Chiari Bridges

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  • Overview: Chiari Malformation [Revised]

    Overview: Chiari Malformation [Revised]

    CHIARI MALFORMATIONS (PRONOUNCED: KEE-AH-REE) ARE STRUCTURAL DEFECTS IN WHICH THE CEREBELLUM, THE HIND PART OF THE BRAIN, DESCENDS BELOW THE FORAMEN MAGNUM INTO THE SPINAL CANAL.

    While Arnold Chiari Malformation (Type 2) was first identified in the late 19th century by the Austrian pathologist Hans Chiari, much of the current medical knowledge has developed since 1985 with the expanded use of Magnetic Resonance Imaging (MRI). The number of patients diagnosed with Chiari malformations continues to increase, and with that increase Chiari Malformation is getting some of the attention the condition has always demanded.

    Chiari malformations (“CMs”) are neurological disorders in which the cerebellum extends out of the skull and into the spinal canal, which in turn blocks the flow of cerebrospinal fluid, puts pressure on the brainstem and spine, and may result in varying degrees of nerve compression. Once thought to occur in 1 in 1000 people, it is now believed to be much more frequent of an occurrence. A 2016 pediatric study found it to occur in 1 in 100 children[1]. However, since the most common type (Type 1) tends to become symptomatic during late teens and early adulthood, it is likely to be much more common when adults are factored in. Females are more likely than males to have a Chiari Malformation (at a ratio of 3:1), and significantly higher amongst those with both Chiari Malformation and Ehlers-Danlos Syndrome (9:1)[2]. We affectionately refer to those that live with this condition, including the attendant pain and frequent disregard from the medical community, as Chiarians (regardless of whether they have had surgical intervention or not).

    While some Chiarians are symptomatic throughout their lifetime, the vast majority of Chiarians (those with Type 1) develop symptoms in their late teens or early adulthood. Those symptoms can range from mild to crippling, and can become severe enough to cause paralysis (often associated with syringomyelia) or death.


    WHAT CAUSES A CHIARI MALFORMATION?

    Multiple factors have been identified which can either cause or attribute to Chiari malformations. Although they too were once thought to be rare, Acquired Chiari malformations are now being diagnosed in increasing numbers. A brief overview of what each of these labels entail, together with a summary of the different types of CM’s, is provided below:

    • Congenital Chiari, is believed to be caused by a posterior cranial fossa hypoplasia (PCFH)[3], which can also be caused by a connective tissue disorder such as Ehlers-Danlos.[4] While the cerebellum continued to grow in utero, the posterior skull failed to grow proportionately. Problems resulting from this size discrepancy continue and eventually the overcrowding of the hindbrain squeezes the cerebral tonsils downward into the opening of the spinal canal (cranial constriction). While the herniation of the cerebellar tonsil(s) can take place during gestation or after birth, because the cause is 100% congenital, and the process most likely began in utero, it is usually considered a Congenital Chiari Malformation when the only pathology found is a small posterior cranial fossa. In one large study, they found those with a Chiari Malformation and no associated etiological/pathological co-factors, with only slightly over 52% having a small PCF. When other co-factors were present, the number of Chiarians found with a small PCF plummeted, and therefore it should be considered acquired until proven otherwise.[5]

    • Acquired Chiari can have one or more possible pathological co-factors; any of which can result in the descent of the cerebellar tonsils. Many Chiarians often mistakenly conceptualize an Acquired Chiari Malformation as being brought on only by trauma; however, “acquired” is an antonym for “congenital,” so an Acquired Chiari Malformation in medical terms is one that a person was not born with. While this can include Acquired Chiari malformations resulting from trauma, it can also include Acquired Chiari malformations resulting from a variety of other medical conditions:
      • Heritable Disorders of Connective Tissue (HDCTs), most commonly Ehlers-Danlos Syndromes (EDS), make the tonsils more prone to prolapse below the foramen magnum.
      • Multiple conditions are known to create a pushing/pulling effect that can result in a tonsillar herniation. These conditions include: Intracranial Hypertension (IH), Atlantoaxial Instability and Craniocervical Instability (AAI/CCI), Tethered Cord Syndrome (TCS), and Intracranial Hypotension (cerebrospinal fluid leaks), Hydrocephalus, and a variety of cysts and brain tumors.[2]

      Special care should be taken when any of these co-morbid conditions exist in conjunction with a Chiari Malformation. Before the consideration of decompression surgery, a plan should be developed which addresses each possible comorbid condition before decompression. This can reduce the likelihood of complications and/or a failed decompression surgery.

