Chiari Malformations

Chiari malformations (CMs) are a group of central nervous system Nervous system The nervous system is a small and complex system that consists of an intricate network of neural cells (or neurons) and even more glial cells (for support and insulation). It is divided according to its anatomical components as well as its functional characteristics. The brain and spinal cord are referred to as the central nervous system, and the branches of nerves from these structures are referred to as the peripheral nervous system. General Structure of the Nervous System (CNS) conditions characterized by the underdevelopment of the posterior cranial fossa with subsequent protrusion of neural structures through the foramen magnum. There are 4 types of CM, with type I being the most common. Headaches are the most common symptom. Diagnosis is made by clinical findings and confirmed by magnetic resonance imaging (MRI). Treatment is surgical, based on decompression of the posterior fossa and restoration of CNS flow. Prognosis depends on the type of malformation.

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Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

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Overview

Definition

Chiari malformations (CMs) are a group of disorders defined by structural deficits in the brain and spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. In cross section, the spinal cord is divided into an H-shaped area of gray matter (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter (consisting of ascending and descending tracts of myelinated axons). Spinal Cord leading to limited space in the posterior fossa, which forces cerebellar structures to protrude through the foramen magnum.

Classification

  • Type I: tonsillar herniation > 5 mm inferior to plane of foramen magnum
    • Abnormally shaped cerebellar tonsils
    • No associated brainstem herniation or supratentorial anomalies
    • Associated hydrocephalus and hydrosyringomyelia common
  • Type II: herniation of cerebellar vermis, brainstem, and 4th ventricle into foramen magnum
    • Associated with myelomeningocele and multiple brain anomalies
    • Associated hydrocephalus and syringomyelia are very common.
  • Type III: herniation of cerebellum Cerebellum The cerebellum, Latin for "little brain," is located in the posterior cranial fossa, dorsal to the pons and midbrain, and its principal role is in the coordination of movements. The cerebellum consists of 3 lobes on either side of its 2 hemispheres and is connected in the middle by the vermis. Cerebellum and brainstem compressing spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. In cross section, the spinal cord is divided into an H-shaped area of gray matter (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter (consisting of ascending and descending tracts of myelinated axons). Spinal Cord
    • High cervical or occipital encephalocele containing herniated cerebellar and brainstem tissue
    • Rare and typically incompatible with life
  • Type IV: incomplete or underdeveloped cerebellum Cerebellum The cerebellum, Latin for "little brain," is located in the posterior cranial fossa, dorsal to the pons and midbrain, and its principal role is in the coordination of movements. The cerebellum consists of 3 lobes on either side of its 2 hemispheres and is connected in the middle by the vermis. Cerebellum with exposed skull Skull The skull (cranium) is the skeletal structure of the head supporting the face and forming a protective cavity for the brain. The skull consists of 22 bones divided into the viscerocranium (facial skeleton) and the neurocranium. Skull and spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. In cross section, the spinal cord is divided into an H-shaped area of gray matter (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter (consisting of ascending and descending tracts of myelinated axons). Spinal Cord
    • Hypoplasia or aplasia of cerebellum Cerebellum The cerebellum, Latin for "little brain," is located in the posterior cranial fossa, dorsal to the pons and midbrain, and its principal role is in the coordination of movements. The cerebellum consists of 3 lobes on either side of its 2 hemispheres and is connected in the middle by the vermis. Cerebellum and tentorium
    • Rare and always incompatible with life
Chiari malformations

Chiari type I and II
Chiari malformations are characterized by and underdeveloped posterior cranial fossa, with subsequent protrusion of neural structures through the foramen magnum. Type 1 is characterized by herniation of the cerebellar tonsils only, while type 2 involves more structures.

Image by Lecturio.

