Chiari malformation …

Ryan W Y Lee MD

General Child Neurology

Updated 04.28.2024
Released 08.08.1994
Expires For CME 04.28.2027

Chiari malformation

Author: Ryan W Y Lee MD

See Contributor Disclosures

Editor: Ann Tilton MD

Chiari malformation

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Introduction

Overview

Chiari malformation describes a group of structural defects of the cerebellum characterized by brain tissue protruding into the spinal canal. Chiari malformations are often associated with myelomeningocele, hydrocephalus, syringomyelia, and tethered cord syndrome. Although studies of etiology are few, an increasing number of specific genetic syndromes are found to be associated with Chiari malformations. Management primarily targets supportive care and neurosurgical intervention when necessary. Renewed effort to address deficits in Chiari research involves workgroups targeted at pathophysiology, symptoms and diagnosis, engineering and imaging analysis, treatment, pediatric issues, and related conditions. In this article, the author discusses the many aspects of diagnosis and management of Chiari malformation.

Key points

	• Chiari malformation describes a group of structural defects of the cerebellum, characterized by brain tissue protruding into the spinal canal.
	• Chiari malformations are often associated with myelomeningocele, hydrocephalus, syringomyelia, and tethered cord syndrome.
	• Although studies of etiology are few, an increasing number of specific genetic syndromes are found to be associated with Chiari malformations.
	• Management primarily targets supportive care and neurosurgical intervention when necessary.
	• Renewed effort to address deficits in Chiari research involves workgroups targeted at pathophysiology, symptoms and diagnosis, engineering and imaging analysis, treatment, pediatric issues, and related conditions.

Historical note and terminology

The Chiari malformation, also known as the Arnold-Chiari malformation (or deformity), was first described by Cleland in 1883 in a child with spina bifida, hydrocephalus, and alterations of the cerebellum and brainstem (20; 92). In 1891, Austrian pathologist Hans Chiari wrote an article titled “Concerning alterations in the cerebellum resulting from hydrocephalus.” He described elongation of the cerebellar tonsils and medulla below the plane of the foramen magnum in a 17-year-old woman, now referred to as a type 2 malformation. Chiari’s subsequent studies expanded the spectrum of malformations in a classification system consisting of types 1, 2, 3, and later 4. Otto Mennicke also contributed to our understanding of tonsillar ectopia (35). In 1907, Arnold was credited with publishing four additional cases, and his students Schwalbe and Gredig added his name to the nomenclature. Many authors consider Chiari's contribution to be primary and, therefore, suggest that this condition be designated as Chiari malformation, without including Arnold's name (57).

Chiari type 1 refers to herniation of the cerebellar tonsils alone, and radiologically as simple tonsillar herniation 5 mm or greater below the foramen magnum (31); type 2 refers to herniation of both the cerebellum and lower brainstem; type 3 refers to a rare type of brainstem herniation in association with a cervical or occipital encephalocele; type 4 involves extreme cerebellar hypoplasia and caudal displacement of the posterior fossa contents. Two additional types of Chiari malformation have been described. Chiari type 0 is defined as syringohydromyelia with distortion of contents in posterior fossa but without cerebellar tonsillar herniation (106). Chiari type 1.5 has been characterized as caudal migration of the brainstem and cerebellar tonsils often associated with syringomyelia but without spina bifida (92; 106).

Clinical manifestations

Presentation and course

Clinical presentations resulting from Chiari malformation vary along a spectrum of severity and depend on anatomic involvement (32). One may approach clinical presentations by their underlying pathology or pathophysiology. Another approach involves identifying cases by the presence or absence of myelomeningocele. Many individuals with Chiari 1 malformation do not have symptoms and go undiagnosed until adolescence. Alternatively, because of brainstem involvement, type 2 malformations are typically diagnosed earlier in childhood. Therefore, some categorize type 1 malformations as “adult type” and type 2 malformations as “congenital type.” Headache and neck pain are the most common presenting symptoms of Chiari 1 malformations (04). Suboccipital pain may be a presenting symptom (38). Chiari 1 malformation may present with seizures and developmental delay in children (16). A review of Chiari type 1 malformation in infants and toddlers was published (39). An update on diagnosis and treatment provides practical implications on management and surgical interventions (88).

