Chiari Bridges

Tag: Idiopathic Intracranial Hypertension

  • The Important Questions to Ask Your Neurosurgeon [Revised]

    The Important Questions to Ask Your Neurosurgeon [Revised]

    Most Chiarians go to see a surgeon with an expectation of them being knowledgeable in their field. However, while they might be a neurosurgeon, their knowledge of Chiari and its comorbid/pathological conditions might not rank high in their practice. Make the most of your initial appointment by interviewing them and what they really know about Chiari Malformations. Be cautious of inflated success rates. Chiari decompression in general offers a just over a 50% success rate (which means it has a nearly 50% failure rate). Surgeons that claim a 100% (or near 100% success rate) are usually not basing their success on how their patients feel afterward, it is based on if they were successful with the aspects of the surgery:
             Removal of the occipital bone ✓
              Opening the dura and adding the patch/graft ✓
              Laminectomy ✓
              Cauterization/resection of cerebellar tonsils ✓

    WE DESERVE BETTER THAN THAT!

    HERE IS A LIST OF CHIARI QUESTIONS WE RECOMMEND ASKING AT YOUR FIRST NEUROSURGERY APPOINTMENT:

    General Questions:

    • How do you define a Chiari Malformation?
    • What do you believe causes a Chiari malformation?
      • Are all Chiari malformations from a small posterior fossa?
      • Do I have a small posterior fossa? If yes, how big is it? If size is unknown, was my posterior fossa measured? If not, why not? How did you come to the conclusion that I have a small posterior fossa?
      • How common do you believe Acquired Chiari malformations to be?
    • Do you always recommend decompression surgery for all of your patients with herniated cerebellar tonsils? Why/why not?
    • In an average month, how many Chiari decompressions do you perform? How many tethered cord releases? How many craniocervical fusions? What percentage of your practice is spent treating patients with these connective tissue related conditions?
    • Looking at my brain scan, is any part of my “brainstem” herniated (below the posterior fossa)? If so, does that make me a Chiari 1.5?

    Intracranial Hypotension (low pressure) Questions:
    *Article to help you understand CSF Leaks & Intracranial Hypotension prior to your appointment.
    If you have SYMPTOMS OF LOW INTRACRANIAL PRESSURE and/or suspect a cerebrospinal fluid leak, we recommend asking the following questions:

    • S.E.E.P.S.
      • Looking at my brain scan, do you see any Subdural fluid collections?
      • Looking at my brain scan, do you see an Enhancement of pachymeninges?
      • Looking at my brain scan, do you see an Engorgement of my venous structures? Should we do an MRV to make sure?
      • Looking at my brain scan, does my Pituitary appear to be enlarged?
      • Looking at my brain scan, does my brain appear to be Sagging?
    • Looking at my corpus callosum:
      • Does there appear to be a depression?
      • Is there an inferior pointing of the splenium?

    If he/she answers affirmatively to any of the above S.E.E.P.S. questions, ask: 

    • What should be done to find/repair a potential leak?
    • Are you aware that it is common for CSF Leaks to not show up on MRI?
    • Are you willing to do a CT Myelogram and/or a digital subtraction myelogram, if I develop symptoms of a leak and none can be found on MRI?
    • Are you aware that it can often take multiple epidural blood patches to try and seal a leak, and sometimes when a blood patch fails to work, a surgical dural repair might be necessary?

    Intracranial Hypertension (high pressure) Questions:
    *Article to help you understand Intracranial Hypertension prior to your appointment.
    If you have SYMPTOMS OF HIGH INTRACRANIAL PRESSURE, we recommend asking the following questions:

    • Looking at my brain scan, do I have cerebrospinal fluid in my sella turcica (Empty Sella Syndrome)?
    • Looking at my brain scan, do you see any evidence of my optic nerves are swollen (papilledema)?
      • If so, should I be referred to a neuro-ophthalmologist?
    • Looking at my brain scan, do my lateral ventricles appear small or flattened?
      • If so, do I need to have my pressures checked?
        • If yes, are you aware of the risks of developing a CSF Leak from a lumbar puncture?
      • What are the symptoms of a CSF Leak, should one develop?
        • What is your plan of action if I should develop these leak symptoms?
        • Are you aware that it is common for CSF Leaks to not show up on MRI?
        • Are you willing to do a CT Myelogram if I develop symptoms of a leak, and none can be found on MRI?
      • Should a leak be found, are you aware that it can often take multiple epidural blood patches to try and seal a leak?