    SEVEN TYPES OF CHIARI MALFORMATIONS WORTH DISCUSSING (asterisks “*” indicate commonly known types)

    Chiari Zero:  The lower part of the cerebellum (the cerebral tonsils) are blocking the foramen magnum, but are not descended through. Because of the cerebellum’s position, it blocks the flow of cerebrospinal fluid and all the effects of that blockage are comparable to Type 1.

    Diagnosis Requirements: Symptomology; MRI showing no herniation but the low-lying tonsils that are pressing against the top of the foramen magnum; MRI showing a syrinx (despite the name, Chiari Zero is classified under Syringomyelia and not Chiari Malformation – so a syrinx is technically required for diagnoses). [6][7]

    Treatment Options: With few symptoms, non-surgical treatments might be recommended. When a syrinx is present, a decompression is often recommended before the syrinx has a chance to further develop and cause additional damage to the spine. However, even when a syrinx is present, all pathological cofactors should be explored and addressed prior to decompression surgery.

    Chiari 0.5: In cases of Chiari 0.5, the lower part of the cerebellum (the cerebral tonsils) are descended through the foramen magnum, but descends < 5mm (which is the measurement that some doctors use to define Chiari). Usually labeled “tonsillar ectopia” on radiology reports, the symptoms and effects of the obstruction are generally the same as those experienced with Type 1 or Chiari 1.5.[3]

    Diagnosis Requirements: Symptomology; MRI showing a herniation of < 5mm, unless already properly diagnosed with a Type 1 or Chiari 1.5; presence of a syrinx is not “required” for diagnosis, but as with Chiari Zero, it illustrates that it is causing a problem obstructing the flow of cerebrospinal fluid and may be relevant when deciding between various courses of treatment.

    Treatment Options: The same as Type 1 or Chiari 1.5, respectively.

    *Chiari Malformation Type 1: The most common type of Chiari Malformation, Type 1 is diagnosed when the cerebral tonsils descend below the foramen magnum. Medical professionals unfamiliar with current research surrounding Chiari Zero and Chiari 0.5 (and the symptomology surrounding the blockage of cerebrospinal fluid), believe that a tonsillar herniation of less than 5mm is simply a tonsillar ectopia and only diagnose a Chiari Malformation when the descent is > 5mm. However, the 5mm requirement is controversial, and many doctors now base their diagnoses not solely on measurements, but rather on symptomology and a combination of other factors, including cine MRI’s, a patient’s symptoms, and other relevant factors.[6] Many people with a Chiari Zero, Chiari 0.5, or Type 1 can be asymptomatic for a lifetime: one large study found that approximately 30% of those with a CM measuring between 5-10mm were asymptomatic.[8] If symptoms develop, they often present in adolescence or early adulthood. Anecdotal evidence supports the proposition that once symptoms start, the symptoms often progress rapidly until the damage is stopped surgically.

    Diagnosis Requirements: Symptomology; MRI indicating at least one herniated tonsil (without the brainstem descending as well).[9]

    Treatment Options: Prior to surgery any/all comorbidities should be explored and treated especially if you are found to have a normal sized posterior fossa. However, if you have classic Chiari 1 Malformation with a small posterior fossa, the risks of surgery should be weighed against the severity of symptoms and the impact that symptoms are having on the patient’s quality of life. It is often recommended to treat mild symptoms with medication, with surgical options typically reserved for cases in which symptoms cause more serious medical and quality of life problems. However, symptoms do tend to progress, and studies have shown a correlation between successful decompression surgery and the amount of time between the onset of any symptoms and surgical intervention[10]. See “Decompression Surgery” below.

    Chiari 1.5: This type of CM (often referred to as a “Complex Chiari”) is often acquired as opposed to congenital.  Chiari 1.5 should be the diagnosis when the tonsil(s) and all/part of the lower brainstem (the medulla oblongata) has descended past the foramen magnum. This is usually indicative of another comorbid condition pushing the brainstem downward from above or pulling downward from below.[5][11][12]

    Diagnosis Requirements: symptomology; MRI indicating at least one herniated tonsil AND a downward displacement of all/part of the brainstem; without the other radiological findings associated with Type 2.

