Chiari malformation type 2

• Rehabilitation in a child with Chiari II malformation, lumbosacral meningomyelocele, achondroplasia and impaired respiratory regulation - a case report and literature review
• Clinical outcome of different surgical approaches for symptomatic Chiari malformation without syringomyelia: a 13-year retrospective study
• A Novel Metric for Assessing Long-Term Outcomes in Adults with Chiari Malformation Type I: Occipitocervical Dura Angulation (ODA)-Applications and Value
• A Computed Tomography Study of the Sella Turcica in Chiari Malformation Type 2
• Vogt Koyanagi Harada disease with bilateral disc edema diagnosed as Arnold Chiari malformation with papilledema: The blurred margin between ophthalmology and neurology
• Using Patient-Reported Outcome Measures for Adult Chiari Malformation Type 1
• Extended Laminectomy in Chiari Malformation Treatment: A Systematic Review
• Surgical Treatment of Basilar Invagination without Evident Atlantoaxial Instability (Type B) - A Systematic Review

Chiari II malformation is a relatively common congenital disorder of the spine and posterior fossa characterised by myelomeningocele and a small posterior fossa with descent of the brainstem.

All cases of CM II are associated with a myelomeningocele which can be further complicated by hydrocephalus, syringomyelia, heterotopias, and agenesis of the corpus callosum but numerous associated abnormalities are also frequently encountered ^{1) 2) 3)}.

The differential is predominantly one of definition, and the term Chiari type II is often inappropriately used to designate a variety of malformations. Provided both a myelomeningocoele and brainstem descent are present the diagnosis is usually straight forward.

Chiari II malformations are encountered relatively commonly with an incidence of ~1:1000 live births.

When a child is born with a myelomeningocoele the vast majority (~95%) have an associated Chiari II malformation.

Although there are several proposed hypotheses describing the pathogenesis of CM II, the exact mechanism remains elusive. Animal models have demonstrated that open neural tube defects (NTD) are causative in the case of CM II. NTD that were surgically created in mouse, rat, and sheep models replicate the hindbrain herniation through the foramen magnum that is stereotypical of CM II ^{4) 5) 6)}.

This finding has two important implications; firstly it lends considerable evidence to the widely accepted “unified theory” of CM II ⁷⁾. This theory alleges the loss of CSF through the open caudal NTD causes a subsequent drop in ICP. This loss of pressure at a critical point during fetal development results in poor cranial vault expansion culminating into a small posterior fossa. The unexpectedly narrowed posterior fossa leads to the caudal displacement of the brainstem and cerebellum through the foramen magnum ⁸⁾.

The genetic mutation responsible for this phenotype in mouse models was mapped to the human Pax-3 gene on chromosome 1, encodes transcription factors which play various roles in embryogenesis ^{9) 10)}. Further studies in humans however, demonstrated that mutations in Pax-3 generate distinct features not commonly seen in CM II, namely deafness and abnormal pigmentation which were later characterized into a distinct Waardenburg Syndrome ^{11) 12)}.

Given the wide range of anatomical severity as well as the large number of associated abnormalities which are sometimes encountered, it should be no surprise that the clinical presentation of patients with Chiari II malformations is also varied both in character and severity. The presentation can be divided according to the age of the individual (although most will have life long sequelae) as follows:

neonatal

myelomeningocoele

brainstem dysfunction resulting in cranial nerve palsies

neurogenic bladder

child

musculoskeletal

hydrocephalus

young adult

syrinx and scoliosis

Associations

spinal

syringohydromyelia

scoliosis

segmentational anomalies: 50%

Klippel-Feil syndrome

atlanto-axial assimilation

diastematomyelia

cerebral

dysgenesis of corpus callosum

absent septum pellucidum

obstructive hydrocephalus

fenestration of the falx with interdigitated gyri or absent falx. heart shape incisura

stenogyria/polymicrogyria (probably not the same as polymicrogyia encountered in schizencephaly 7)

Tectal beaking

cranial vault

scalloping of petrous temporal bone

enlarged foramen magnum

Luckenschadel skull

small posterior fossa

skeletal

clubfoot

The malformation is characterised by a displacement of the medulla, fourth ventricle and cerebellum through the foramen magnum likely a result of a small posterior fossa.