Epidemiology

Incidence:

  • Type I:
    • Most common form
    • 1 in 1,000–5,000 live births 
    • Slight female predominance
  • Type II:
    • Approximately 1 in 2,000 live births 
    • Decreased incidence with prenatal folate Folate Folate and vitamin B12 are 2 of the most clinically important water-soluble vitamins. Deficiencies can present with megaloblastic anemia, GI symptoms, neuropsychiatric symptoms, and adverse pregnancy complications, including neural tube defects. Folate and Vitamin B12 supplementation
    • No gender predominance
    • Always associated with myelomeningocele 
  • Type III: 
    • Rarest form
    • Makes up 1%–4.5% of all CMs

Associated conditions:

  • Pierre Robin sequence Pierre Robin sequence Pierre Robin sequence, also known as Pierre Robin syndrome or simply Robin sequence, is a condition in infants that is characterized by a smaller-than-normal mandible, a tongue that retracts back into the throat, and difficulty breathing. Pierre Robin Sequence
  • Noonan syndrome
  • Neurofibromatosis type 1 Neurofibromatosis type 1 Neurofibromatosis type 1 (NF1), also known as phakomatosis, is a neurocutaneous disorder that is most commonly of autosomal dominant inheritance due to mutations in the NF1 gene. Neurofibromatosis type 1 presents a range of clinical manifestations with the most prominent features being various pigmented skin lesions called café au lait macules (CALMs), neurofibromas, freckling of the inguinal and axillary regions, and iris hamartomas. Neurofibromatosis Type 1

Etiology and Pathophysiology

Etiology

  • Mechanism for herniation
    • Formation of small posterior fossa ➝ limited growth of cerebellum Cerebellum The cerebellum, Latin for "little brain," is located in the posterior cranial fossa, dorsal to the pons and midbrain, and its principal role is in the coordination of movements. The cerebellum consists of 3 lobes on either side of its 2 hemispheres and is connected in the middle by the vermis. Cerebellum and nearby structures 
    • Growing structures herniate through foramen magnum or vermis.
  • Multiple proposed causes:
    • Genetics Genetics Genetics is the study of genes and their functions and behaviors. Basic Terms of Genetics:
      • Abnormal segmentation of hindbrain 
      • Causes abnormal embryonic development of bony and nervous tissues
    • Restricted growth of posterior fossa causes compression of neural tissues.
    • Progressive hydrocephalus pushes structures downward.

Pathophysiology

Neurologic symptoms are caused by:

  • Compression of central nervous system Nervous system The nervous system is a small and complex system that consists of an intricate network of neural cells (or neurons) and even more glial cells (for support and insulation). It is divided according to its anatomical components as well as its functional characteristics. The brain and spinal cord are referred to as the central nervous system, and the branches of nerves from these structures are referred to as the peripheral nervous system. General Structure of the Nervous System (CNS; cerebellum Cerebellum The cerebellum, Latin for "little brain," is located in the posterior cranial fossa, dorsal to the pons and midbrain, and its principal role is in the coordination of movements. The cerebellum consists of 3 lobes on either side of its 2 hemispheres and is connected in the middle by the vermis. Cerebellum, brainstem) against foramen magnum and spinal canal
  • Formation of cavitations in spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. In cross section, the spinal cord is divided into an H-shaped area of gray matter (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter (consisting of ascending and descending tracts of myelinated axons). Spinal Cord (syrinx or syringomyelia) due to backup of CSF outflow
Pressure on the cns due to chiari malformation

Syrinx seen with Chiari malformation
Cavities filled with cerebrospinal fluid (CSF) are commonly seen with CMs. They cause symptomatology commonly associated with the malformation by putting pressure on the surrounding neural tissue.

Image by Lecturio.

Clinical Presentation

Type I

Symptoms:

  • Asymptomatic in some cases
  • Headache:
    • Most common symptom (60%–70%) 
    • Usually occipital and upper cervical
    • Occipital headache worse on Valsalva maneuver
  • Ataxia and nystagmus (due to compression of cerebellum Cerebellum The cerebellum, Latin for "little brain," is located in the posterior cranial fossa, dorsal to the pons and midbrain, and its principal role is in the coordination of movements. The cerebellum consists of 3 lobes on either side of its 2 hemispheres and is connected in the middle by the vermis. Cerebellum
  • Compression of cranial nerves Cranial nerves There are 12 pairs of cranial nerves (CNs), which run from the brain to various parts of the head, neck, and trunk. The CNs can be sensory or motor or both. The CNs are named and numbered in Roman numerals according to their location, from the front to the back of the brain. Overview of the Cranial Nerves can lead to:
    • Hoarseness
    • Vocal cord paralysis
    • Tongue asymmetry
  • Central sleep Sleep Sleep is a reversible phase of diminished responsiveness, motor activity, and metabolism. This process is a complex and dynamic phenomenon, occurring in 4-5 cycles a night, and generally divided into non-rapid eye movement (NREM) sleep and REM sleep stages. Physiology of Sleep apnea

