What is Craniocervical Instability?

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Craniocervical Instability (CCI), also known as the Syndrome of Occipitoatlantialaxial Hypermobility, is a structural instability of the craniocervical junction which may lead to a pathological deformation of the brainstem, upper spinal cord, and cerebellum. It primarily occurs in patients with Ehlers-Danlos Syndrome and other hereditary disorders of connective tissue.

What is Ehlers-Danlos Syndome?

Ehlers-Danlos Syndome (EDS) is a genetic connective tissue disorder that is caused by a defect in the structure, production, or processing of collagen or proteins that interact with collagen. Collagen is kind of like your body’s glue -it is what holds your skin, joints, blood vessels, and other major organs in place. It typically presents itself in childhood or young adulthood with hypermobile joints prone to misalignment, stretchy skin that tears easily, and fragile blood vessels prone to cardiovascular complications (such as aneurysms).

EDS is currently considered to be a rare disease as it affects approximately 1 in 5000 people world wide (however, due to it’s vast underdiagnosis, a presumed frequency of 1 in 200 has been proposed).

EDS can be diagnosed by a skin biopsy, DNA blood testing, or clinically by a geneticist.
For more information on Ehlers-Danlos Syndrome click here.

How does Craniocervical Instability occur?

About 1 in 15 people with EDS will go on to develop CCI due to a lack of connective tissue support at the craniocervical junction. While some EDS patients present with this condition after a head and neck injury (such as whiplash), for the most part this condition tends to manifest gradually through repetitive stretch injuries from actions as simple as turning one’s head.

These stretch injuries can result in one or more (and in many times, all) of the following:

  1. Nerve dysfunction: deformative stress of repetitive stretching of the cranial-cervical nerves can lead to cell dysfunction and nerve death in this area.
  2. Thickened odontoid capsule (pannus formation): when joints are hypermobile, pannus may grow in a tumor-like fashion where it may erode articular cartilage and bone. When this occurs on the odointoid bone (a bone in our upper neck that acts as our head’s axis) it can compress the brainstem.
  3. Retroflexed Odontoid: Loose ligaments can misalign the proper angle of the odontoid bone causing it to push backwards, compressing the brainstem.
  4. Chiari Malformation: a downward displacement of the cerebellar tonsils (part of the brain) that puts pressure on the cerebellum and brainstem, progressively damaging them over time, and blocking the flow of cerebral spinal fluid (CSF).
  5. Cranial Settling: the skull sinking downward onto the spine. In severe cases basilar invagination occurs, where the tip of the odontoid process projects above the foramen magnum (the opening at the bottom of the skull).
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Left: Retroflexion of the odontoid bone compressing the brain stem. Right: Basilar invagination occurs when the odontoid process goes above the foramen magnum (as shown by yellow line)

Unsurprisingly, the histopathological changes in neurons that are undergone in these situations (1) would not show up on any routine diagnostic test. In many cases, however, Chiari (4), cranial settling (5), and a retroflexed odontoid (3) may be demonstrable on MRIs, but typically only when imaged in the upright position. This would explain why many of these patients’ diagnostic imaging reports state negative results.

The following image shows a healthy looking MRI of an individual with EDS and CCI lying supine on the left compared with an MRI of the same individual in the upright position on the right. In the first image, the cerebellar part of the brain is neatly contained within the skull (i.e. where it should be) and the angle of the odontoid bone is within the normal limits. It is a radiographically normal MRI.

In the second image, however, there is a downward displacement of the cerebellar tonsils (demonstrated by downward arrow). The connective tissues here are too weak to hold up the cerebellum resulting in tonsillar herniation. Additionally, the odontoid bone is retroflexed, putting pressure on the brainstem.

Up right MRI

Woman with EDS supine (left) vs upright (right)

What are the Symptoms of Craniocervical Instability?

  • a heavy headache: a constant to near constant headache that can be described as feeling like the head is too heavy for the neck to support (feeling like a “bobble-head”)
  • a pressure headache: an impairment of CSF flow causes intracranial pressure which would be aggravated by “valsalva maneuvers” such as yawning, laughing, crying, coughing, sneezing or straining.
  • Dysautonomia: brainstem compression can lead to a dysfunctional autonomic nervous system (the involuntary regulator of all body functions). Symptoms of this include, but are not limited to:
    • tachycardia (rapid heart)
    • heat intolerance
    • orthostatic intolerance (low blood pressure when standing)
    • syncope (fainting)
    • polydipsia (extreme thirst)
    • delayed gastric emptying
    • chronic fatigueOCF
  • Other symptoms include:
    • neck pain
    • central or mixed sleep apnea
    • facial pain or numbness
    • balance problems
    • muscle weakness
    • dizziness and vertigo
    • vision problems
    • reduced gag reflux and difficulty swallowing
    • ringing in the ears and hearing loss
    • nausea and vomiting
    • impaired coordination
    • downward nystagmus (irregular eye movements)
    • paralysis
    • and more

How is Craniocervical Instability Diagnosed:

Upright MRI and Rotational 3d CT scans are the standard imaging techniques used to determine if CCI is present individuals with EDS. A definitive diagnosis of CCI can be made by a technique known as Invasive Cervical Traction (ICT). ICT is an inpatient procedure where the paitent’s head is pulled upward by a pulley system. If, over the course of 48 hours, the patient’s symptoms are cleared, CCI is confirmed.  Because ICT is rarely available in typical hospitals, as an alternative a doctor may simply pull the patient’s head up off the spine in the doctor’s office. If there is a reduction in pain and symptoms, it confirms the diagnosis. Patients may also have an extreme worsening of symptoms if their head is pushed downward.

What is the treatment for Craniocervical Instability?

Craniocervical fusion: a procedure in which the skull is pulled upward (cervical traction), placed into the corrected position, and then the occipital bone of the skull is fused to the upper cervical vertebrae to hold the corrected position. This procedure typically involves the use of rigid hardware, typically titanium (instrumented fusion) but can also involve a fusion construct (combination of bone, bone matrix, and sometimes bone morphogenic proteins) without hardware (noninstrumented fusion). Patients usually undergo rigid cervical immobilization following this procedure (cervical brace, halo vest, or custom minerva) until the occipital and cervical bones completely fuse together. In patients who also have a Chiari Malformation, the droopy and damaged cerebellar tonsils may be shrunk with electrocautery. This shrinkage ensures that there is no blockage of CSF flow out of the 4th ventricle.

 

References:

These Great Medical Conference Presentations:

WEBSITES:

http://csfinfo.org/education/physician-information/fusion-chiari-surgery/

ACADEMIC JOURNAL ARTICLES:

Milhorat, T. H., Bolognese, P. A., Nishikawa, M., McDonnell, N. B., & Francomano, C. A. Syndrome of occipitoatlantoaxial hypermobility, cranial settling, and chiari malformation type I in patients with hereditary disorders of connective tissue. Journal of Neurosurgery. 7, 601-609.

 

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