Compiled by Robin Armstrong Griffin
When I hear a member in the support groups is diagnosed with Chiari the next question they often ask is why then should I concern over Ehlers-Danlos Syndrome (EDS) or Tethered Cord (TC)? Isn't chiari just caused by a small skull so the brain is forced down?
Chiari is a hind brain herniation of the cerebellar tonsils/lower brain down out of the skull and into the neck. It is caused by a malformation of bones within or near the skull or the pulling from below by Tethered Cord Syndrome, (explained below). In other words, chiari is a symptom caused by a malformation/underlying condition of something else. And a small skull is not the only condition that can be present to cause it, which many doctors feel is the case. So knowing the true underlying condition is key to the proper treatment of your Chiari.
Ehlers-Danlos Syndrome (EDS) is a connective tissue disorder. Connective tissue acts like "glue" in the human body, holding everything together. Collagen, a protein that adds strength to the connective tissues, is not produced correctly in an individual with EDS. The resulting weak connective tissues are too weak to hold the organs, ligaments, joints, etc.of the body in place. Ehlers-Danlos Syndrome is currently separated into 6 major types. Hypermobility, Classic, Vascular, Kyphoscoliosis, Arthrochalasis and Dermatosparaxis. More and more individuals with Chiari are being found to also have EDS and/or Tethered Cord (TC). (The EDS and/or TC being the CAUSE of the hind brain herniation/chiari.) Although at risk for any type, Hypermobility or Classic are seen the most, some the more rare Vascular type.
Individuals with Ehlers-Danlos Syndrome (EDS) are at risk for cranio-spinal instability (CSI), which often results in cranial settling. In cranial settling the tissues in the neck are so weak (due to EDS) that the cervical bones are not held in place. Slumping or collapsing onto itself occurs. These usually leads to abnormal angles/malformations of various bones and this can lead to both anterior and posterior brain stem compression. Many chiari surgeries (Decompression) fail because only the posterior brainstem compression was addressed. And since most have an MRI laying down the true picture isn't seen because the patient wasn't upright for gravity to reflect to true image. Hence the importance of upright MRI's. These malformations force the cerebellar tonsils out of the skull into the spinal column through the small hole at the base of the skull called the foramen magnum, a phenomena called cerebellar herniation, AKA Chiari. When the cerebellar tonsils are out of place, they take up space normally allotted for the cerebral spinal fluid (CSF), the brainstem, and all the arteries and veins leading through this area to the brain. Blockage can be both posterior and anterior. The cerebellar tonsils are the lowest part of the cerebellum, which controls the sensory perception and motor control systems of the body. The brainstem controls the autonomic nervous system, or everything your body does without you having to think about it, heart rate, respiration, blood pressure control, etc. Damage to these systems is very serious. CSI may also allow the Odontoid bone at the front of the neck to angle into the brainstem (Retroflexed Odontoid), causing even more concerns, such as Basilar Invagination or Basilar Impression. (Brain Stem Compression).
Postural Orthostatic Tachycardia Syndrome (POTS) is a type of dysautonomia. It is also commonly seen with individuals who have EDS and EDS with Chiari as a result of brainstem concerns. In addition to this, an individual with EDS and instability is at risk of subluxation (partial dislocation of bones) of the neck or abnormal sliding of the skull in flex/extension, further compromising the brainstem, tonsils and vertebral arteries. Making this life threatening. When you flex and extend your head, your skull should shift up to 1-2mm, with instability your skull can exceed that, (Stephens' is 8mm) further endangering the individual and for some is even life threatening.
As shared from Dr. Clair Francomano at Harvey Institute of Genetics. "The term "Chiari Malformation" is used to describe the situation where the cerebellum, a structure at the base of the brain, is extending through the opening at the base of the skull, which is called the foramen magnum. The extension through the foramen magnum is called "herniation." This can result from cranial settling, which "pushes" the cerebellum through the opening, or tethered cord, which pulls the cerebellum from below. The conventional definition of a Chiari Malformation states the cerebellum tonsils must protrude at least 5mm below the foramen magnum. However, patients with less extreme herniations can also experience significant neurological symptoms involving the brain stem and cerebellar functions.
A wide variety of neurologic symptoms include headaches, neck pain, tinnitus, swallowing difficulties, visual disturbances, a sensation of pressure behind the eyes, autonomic nervous system dysfunction (POTS, neurally mediated hypotension), sleep disturbances, brain fog and memory issues may result from Chiari Malformations.
Another complication of hereditary connective tissue disorders is called occult tethered cord. In this condition, a band of connective tissue called the filum is wrapped around the base of the spinal cord and exerting pressure on the nerves that go to the legs, pelvis, bladder and bowel. This condition may cause numbness in the legs and pelvis area as well as severe incontinence as well. Because of the hyperextensibility of the connective tissue in patients with this disorder, the filum may become stretched out over the years and is not visible on an MRI. This is why it is called "occult", it cannot be seen using current imaging techniques. Diagnosis is usually made based on clinical findings and also the consequences of tethering which may be seen on a cervical and brain MRI, affecting the angles between specific landmarks in the spine and skull (Milhorat TM et al. Association of Chiari Malformation type 1 and tethered cord syndrome: preliminary results of sectioning filum terminale. Surgical Neurology 72: 20-25, 2009). At this time, it is not known why this condition occurs more frequently in patients with hereditary disorders of connective tissue."
The problem is if you have EDS and it isn't known and you have decompression, ESP with laminectomy, it adds instability. This can greatly effect the success of the decompression because you've added more instability and only addressed the posterior issues and not the anterior issues often seen with cranial settling. Often times those with EDS & Chiari need fusion done at the same time or known to be needed at a later time or tethered cord release done first or soon after. Many also chose to wear cervical collars to help with the instability symptoms and pain. The decompression alone often treats only a part of the issue, not all and even if CSF flow is restored posterior the pain and neuropathy issues still remain due to cranio-instability and continued brainstem compression in other areas or tethered cord still pulling the tonsils from below. Thank you for reading!
Resources: Dr. Clair Francomano, Harvey Institute of Genetics and www.MedicalZebras.com