    Treatment Options: Treatment options can vary significantly from patient to patient depending on the cause of the Chiari 1.5. While a variety of medical options might initially be used to treat symptoms, it is extremely important that all possible causes and/or comorbidities are thoroughly investigated and treated prior to the consideration of decompression surgery. Failure to identify and treat any such conditions can increase the likelihood of a failed decompression and further complications such as brain slumping, increased cervical instability, etc.

    *Chiari Malformation Type 2 (also known as Arnold Chiari Malformation): Type 2 involves a herniation of the cerebellar tonsils and lower part of the brainstem (the medulla oblongata). Unlike in Chiari 1.5, in Type 2 the fourth ventricle is usually herniated, all/part of the cerebellar vermis (the tissue connecting both halves of the cerebellum) is missing or herniated, the corpus callosum (nerve fibers connecting both hemispheres of the brain) is fully/partially absent (agenesis), and it is almost always accompanied by a myelomeningocele (the most serious form of Spina Bifida, a congenital neural tube defect where the spinal canal does not close properly).[13][14][15]

    Diagnosis Requirements: While a myelomeningocele is usually evident and diagnosed at birth, a brain MRI should confirm the radiological aspects of Type 2.

    Treatment Options: Myelomeningocele is usually treated surgically at birth. If other related problems develop, such as hydrocephalus and/or tethered cord, they are often dealt with surgically as they become problematic. While some with Type 2 are decompressed, anecdotal evidence reflects a general trend of an increased failure rate with decompression surgeries as compared to those with Type 1. Because of this, some neurosurgeons choose not to decompress those with Type 2.

    *Chiari Malformation Type 3: Type 3 is a serious type of Chiari Malformation involving herniated cerebellar tonsils, brainstem, and fourth ventricle. However, in most cases of Type 3, a sac forms out of the back of the skull (encephalocele) that contains brain matter from the cerebellum and the meninges. Type 3 causes severe neurological problems that are evident at birth and has a high infant mortality rate.[16][17]

     *Chiari Malformation Type 4: Type 4 is the most severe type of Chiari Malformation, but does not involve a hindbrain herniation (and therefore arguments have been made that it is not a Chiari Malformation). Instead, it consists of an undeveloped or underdeveloped cerebellum. Most infants born with Type 4 die in infancy.[16][17]


    S    URGICAL INTERVENTION 

    Decompression surgery is currently the only available means of attempting to stop the progression of symptoms of a congenital chiari (with no other pathological cofactors), but decompression is not a cure (not even close). Statistics show that up to 69% of decompressed patients find some measure of relief from surgery (usually headaches)[18]. Most neurosurgeons will give only a 50% chance of helping each individual symptom. Some of the symptoms are irreversible once they develop. Recent studies show that there is a correlation between early surgical intervention and positive post-surgical outcomes.[19] However, we cannot over emphasize the importance of your doctors taking time to find, diagnose, and treat co-morbid conditions BEFORE decompression surgery. If they are not willing to consider comorbidities, they are probably not the doctor for you!

     

     

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    *Original version released January 2018, revised October 2018.

     

    References:

    1     Eltorai, Ibrahim M. “Rare Diseases and Syndromes of the Spinal Cord” Cham: Springer International Publishing: Imprint: Springer, 2016. Page 43, 15.2, <www.springer.com/us/book/9783319451466>.

    2 Henderson, Fraser C., et al. “Neurological and Spinal Manifestations of the Ehlers–Danlos Syndromes.” American Journal of Medical Genetics Part C: Seminars in Medical Genetics, 21 Feb. 2017, <www.onlinelibrary.wiley.com/doi/10.1002/ajmg.c.31549/full>.

    3 Sekula, Raymond F, et al. “Dimensions of the Posterior Fossa in Patients Symptomatic for Chiari I Malformation but without Cerebellar Tonsillar Descent.” Cerebrospinal Fluid Research, BioMed Central, 2005, <www.ncbi.nlm.nih.gov/pmc/articles/PMC1343586>.

