Arnold–Chiari Malformation

What is Arnold–Chiari malformation?

Arnold–Chiari malformation is referred to as the brain malformation or cerebellar structural defects. The cerebral tonsils get displaced downwards via the foramen magnum, resulting in cerebrospinal fluid outflow obstruction causing non-communicating hydrocephalus. This CSF outflow occurs due to the difference of phase in the influx and outflow of blood in the brain vasculature.

Arnold–Chiari malformation Synonyms

• Arnold-Chiari Malformation
• ACM
• Cerebellomedullary Malformation Syndrome

History

Hans Chiari, an Austrian pathologist was the one, who first described the cerebellar malformations in the 1890’s. The credit for the formation of definition goes to Professor Chiari’s colleague Dr. Julius Arnold, and his students Gredig and Schwalbe gave the idea of naming cerebellar malformation as “Arnold-Chiari malformation.”

Epidemiology

ACM type I

• ACM is rare and is seen in all age groups at a rate of 0.6 %, whereas it is 0.9%in the pediatric category.
• Female dominance (3:2 ratio).
• Age: 6 – 60 years, mean age = 40.

ACM type II

• Frequency is 1 in 1,000 cases in the United States.

Picture : Difference between chiari malformation and a normal brain

Image source : nursingcrib.com

Causes

In children (Congenital CM):

• Exposure to hazardous substances/chemicals
• Infection
• Structural defects of spinal cord and brain\
• Vitamin and nutrient deficiency in the diet
• Illegal drug intake
• Alcohol consumption

In adults (Acquired CM):

• CSF leakage
• Infection
• Injury
• Exposure to harmful substances

Arnold-Chiari malformation – Associated conditions

1. Spina bifida:

Spina bifida is the incompletely developed spinal cord. The vertebrae do not form properly resulting in an exposed spinal cord, thereby paralysis results. Myelomeningocele is seen in Type II CM.

2. Hydrocephalus:

Normal CSF flow is interrupted due to hydrocephalus. Most commonly seen in Type II CM.

3. Syringomyelia:

Here, a tubular cyst filled with CSF is formed inside the central canal of spinal cord. Hence, this growing syrinx causes pain, stiffness of shoulder, back, arms and legs, weakness, along with headache, inability to feel cold or hot sensation, especially the hands, in particular

4. Spinal curvatures:

Spinal curvatures like scoliosis and kyphosis may be seen in those children whose skeletal system is not developed.

5. Tethered cord syndrome:

It is caused when the spinal cord gets abnormally stretched, and the nerves and muscles of lower limb get damaged, thereby increasing the risk of tethered cord later, especially in children with myelomeningocele.

Other conditions:

Eg:- Hereditary syndromes and disorders affecting formation and growth of bone, fusion of bone segments in the neck region and the extra folds present in the brain.

Symptoms

Type I CM does not exhibit any symptoms. However, the common symptoms are as follows.

• Headache that aggravates on Valsalva maneuvers like laughing, yawning, coughing, sneezing, crying and straining.
• Dizziness/vertigo
• Tinnitus
• Nausea
• Facial pain
• Nystagmus
• Impaired gag reflex
• Muscle weakness
• Impaired coordination
• Restless leg syndrome
• Difficulty in swallowing (Dysphagia)
• Sleep apnea
• Increased ICP (intracranial pressure)
• Rapid heart (Dysautonomia tachycardia)
• Pupillary dilatation
• Polydipsia
• Fainting (Syncope)
• Hearing loss
• Fatigue

Symptoms In infants:

• Difficulty swallowing
• Breathing problems
• Weak cry
• Drooling salivaStiff neck
• Irritability when fed
• Vomiting or gagging
• Loss of ability to gain weight
• Arm weakness
• Developmental delay
• Opisthotonic posture
• Scoliosis

Classification

Depending on the disorder severity and the brain parts, which bulge into the spinal canal, CM is classified.

Type 1 CM:

Here, the cerebellum’s lower part (cerebellar tonsils) gets extended into the foramen magnum, excluding the brain stem. Usually, spinal cord alone passes through the opening. This is the most common type noticed in the adolescent period or adulthood, and may not exhibit symptoms. Moreover, it is usually diagnosed following other conditions, as it is an acquired CM.

Type II CM (classic CM/ adult-onset CM):

This type is specific for the name allotted (Chiari malformation). Here, both the brain stem and the cerebellar tissues extend into the foramen magnum. Also, the vermis of the cerebellum may be either absent or partially complete. This type is mostly accompanied by a condition called as myelomeningocele, where the spinal cord protrudes through an opening resembling sac. Hence, partial paralysis or complete paralysis occurs below the spinal opening.

Type III CM:

This being the most serious, the brain stem and cerebellum herniates or bulges through the magnum and the spinal cord as well, causing serious neurological deficits. The spinal cord or brain covering bulges through the back of skull (occipital encephalocele) or back.

Type IV CM:

It is a rare form. Here, an underdeveloped or incomplete cerebellum, otherwise known as cerebellar hypoplasia is seen. Though, the cerebellar tonsils are situated normally, but the cerebellar parts are missing, thereby making portions of spinal cord visible.

Type 0 CM:

This type is still under debate. Here, no protrusion is present, yet the symptoms may be seen.

