CHIARI (KEE-AR-EE) MALFORMATIONS ARE FAR FROM RARE, THEY ARE JUST RARELY UNDERSTOOD, EVEN BY MOST MEDICAL PROFESSIONALS. A CHIARI MALFORMATION EXISTS WHEN THE LOWEST PART OF THE HIND BRAIN (THE CEREBELLAR TONSILS) PROLAPSES INTO THE HOLE AT THE BOTTOM OF THE SKULL (FORAMEN MAGNUM), ENTERS THE SPINAL CANAL AND OBSTRUCTS THE FLOW OF CEREBROSPINAL FLUID(CSF), PUTS PRESSURE ON THE BRAIN STEM AND SPINE, AND MAY RESULT IN VARYING DEGREES OF NERVE COMPRESSION.
PREVALENCE OF CHIARI: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]. Since Chiari Malformation Type 1, the most common type, tends to become symptomatic during late teens and early adulthood, it is likely to be much more common when adults are factored in.
THE CONNECTION:Chiari malformations were originally believed to be caused by a posterior fossahypoplasia (small area inside the back of the skull) and doctors speculated that lack of maternal prenatal care or drug abuse caused the deformity. However, as studies continue, they are finding that many with this hind brain herniation have connective tissue disorders, such as Ehlers-Danlos Syndromes. Ehlers-Danlos Syndromes involve a mutation in one of the collagen genes. Collagen is a protein that is often described as a “cellular glue” that helps hold the body together. When that glue fails to hold, everything seems to go awry; specifically, as related to Acquired Chiari Malformations: organs tend to prolapse, and bones begin to shift as joint laxity increases (including the bones/vertebrae at the craniocervical junction). They are finding that these acquired Chiari malformations are far more common than originally thought. There are many pathological co-factors that can cause or attribute to the formation of a Chiari Malformation, and most can be linked to these Heritable Disorders of Connective Tissues(HDCTs), including a posterior fossahypoplasia. In one large study, they found those with a Chiari malformation and no associated co-factors, with only slightly over 52% having a small Posterior Cranial Fossa (PCF). When other co-factors were present, the number of Chiarians found with a small PCF plummeted and therefore it is should be considered acquired until proven otherwise.[2]
DIAGNOSES: A decade ago, it took 10-20 years from the onset of symptoms to be diagnosed and now it takes an average of 1-2 years, because medical professionals are slowly beginning to look for it. Magnetic Resonance Imaging (MRI) remains the best tool for diagnosis. Some medical professionals 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, a patient’s symptoms, and other relevant factors). Due to the prevalence of connective tissue issues, gravity often proves to be a significant factor and should be taken into account by use of an upright MRI whenever possible.[3]EDS should be diagnosed by a geneticist before surgery is considered.
TREATMENT OPTIONS: There is no cure for a Chiari malformation, but there are treatment options. When symptoms are minimal and not life-altering, pain management is usually offered. However, it is important to know that while medications may ease some symptoms, Chiari symptoms tend to be progressive. Decompression surgery is the only treatment available to attempt to halt the progression of the damage being done to your Central Nervous System (CNS). The most common reason that decompression surgeries fail, is undiagnosed co-morbid conditions, especially those that can be etiological/pathological co-factors. More than one surgery might be necessary to successfully treat a Chiari malformation and any/all co-morbid conditions and there is a correlation between early surgical intervention and positive surgical outcomes[4].
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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 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>.
3 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>.
Cerebrospinal fluid(CSF) is the clear, colorless liquid that surrounds the brain and spinal cord and is contained within a lining called the dura. The cerebrospinal fluid protects and cushions the brain and central nervous system. Among other functions, this fluid provides buoyancy to the brain, allowing it to float and weigh less, thus reducing the pressure at the base of the brain. A cerebrospinal fluid(CSF) leak occurs when there is a tear or hole in the dura that then allows this fluid to escape[1]. When leaks occur, the overall volume and pressure within the skull drops, and the cushioning and buoyancy effect is reduced, causing the brain to slump. In many cases, this leads to a condition known as intracranial hypotension and a vast range of symptoms.