    Tethered Cord Questions: 
    *Article to help you understand Tethered Cord: Sorry, Coming Soon.
    If you have SYMPTOMS OF TETHERED CORD, we recommend asking the following questions:

    • Looking at my brain/cervical scan, does my brainstem appear to be elongated?
    • Looking at my cervical scan, does my spinal cord appear to be stretched?
    • Looking at my lumbar scan, does my conus reach my mid/low L2?
    • Looking at my thoracic and lumbar scan, does my spinal cord appear to be pulling to the back, or one particular side?
      • If so, should we do a prone MRI to see if it has actually adhered to that side?
    • Looking at my lumbar scan, do I appear to have fatty tissue inside the epidermis?
      • If the answer to any of these questions is affirmative, do you suspect that I have a tethered spinal cord?
      • If so, should we plan for a Tethered Cord Release before or soon after decompression surgery, so the likelihood of a failed decompression is reduced?
      • If I have urological issues, can I get a referral for urodynamic testing to rule out any other potential causes of my urological issues?

    Craniocervical Instability (CCI) & Atlantoaxial Instability (AAI):
    *Article to help you understand CCI & AAI prior to your appointment.
    If you have SYMPTOMS OF CRANIOCERVICAL INSTABILITY or SYMPTOMS OF ATLANTOAXIAL INSTABILITY, we recommend asking the following questions:

    • Looking at my brain/cervical scans, what are the measurements of my clivoaxial angle and Grabb-Oakes?
    • Do these measurements meet the diagnostic criteria for Craniocervical Instability?
    • Looking at my flexion and extension imaging, how many millimeters of translation are there between flexion and extension?
    • Does Chamberlain’s Line cross my odontoid? If so, does it cross at a level that would indicate Basilar Invagination?
    • Looking at my rotational imaging, what is the percentage of uncovering of the right and left articular facets on rotation?
    • Do the percentages from my rotational imaging meet the diagnosis criteria for Atlantoaxial Instability?

    IF A DIAGNOSIS CRITERIA IS MET IN ANY OF THE ABOVE, WE STRONGLY RECOMMEND THAT YOU WAIT ON DECOMPRESSION AND PURSUE THE TREATMENT OF SAID CONDITION(S) AND THAT OF EHLERS-DANLOS SYNDROME, AS EACH OF THESE CONDITIONS CAN BE PATHOLOGICAL TO AN ACQUIRED CHIARI AND EACH IS A STRONG INDICATOR THAT A CONNECTIVE TISSUE PROBLEM EXISTS. 

    *The questions in this article will periodically change as we are able to expand our recommended questions.

    *Original version released September 2018, revised 2023.

  • Understanding Your Head and Neck Pain

    Understanding Your Head and Neck Pain

    You Might Have More Than A Migraine If…

    High-Pressure Headaches

    Those that suffer from high pressure tend to feel pressure behind the eyes (often mistaken for sinus headaches) and report feeling like their “head is going to explode” from the pressure. High-pressure headaches are generally characterized by being worse when laying down – often awaking in the middle of the night or first thing in the morning with a headache, and the headache tends to dissipate to some degree after being upright for a period of time (and that period of time is different for everybody). Caffeine generally exacerbates high-pressure headaches.

    High pressure headaches are typically worse when you lay down and relieved by being upright.
    • For more on Intracranial HYPERtension: http://chiaribridges.org/brain-pressure-understanding-intracranial-hypertension/
    • For a list of common high-pressure symptoms:: http://chiaribridges.org//glossary/symptoms-of-intracranial-hypertension/.