Prognosis

Type I CM

• Some are asymptomatic and some develop serious neurological consequences, where a greater degree of herniation of tonsil is seen.
• The prognosis in the surgically treated patients varies, and it mainly depends on factors like the symptoms during the time of diagnosis and the spinal cord’s recovery potential.
• Adult patients having associated syringomyelia or scoliosis develop the complications faster and have a poor prognosis to the surgical management.
• Spontaneous recovery is seen in very few patients.

Type II CM

• Infants under the age of 2 are at risk for developing complications and fatalities as a result of hindbrain herniation.
• The faster the diagnosis, greater is the prognosis.
• Surgical treatment shows greater prognosis

Diagnosis

1. Physical examination:

Functions of the cerebellum are assessed by checking the patient’s cognition, memory, balance, whereas the function of spinal cord is assessed by checking touch, sensation, motor skills and reflexes.

2. Radiograph:

However, head and neck X-ray may not rule out Chiari malformation, but the associated bone abnormalities may be identified, as the electromagnetic energy in the x-rays may produce images of certain tissues and bones.

3. Ultrasound:

Diagnosis can be made at the prenatal stage.

4. CT scan:

• It identifies hydrocephalus as well as bony abnormalities associated with Chiari malformation. It demonstrates the displacement (caudal) of the fourth ventricle.
• 3-D CT may be useful in determining, whether the brainstem is compressed by the surrounding pulsating arteries.

5. MRI scan:

• It is a non-invasive technique used for diagnosing CM, as neural tissue loss and excessive CSF accumulation are identified. The extent to which the cerebellar tonsils herniate downwards below the foramen magnum is the diagnostic criteria for CM, i.e., >5 mm.
• In Occipitoatlantoaxial Hypermobility, the herniation may be visible only with an ‘up-right’ scan. Retroflexed odontoid is also diagnosed using a 3-D CT scan. Invasive cranial traction confirms the diagnosis.

Treatment

Certain CMs do not exhibit any symptoms; hence, it does not cause interference in the daily living activities of a person. In the rest of the cases, medications may be given for pain relief.

Non-surgical management:

All patients should be given the following, irrespective of the need for surgery.

• Psychological support
• Rehabilitative therapy

Surgery

• The only treatment available for correcting the functional disturbances or halting the damage progression to the CNS is surgery.
• Surgical intervention causes a reduction in the presenting symptoms and prolonged relative stability, though multiple surgeries may be needed for treatment.

Type I CM (surgery):

It is important to determine,

• The anatomical malformation
• The main symptoms causing disability
• The relation of malformation to the symptoms seen

Things to do before proceeding to surgery

1. A multidisciplinary assessment involving the neurologist, neurosurgeons as well as the rheumatologists.
2. Correlation of opinions with the imaging results.

Surgical interventions:

1. Upper cervical laminectomy and suboccipital craniectomy:

This intervention decompresses the malformation seen at the foramen magnum, along with cord drainage. This gives good results.

2. Endoscopic third ventriculostomy:

This provides sufficient decompression. Patient with neurological signs like absent gag reflex, nystagmus, and abnormal cerebrospinal fluid flow into the hind brain benefit greater. Syringomeyelia associated with CM can be treated with surgery.

3. Electrocautery:

This enables the shrinkage of cerebellar tonsils by destruction of tissues that have high-frequency electric currents in them.

4. Spinal laminectomy:

This removes the spinal canal’s arched bony roof for increasing the spinal canal size, and relieves the pressure occurring on the nerve roots and the spinal cord as well.

5. Incision in brain dura:

This not only examines the spinal cord and brain, but also adds additional tissues to the dura for creating ample space for the CSF to flow.

Type II CM (surgery):

In infants under the age of 2, the meningomyelocele is decompressed surgically, and yields a better prognosis in morbidity and mortality reduction.

Recent research

• NINDS (The National Institute of Neurological Disorders and Stroke) coming under the National Institutes of Health supports as well as frequently conducts researches on the CNS disorders, which include Arnold-Chiari Malformation as well. The scientists are conducting researches for locating the responsible malformation causing genes seen in family members with CM or syringomyelia.
• Another study is being conducted to review an alternate surgical intervention for syringomyelia, which may correct the malformation excluding the need for cutting the spinal cord.
• A study is even comparing the conventional surgical intervention done post-birth for closing the opening seen on spine to the prenatal surgery. This study enrolls 200 women with fetuses having spina bifida to compare the efficacy and safety of the different available surgeries.
• Intrauterine myelomeningocele closure suggests that this procedure decrease the incidence of hydrocephalus (shunt dependent), and also restores the normal function of cerebellum and brainstem. After a year or two and half years post-operatively, the children’s bladder, kidney, motor function, brain development and developmental progress will be tested.

References

http://en.wikipedia.org/wiki/Arnold%E2%80%93Chiari_malformation

http://www.ninds.nih.gov/disorders/chiari/detail_chiari.htm

http://www.patient.co.uk/doctor/Arnold-Chiari-Malformation.htm

http://www.webmd.com/migraines-headaches/arnold-chiari-malformation-10486

http://www.columbianeurosurgery.org/conditions/chiari-malformation/