The main symptom of a CSF leak is a headache that is worse when upright and improves when lying down horizontally. This is sometimes called a “positional” or “orthostatic” headache. However, not all positional headaches can be attributed to a CSF leak, and not all CSF leak headaches are positional. This is particularly the case in the chronic (vs acute) phase of CSF leaks, where the “positional” or “orthostatic” characteristic of symptoms may become more constant, lessen, or disappear entirely, including headache. Symptoms often worsen as the day goes on. Other leak symptoms can include, but are not limited to: nausea, vomiting, neck pain or stiffness, heaviness of head, pain between the shoulder blades, feeling of pressure within the head, changes in hearing (muffled or underwater sensation), tinnitus (ringing, buzzing, or pulsatile), feeling of liquid in the ears, sense of imbalance, sensitivity to light, sensitivity to sound, pain or numbness in the arms, changes in cognition (“brain fog,” memory loss, or loss of concentration), dizziness or vertigo, scalp sensitivity or tingling sensation within the scalp, visual changes (blurring, double vision, visual field defects), pain behind the eyes or when moving eyes, facial numbness or pain, sinus pressure, temporomandibular joint pain and stiffness, and subdural hematoma[2]. Cranial leak specific symptoms can vary even more and can include: fluid discharge from ears, nose (usually only one side) and to back of throat often reported as salty or metallic tasting, recurring or chronicmeningitis, loss of sense of smell, change in hearing or ringing in the ears, and less frequently cognitive changes. Rare signs or complications of CSF leaks can include: quadriplegia, dementia (often mimicking Frontotemporal Lobe Dementia), Parkinsonism, other movement disorders, ataxia (unsteady gait), hypersomnolence, stupor, coma, stroke (hemorrhagic or ischemic), and even death.
CSF leaks are often very hard to locate, if ever. Approximately 50% of leaks cannot be found on imaging. Imaging and other tests used to attempt to find leaks are often read as “normal” even when there is a leak present. Other times, especially (but not always) in the case of chronic leaks, the positional symptoms either lessen or go away altogether, including the headache. Many who are leaking are not even aware that they are leaking. Leaks are often misdiagnosed as well[3]. Some of those common misdiagnoses are Postural Orthostatic Tachycardia Syndrome (POTS), migraines, sinus headaches, Meniere’s Disease, ChronicFatigue Syndrome, Parkinson’s Disease (sometimes other neurodegenerative diseases), Fibromyalgia, Ehlers-Danlos Syndrome, Tarlov Cyst, Chiari Malformation, Cervical Spine Disease, cervicogenic headache, tension headache, and Sinusitis. To make diagnosis even more complex and elusive, CSF leaks can and do often occur along with any of these disorders and perhaps several simultaneously. A leak can cause an acquired Chiari malformation or coexist and complicate an existing congenital Chiari malformation[4]. Some patients have had unnecessary decompression surgeries when the underlying, sole cause was a leak all along.
Leaks can be caused by:
Medical procedures (also called iatrogenic leaks) for various diagnostic or therapeutic reasons such as lumbar punctures to collect fluid for analysis if meningitis is suspected, lumbar puncture for injection of contrast (myelography), spinal anesthesia, epidural injections, epidural steroid injections, prior skull base or spinal surgery, CSFshunt over-drainage, prior sinonasal surgery, and chiropractic or other spinal manipulations.
Traumatic injuries such as brachial plexus injuries falls, sports injuries, motor vehicle accidents, roller coaster rides, and other whiplash injuries.
Spontaneous leaks that occur with minimal or no clear cause. Sometimes spontaneous leaks may be associated with some sort of spinal pathologies such as calcified disk material or bone spurs. These leaks are usually ventral (or in front of the spinal cord).
There is growing evidence suggesting that a significant number of spontaneous CSF leaks occur as the result of a preexisting weakness in the dura[5]. Heritable Disorders of Connective Tissues (HDCT’s) such as Marfan Syndrome, Ehlers-Danlos Syndrome (both classical and hypermobility type), autosomal dominant Polycystic Kidney Disease, and other HDCT’s predispose patients to CSF leaks. One leak expert estimates that “slightly less than 100% of patients with spontaneous CSF leaks have an underlying connective tissue disorder.”[6] The dura is made out of connective tissue and patients with HDCT’s have thinner dura mater, that is more susceptible to tears and leaks. HDTC patients are more prone to spinal conditions such as perineural cysts, meningeal diverticula, and other HDCT defects such as aneurysms and dilatations. Oftentimes, a CSF leak is the first sign of an underlying HDCT.
Lumbar punctures (LP’s or spinal taps) should be avoided in patients with Chiari Malformation and/or in patients with HDCT’s[7]. There is a risk of causing a herniation of the cerebellar tonsils or making an existing herniation worse from the pull-down mechanism involved in lumbar punctures. Unfortunately, lumbar punctures are not always avoidable and sometimes very necessary, especially in cases to rule out life-threatening viral or bacterial conditions such as meningitis, subarachnoid hemorrhage, encephalitis, or syphilis. In these cases, measures can be taken to minimize LP risks such as using a certain needle type and size, limit the number of cc’s collected (by spontaneous drip ONLY), and, of course, always done under fluoroscopy by a competent physician[8]. Additionally, it is important to be aware that patients with HDCT’s are at greater risk for the dura to fail to heal following an LP. Patient’s should be aware of post-dural puncture headache (PDPH) symptoms and speak with their physicians if they suspect a leak following an LP.
