Part I of our Chiari Malformation Awareness Month Series
It’s Chiari Malformation Awareness Month and time to put this important neurological condition in the spotlight. It’s a subject near and dear to many EDS zebras, as it is a common comorbid condition to the Ehlers-Danlos Syndromes. Chiari Malformation can also be congenital and is believed to be the widest known cause of CM today, however it is possible this may be a misconception due to the failure of many to recognize the role that hypermobility and craniocervical instability may well play in the development of Chiari later in life.
There are also a number of socio-political factors that block the treatment and discovery of Chiari, which will be explored in the second part of this two part series. Part two will also include the firsthand perspectives and experiences of people who have a confirmed Chiari Malformation (CM) diagnosis so we can get an intimate picture of what it’s like to live with the condition, though it’s important to understand that like most chronic illnesses, no two people seem to experience CM quite the same. In this first post, we will walk through the basics of CM, learning what Chiari Malformation is, the four known types and how they are classified. Of course no informational post on a condition would be complete without exploring the known causes, symptoms, and treatments.
What is a Chiari Malformation?
It is said that the Chiari Malformation affects 1 in 1,000 people: However, the increased use of diagnostic imaging has shown that Chiari malformation may be much more common(1). Chiari Malformations are structural defects located at the in the base of the skull where the spine meets it. These structural defects can cause the brain to sag into the spinal canal, causing herniation of a portion of the cerebellum, cerebellar tonsils and/or the fourth ventricle. Depending on the severity, there are a variety of symptoms and complications that come with Chiari Malformation.
The cerebellum is the part of the brain that controls balance, memory, cognition and motor skills. Normally the cerebellum and parts of the brain stem sit above an opening in the skull that allows the spinal cord to pass through it. This is called the foramen magnum. In CM, part of the cerebellum extends below the foramen magnum and into the upper spinal canal, causing pressure on the cerebellum and brain stem that may affect functions controlled by the cerebellum and block the flow of cerebrospinal fluid (CSF).
Learn about Cerebrospinal Fluid and Lumbar Puncture: here.
There are four types of chiari malformation. According to the American Association of Neurological Surgeons, they are classified in the following ways:
Type I occurs during fetal development and is characterized by downward displacement by more than four millimeters, of the cerebellar tonsils beneath the foramen magnum into the cervical spinal canal. Anomalies of the base of the skull and spine are seen in 30-50 percent of patients with Chiari I malformation.
Type I is also believed to include the formation of Chiari Malformation through Craniocervical Instability, where CM often meets with EDS or another Hypermobility Spectrum Disorder (HSD), such as JHS, Marfan Syndrome, or Loey-Dietz Syndrome. According to the Pain Relief Foundation, “Craniocervical Instability (CCI), also known as the Syndrome of Occipitoatlantialaxial Hypermobility, is a structural instability of the craniocervical junction which may lead to a pathological deformation of the brainstem, upper spinal cord, and cerebellum. It primarily occurs in patients with Ehlers-Danlos Syndrome and other hereditary disorders of connective tissue (4).”
The Ehlers-Danlos Society notes that we need to develop a better understanding of the prevalence and variance of CM in EDS/HSD, along with educating neurosurgeons on the role of hypermobility may play in chiari malformations (5).
Type II is characterized by downward displacement of the medulla, fourth ventricle and cerebellum into the cervical spinal canal, as well as elongation of the pons and fourth ventricle. This type occurs almost exclusively in patients with myelomeningocele, a congenital condition in which the spinal cord and column do not close properly during fetal development.
Type III includes a form of dysraphism (a spectrum of congenital anomalies resulting from incomplete or aberrant neural tube fusion, 3.) with a portion of the cerebellum and/or brainstem pushing out through a defect in the back of the head or neck. These malformations are very rare and are associated with a high early mortality rate or severe neurological deficits in patients that survive.