Physical signs:

  • Syringomyelia and central cord syndrome Central Cord Syndrome Central cord syndrome (CCS) is a neurological syndrome caused by an injury to the center of the spinal cord, affecting the spinothalamic tracts ((STTs) sensory) and medial aspect of the corticospinal tracts ((CSTs) motor), most often due to trauma in patients with cervical spondylosis. Central Cord Syndrome (CCS):
    • Develops at level of C8–T1
    • “Cape-shaped” area of pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain and temperature sensation loss due to spinothalamic tract involvement
    • Flaccid paralysis and muscle atrophy due to lower motor neuron involvement
  • Scoliosis Scoliosis Scoliosis is a structural alteration of the vertebral column characterized by a lateral spinal curvature of greater than 10 degrees in the coronal plane. Scoliosis can be classified as idiopathic (in most cases) or secondary to underlying conditions. Scoliosis: due to asymmetric development of vertebral columns

Type II

Symptoms:

  • Signs of brainstem dysfunction (e.g., ataxia, urinary incontinence Urinary incontinence Urinary incontinence (UI) is involuntary loss of bladder control or unintentional voiding, which represents a hygienic or social problem to the patient. Urinary incontinence is a symptom, a sign, and a disorder. The 5 types of UI include stress, urge, mixed, overflow, and functional. Urinary Incontinence)
  • Swallowing and feeding difficulties
  • Stridor/difficulty in breathing/apnea
  • Weak cry
  • Nystagmus
  • Occipital headaches

Physical signs:

  • Myelomeningocele: protrusion of CNS and meninges Meninges The brain and the spinal cord are enveloped by 3 overlapping layers of connective tissue called the meninges. The layers are, from the most external layer to the most internal layer, the dura mater, arachnoid mater, and pia mater. Between these layers are 3 potential spaces called the epidural, subdural, and subarachnoid spaces. Meninges
    • Commonly lumbosacral or thoracic
    • Usually prenatally diagnosed
  • Hydrocephalus (< 10%):
    • Tense/bulging fontanelles 
    • Increased head circumference > 98th percentile
    • Nuchal rigidity and neck tenderness
    • Cognitive deterioration
    • Imbalance and gait disturbances
    • Urinary incontinence

Type III

There is high infant mortality with this type.

Symptoms:

  • Severe neurological, developmental, and cranial nerve defects
  • Seizures Seizures A seizure is abnormal electrical activity of the neurons in the cerebral cortex that can manifest in numerous ways depending on the region of the brain affected. Seizures consist of a sudden imbalance that occurs between the excitatory and inhibitory signals in cortical neurons, creating a net excitation. The 2 major classes of seizures are focal and generalized. Seizures
  • Respiratory insufficiency
  • Upper and lower motor neuron paralysis

Physical signs:

  • Encephalocele: protruding defect that contains part of cerebellum Cerebellum The cerebellum, Latin for "little brain," is located in the posterior cranial fossa, dorsal to the pons and midbrain, and its principal role is in the coordination of movements. The cerebellum consists of 3 lobes on either side of its 2 hemispheres and is connected in the middle by the vermis. Cerebellum and higher structures
  • Spastic or flaccid paralysis

Type IV

  • CNS is undeveloped.
  • Infants die shortly after birth.

Diagnosis

Work-up

  • Rule out other causes of tonsillar herniation (e.g., intracranial mass lesion, hydrocephalus).
  • Antenatal:
    • Obstetric ultrasounds looking for congenital abnormalities in 18th week of gestation (absent vermis)
    • Amniocentesis and karyotyping
  • Postnatal:
    • Ultrasound of head preferred in neonates
    • MRI scan preferred in older children and adults

Diagnosis

  • Clinical findings with diagnostic imaging to confirm
  • Can be done prenatally
Chiari i malformation

Magnetic resonace imaging scan showing a type I CM. Notice the tonsillar herniation.

Image: “Sagittal MRI scan of brain of patient with Chiari malformation” by Raymond F Sekula Jr et al. License: CC BY 2.0

Prognosis

  • Favorable prognosis with normal life expected after intervention
  • Chiari III malformation has the poorest prognosis.