Chiari malformation without myelomeningocele. Symptomatic Chiari malformation can present at any age. Children and adults present with similar symptoms and signs (27; 28). Saez and colleagues grouped presentations into six categories: (1) foramen magnum compression, (2) central cord syndrome, (3) cerebellar dysfunction, (4) bulbar palsy, (5) paroxysmal intracranial hypertension, and (6) spasticity (91). Pillay and colleagues presented a simplified system, classifying patients as type A (with concomitant syrinx and central cord symptoms) or type B (with significant brainstem herniation and signs and symptoms of brainstem and cerebellar compression) (81). In their study of 35 patients, Pillay and colleagues found the frequency of clinical presentations to be the following: headache and neck pain, 73%; sensory dysesthesias or numbness, 56%; gait problems, 43%; upper extremity weakness, 25%; cranial nerve dysfunction, 23%; blurred vision, 17%; and lower extremity weakness, 15%. This system does not account for the important category of intermittent symptoms most often associated with paroxysmal intracranial hypertension. A system that adds the group with intermittent presentations to the two in Pillay's system is probably an adequate classification.

Some authors have stressed disorders of oculomotor motility, particularly downbeat nystagmus, as being important in making the diagnosis of a symptomatic Chiari malformation. Indeed, a variety of eye movement disturbances has been identified as a feature of this condition, including convergence nystagmus, internuclear ophthalmoplegia (Chiari malformation type 2), oscillopsia, horizontal nystagmus, and ophthalmoplegia.

Although eye movement disturbances may be seen, other signs are usually more prominent on presentation as the above-described classification systems attest. Particular attention should be paid to the following:

Presentations due to an accompanying syrinx. Syringomyelia, when associated with a Chiari 1 malformation, usually involves the cervical spinal cord, with accompanying symptoms or signs of upper extremity involvement. Cases involving thoracic syrinx can cause scoliosis without upper extremity findings. Idiopathic scoliosis in children can be the only manifestation of Chiari malformation with syrinx or hydromyelia.

Progressive brainstem or cerebellar dysfunction. This includes sleep apnea in adults, dysphagia, progressive myelopathy, sensorineural hearing loss, and vertigo if accompanied by neck pain or weakness, as well as other otolaryngological symptoms, disturbances of respiratory drive (Ondine curse and pneumonia with respiratory failure), and trigeminal neuralgia. Cervical pain may be a complaint.

Paroxysmal symptoms. Headache, autonomic dysfunction, syncope, and pain can be a presenting complaint of Chiari malformation or can accompany the more classic presentations noted above. These intermittent symptoms can be cough induced.

The nature of head pain or headaches in Chiari malformation varies and can be exertional, with characteristics of a spinal headache, either migrainous or cough-induced (79; 96). In rare cases, glossopharyngeal neuralgia may be a presenting sign of Chiari 1 malformation (63). Chiari 1 malformation has been implicated as a cause of such syndrome complexes as chronic fatigue syndrome and neurally mediated orthostatic hypotension. Techniques for early identification of Chiari malformation are being proposed, including decreased ratio of downward to horizontal smooth pursuit eye movement velocity (56).

The presence and degree of hydrocephalus and ventriculomegaly. Chiari malformation can be accompanied by hydrocephalus, which is often compensated for, without signs or symptoms of, increased intracranial pressure. Hydrocephalus may also be of the intermittent obstructive type.

Chiari malformation in those with myelomeningocele. The Chiari malformation is a common problem in patients with spina bifida, particularly myelomeningocele, where it occurs in more than 90% of individuals. Clinical manifestations of Chiari malformation in children and adults with myelomeningocele can be similar to those discussed above. The presence and severity of hydrocephalus and ventriculomegaly are particularly important clinical matters in such cases. Added to this is the infantile presentation of Chiari malformation seen in 10% to 20% of patients with myelomeningocele. Because of its severity, along with the potentially poor prognosis, the infant brainstem syndrome of myelomeningocele is considered separately. A form of herniation of the occipital lobe through the foramen magnum is rare and has been proposed as Chiari type 5 (103).