The procedures and tests used to diagnose leaks will vary between patients and certain criteria are used to diagnose leaks[9]. Some of these tests and procedures might be: endoscopic exam and fluid collection and Beta-2-Trasnferrin testing (cranial leaks), Cisternography (including radioisotope cisternogram), Magnetic Resonance Imaging (MRI) including Magnetic Resonance (MR) myelography, Dynamic CT myelography, Digital Subtraction myelography, and Intrathecal saline infusion-enhanced myelography, a lumbar puncture to collect and test fluid and measure opening pressure. This imaging often includes both brain and spinal imaging. The normal opening pressure is not uncommon and does not rule out a leak. High pressure can also occur while leaking. Pre-existing intracranial hypertension can be related to the development of spontaneous spinal CSF leaks. Some reports suggest that spontaneous cerebrospinal fluid(CSF) leaks are strongly associated with idiopathic intracranial hypertension (IIH). There are 5 main findings on imaging that doctors look for, however, the absence of these findings does not rule out a CSF leak. The mnemonic SEEPS is used for most of these findings: subdural fluid collection, enhancement of pachymeninges, engorgement of venous structures, pituitary hyperemia, and sagging of the brain[10]. Other imaging findings that might be seen are small ventricles, cisterns might have less fluid, optic chasm might flatten over pituitary, pituitary might enlarge, empty sella, fluid in front of the pons, or pons might become flatter than normal. Repeat imaging is often necessary.
Treatment of leaks can either be medical or surgical. Conservative treatment is often recommended, if possible. This can include bed rest and avoidance of coughing, sneezing, straining, bending, twisting, and lifting, increased fluid intake and caffeine, the use of an abdominal binder, and sometimes steroids are recommended. Others may have a lumbar drain placed in the low back to decrease the pressure of the CSF around the area of the leak in an attempt to allow this area to heal. Some patients may need an epidural blood patch. Where a blood patch is not successful, a fibrin glue patch may be tried. About 30-40% of leaks occur at multiple sites, especially in those with an HDCT. Multisite patches may be required. Higher volumes of blood may be needed in order to reach where it needs to go, and/or the position of the needle may need to vary from the standard placement (transparietal or lateral placement)[11]. It is not uncommon for several patches to be tried. Many doctors make the mistake that if an EBP fails, there was no leak as well. Sometimes when more conservative and less invasive treatments have failed, neurosurgery may be necessary. Surgical repairs vary and are tailored according to the type and location of the leak. Sometimes in a select set of patients, other procedures have been used including epidural saline infusions through an implanted epidural catheter or lumbar dural reduction surgery. A condition known as rebound intracranial hypertension (RHP) may occur following any of these treatments[12]. Usually, but not always, there is a different pattern to the headache where one feels worse when horizontal and better when upright. Sometimes, acetazolamide (Diamox) or a similar medication is prescribed to help treat RHP.
Leaks are poorly recognized, poorly understood, under-researched, understudied, often misdiagnosed, can complicate existing conditions, are difficult to find, mimic many other disorders (including Chiari Malformation), and can be comprised of a vast array of symptoms. Most doctors are familiar with the symptoms of a leak in the acute phase. Very few doctors are familiar with how long-term, chronicCSF leaks “present” in regard to headaches and other leak symptoms and often miss the more subtle symptoms of chronic leaks. Like Chiari and other related disorders, no two patients with CSF leaks have the same symptoms and often experience misdiagnosis, delayed diagnosis, are disbelieved concerning their symptoms of the severity thereof, and all too often dismissed to suffer excruciating pain, decline, and debility. Educating yourself as much as possible about CSF leaks will help guide and empower you and those around you who may have existing, suspected or potential future complications that may arise due to CSF leaks.
7 Erbay, Sami H., et al. “Is Lumbar Puncture Contraindicated in Patients with Chiari I Malformation?” American Journal of Neuroradiology, American Journal of Neuroradiology, 1 Apr. 2005, <www.ajnr.org/content/26/4/985>.
9 Schievink, W. l., et al. “Diagnostic Criteria for Spontaneous Spinal CSF Leaks and Intracranial Hypotension.” American Journal of Neuroradiology, American Journal of Neuroradiology, 1 May 2008, <www.ajnr.org/content/29/5/853>.