Management and Complications

Surgical therapy

  • Decompression of cervicomedullary junction → restoring normal CSF dynamics 
  • Options:
    • Posterior fossa craniectomy 
    • Electrocautery of cerebellum Cerebellum The cerebellum, Latin for "little brain," is located in the posterior cranial fossa, dorsal to the pons and midbrain, and its principal role is in the coordination of movements. The cerebellum consists of 3 lobes on either side of its 2 hemispheres and is connected in the middle by the vermis. Cerebellum via high-frequency electric currents
    • Spinal laminectomy to remove pathological bony roof of spinal canal

Conservative management

  • Analgesics and muscle relaxants for headaches and neck pains
  • Occasional use of soft neck collar
  • Special education needed in event of delayed developmental milestones Developmental milestones Developmental milestones are the skills or abilities that most children are able to perform when they reach a certain age. Understanding the appropriate milestones and at what age they are reached helps clinicians identify symptoms of delayed development. Developmental milestones are divided into 5 important domains: gross motor, fine motor, language, social, and cognitive. Developmental Milestones and Normal Growth

Complications

  • Hydrocephalus: accumulation of CSF within cranial cavity; CM is obstructive, or non-communicating, cause of hydrocephalus
  • Pseudomeningocele formation and CSF leakage
  • Meningitis Meningitis Meningitis is inflammation of the meninges, the protective membranes of the brain, and spinal cord. The causes of meningitis are varied, with the most common being bacterial or viral infection. The classic presentation of meningitis is a triad of fever, altered mental status, and nuchal rigidity. Meningitis and wound infection post-surgery
  • Neurovascular injury during surgery
  • Cerebellar ptosis in large occipital craniectomy

Differential Diagnosis

  • Hydrocephalus: potentially life-threatening condition caused by excess accumulation of CSF within the ventricular system Ventricular System The ventricular system is an extension of the subarachnoid space into the brain consisting of a series of interconnecting spaces and channels. Four chambers are filled with cerebrospinal fluid (CSF): the paired lateral ventricles, the unpaired 3rd ventricle, and the unpaired 4th ventricle. Ventricular System. Clinical presentation is nonspecific and includes headache, behavioral changes, developmental delays, or nausea and vomiting. Diagnosis is confirmed with neuroimaging (ultrasound, head CT, or MRI) showing ventriculomegaly. Treatment is placement of CSF shunt.
  • Meningitis Meningitis Meningitis is inflammation of the meninges, the protective membranes of the brain, and spinal cord. The causes of meningitis are varied, with the most common being bacterial or viral infection. The classic presentation of meningitis is a triad of fever, altered mental status, and nuchal rigidity. Meningitis: inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body's defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation of leptomeninges, usually due to infectious agent. Patients will present with headache, fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever, and a stiff neck. Diagnosis is suspected by clinical presentation and confirmed by lumbar puncture. Treatment is aimed at the causative infection. 
  • Neural tube disorders: disorders caused by failure of the neural tube to close properly during embryological development. Symptoms range from asymptomatic to very severe malformations of spine and brain. Etiologies are multifactorial, ranging from maternal nutrition to genetic determinants. Prenatal diagnosis is by ultrasound and maternal α-fetoprotein level. Management is mainly surgical.

References

  1. Tubbs, R. S., & Oakes, W. J. (2017). Chiari malformations. Neurological surgery. pp. 1531–1540. doi:http://dx.doi.org/10.1016/B978-0-323-28782-1.00190-8.
  2. Schijman, E. History, anatomic forms, and pathogenesis of Chiari I malformations. Childs Nerv Syst 20, 323–328 (2004). https://doi.org/10.1007/s00381-003-0878-y
  3. Khoury, C. (2020). Chiari malformations. UpToDate. Retrieved December 1, 2020 from https://www.uptodate.com/contents/chiari-malformations.
  4. Abd-El-Barr MM, Strong CI, Groff MW. Chiari malformations: diagnosis, treatments and failures. J Neurosurg Sci. 2014 Dec. 58 (4):215–21.
  5. McClugage, S and Oakes, J. The Chiari I malformation. JNSPG 75th Anniversary Invited Review Article. DOI: https://doi.org/10.3171/2019.5.PEDS18382.
  6. Langridge B, Phillips E, Choi D. (2017). Chiari Malformation Type 1: A Systematic Review of Natural History and Conservative Management. World Neurosurg.

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