    Low-Pressure Headaches

    Those that suffer from low-pressure headaches tend to report feeling like there is an invisible pressure pushing down from the top of the head, often making it feel like your “head is going to implode.” Low-pressure headaches are characterized by being worse when upright and relieved by laying down. Low-pressure headaches are typically a sign of a cerebrospinal fluid leak (CSF Leak). The longer that the leak has existed, the less obvious the positional element is – meaning the patient can be upright longer before they feel the pressure at the top of their head, and they tend to need to lay down longer before getting any measure of relief. Caffeine often helps relieve low-pressure headaches.

    Low pressure headaches are typically worse when upright and relieved by laying down.
    • For more on Intracranial HYPOtension & CSF Leaks: http://chiaribridges.org//cerebrospinal-fluid-leaks/
    • For a list of common low-pressure symptoms:: http://chiaribridges.org//glossary/symptoms-of-intracranial-hypotension/

    Occipital Headaches

    Chiari headaches are felt at the occiput – at the base of the back of the skull and upper neck. They are generally tussive in nature, where they are exacerbated by valsalva maneuvers, which generally include: coughing, sneezing, heaving, laughing hard, or bearing down (like with a bowel movement or childbirth). These maneuvers reduce cardiac output (the amount of blood coming from the heart with each heartbeat), which in turn affects the attempted flow of cerebrospinal fluid, and it increases vagal stimuli.

    Occipital headaches occur at the back of the lower skull (occiput) and upper neck, on one or both sides of the upper spinal cord.
    • For more on Chiari Malformation: http://chiaribridges.org//chiari-malformation/
    • For an expansive review of the name and definition of Chiari Malformation: http://chiaribridges.org//whats-in-a-name-chiari-malformation/

    Connecting the Three Headaches

    • Untreated high pressure can cause cranial leaks (which leads to low pressure) – often accompanied by cerebrospinal fluid leaking through the nose or ears.
    • CSF leaks can sometimes seal on their own leading to rebound high pressure (which is temporary) or continued high pressure if they originally had high pressure.
    • Untreated high pressure can push the cerebellar tonsils down into the foramen magnum where it blocks the flow of cerebrospinal fluid, leading to occipital headaches (often diagnosed as a Chiari 1 Malformation) AND in return, the blockage of cerebrospinal fluid further increases intracranial pressure.
    • Untreated low pressure can cause the brain to sag and as it sags the cerebellar tonsils can get lodged into the foramen magnum where it blocks the flow of cerebrospinal fluid, leading to occipital headaches (often diagnosed as a Chiari 1 Malformation).
    • Untreated spinal leaks can create a suctioning or pulling down effect where the cerebellar tonsils can get lodged into the foramen magnum where it blocks the flow of cerebrospinal fluid, leading to occipital headaches (often diagnosed as a Chiari 1 Malformation).
    • All of the above is most common in patients with a connective tissue disorder such as Ehlers-Danlos Syndrome.

    Major Problem Regarding Our Diagnoses & Treatment Options:

    1. Doctors and radiologists alike, tend to see the herniated tonsils and assume a small posterior fossa.
    2. Most do not check for high pressure or low pressure, even when directly asked and symptoms are present.
    3. When a posterior fossa decompression is finally offered, the high or low pressure is often left untreated which leads to a failed decompression.
    4. By the time sufferers get a name to go with their symptoms, we jump at the opportunity for relief.

    The “Bobble-head Sensation” – When It Feels Like Your Neck Can No Longer Hold Up Your Head

    While most of us experience this feeling either intermittently or continuously, it is generally related to structural instability issues:

    • Craniocervical Instability (CCI, also known as Syndrome of Occipitoatlantialaxial Hypermobility) involves vertical hypermobility (back and forth sliding) of the craniocervical junction (interface between the occipital bone and the 1st and 2nd vertebrae), where the neck is no longer properly supporting the cranium. This condition can be dangerous as it often involves brain stem compression that can lead to a vast array of symptoms of Dysautonomia (dysfunction of the Autonomic Nervous System – ANS).
    • For more on Craniocervical Instability and Other Related Disorders: http://chiaribridges.org/craniocervical-instability-related-disorders/
    • For a list of common CCI symptoms: http://chiaribridges.org//glossary/symptoms-of-craniocervical-instability/
    • For a list of common AAI (a condition commonly seen with CCI) symptoms: http://chiaribridges.org//glossary/symptoms-of-atlantoaxial-instability/
    • Subaxial Instability (SAI; also known as Cervical Instability) involves hypermobility of the C2/C3 to the C7 intervertebral discs. This condition (like most conditions involving the cervical spine) is a major cause of muscle spasms (in the neck and throughout the body at any point below the disc issues. When these neck spasms occur, they can cause the “Bobble-head sensation” where it feels like your neck can no longer hold up your head. This disc degeneration can lead to paralysis as discs compress the spinal cord.

    Important Questions to Ask Your Neurosurgeons: http://chiaribridges.org/important-questions-for-your-neurosurgery-appointment/

    Originally written 10/2019
    Updated 12/2022

  • Overview: Chiari Treatment Options & Potential Pitfalls

    Overview: Chiari Treatment Options & Potential Pitfalls

    Once diagnosed, you will usually be referred to a specialist (not a Chiari Specialist, but an everyday, run-of-the-mill neurologist or neurosurgeon). They tend to come in one of two types: Either they are very passive and just want to wait and see how bad it gets, or they are very pro-surgery and while they will still usually give you a 50% chance of helping your symptoms, they will tell you how decompression surgery really is your best option. Both are problematic.

    FOR THE ASYMPTOMATIC CHIARIAN:
    Without a doubt, the passive approach is by far the best plan of action for the asymptomatic Chiari patient. Approximately 30% of those with a Chiari 1 malformation can go their entire lives without having symptoms (in fact, many remain undiagnosed and don’t even know they have it because they have no symptoms).[1] The Chiari is often discovered while looking for something else entirely and is therefore considered an “Incidental Finding.” While there is a chance that the Chiarian will become symptomatic one day, the risks of surgical complications exceed the potential benefit on something that has not and might not ever affect their life.

    FOR THE SYMPTOMATIC CHIARIAN:
    If the Chiarian is symptomatic, however, “Decompression Surgery is the only treatment available [at this time] to correct functional disturbances or halt the progression of damage to the central nervous system. Most individuals who have surgery see a reduction in their symptoms and/or prolonged periods of relative stability. More than one surgery may be needed to treat the condition.”[2] Despite the reasons for haste however, we do recommend slowing down and making sure that adequate testing is done to ensure that the Chiari is a “Congenital Chiari” formed only by a small posterior fossa, with no other etiological/pathological co-factors that could make it an “Acquired Chiari Malformation.” If not identified and addressed, these etiological/pathological co-factors can cause complications and even lead to a failed decompression surgery. (Note: most are told at diagnosis that it is a “congenital defect.” However, that is usually a presumption on their part, stemming from a lack of knowledge of Chiari and its comorbidities, and them giving too much credence to the paragraph or two on Chiari malformations in their medical school textbooks. That is not the reality that many are dealing with; so, testing is imperative!)

    TESTING:
    If you have been diagnosed with a Chiari malformation or a tonsillar ectopia (regardless of the size of tonsillar descent), you should have the following tests/images done.

    1. A sleep study to check for Sleep Apnea.

    • Central Sleep Apnea (CSA) is more common with Chiari, especially when there has been damage to the brainstem or Vagus Nerve.

    • Obstructive Sleep Apnea (OSA) is commonly linked with obesity in the general population, it is also very common amongst those with Connective Tissue Disorders (such as Ehler’s-Danlos Syndrome).

    • Both CSA and OSA can be present in the Chiarian with a Connective Tissue Disorder. When both are causing apnea, it becomes known as “Complex Sleep Apnea.”

    • Sleep Apnea, regardless of the type, is a common “killer” amongst Chiarians.