From Intracranial Hypertension (formerly known as Pseudotumor Cerebri), Hydrocephalus, Tethered Cord Syndrome, to conditions related to the presence of a connective tissue disorder, such as Ehler’s-Danlos Syndrome, the primary reason for post-decompression complications seen in the Chiari Patient Community continues to be largely related to undiagnosed and untreated comorbid conditions. Time and time again, we see decompression failure, or a recurrence of symptoms after decompression, because there are other underlying conditions that need to be addressed. For this reason, we strongly recommend that patients get evaluated for the possibility of these known comorbid conditions before undergoing decompression surgery, unless circumstances require emergency surgery. (More information about the testing we recommend can be found in “The Treatments” article). Potential complications of decompression surgery may vary, depending upon the specific technique used, such as whether a duraplasty is performed, and how much bone is removed during a suboccipital craniectomy. The most common complications are infection, CSF leak, and Pseudomeningocele in adult patients.
INFECTIONS
Surgical site infections:
A surgical site infection is a risk of any surgery. While hospitals and surgical staff strive to maintain a sterile environment, hospitals are known for harboring pathogens, including many that are antibiotic resistant. Patient factors, including diabetes, age, being overweight, and being a smoker can also increase a patient’s risk of developing a post-operative infection.[1] Antibiotics are typically given post-surgically (and sometimes before surgery) in order to reduce the risk of infection. Some infections require wound revision surgery, to remove pus and infected tissue in order to improve healing.
Meningitis is an additional surgical risk when the dura is opened during a decompression. It is characterized by inflammation of the meninges, the linings of the brain. There are three main types of meningitis: aseptic, bacterial and chemical.
♦ Aseptic Meningitis is by far the most common type, and is generally less severe than the bacterial type. Most cases of aseptic meningitis are caused by viruses, but may rarely be fungal, autoimmune, parasitic or drug-induced.[2] The treatment for aseptic meningitis is usually supportive care.[3] Chemical meningitis is also a risk any time surgery or other procedures or treatments are performed on the brain or spine.[4]
♦ Bacterial Meningitis is much more serious and can be life threatening. Three types of bacteria cause most cases: streptococcus pneumoniae, Group B streptococcus, and Neisseria meningitidis. Typical treatment includes antibiotics and supportive care.
Duraplasty leak:
Post-decompression CSF leaks are a risk of decompression surgery whenever the dura is opened. The risk of a CSF leak dramatically increases with the presence of untreated hydrocephalus[5], intracranial hypertension (IH)[6], and connective tissue disorders, such as Ehlers-Danlos Syndrome. Nationwide statistics indicate that the risk of a CSF leak post-duraplasty is 10-15%. However, some surgeons report a significantly lower incidence of CSF leaks in their patients.[7] The use of biologic glue to seal the dural suture line has greatly reduced the incidence of post-duraplasty CSF leaks. A common sign of a leak is clear fluid leaking from the incision site.
Pseudomeningocele:
A pseudomeningocele is a type of CSF leak, where the leak creates a pocket in the muscles in the back of the neck. It is one of the most common complications of duraplasty. While some surgeons have managed to keep the incidence of pseudomeningocele low in their patients, some report an incidence as high as 18%.[8] A study at Vanderbilt University at 2013 showed that the development of a pseudomeningocele after decompression significantly reduced the benefit of decompression at one-year post-op on pain, disability and quality of life.[9] A smaller pseudomeningocele may re-absorb on its own. However, with large and persistent PM’s, the duraplasty may adhere to the cerebellar tonsils, blocking flow and making a revision surgery more difficult. There is much debate among neurosurgeons as to whether doing routine duraplasty as part of decompression outweighs the risks. Some argue that duraplasty increases the risk of complications, while others say that failure to perform duraplasty often results in inadequate decompression, reduced benefit, and the need for additional surgeries. Some experts argue that duraplasty using the patient’s own pericranial tissue and using water-tight sutures and biologic glue minimizes the risk of a leak and makes routine duraplasty the best option for most patients. A squishy pocket of fluid is often seen near the base of the skull and a PM can be confirmed and monitored with an MRI. In some cases, a surgeon may try draining the pocket of fluid with a needle and syringe.
BLEEDING AND ANESTHESIA-RELATED COMPLICATIONS
Excessive Blood Loss:
Excessive blood loss is a risk of any major surgery, but can be minimized by a careful surgical technique. Patients with connective tissue disorders may have an increased risk of bleeding complications, due to fragile blood vessels, particularly with vascular EDS or vascular crossover symptoms. Cessation of blood-thinning medications, such as warfarin, aspirin and NSAIDS also reduces the risk of bleeding.