Type IV is the most severe form and the rarest. The cerebellum fails to develop normally. There may be other associated malformations of the brain and brainstem. Most babies born with this malformation do not survive infancy (2).
Symptoms Associated with Chiari Malformation
According to the NIH’s Chiari malformation Fact List, the hallmark sign of Chiari malformation is headache, especially after sudden coughing, sneezing, or straining. Other symptoms may vary among individuals:
- neck pain
- hearing or balance problems
- muscle weakness or numbness
- difficulty swallowing or speaking
- ringing or buzzing in the ears (tinnitus)
- curvature of the spine (scoliosis)
- problems with hand coordination and fine motor skills
Some individuals with CM may not show any symptoms and symptoms may change or fluctuate, depending on personal physiology, the compression of the tissue and nerves and on the buildup of CSF pressure.
Infants with Chiari malformation may experience the following:
- difficulty swallowing
- irritability when being fed
- excessive drooling
- a weak cry
- gagging or vomiting
- arm weakness
- a stiff neck
- breathing problems
- developmental delays
- inability to gain weight (1).
Of course, this is just a basic list of the most common symptoms of CM. As mentioned, it is possible for a Chiari malformation to be present, but completely asymptomatic (free of any noticeable symptoms). In these patients, the condition is usually discovered through MRI taken for unrelated reasons. However, patients may experience symptoms in the future. It has also been known for symptoms to fluctuate over time.
As the condition progresses, there are many comorbid conditions that can develop with CM and different types have different symptoms. According to the NIH, common comorbid conditions include:
Hydrocephalus is an excessive buildup of CSF in the brain. A CM can block the normal flow of this fluid and cause pressure within the head that can result in mental defects and/or an enlarged or misshapen skull. Severe hydrocephalus, if left untreated, can be fatal. The disorder can occur with any type of Chiari malformation, but is most commonly associated with Type II.
Spina bifida is the incomplete closing of the backbone and membranes around the spinal cord. In babies with spina bifida, the bones around the spinal cord do not form properly, causing defects in the lower spine. While most children with this birth defect have such a mild form that they have no neurological problems, individuals with Type II Chiari malformation usually have myelomeningocele, and a baby’s spinal cord remains open in one area of the back and lower spine. The membranes and spinal cord protrude through the opening in the spine, creating a sac on the baby’s back. This can cause a number of neurological impairments such as muscle weakness, paralysis, and scoliosis.
Syringomyelia is a disorder in which a CSF-filled tubular cyst, or syrinx, forms within the spinal cord’s central canal. The growing syrinx destroys the center of the spinal cord, resulting in pain, weakness, and stiffness in the back, shoulders, arms, or legs. Other symptoms may include a loss of the ability to feel extremes of hot or cold, especially in the hands. Some individuals also have severe arm and neck pain.
Tethered cord syndrome occurs when a child’s spinal cord abnormally attaches to the tissues around the bottom of the spine. This means the spinal cord cannot move freely within the spinal canal. As a child grows, the disorder worsens, and can result in permanent damage to the nerves that control the muscles in the lower body and legs. Children who have a myelomeningocele have an increased risk of developing a tethered cord later in life.
Spinal curvature is common among individuals with syringomyelia or CM Type I. The spine either may bend to the left or right (scoliosis) or may bend forward (kyphosis).(1)
Diagnosis of Chiari Malformation
CM is typically diagnosed by a neurologist, preferrably one with an expertise in treating CM. The doctor will perform a physical exam and check the person’s memory, cognition, balance (functions controlled by the cerebellum), touch, reflexes, sensation, and motor skills (functions controlled by the spinal cord). The physician may also order an MRI, X-ray or CT. The most common imaging used is MRI. There are problems with diagnosing Chiari through the use of traditional supine positioning: However, this will be covered in our next post in this series.
Other tests the doctor might order, according to the AANS, include sleep or swallowing studies, a BAER test, myleogram, or SSEP (2).