For children, adolescents, and adults with myelomeningocele, clinical manifestations are similar to those without myelomeningocele. Sleep apnea appears to be common in this group, both the central and obstructive types (21). Some cases of obstructive sleep apnea appear to be related to abnormal control of pharyngeal airway patency in sleep (113). Symptoms from accompanying syrinx or hydromyelia are also common, especially those of progressive upper extremity dysfunction, scoliosis, or both.

Symptoms of brainstem dysfunction such as stridor, apnea, and dysphagia, are seen in 10% to 20% of newborns and infants with myelomeningocele and can be ominous signs. In some series, up to one half of these children died. Persistent crying has been reported as a presenting sign (65). Some authors have called this group of symptoms in the newborn with myelomeningocele the infantile brainstem syndrome.

Prognosis and complications

Complications are related to severity of injury, quality of assessment and management, and technical expertise of surgical repair. There are reports of symptoms secondary to Chiari malformation stabilizing or improving with time, including newborns with myelomeningocele and symptomatic Chiari malformation. Craniocervical decompression may improve functional outcome (12; 82). Bone regrowth and recurrence of symptoms have also been reported (49; 99). A study from Duke University reported the most common symptoms for readmitted patients were fever/presumed infection (40%) and altered mental status (40%), followed by new sensory/motor deficits (30%) (30). This study suggests that infection, altered mental status, and new sensory/motor deficits were the primary complications leading to unplanned 30-day readmission after cranial neurosurgery. Posterior reversible encephalopathy syndrome has been reported in a patient with Chiari 1 malformation (44). Other complications that may occur are cough syncope, uveitis, and central sleep apnea (29; 54; 67). There have been reports of spontaneous resolution of Chiari malformation and syringomyelia (15; 102).

Arachnoid pathology in Chiari 1 malformation has an impact on clinical symptoms and postoperative results. Decompressions with arachnoid dissection and an alloplastic duraplasty performed by surgeons experienced with this pathology offer a favorable long-term prognosis (55). Analysis of a large nationwide health care network showed recently increasing rates of Chiari malformation decompression in children and adults over the past 14 years (114). Studies in pre- and postoperative diffusion tensor imaging as a tool to evaluate outcome of decompression surgery suggest a normalization of white matter integrity not apparent in conventional imaging (01). Disability scores such as the Chicago Chiari Outcome Scale and intraoperative MRI are also being investigated as potential methods for measuring treatment efficacy (10; 45; 37). Preoperative factors of headache resolution after surgery are an attack duration under 5 minutes, triggering by Valsalva maneuvers, severe intensity of attack, occipital location, and a higher number of headache days per month. These characteristics are each part of the IHS diagnostic criteria for headache attributed to Chiari, highlighting the relevance of their systematic use before surgery to guide the neurosurgeon. Postoperative improvement is inversely correlated with the Chiari Severity Index, a preoperative grading system (40).

A multicenter study of over 600 Chiari patients showed an immediate recall deficit relative to controls, regardless of surgical status (03). High levels of reflection were associated with better-delayed recall performance in nondecompressed Chiari patients with lower pain levels. High levels of chronic pain may overwhelm increased focused attention abilities, but higher levels of reflection partially overcome the distracting effects of pain, and this may represent a type of resilience (03).

Preoperative and intraoperative factors may help to provide better clinical decision-making for Chiari malformation type 1 surgery (34). Patients with symptoms consisting of occipital headache, cranial nerve symptoms, and brainstem or spinal cord symptoms had a higher risk, whereas those who underwent arachnoid dissection or adhesion lysis had 75% lower likelihood of clinical worsening postoperatively. Patients with evidence of brainstem or spinal cord symptoms, scoliosis, and preoperative syrinx had a significantly higher likelihood of postoperative worsening of syrinx. Patients with symptoms consisting of occipital or tussive headache, cranial nerve symptoms, and nonspecific symptoms had significantly higher likelihood, whereas patients with foramen magnum 34 mm or larger and those who underwent arachnoid dissection or adhesion lysis had 73% and 70% lower likelihood of reoperation, respectively. The Kaplan-Meier curve showed that patients with foramen magnum size 34 mm or larger had significantly better clinical and syrinx improvement postoperatively when the tonsils were resected (34).