    2. A brain and full spine MRI (upright recommended) with and without contrast.

    What they should be looking for in these MRIs:

    a) Do you have a syrinx (Syringomyelia or Syringobulbia)?

    • If you have either, that is proof that the blockage of CSF is significant enough to cause these potentially serious complications.

    b) Is any part of your brainstem below the foramen magnum?

    • If it is, you have a variant of Type 1, known as a Chiari 1.5[3] or Type 2, both indicate that there is something else going on causing the brainstem to herniate along with the cerebellar tonsils. 

    c) Do you have a cyst/tumor causing increased intracranial pressure that is pushing the cerebellar tonsils down?

    • If you have either, and they are operable, there is a chance that surgically removing it could decrease the intracranial pressure and allow the cerebellar tonsils (and brainstem if it is below the foramen magnum at all) to go to proper position. Furthermore, if the cyst/tumor is not addressed before, during, or soon after decompression surgery, the chances of your tonsils herniating again after decompression are high.[4]

    d) Do you have Hydrocephalus causing increased intracranial pressure that is pushing the cerebellar tonsils down?

    • If you do, there is a chance that the placement of a Ventriculoperitoneal Shunt could decrease the intracranial pressure enough to allow the cerebellar tonsils (and brainstem if it is below the foramen magnum at all) to go to their proper position. Furthermore, if the Hydrocephalus is not addressed before, during, or soon after decompression surgery, the chances of your tonsils herniating again after decompression are high.[5]

    e) Do you have signs/symptoms of Idiopathic Intracranial Hypertension (often shows as excessive fluid above the lateral ventricles, with small, “slit-like” lateral ventricles; usually accompanied by Papilledema and/or Empty Sella Syndrome), which can cause enough cranial pressure that it can push your cerebellar tonsils down?

    • If you do, there is a chance that a prescription for Diamox or Topamax, or the surgical placement of a Ventriculoperitoneal Shunt, could reduce the pressure enough to allow the cerebellar tonsils (and brainstem if it is below the foramen magnum at all) to go into proper position. Studies exist both in favor of shunting first and doing the decompression first; there are documented cases where unresolved IH has led to failed decompression surgeries, while other cases attribute a Chiari decompression as being that which resolved IH symptoms.[6/7]

    f) Do you have signs/symptoms of Tethered Cord Syndrome that could be pulling on the spine from below?

    • If you do, there is a chance that a less invasive surgery known as a Tethered Cord Release, could stop the downward pulling of the spinal cord and allow the cerebellar tonsils (and brainstem if it is below the foramen magnum at all) to go into proper position. Furthermore, if the Tethered Cord is not addressed before, during, or soon after decompression surgery, the chances of your tonsils herniating again after decompression are high. (Note: not all Tethered Cords are easily visible by MRI, when they are not visible, it is called Occult Tethered Cord (OTC) and surgery on a OTC remains controversial.)[8]

    g) Do you have signs/symptoms of Intracranial Hypotension (CSF Leak) that could be pulling or creating a suctioning effect from below?

    • If you do, there is a chance that a less invasive blood patch or a Dural Tear Repair Surgery, could stop the downward pulling/suctioning effect on the spinal cord and allow the cerebellar tonsils (and brainstem if it is below the foramen magnum at all) to go into proper position. Furthermore, if the leak(s) are not addressed before, during, or soon after decompression surgery, the chances of your tonsils herniating again after decompression are high. (Note: not all leaks are easily visible by MRI.)[9]

    h) Do you have signs of Spina Bifida (Myelomeningocele, Meningocele, or Spina Bifida Occulta)?

    • While it is important to know if any of these exist, a Myelomeningocele would put you at an increased risk of having a Chiari Type 2. While all Chiari Malformations with a Myelomeningocele do not meet the standards for Type 2, 90% of those with a Myelomeningocele have a Chiari Type 2. Most neurosurgeons will not perform a decompression on someone with a Myelomeningocele because of the risk of further complications.[10]

    i) Do you have signs/symptoms of disc degeneration problems and/or stenosis, especially in the cervical spine where it can damage the Vagus Nerve?