    4 Stagi, Stefano, et al. “The Ever-Expanding Conundrum of Primary Osteoporosis: Aetiopathogenesis, Diagnosis, and Treatment.” Italian Journal of Pediatrics, BioMed Central, 2014, <www.ncbi.nlm.nih.gov/pmc/articles/PMC4064514>.

    5 Milhorat, Thomas H., et al. “Mechanisms of Cerebellar Tonsil Herniation in Patients with Chiari Malformations as Guide to Clinical Management.” Acta Neurochirurgica, Springer Vienna, July 2010, <www.ncbi.nlm.nih.gov/pmc/articles/PMC2887504>.

    6 Isik, N, et al. “A New Entity: Chiari Zero Malformation and Its Surgical Method.” Turkish Neurosurgery., U.S. National Library of Medicine, <www.ncbi.nlm.nih.gov/pubmed/21534216>.

    7 “JNS JOURNAL OF Neurosurgery OFFICIAL JOURNALS OF THE AANS since 1944.” The Resolution of Syringohydromyelia without Hindbrain Herniation after Posterior Fossa Decompression | Journal of Neurosurgery, Vol 89, No 2, <www.thejns.org/doi/abs/10.3171/jns.1998.89.2.0212?url_ver=Z39.88-2003&rfr_id=ori%3Arid%3Acrossref.org&rfr_dat=cr_pub%3Dpubmed>.

    8 Elster, A D, and M Y Chen. “Chiari I Malformations: Clinical and Radiologic Reappraisal.”Radiology., U.S. National Library of Medicine, May 1992, <www.ncbi.nlm.nih.gov/pubmed/1561334>.

    9 Wilson, Eugene. “Chiari.” CEDSA Home, <www.cedsa.org/index.php/59-quick-reference/73-chiari.html>.

    10 Hindawi. “Surgical Management of Patients with Chiari I Malformation.” International Journal of Pediatrics, Hindawi, 28 June 2012, <www.hindawi.com/journals/ijpedi/2012/640127>.

    11 Kim, In-Kyeong, et al. “Chiari 1.5 Malformation : An Advanced Form of Chiari I Malformation.”Journal of Korean Neurosurgical Society, The Korean Neurosurgical Society, Oct. 2010, <www.ncbi.nlm.nih.gov/pmc/articles/PMC2982921>.

    12 Malik, Amita, et al. Chiari 1.5: A Lesser Known Entity. Annals of Indian Academy of Neurology, <www.annalsofian.org/article.asp?issn=0972-2327;year=2015;volume=18;issue=4;spage=449;epage=450;aulast=Malik>.

    13 Wolpert, Samuel M, et al. “Chiari II Malformation: MR Imaging.” American Journal of Roentgenology, <www.ajronline.org/doi/pdf/10.2214/ajr.149.5.1033>.

    14 Yumer, M H, et al. “Chiari Type II Malformation: a Case Report and Review of Literature.”Folia Medica., U.S. National Library of Medicine, <www.ncbi.nlm.nih.gov/pubmed/16918056>.

    15 Kim, Irene. “Chiari II Decompression in Patients with Myelomeningocele in the National Spina Bifida Patient Registry (NSBPR).” <http://spinabifidaassociation.org/sbworldcongress/wp-content/uploads/sites/10/2017/04/B.4-Kim-Neurosurgery.pdf>.

    16 “Chiari Malformation Fact Sheet.” National Institute of Neurological Disorders and Stroke, U.S. Department of Health and Human Services, <www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Fact-Sheets/Chiari-Malformation-Fact-Sheet>.

    17 “Chiari Malformations.” NORD (National Organization for Rare Disorders), <www.rarediseases.org/rare-diseases/chiari-malformations>.

    18 14 Aliaga, L, et al. “A Novel Scoring System for Assessing Chiari Malformation Type I Treatment Outcomes.” Neurosurgery., U.S. National Library of Medicine, Mar. 2012, <www.ncbi.nlm.nih.gov/pubmed/21849925>.

    19  Siasios, John, et al. “Surgical Management of Patients with Chiari I Malformation” International Journal of Pediatrics, Article ID 640127, Hindawi, 2012, <www.hindawi.com/journals/ijpedi/2012/640127>.