Clinical vignette

A 28-year-old female patient was followed in a neurology clinic for 14 years. She presented at the age of 14 with partial complex seizures. Headaches were not a prominent symptom. Her neurologic exam did not reveal any focal findings. EEG showed bilateral temporal spikes. CT scan of the brain showed moderate ventriculomegaly. MRI revealed a Chiari 1 malformation with tonsillar herniation down to C3. There was also a rather large cervical syrinx.

The patient was stable for the next 12 years. She then began to have frequent headaches that were moderately disabling. She denied a change in hand coordination, gait, or in the ability to chew and swallow.

Her exam remained without focal neurologic findings. There was no nystagmus or papilledema. Her tongue was normal and there was no atrophy of her hand muscles. Her gait and reflexes were normal.

MRI at this time revealed continued tonsillar herniation down to C3. The cervical syrinx was slightly larger. The patient underwent a suboccipital craniectomy, as well as C1 laminectomy and dural decompression. She did well postoperatively with resolution of her headaches.

Her clinical status has remained good for 2 years. She remains headache-free. There has been no increase in the size of her syrinx or ventricles.

Biological basis

Etiology and pathogenesis

Although the etiology of Chiari malformation is not clearly understood, the literature suggests a condition with heterogeneous causes.

Most evidence points to two major causes of Chiari malformation. For most patients, Chiari malformation is a congenital malformation, arising from an embryologic defect in the formation of neural and craniovertebral structures. Stovner performed measurements of posterior fossa size and found patients to have smaller posterior cranial fossae (96). Although the small posterior cranial fossa appeared to have little or no clinical significance, the author suggested that it might be the primary developmental anomaly. Nishikawa and colleagues suggest underdeveloped occipital enchondrium and basilar invagination as exacerbating overcrowding in the posterior cranial fossa (75).

There is evidence that altered CSF dynamics may contribute to the formation of an acquired Chiari malformation. MRI techniques may be used to evaluate cerebrospinal fluid dynamics (05). Chiari malformation has also been seen after lumboperitoneal shunting.

Herman and colleagues were the first to report symptomatic Chiari malformation type 1 in siblings (46).

There is a paucity of studies investigating the role of genetics in Chiari malformations. Genome-wide linkage analysis in subjects with Chiari type 1 identified candidate loci on chromosome 15q21.2-q22.3 and chromosome 9q22.31 (14). Finally, an increasing number of specific genetic syndromes with radiographic evidence of Chiari malformations are being published (41; 87; 66). Chromodomain genes and excessive brain growth are implicated in the pathogenesis of Chiari malformation 1 (90).

There is a multifactorial nature to the pathogenesis of symptoms and signs referable to Chiari malformation, including a relationship to hydrocephalus, vascular compromise, direct neuronal distortion, and congenital neural malformation. There is a high likelihood that other associated conditions coexist with Chiari malformation and may be important contributors to the pathogenesis of symptoms. This is particularly true for individuals with spina bifida (07).

Morphometric measures of posterior cranial fossa by CT and MRI have revealed clues concerning the pathogenesis of cerebellar tonsillar herniation. Radiographic evidence shows that a greater degree of cerebellar tonsillar herniation is associated with a shorter clivus length, a wider anteroposterior diameter of foramen magnum, and a wider Boogaard angle (26). The mechanisms suggested include cranial constriction, cranial settling, spinal cord tethering, intracranial hypertension; and intraspinal hypotension (73). Researchers have found differences in cerebrospinal fluid velocities and pressures in patients with type I Chiari malformation compared to healthy subjects (94). Chiari 1 decompression can be caused by posterior cranial fossa surgery (25). Minor head or neck trauma can precipitate the onset of symptoms in a small number of previously asymptomatic patients with Chiari 1 malformations (112). A diffusion tensor imaging study revealed widespread microstructural abnormalities in white matter in adolescents with myelomeningocele and Chiari 2 malformation, suggesting ventricular dilation may have additional effects on white matter microstructure (77).