    • If you do, these could be another sign of a connective tissues disorder. If you have a syrinx above a herniated/bulging disc, there is a good chance that the disc is attributing to it. Herniated/bulging discs in the cervical spine can be quite troublesome. They can usually be addressed by a second procedure called an Anterior Cervical Discectomy and Fusion (ACDF), but if there are multiple cervical problems and Craniocervical Instability, some surgeons will opt to do a fusion at the time of decompression.[11]

    j) Do you have signs and symptoms of a cervicomedullary syndrome[12], which are often the result of Craniocervical Instability (CCI), Atlantoaxial Instability (AAI), or both. (CCI and AAI can be confirmed with: An upright c-spine MRI with flexion, extension, and neutral views or a 3D cervical CT with rotational views.)

    • CCI/AAI can produce many of the same symptoms as Chiari 1 malformation, including occipital or craniocervical junction headaches made worse by Valsalva maneuvers. It has been theorized that CCI/AAI may also be capable of causing or worsening a herniation of the cerebellar tonsils, and it has been demonstrated that CCI can cause ventral brainstem compression and deformative stress injury to the brainstem.[13] Failure to diagnose and treat CCI before or along with decompression has also been linked to decompression failure. CCI and AAI, while rare in the general population, are relatively common in patients with HDCT’s (Heritable Disorders of Connective Tissue), such as Ehlers-Danlos Syndrome. CCI, when identified to be the root cause of significant symptoms, can be treated conservatively, and in the short term, with the use of a hard-cervical collar, physical therapy and, possibly, traction. More permanent treatment in the form of a fusion and stabilization surgery (fusing the occiput to C1, C2, and sometimes additional vertebrae).[12/13]

    3. A preliminary check for connective tissue disorder (especially Ehler’s-Danlos Syndrome). If preliminary results indicate the presence of a connective tissue disorder, genetic testing should be done to rule out more serious types.


    IF NONE OF THESE PROBLEMS APPEAR TO EXIST: 
    Some doctors and patients prefer to wait and just treat the symptoms medically. That is your choice to make and you should never let anyone try to bully you or manipulate you into having surgery or not; although it is important to know that statistics show that those who have had a shorter duration of onset of symptoms and surgery tend to have a better surgical outcome.[14]

    Statistics show that 80% of decompressed patients report some relief from some of their symptoms; headaches are the most commonly reported symptom to gain relief (81%).

    Most surgeons will give a 50% chance of relieving each symptom individually, with the exception of pain associated with damaged nerves.

    While some surgeons prefer a conservative approach to surgery such as a “bone only” decompression or a “Minimally Invasive Subpial Tonsillectomy,”[15] a full decompression usually consists of:

    ♦ Craniectomy: removal of part of the sub-occipital skull.

    ♦ Laminectomy of C1 (and sometimes C2): removal of the lamina from the vertebra.

    ♦ Duraplasty: opening of the dura (the outermost membrane enveloping the brain and spinal cord) and patching it so there is more room.

    ♦ Cerebellar Tonsillectomy: removal/cauterization of the cerebellar tonsils.


    IS DECOMPRESSION SURGERY A CURE FOR A CHIARI MALFORMATION? 
    There is a fundamental problem with the question and what many neurologists and neurosurgeons believe about decompression surgery. For the patient, the symptoms are synonymous with the condition. If we continue to struggle living our lives because of these symptoms, having a doctor that refuses to validate that struggle, can add insult to injury. Decompression surgery should NEVER be considered a cure to the symptoms of a Chiari malformation, it is merely the only treatment available [at this time] to correct functional disturbances or halt the progression of damage to the central nervous system. The likelihood of continued symptoms is almost absolute, Decompression is only a means of reestablishing the flow of CSF between the brain and spinal canal (which is imperative). Once flow is restored, there should be some relief from many of the symptoms. Complications such as Syringomyelia should be reduced or resolved, so the possibility of paralysis is significantly reduced. With as bad as the pain and symptoms are, it really can get worse if left untreated. Finding a specialist that is not only experienced with decompression surgeries, but who fully understands the correlation and treatment of etiological/pathological co-factors and co-morbid conditions, substantially increases the likelihood of a positive surgical outcome.