Radiographic features

Antenatal ultrasound

Classical signs described on ultrasound include:

lemon sign

banana cerebellum sign

There may also be evidence of fetal ventriculomegaly due to obstructive effects as a result of downward cerebellar herniation. Additionally many of the associated malformations (e.g. corpus callosal dysgenesis) may be identified.

MRI is the modality of choice for detecting and characterising the full constellation of findings associated with Chiari II malformations. The key features are discussed below, whereas the wide range of associated abnormalities (see above) are discussed separately. Posterior fossa

small posterior fossa with a low attachment of the tentorium and low torcula

the brainstem appears 'pulled' down with an elongated and low lying fourth ventricle

the tectal plate appears beaked: inferior colliculus is elongated and points posteriorly, with resulting angulation of the aqueduct which results in aqueductal stenosis and hydrocephalus

cerebellar tonsils and vermis are displaced inferiorly through foramen magnum which appears crowded

Spine

spina bifida aperta / myelomeningocoele

tethered cord

Chiari malformation type 2 treatment.

68% had complete or near-complete resolution of symptoms, 12% had mild to moderate residual deficits, and 20% had no improvement (in general, neonates fared worse than older children) ¹³⁾. Respiratory arrest is the most common cause of mortality (8 of 17 patients who died), with the rest due to meningitis/ventriculitis (6 patients), aspiration (2 patients), and biliary atresia (1 patient) ¹⁴⁾. In follow-up ranging 7 mos-6 yrs, 37.8% mortality in operated patients. Pre-op status and the rapidity of neurologic deterioration were the most important prognosticators. The mortality rate is 71% in infants having a cardiopulmonary arrest, vocal cord paralysis or arm weakness within 2 weeks of presentation, compared to 23% mortality in patients with more gradual deterioration. Bilateral vocal cord paralysis was a particularly poor prognosticator for a response to surgery ¹⁵⁾.

A single-center retrospective analysis was performed of fetal MRI examinations revealing open spinal dysraphism from 2004 through 2016 with available diagnostic postnatal spinal MR images in conjunction with neurosurgical follow-up findings. Images were reviewed by two board-certified fellowship-trained pediatric neuroradiologists. Relevant clinical data were recorded.

The study of the Department of Radiology and Medical Imaging, Department of Pediatric Neurosurgery, Department of Pediatric Surgery, Department of Biostatistics and Epidemiology, Cincinnati Children's Hospital Medical Center, included 119 fetal MRI examinations of patients with open spinal dysraphism. Myeloceles were found in 29.4% (35/119) of these examinations and myelomeningoceles in the others. All (35/35) myeloceles showed grade 3 (severe) Chiari II malformations. Only 73.8% (62/84) of myelomeningoceles showed grade 3 Chiari II malformation. Clinically significant spinal kyphosis was found in 5.0% (6/119) of fetuses, and all of these fetuses had grade 3 Chiari II malformations. The size of the spinal dysraphic defect had significant positive correlation with lateral (p < 0.0001) and third (p = 0.006) ventricular size. Mean volume of the myelomeningocele sac was significantly different among Chiari II grades and inversely proportional to Chiari II grade (p = 0.0009).

Larger spinal dysraphic defects correlated with increased ventricular size at fetal MRI. All of the fetuses with myelocele or kyphosis had severe Chiari II malformations. Larger myelomeningocele sac size was associated with lower grade of Chiari II malformation, suggesting that myelomeningocele sac formation may be protective against hindbrain herniation. ¹⁶⁾.

Twenty-one adults with a median age of 35 years were investigated. All had treated hydrocephalus, and eight had foramen magnum decompression for headache or progressive brainstem symptoms with stabilisation of symptoms in seven and improvement in one. Only eight patients were living independently, five were in paid employment and five work voluntarily. HOQ scores for cognitive function were lower (0.56 ± 0.20; mean ± standard deviation (SD)) than those for physical (0.64 ± 0.15) and social-emotional (0.65 ± 0.17) health. Cognitive function varied across the cohort with attention most severely affected (73.9 ± 17.0; mean ± SD). Repeated episodes of shunt malfunction or foramen magnum decompression were not associated with a worse cognitive function.

Despite intervention in childhood and adequate Cerebrospinal fluid shunt the prognosis for independent living into adulthood remains poor. All patients have elements of cognitive impairment. Structural brain abnormalities may be more important determinants of cognitive outcome than shunt malfunction ¹⁷⁾.