CSF flow modeling in 3D and 4D have emerged as a technique for evaluating characteristics of flow dynamics when comparing typically developing subjects and those with Chiari malformation (17; 64). These techniques show promise for improved diagnostic and therapeutic management.

Diagnostic workup

The cornerstone of the workup of a suspected Chiari malformation is MRI of the brain, brainstem, and cervical spinal cord. Guidelines have been established for diagnosis and treatment for clinicians (11; 80).

The prevalence of incidental findings is much more frequent in children than previously reported in adults. In a meta-analysis and systematic review, clinically meaningful incidental findings were present in less than 1 in 38 children (22). Sagittal views of the brainstem are particularly important in determining the degree of cerebellar and brainstem herniation. CT scanning may show anomalies such as a beaked tectum and cerebellar tissue around the brainstem on axial views, but it cannot adequately identify the degree of herniation, and may miss Chiari malformations (especially type 1). Measurement of cerebellar tonsillar ectopia can show poor interoperator reliability when attempting to diagnose Chiari 1 malformation (62). The cervical cord should be imaged to look for an accompanying syrinx or hydromyelia. Individuals with myelomeningocele should have their entire neuraxis imaged because of the high likelihood that tethered cord or hydromyelia are also present. They should also be assessed for uncompensated hydrocephalus. Posterior cranial fossa structures reliably differ in adult female Chiari patients relative to healthy controls (48). These differences reflect structural abnormalities in the osseous and soft tissue structures of the clivus, odontoid process, and cerebellum.

A study of 156 patients found that all subjects presenting with a “tonsillar blackout sign” (TBS) had Chiari malformation type 1 (107). TBS is highly suggestive of Chiari malformation type 1 and is potentially useful in differentiation of symptomatic and asymptomatic Chiari malformation type 1. Rare cases may present with vocal cord palsy causing stridor (118).

Based on MRI findings, it has been found that most patients with spinal symptoms had syringomyelia, and a number of individuals with significant tonsillar herniation were clinically asymptomatic (31). It appears that most patients with severe herniation (below the second or third cervical vertebrae) are symptomatic. Cine-MR flow imaging has provided insight as to the dynamic process involved in the evolution of this pathophysiology (69; 70). Microstructural tissue alterations seen on DTI may be present in Chiari malformation type 1 (33). Additionally, there may be a specific role for the middle cerebellar peduncles in Chiari malformation type 1 (33).

Deformities of the midbrain can be seen with Chiari malformation type 1 and mistaken for tumor on CT scan (50); however, this is an unusual finding. Type 1 Chiari malformation appears mainly to be associated with syringomyelia and craniovertebral changes, whereas type 2 Chiari malformation has many associated intracranial findings, including breaking of the midbrain tectum, caudal displacement of the fourth ventricle, large massa intermedia, kinking of the lower brainstem, craniolacunia, and hypoplasia of the falx with interdigitation of the cerebral gyri. The degree of tectal beaking has been shown to be associated with the severity of nystagmus in Chiari type 2 (105). Ultrasonography can be used to identify the presence of type 2 Chiari malformation prenatally, especially when accompanied by spinal dysraphism by detecting the so-called lemon and banana signs (109).

Sometimes neurophysiologic tests, such as brainstem auditory response and somatosensory-evoked potential, are useful adjuncts in evaluating patients who appear to be symptomatic from a Chiari malformation.

Fetal MRI features related to Chiari malformation are being investigated and may add to ultrasound, with more specificity for abnormalities such as the degree of downward displacement of cerebellum, signal changes within brain parenchyma, and the type of meningocele (86). Agreement, repeatability, and reproducibility of 2D phase-contrast MRI and 4D flow detection of peak CSF velocities were quantified using a patient-specific in vitro model of Chiari malformation. Studies are being conducted to gain a better understanding of the application of 2D phase-contrast MRI and 4D flow techniques as diagnostic tools for CSF dynamics quantification in Chiari malformation and related diseases (115).