  • Overview: Craniocervical Instability and Related Disorders

    Overview: Craniocervical Instability and Related Disorders

    Craniocervical Instability and related pathologies of the craniocervical junction are an important topic for anyone diagnosed with Chiari 1 malformation. “Complex Chiari,” or the presence of craniovertebral abnormalities or instability in addition to the presence of cerebellar tonsillar herniation, is present in approximately one fourth of all cases of Chiari 1 malformation[1]. These cases usually involve the presence of a genetic connective tissue disorder and are thought by experts to be the cause of most Chiari decompression failures[2]. When the doctor and patient alike are not knowledgeable about these conditions and the additional symptoms that often accompany them, these more complex cases are often treated with a standard decompression, which can actually weaken the stability of the craniocervical junction more, and result in an increase of symptoms rather than a clinical improvement. Understanding what signs and symptoms to look for that may indicate that your Chiari is more complex, is vital in receiving the appropriate treatment the first time. This is especially important considering that, according to Chiari expert Paolo Bolognese, M.D., “[with revision surgeries], the results are not as good as if you had done the posterior decompression well the first time.”[3]

    Punjabi and White define instability as the “loss of the ability of the spine under physiological loads to maintain relationships between vertebrae in such a way that there is no damage or subsequent irritation of the spinal cord, (brain stem) or nerve roots, and in addition that there is development of deformity or incapacitating pain due to structural changes.”[4] This means that the ligaments and muscles that normally hold the spine together, are too weak or damaged to handle the normal range of motion and weight of anatomic structures. For example, in Craniocervical Instability, the neck is not strong enough to support the normal weight of the head, without elements of the spine moving in such a way that it causes pain or damage to the nervous system (spinal cord, brain stem, and even cranial nerves). The result is that the bones that make up the lower skull and upper spine get pushed out of their normal anatomic location and begin to impinge on or cause stretching of these parts of the nervous system.

    Craniocervical Instability can result from or be exacerbated by a trauma, such as a severe whiplash injury. However, many cases of CCI are associated with some sort of connective tissue disorder, such as a heritable disorder of connective tissue (HDCT, like Ehlers-Danlos Syndrome or Marfan’s), or an autoimmune condition that affects the connective tissue (such as Rheumatoid Arthritis), or a few other rarer conditions that affect the integrity of bony structures in the skull and spine. Instability can result either from lax ligaments and other connective tissues, soft bones (also seen in HDCTs) or from something like pannus formation, where repeated rubbing together of the joints causes a build-up of granulated tissue around bony structures and changes the way certain bones lie in relationship to one another[5]. Craniocervical Instability can also result as a complication of Chiari decompression surgery, when too much bone is removed from the skull, resulting in the instability of the skull on the top of the spine[6].

    In the patient community, the term “CCI” is often used in reference to both Craniocervical Instability and Atlantoaxial Instability (AAI). CCI is often used to refer to the commonly seen combination of issues with the craniocervical junction, that include the instability of the joints where the skull meets the C1 vertebrae (which is true CCI), the instability of the joints between C1 and C2 (true AAI), a retroflexed odontoid, pannus formation, and a kyphotic clivo-axial angle (which are all forms of basilar impression/invagination). But CCI really should refer to the movement of the skull with respect to the spine. This sliding is referred to as “translation” and is measured on dynamic imaging in millimeters. The pathological threshold for the degree of translation of the basion with respect to the odontoid process between flexion and extension is 2mm, and any amount of translation greater than 1mm is capable of producing symptoms7. Likewise, at the C1-C2 joint, instability in the form of AAI can cause an excessive uncovering of the joint facets. Facets are the surfaces of the vertebrae that articulate with next vertebra. An uncovering of the facets that exceeds 20% is considered pathological.

    The occipito-atlantic joint allows for about half of the cervical spine’s ability to flex and extend (tilt forward and backward). Likewise, the atlantoaxial joint [the articulation between C1 (atlas) and C2 (axis)] accounts for about half of the cervical spine’s ability to rotate the head. Because of this, these vertebrae lack the same amount of stability as the remainder of the spine, and ligaments are largely responsible for their stability[8]. Therefore, ligamentous laxity, as seen in connective tissue disorders, make these areas of the spine particularly prone to pathologic instability. Symptoms of AAI may include visual changes, syncope (fainting) or near-syncopal episodes, dizziness, nausea, facial pain, difficulty swallowing, choking, respiratory issues, and upper cervical tenderness. These symptoms will usually improve with the use of a neck brace[9]. For patients with connective tissue disorders, as are seen in 12-20% of patients diagnosed with Chiari, dynamic imaging is very important in identifying potential instability. The ideal tests to diagnose CCI and AAI are an upright MRI with flexion and extension and a 3D CT with rotational views, respectively[10]. It is important to note that ventral brain stem compression may not be seen on traditional supine MR imaging, while it may be very evident on dynamic imaging.