Anesthesia Risks:
While risks of general anesthesia are quite low, the risk may be higher if you or someone related to you has had previous adverse interaction to general anesthesia. Some EDS patients are also prone to anesthesia issues, such as requiring more anesthesia or ineffectiveness of local anesthetics. Therefore, it is important to inform your anesthesiologist of your pertinent medical history.[10]
BONY REGROWTH
Regrowth of the bone removed during decompression is a risk associated with the pediatric patient population, particularly patients under the age of 2. Surgeons have reported as much as a 50% incidence of bony regrowth in patients under the age of 5, and as much as 80% in patients under age 2. Regrowth of bone may result in the need for future surgery.[5]
While Craniocervical Instability is not uncommon among those with connective tissue disorders, it is pretty rare in the general population. However, aggressive bone removal during decompression surgery can create an unstable craniocervical junction. It is important to discuss with your surgeon how much bone they plan to remove, and the risks and benefits of laminectomy, particularly if you also have a connective tissue disorder, which increases your risk for developing instability.
Cerebellar slumping (aka cerebellar ptosis) occurs as a result of too much bone being removed around the foramen magnum that there is no longer enough bone to support the weight of the cerebellum. The brain slumps downward toward the spine, re-herniating the cerebellar tonsils, and often compressing the cerebellum itself against the back of the skull and brain stem. This can often result in worse symptoms than the patient had before decompression. Surgical techniques have been developed to revise the decompression and provide more support to the cerebellum.[11]
Occipitalneuralgia is nerve pain, often accompanied by numbness and/or tingling, of the occipital nerve in the back of the head. It can be caused by compression of or damage to the occipital nerve. While the presence of a Chiari malformation itself can cause compression of the cranial nerves, including the occipital nerve, decompression surgery can also cause occipitalneuralgia. This can be due to compression of the nerve from the use of retractors to hold apart musculature during surgery, or the build-up of scar tissue around the nerve. More conservative treatment of occipitalneuralgia may include medications, such as lidocaine patches and medication that target nerve pain, physical therapy, cutaneous nerve stimulators, and nerve root blocks. Severe and persisting occipitalneuralgia may require surgical decompression of the nerve or occipital neurectomy, surgical removal of the occipital nerve.[12]
SCAR TISSUE AND ADHESIONS
Like with occipitalneuralgia and pseudomeningocele, the development of scar tissue and adhesions can cause symptoms to return or failure to relieve symptoms after a decompression surgery. Adhesions and scar tissue can develop wherever tissue is cut, including the dural graft, cauterized tonsils and the skin incision. Scar tissue and adhesion can inhibit or block CSF flow and often require revision surgery to remove the scar tissue. A careful selection of the graft material used for a duraplasty may reduce the risk of developing adhesions and scar tissue.[13]
DECOMPRESSION FAILURE
While perhaps technically not a complication, the failure rate of decompression surgery to alleviate symptoms deserves a mention here. While proper complications can often result in the failure of a decompression to relieve symptoms, or in fact, may make them worse than before decompression, even complication-free decompressions surgeries have a high rate of failure, as much as 40%, depending upon the study. Some reasons for decompression failure in the absence of the above-listed complications include failure to diagnose and treat comorbid conditions that may be causing symptoms, an inadequate decompression (failure to create enough space by removing bone and performing a duraplasty), and some or all of the symptoms being due to another cause, such as migraines. In cases of an inadequate decompression, a more aggressive decompression revision surgery may provide relief. In cases where a comorbid condition exists, that condition must be diagnosed and treated. However, there are still a small percentage of patients who do not get relief, even with further decompression and other treatments. The reason for this is not clearly understood.[5]
9 Parker, S. L., et al. “Effect of Symptomatic Pseudomeningocele on Improvement in Pain, Disability, and Quality of Life Following Suboccipital Decompression for Adult Chiari Malformation Type I.” Journal of Neurosurgery., U.S. National Library of Medicine, Nov. 2013, <www.ncbi.nlm.nih.gov/pubmed/24010974>.
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 geneticconnective 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 C1vertebrae (which is true CCI), the instability of the joints between C1 and C2 (true AAI), a retroflexed odontoid, pannus formation, and a kyphoticclivo-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.
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.
The Harris measurement is the distance between the basion and the PosteriorAxial 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.
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)
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:
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 hereditaryconnective 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.
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/>.
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 HypermobilityConnective 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>.
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/>.
Disclaimer: The information provided on our website is strictly for educational purposes in order to help further the understanding of Chiari and its associated conditions. You should in no way use this site as a replacement for diagnosis, treatment, or medical advice from a qualified medical professional.