A whole-genome study of Chiari malformation type 1 showed that clustering analyses resulted in the significant identification of patient classes (subtypes), with the pure biological classes derived from patient blood and dura mater samples demonstrating the strongest evidence. Those patient classes were further characterized by identifying enriched biological pathways, as well as correlated cranial base morphological and clinical traits. These results implicated several strong biological candidates, warranting further investigation from the dura expression analysis, and the results also identified a blood gene expression profile corresponding to a global downregulation in protein synthesis (68). Candidate genes from whole exome sequencing and other genetic studies suggest a significant genetic contribution from inherited and de novo germline variants impacting transcription regulation, craniovertebral osteogenesis, and embryonic developmental signaling. More extensive whole exome sequencing may identify clinically relevant, genetically defined CM1 subtypes distinguished by unique neuroradiographic and neurophysiological endophenotypes (72).

Management

An organized approach is essential to comprehensive management of this group of disorders. Management of Chiari malformation relates to two primary issues: (1) surgical management of the primary disorder and (2) management of neurologic impairment and disability. Specialists with experience in management of Chiari malformations may improve outcome. Renewed effort to address deficits in Chiari research involves workgroups targeted at pathophysiology, symptoms and diagnosis, engineering and imaging analysis, treatment, pediatric issues, and related conditions (58).

One study reported that the overwhelming majority of patients with Chiari 1 malformation (92.9%) managed conservatively do not experience clinical or radiological progression, and a sizeable minority (41.7%) of those who present with symptoms improve (83). However, appropriately selected symptomatic patients (sleep apnea and dysphagia) and those presenting with syringomyelia should be considered surgical candidates because of the high rates of clinical (75%) and radiological improvement (87.5%).

The Chiari Health Index for Pediatrics (CHIP) is a patient-reported, Chiari 1 malformation–specific health-related quality of life instrument, with construct validity in assessing pain-, cognitive-, and emotion-related quality of life, as well as symptomatic features unique to Chiari 1 malformation (60). It holds promise as a discriminative health-related quality of life index in Chiari 1 malformation outcomes assessment.

There continues to be controversy regarding the optimal surgical technique to address Chiari malformations. The recommended treatment for Chiari 1 malformations consists of decompressive suboccipital craniectomy and duraplasty when abnormal cine-flow MRI is observed preoperatively and blockage of CSF flow persists intraoperatively despite bony decompression. In order to avoid unnecessary surgical procedures, proper diagnostic studies and patient selection are needed to optimize outcomes (09; 95). The occipital condyle-atlas joint complex might affect the biomechanical integrity of the craniovertebral junction in children with Chiari malformation type 1 and syringomyelia. The atlanto-occipital joint axis angle metric is an independent predictive factor for the occurrence of occipitocervical fusion following posterior fossa decompression. Preoperative identification of these skeletal abnormalities may be used to guide surgical planning and treatment of patients with complex Chiari malformation type 1 and coexistent osseous pathology (117).

With regard to surgical management of the primary disorder, issues to consider are: the need for and degree of decompression of the posterior fossa; management of accompanying syrinx of hydromyelia; concurrent craniovertebral anomalies such as basilar impression or invagination (101); associated problems such as hydrocephalus; and shunting or shunt replacement. Optimal neurosurgical management of Chiari malformation is evolving. Advancements in techniques such as endoscopic suboccipital craniectomy and upper cervical laminectomies have made Chiari decompression in pediatric populations comparable with the conventional procedure in terms of minimal surgical invasiveness, recovery time, and complexity of the procedure (24). Many patients improve with decompression and release of adhesions in the posterior fossa (28; 111; 12). Dyste and colleagues were able to develop a predictive model showing the presence or absence of atrophy, ataxia, and scoliosis at the time of the preoperative examination allows prediction of long-term outcome for patients with type 2 Chiari malformation (28). Nohria and colleagues showed a positive correlation between improvement in hydromyelia or syringomyelia and improvement in signs and symptoms after decompression. The effect of Chiari surgery on scoliosis was inconclusive in that series (76). Cases with an associated syrinx may also need to be managed with shunting of the cyst, either with a syringosubarachnoid or shunt, particularly if the syrinx is large. Neurosurgical intervention for symptomatic syringomyelia associated with Chiari malformation is generally considered an effective and safe treatment, with a 90% chance of long-term stabilization or improvement (119; 02). Repeat decompression surgery is sometimes needed (89). Fetal surgery for myelomeningocele may improve hydrocephalus and hindbrain herniation associated with Chiari 2 malformation (47). There is little evidence fetal repair of myelomeningocele improves neurologic function. Further studies are required in the area of fetal surgical repair, safety, and outcome.