    Basilar Invagination and Basilar Impression are also often seen with instability. They are almost identical to one another, and refer to upward displacement of the bones of the spine. However, technically, Basilar Invagination is caused by this deformation with normal bone, while Basilar Impression results from softening of bone[11]. For our purposes, this distinction is less important, but we will discuss any displacement in terms of “Basilar Invagination,” or “BI” for short. Forms of Basilar Invagination now include the prolapse of the odontoid process through the foramen magnum (the original condition described by the term), cranial settling, a kyphotic clivo-axial angle, and a retroflexed odontoid[12]. The kyphotic clivo-axial angle is an important and relatively easy measurement to indicate potential deformative stress on the brain stem. The clivus is a wedge-shaped bone that normally lies above and ventral to the top of spine. When it lies more horizontally, it creates a sharp angle that results in a bending of the brainstem. The odontoid peg (also called the odontoid process or the dens) is the part of the C2 vertebrae, or Axis, that the skull pivots upon, so named because of its tooth-like shape. A retroflexed odontoid occurs when the odontoid is bent backwards, often compressing the front of the brain stem. Other important measurements involving ventral brain stem compression for a kyphotic clivo-axial angle and/or retroflexed odontoid include the Grabb-Oakes and Harris measurements.

    • The clivoaxial angle is measured by drawing a line along the posterior (back, or when lying more horizontal, the top) side of the lower clivus and intersecting that line with a line drawn on the posterior side of the axis.  If the angle created is less than 135°, it is considered pathological.  Like instability, a kyphotic clivoaxial angle is often seen in patients with connective tissue disorders and degenerative rheumatoid disease[13].  See figure 1 below.
    Left – Clivoaxial Angle (CXA). Right – Grabb-Oakes measurement.

    For the Grabb-Oakes measurement, a line is drawn from the basion (the midpoint of the anterior margin of the foramen magnum) to the inferior posterior C2. A perpendicular line is then drawn from the center of this line to the dura of the brain stem. A Grabb-Oakes measurement greater than 9 mm denotes a form of basilar invagination. This is a very helpful measurement for determining how much a retroflexed odontoid is compressing the brain stem. See Figure 2 above.

    The Harris measurement is the distance between the basion and the Posterior Axial Line. This distance should not be more than 12 mm. A measurement of more than 12 mm also denotes instability. This measurement can also be used to measure the translation between flexion and extension in dynamic imaging[14]. See Figure 3.

    Harris measurement

    Symptoms of ventral brain stem compression can occur with various types of BI and instability. They may be referred to together as a “cervicomedullary syndrome” and may include[15]:

    • A heavy headache (often referred to as feeling like a “bobblehead” or feeling like the head is a “bowling ball”)
    • A Chiari-type pressure headache aggravated by Valsalva maneuvers (because these conditions, like Chiari, can also cause flow issues)
    • Dysautonomia (including tachycardia, heat intolerance, orthostatic intolerance, syncope (fainting), polydipsia (extreme thirst), delayed gastric emptying, chronic fatigue)
    • Neck pain (often severe)
    • Central or mixed sleep apnea
    • Facial pain or numbness – Occasionally, including Trigeminal Neuralgia
    • Balance and coordination impairment
    • Muscle weakness
    • Dizziness and vertigo
    • Vision problems, including double vision and downward nystagmus
    • Reduced gag reflex and dysphagia (difficulty swallowing)
    • Tinnitus (ringing in the ears) and hearing loss
    • Nausea and vomiting
    • Paralysis
    • In more severe cases, non-epiform seizures have also been documented

    In addition to producing significant pain and neurological symptoms, the compression and kinking of the brain stem can cause significant injury to the brain stem neurons by stretching the axons of the nerves to the point that they break and recoil, producing what are called “axon retraction bulbs” that can be seen on microscopic examination of the cells. The stress placed on the brain stem by both compressing and stretching simultaneously is much greater than the mere sum of these two mechanisms. Interestingly, during the flexion of the normal spine, it stretches 17% of its length. Research has shown that the axon of a giant squid fails when stretched to 20% if its length. Therefore, the normal motion of the human neck brings us very close to injuring our brain stem. Consequently, it only takes a slight alteration of our normal anatomy to cause injury to these delicate nervous tissues[16].

