. Two children had non-syndromic craniosynostosis, one of these having vitamin D-resistant rickets. The latter 2 were treated with posterior cranial vault expansion, and one also had a craniocervical junction decompression performed. Post-operatively, symptoms of raised intracranial pressure resolved in all cases, and there was radiological evidence of re-establishment of normal CSF pathways. Although a rare condition, cranial expansion operations can be successful in appropriately selected cases of craniocephalic disproportion.

Posterior Cranial Fossa Volume in Patients with Rickets: Insights into the Increased Occurrence of Chiari I Malformation in Metabolic Bone Disease

OBJECTIVE

Some have proposed that the calvarial thickening seen in patients with rickets results in an increased rate of Chiari I malformation (CIM) in these patients. The present study measures the posterior fossa volume in children with rickets to verify previous case reports indicting a small posterior fossa as the cause for an increased rate of CIM in children with rickets.

METHODS

Patients were chosen by use of a computer database to search for individuals diagnosed with rickets. Nineteen patients were identified with this diagnosis. Seven patients were found from this cohort to have imaging of the head. Axial computed tomographic and magnetic resonance images were analyzed by use of the Cavalieri method to define posterior fossa volumes. These data were then compared with those from age-matched control subjects.

RESULTS

Mean volumes of the posterior fossa were significantly reduced in all patients compared with age-matched control subjects (P < 0.0001).

CONCLUSION

We have found that the volume of the posterior fossa is significantly smaller in children with rickets versus age-matched control subjects. Furthermore, 29% of our study group had an associated CIM. We may hope that these data will aid in the further understanding of the pathophysiology of CIM in cases of metabolic bone disease.

Association of the Adult Chiari Malformation and Idiopathic Intracranial Hypertension: more than a coincidence

There are significant similarities between the Adult Chiari Malformation (ACM) and Idiopathic Intracranial Hypertension (IIH). They include similar demographics, clinical presentation, and response to treatment. There is an eightfold increase in the incidence of significant tonsillar herniation in patients with IIH. Based on these findings and our observation in a subgroup of patients with failed ACM decompression, we suggest that these disorders are interrelated in a group of patients. The physiopathology is that of craniocephalic disproportion, i.e., a disproportion between the skull and the brain, due to a small skull or posterior fossa (like in ACM) and/or an engorged brain (like in IIH). This will occasionally lead to tonsillar ectopia. The craniocephalic disproportion will alter the brain compliance and lead to the symptomatology.

Definition of the adult Chiari malformation: a brief historical overview

With the widespread use of newer neuroimaging techniques and modalities, significant tonsillar herniation is being diagnosed in more than 0.5% of patients, some of whom are asymptomatic. This puts the definition of the adult Chiari malformation to the test. The author provides a historical review of the evolution of the definition of the adult Chiari malformation in the neurosurgery, radiology, and pathology literature.

Ossification of the posterior longitudinal ligament in vitamin D-resistant rickets: case report and review of the literature

STUDY DESIGN

A case report of cervical myelopathy caused by ossification of the posterior longitudinal ligament in a patient with vitamin D-resistant rickets is presented together with a review of literature.

OBJECTIVE

To report the diagnosis of ossification of the posterior longitudinal ligament in a white woman with vitamin D-resistant rickets.

SUMMARY OF BACKGROUND DATA

The association between ossification of the posterior longitudinal ligament and untreated vitamin D-resistant rickets has been reported in Japan, but infrequently in white populations. In whites, ossification of the posterior longitudinal ligament is closely associated with diffuse idiopathic skeletal hyperostosis. A clear association between ossification of the posterior longitudinal ligament and vitamin D-resistant rickets in white populations has not yet been established.

METHODS

The medical record and imaging studies of a patient treated at the authors' institution for cervical myelopathy caused by ossification of the posterior longitudinal ligament in the setting of treated vitamin D-resistant rickets were reviewed. A Medline search of the medical literature between 1966-1999 was performed to identify pertinent studies and similar case reports.

RESULTS

The occurrence of spinal stenosis in untreated adults with vitamin D-resistant rickets has been reported in all regions of the spine in Japanese patients. The association between ossification of the posterior longitudinal ligament and untreated vitamin D-resistant rickets was first reported in Japan, where ossification of the posterior longitudinal ligament is endemic. This association may be incidental, because reports on ossification of the posterior longitudinal ligament in whites are not as frequent as in Japanese, reflecting the higher prevalence of this condition in Japan.

CONCLUSION

Ossification of the posterior longitudinal ligament and ossification of the posterior longitudinal ligament associated with deranged calcium or phosphate metabolism may be different pathologic entities sharing a common outcome. Adequate treatment of vitamin D-resistant rickets may not always prevent or reverse ossification of the posterior longitudinal ligament.