     

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    References:

    1 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>.

    2 “Chiari Malformation Fact Sheet.” National Institute of Neurological Disorders and Stroke, U.S. Department of Health and Human Services, June 2017, <www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Fact-Sheets/Chiari-Malformation-Fact-Sheet>.

    3 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/>.

    4 Wang, J, et al. “Acquired Chiari Malformation and Syringomyelia Secondary to Space-Occupying Lesions: A Systematic Review.” World Neurosurgery., U.S. National Library of Medicine, Feb. 2017, <www.ncbi.nlm.nih.gov/pubmed/27894943>.

    5 Graham, A, et al. “An Unusual Cause of Neck Pain: Acquired Chiari Malformation Leading to Brainstem Herniation and Death.” The Journal of Emergency Medicine., U.S. National Library of Medicine, Dec. 2012, <www.ncbi.nlm.nih.gov/pubmed/21215551>.

    6 Fagan, L H, et al. “The Chiari Pseudotumor Cerebri Syndrome: Symptom Recurrence after Decompressive Surgery for Chiari Malformation Type I.” Pediatric Neurosurgery., U.S. National Library of Medicine, 2006, <www.ncbi.nlm.nih.gov/pubmed/16357496>.

    7 Park, Michael S., et al. “Coexistent Chiari Malformation and Idiopathic Intracranial Hypertension: Which Should Be Treated First?- Case Report and Review.” JSM Neurosurg Spine, vol. 2, no. 3, ser. 1025, 20 Mar. 2014. 1025, <www.jscimedcentral.com/Neurosurgery/neurosurgery-2-1025.pdf>.

    8 Milhorat, T H, et al. “Association of Chiari Malformation Type I and Tethered Cord Syndrome: Preliminary Results of Sectioning Filum Terminale.” Surgical Neurology., U.S. National Library of Medicine, July 2009, <www.ncbi.nlm.nih.gov/pubmed/19559924>.

    9 Atkinson, J L, et al. “Acquired Chiari I Malformation Secondary to Spontaneous Spinal Cerebrospinal Fluid Leakage and Chronic Intracranial Hypotension Syndrome in Seven Cases.” Journal of Neurosurgery., U.S. National Library of Medicine, Feb. 1998, <www.ncbi.nlm.nih.gov/pubmed/9452230>.

    10 Vandertop, William P., et al. Surgical Decompression for Symptomatic Chiari II Malformation in Neonates with Myelomeningocele. Oct. 1992, <www.thejns.org/doi/abs/10.3171/jns.1992.77.4.0541>.

    11 Dahdaleh, Nader S., and Arnold H. Menezes. Incomplete Lateral Medullary Syndrome in a Patient with Chiari Malformation Type I Presenting with Combined Trigeminal and Vagal Nerve Dysfunction. 2008, <www.thejns.org/doi/pdf/10.3171/PED.2008.2.10.250>.

    12 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>.

    13 Henderson, FC, et al. “Deformative Stress Associated with an Abnormal Clivo-Axial Angle: A Finite Element Analysis.” Surgical Neurology International, 16 July 2010, <www.europepmc.org/articles/PMC2940090/>.

    14 Ma, J, et al. “Cerebellar Tonsillectomy with Suboccipital Decompression and Duraplasty by Small Incision for Chiari I Malformation (with Syringomyelia): Long Term Follow-up of 76 Surgically Treated Cases.” Turkish Neurosurgery., U.S. National Library of Medicine, 2012, <www.ncbi.nlm.nih.gov/pubmed/22664992>.

    15 Beecher, Jeffrey S., et al. “Minimally Invasive Subpial Tonsillectomy for Chiari I Decompression.” Acta Neurochirurgica, Springer Vienna, 5 July 2016, <www.ncbi.nlm.nih.gov/pmc/articles/PMC4980444/>.