    Treatment of Craniocervical Instability typically begins with more conservative medical management, such as neck bracing, activity limitation, physical therapy (including isometrics, sagittal balance, core strengthening and cardio), and pain management. Other causes of symptoms such as co-morbid conditions, multiple sclerosis, dystrophy, mitochondrial disorders, vitamin deficiencies and Lyme disease should be ruled out or treated. However, surgical intervention via a craniocervical fusion is indicated when the following criteria are met:

    Severe headache or neck pain >7/10
    AND cervicomedullary syndrome
    AND neurological deficits referable to the craniocervical junction
    AND radiological findings indicative of instability

    Surgeons and patients alike should consider surgery after medical management has been maximized and the patient has shown a positive response to neck bracing[10].

    Various specific surgical techniques are applied in craniocervical fusions. A more common technique is the open reduction and fusion stabilization procedure. This procedure involves stabilizing the head with screws, making an incision that exposes the occiput through C2, and fixing plates to the occiput which attach to the C1 and C2 (and sometimes C3) vertebrae with rods. A newer technique adapted by Dr. Paolo Bolognese is using a less invasive Chiari decompression surgery known as MIST (minimally invasive subpial tonsillectomy) along with a fusion using screws placed in the occipital condyles. Although the dura is opened to partially resect the tonsils, a duraplasty is not done. Advantages of this procedure include a smaller incision, smaller hardware, less bone removal, and a thicker bone for which to insert screws in the occiput. Risks of both methods include vertebral artery injury, and a slightly increased risk for segmental instability below the fusion, along with the standard risks of any surgical procedure, such as bleeding, infection, and complications from anesthesia. Both procedures demand the hands of a very skilled and experienced surgeon because vital structures lie in and around the area. Using condylar screws may increase the risk of injury to major vessels, particularly in the hands of a less experienced surgeon. An important cranial nerve also lies just deep to the occipital condyles, making precise screw placement extremely important. This may limit the procedure in becoming more widely used, but the resulting fusion may be stronger, despite the reduced amount of hardware[17].

    In the presence of a retroflexed odontoid, an open reduction, fusion and stabilization procedure may be enough to relieve ventral brain stem compression. However, in more severe cases, a further surgery called an odontoidectomy may be needed to remove the odontoid process. This surgery may be done through the mouth or the nose[18].

    Every Chiari patient should be aware of hereditary connective tissue disorders and the signs and symptoms of Craniocervical Instability and Basilar Invagination. Many neurosurgeons do not evaluate their patients for these conditions prior to performing Chiari decompression surgery, often resulting in the need for revision surgeries and poor results. Being an educated patient can help you ask the right questions and insist on the proper evaluation and testing to avoid the pitfalls that many other patients have faced.

    References:

    1 Bolognese, Paolo A, director. Surgical Techniques for Chiari Malformations. YouTube, American Syringomyelia Chiari Alliance Project, 16 Mar. 2015, <www.youtu.be/KfYmJnB6sPQ>.

    2 Bolognese, Paolo A. “Modern Classification and Subclassification of Chiari Malformations.”YouTube, American Syringomyelia Chiari Alliance Project, 16 Mar. 2015, <www.youtu.be/ZQ9ZmquN-M0>.

    3 Bolognese, Paolo A. “2016 ASAP CM/SM Conference – ‘Complex Posterior Fossa’ – Bolognese.” YouTube, American Syringomyelia Chiari Alliance Project, 7 Dec. 2016, <www.youtu.be/3jKH_DHadO8>.