Chiari Malformation Treatment
In the case of asymptomatic patients, no intervention is needed. However, monitoring of the patient, including regular check-ups, is usually recommended. In many cases, Chiari Malformation symptoms and disease progress may only be relieved or halted through surgical intervention. According to the NIH, these procedures are as follows:
The most common surgery to treat Chiari malformation is posterior fossa decompression (PFD). In the case of type II CM, a PFD is usually followed by a spinal fusion, where hardware is placed to create a supportive structure for the head and neck. This creates more space for the cerebellum and relieves pressure on the spinal cord.
The surgery involves making an incision at the back of the head and removing a small portion of the bone at the bottom of the skull. This procedure is known as a craniectomy. In some cases the arched, bony roof of the spinal canal, called the lamina, may also be removed to create sufficient space for the cerebellum. This procedure is referred to as a spinal laminectomy. The surgery should help restore the normal flow of CSF, and in some cases it may be enough to relieve symptoms while other patients show no improvement or even a worsening of post-operative symptoms.
Next, the surgeon may make an incision in the dura, the protective covering of the brain and spinal cord. Some surgeons perform a Doppler ultrasound test during surgery to determine if opening the dura is even necessary. If the brain and spinal cord area is still crowded, the surgeon may use a procedure called electrocautery to remove the cerebellar tonsils, allowing for more free space. These tonsils do not have a recognized function and can be removed without causing any known neurological problems.
The final step is to sew a dura patch to expand the space around the tonsils, similar to letting out the waistband on a pair of pants. This patch can be made of artificial material or tissue harvested from another part of an individual’s body.
Infants and children with myelomeningocele may require surgery to reposition the spinal cord and close the opening in the back. Findings from the National Institutes of Health (NIH) show that this surgery is most effective when it is done prenatally (while the baby is still in the womb) instead of after birth. The prenatal surgery reduces the occurrence of hydrocephalus and restores the cerebellum and brain stem to a more normal alignment.
Hydrocephalus may be treated with a shunt or tube that drains excess fluid and relieves pressure inside the head. These tubes drain the excess fluid into either the chest cavity or the abdomen so it can be absorbed and disposed of by the body.
An alternative surgical treatment in some individuals with hydrocephalus is third ventriculostomy, a procedure used to improve the flow of CSF. A small hole is made at the bottom of the brain cavity, diverting the CSF flow to relieve pressure. In cases where surgery was not effective, doctors may open the spinal cord and insert a shunt to drain a syringomyelia or hydromyelia, which is increased fluid in the central canal of the spinal cord (1).
Today, we learned about what Chiari malformation is, the four types and their symptoms, diagnosis and surgical interventions. The next post in this series on CM will explore the outcomes for patients with Chiari Malformation, along with the socio-economic impacts that affect receiving treatment of this complex disorder in both private and public healthcare settings. It’s now available here: The Issues of Diagnosis and Treatment of Chiari and Craniocervical Instability
Then our final post will include interviews by people who have either received, or are awaiting treatment along with information about another group of patients, who strongly suspect CM, but cannot even get the proper the imaging for confirmation due to the strictures these socio-economic factors create. It’s now available here: 7 People with Chiari and CCI Share Their Stories
Let’s start the conversation early! Are you one of the suspected undiagnosed? Have you been diagnosed and/or treated? Let us know your story in the comments! And as always, thanks for joining us for this educational post about Chiari malformation.
Resources and Related Reading:
- National Institute of Health. Chiari Malformation Fact Sheet.
- AANS. Chiari Malformation.
- Science Direct. Learn more about Spinal Dysraphism.
- The Pain Relief Foundation. What is Craniocervical Instability?
- The Ehlers-Danlos Society. Neurological and Spinal Manifestations of the Ehlers-Danlos Syndromes (for Non-experts).
- NORD. Chiari Malformations.
- Conquer Chiari Website
- Piper, RJ, et al. The BMJ. Chiari malformations: principles of diagnosis and management