In a large surgical series of pediatric and adult Chiari malformation between 1965 and 2013, the postoperative neurologic outcomes were as follows: 75% improved, 17% showed no change, and 9% experienced worsening (06). Postoperative headaches improved or resolved in 81% of the patients, with a statistical difference in favor of the pediatric series. Postoperative complications were reported for 41% of the series, most commonly with CSF leak, pseudomeningocele, aseptic meningitis, wound infection, meningitis, and neurologic deficit, with a mean complication rate of 4.5%. Complications were reported for 37% of pediatric, 20% of adult, and 43% of combined series. Mortality was reported for 11% of the series. No difference in mortality rates was seen between the pediatric and adult series (06). Ventral canal encroachment may explain the symptomatology of select patients with type 1 Chiari malformation. Patients with grade I pB-C lines2, with increased ventral canal obstruction, may experience a higher likelihood of syrinx reduction and headache resolution from decompressive surgery with duraplasty than those with grade 0 pB-C2 lines (59).

In a survey of the pediatric section of the American Association of Neurological Surgeons, it was determined that there was substantial agreement that surgery should not be carried out on asymptomatic patients and that surgery was indicated for the treatment of brainstem dysfunction, cranial nerve dysfunction, hydromyelia, and scoliosis associated with these malformations (43). There was substantial disagreement about lesser indications for surgery. This continues to be the case (104). Also, as pointed out in this evidence-based review, the role of shunt malfunction and hydrocephalus in producing “Chiari-like” symptoms continues to be an issue that should be pursued on a case-by-case basis.

Many symptoms of patients with Chiari 1 can be conservatively managed (nonoperative) and improve or remained unchanged over time. In a study, an overall 67% of pediatric patients had improved cough headache, and 71% had improvement of migraines/diffuse headaches (53). The presence of cough headaches is a significant negative predictor of concomitant symptom improvement. This further validates the view that patients with cough headaches should be considered for surgical intervention and provides useful information to counsel patients (53).

There is a role for medical management of the neurologic deficits of Chiari malformation. Clearly, symptoms that persist for months after decompression should be treated. A low threshold should be maintained for repeat imaging to investigate whether postoperative changes are playing a role in new or persistent symptoms. Persistent apnea should be evaluated and treated. Case reports documented therapeutic effectiveness of acetazolamide in hindbrain hernia headache and Chiari 1 malformation (19; 110).

Posterior fossa decompression with duraplasty (PFDD) is commonly performed for Chiari 1 malformation with syringomyelia. A Park-Reeves Syringomyelia Research Consortium study reported that complication rates for dural autograft and nonautologous graft are similar after PFDD for Chiari 1 malformation with syringomyelia, although nonautologous graft results in higher rates of pseudomeningocele and meningitis (116). Rates of meningitis differ among nonautologous graft types. Autograft and nonautologous graft are equivalent for reducing syrinx size, headaches, and neck pain.