    4 Augustus A. White III, Manohar M. Panjabi, et al. “Clinical Biomechanics of the Spine.” By Augustus A. White III, <www.leomed.at/listhoscan/white_90.pdf>

    5 The Pain Relief Foundation, The Pain Relief Foundation, <www.thepainrelieffoundation.com/craniocervical-instability/>.

    6 Bolognese, Paolo. Complex Posterior Fossa revisions. YouTube. December 7, 2016. <www.youtu.be/3jKH_DHadO8>.

    7 Menezes, Arnold H. “Craniovertebral Junction Anomalies: Diagnosis and Management.”Seminars in Pediatric Neurology, vol. 4, no. 3, Sept. 1997, <www.sempedneurjnl.com/article/S1071-9091(97)80038-1/fulltext>.

    8 Yang, Sun Y., et al. “A Review of the Diagnosis and Treatment of Atlantoaxial Dislocations.”Global Spine Journal, Georg Thieme Verlag KG, Aug. 2014, <www.ncbi.nlm.nih.gov/pmc/articles/PMC4111952/>.

    9 Henderson, Fraser C., et al. “Neurological and Spinal Manifestations of the Ehlers–Danlos Syndromes.” American Journal of Medical Genetics Part C: Seminars in Medical Genetics, <www.onlinelibrary.wiley.com/doi/10.1002/ajmg.c.31549/full>.

    10 Henderson, Sr. , Fraser C. “Neurological Management of Hereditary Disoders of Hypermobility Connective Tissue Disorders.” Ehlers-Danlos Society Annual Conference 2015. Ehlers-Danlos Society Annual Conference 2015, 14 Aug. 2015, Baltimore, <www.ehlers-danlos.com/2015-annual-conference-files/Henderson_0.pdf>.

    11 Hain, Timothy C. “Basilar Invagination, Basilar Impression and Atlantoaxial Subluxation.”Basilar Invagination, Basilar Impression and Atlantoaxial Subluxation, 19 Apr. 2013, <https://dizziness-and-balance.com/disorders/central/cerebellar/basilar_invagination.htm>.

    12 Kim, Louis J., et al. “JNS JOURNAL OF Neurosurgery OFFICIAL JOURNALS OF THE AANS since 1944.” Treatment of Basilar Invagination Associated with Chiari I Malformations in the Pediatric Population: Cervical Reduction and Posterior Occipitocervical Fusion | Journal of Neurosurgery: Pediatrics, Vol 101, No 2, Nov. 2004, <www.thejns.org/doi/abs/10.3171/ped.2004.101.2.0189?url_ver=Z39.88-2003&rfr_id=ori%3Arid%3Acrossref.org&rfr_dat=cr_pub%3Dpubmed>.

    13 Henderson, Sr. , Fraser C. “Cranio-Cervical Instability in Patients with Hypermobility Connective Disorders.” OMICS International, OMICS International, 18 Apr. 2016, <www.omicsgroup.org/journals/craniocervical-instability-in-patients-with-hypermobility-connective-disorders-2165-7939-1000299.php?aid=71754#11>.

    14 Bono, C M, et al. “Measurement Techniques for Upper Cervical Spine Injuries: Consensus Statement of the Spine Trauma Study Group.” Spine., U.S. National Library of Medicine, 1 Mar. 2007, <www.ncbi.nlm.nih.gov/pubmed/17334296>.

    15 Henderson, Sr. , Fraser C. “Diagnosis and Treatment of Craniocervical Instability in the Chiari Patient.” Chiari and Syringomyelia Foundation Educational Lecture. 20 July 2011, Greater Metropolitan Washington Area, Greater Metropolitan Washington Area, <www.youtu.be/U33T8JFXvk0>.

    16 Henderson, F C, et al. “Neuropathology of the Brainstem and Spinal Cord in End Stage Rheumatoid Arthritis: Implications for Treatment.” Annals of the Rheumatic Diseases, U.S. National Library of Medicine, Sept. 1993, <www.ncbi.nlm.nih.gov/pmc/articles/PMC1005138/>.

    17 Bolognese, Paolo A. “Surgical Techniques for Chiari Malformations.” YouTube, American Syringomyelia Chiari Alliance Project, 16 Mar. 2015, <www.youtube.com/watch?v=KfYmJnB6sPQ>.

    18 Hwang, Steven W., et al. “C1–C2 Arthrodesis after Transoral Odontoidectomy and Suboccipital Craniectomy for Ventral Brain Stem Compression in Chiari I Patients.”European Spine Journal, Springer-Verlag, Sept. 2008, <www.ncbi.nlm.nih.gov/pmc/articles/PMC2527411/>.