Outcomes

Chiari type 1 deformity is commonly seen in pediatric neurology, neuroradiology, and neurosurgery and may have various clinical presentations depending on patient age (84). Overall, the natural history of asymptomatic Chiari 1 malformation is benign (18). Patients treated nonoperatively are unlikely to progress. If they do progress, this is likely to occur within 2 years of initial consultation. In addition, Chiari type 1 deformity is increasingly found by neuroimaging studies as an incidental finding in asymptomatic children. An accurate and reliable selection of patients based on clinical and neuroimaging findings is paramount for the success of neurosurgical treatment (84). A large multicenter registry of patients with Chiari type 1 reported that syrinx characteristics, but not tonsil position, were related to the presence of scoliosis in patients with Chiari type 1, and there was an independent association of syrinx length and holocord syrinx with scoliosis (98). There does not appear to be evidence of a difference in referral patterns or a delay in time from clinic presentation to surgery based on the traditional social determinants of health categories. Children from households in the lower-income group may have an association with increased severity of pain and non-pain symptoms (52).

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Contributors

All contributors' financial relationships have been reviewed and mitigated to ensure that this and every other article is free from commercial bias.

Author

Ryan W Y Lee MD

Dr. Lee of the John A Burns School of Medicine at the University of Hawaii has no relevant financial relationships to disclose.
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Editor

Ann Tilton MD

Dr. Tilton has received honorariums from Allergan and Ipsen as an educator, advisor, and consultant.
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Former Authors

Stephen L Kinsman MD
Michael V Johnston MD†

Patient Profile

Age range of presentation: 0 month to 65+ years
Sex preponderance: male=female
Heredity: heredity may be a factor
Population groups selectively affected: none selectively affected
Occupation groups selectively affected: none selectively affected

ICD & OMIM codes

ICD-11: Arnold-Chiari malformation type I: LA07.4

Arnold-Chiari malformation type II: LA03
OMIM: Chiari malformation type I: %118420

Chiari malformation type II: %207950

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Chiari malformation

Associated Disorders

Achondroplasia
Epidermal nevus syndrome
Holoprosencephaly
Hydrocephalus
Infantile brainstem syndrome
- Jarcho-Levin syndrome
- Klippel-Feil syndrome
- Myelomeningocele
- Neurofibromatosis
- Spina bifida
- Spinal dysraphism
- Syringomyelia

Differential Diagnosis

brain tumor
hydrocephalus
disorders of the craniovertebral junction
chronic meningitis
multiple sclerosis
- cervical myelopathy
- traumatic syringomyelia

Also Relevant

Central sleep apnea
Cough syncope
Headache associated with spontaneous spinal CSF leak
Hydrocephalus
Klippel-Feil syndrome
- Myelomeningocele
- Nystagmus

Chiari malformation …

Chiari malformation

Introduction

Overview

Key points

Historical note and terminology

Clinical manifestations

Presentation and course

Prognosis and complications

Clinical vignette

Biological basis

Etiology and pathogenesis

Epidemiology

Prevention

Differential diagnosis

Diagnostic workup

Management

Outcomes

Special considerations

Pregnancy

Anesthesia

References

Contributors

Author

Editor

Former Authors

Patient Profile

ICD & OMIM codes

This is an article preview.
Start a Free Account
to access the full version.

Questions or Comment?

Also in This Category

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Pediatric-type diffuse high-grade gliomas (excluding diffuse midline gliomas)

Norrie disease

Chiari malformation

Introduction

Overview

Key points

Historical note and terminology

Clinical manifestations

Presentation and course

Prognosis and complications

Clinical vignette

Biological basis

Etiology and pathogenesis

Epidemiology

Prevention

Differential diagnosis

Diagnostic workup

Management

Outcomes

Special considerations

Pregnancy

Anesthesia

References

Contributors

Author

Editor

Former Authors

Patient Profile

ICD & OMIM codes

This is an article preview. Start a Free Account to access the full version.

Questions or Comment?

Also in This Category

Zika virus: neurologic complications

CNS germinoma

Vein of Galen malformations

Epileptic lesions due to malformation of cortical development

Cerebellar astrocytoma

Rare brain embryonal tumors in infancy and early childhood

Pediatric-type diffuse high-grade gliomas (excluding diffuse midline gliomas)

Norrie disease

This is an article preview.
Start a Free Account
to access the full version.