Chiari I Malformation is defined by a volumetrically small posterior cranial fossa (the compartment in the back of the skull), which leads to overcrowding of the cerebellum and brainstem. This causes a blockage of the flow of cerebro-spinal fluid through the foramen magnum, making it difficult for the fluid to flow around the brain and in and out of the skull. In many cases, the cerebellar tonsils are pushed downward through the foramen magnum. However, this is not a necessary part of diagnosis.
Chiari is generally considered congenital, although certain things like trauma and spinal taps have been shown to cause an acquired form of Chiari. Chiari has come to be better known with the advent of the MRI, leading to more people being diagnosed.
The symptoms of Chiari are caused by raised intra-cranial pressure and compression of the cerebellum and brainstem. Again, it is important to note that symptoms are not caused by herniation of the cerebellar tonsils, thus the length of herniation does not correlate with the severity of symptoms. Chiari symptoms may arise at any time in a person's life. Sometimes, symptoms are brought about by trauma (like surgery, injury, or childbirth), by growth spurts, or by illness. Other times, it is unknown what causes symptoms to set in. The following symptom list is from chiarione.org, and is the best compilation I've found. Please note that these symptoms are reported by patients, so they may be symptoms of related conditions in addition to strictly Chiari symptoms.
* Headache (esp. if daily or at lower back of head)
* Painful tension in neck
* Fatigue
* Migraines
* Dizziness
* Visual disturbances/loss of vision/spots in vision/double vision
* Tingling/numbness in the extremeties
* General imbalance/clumsiness
* Memory loss
* Intolerance to bright light/difficulty adjusting to light change
* Vertigo from position change or sudden standing
* Difficulty walking on uneven ground/feeling ground under feet
* Poor motor skills
* Pressure/pain in the neck
* Pressure/pain behind the eyes (soreness in the eyeballs)
* Back pain
* Neck spasms
* Insomnia
* Ringing in ears (like the tone heard in a hearing test)
* Tingling/crawling feeling on scalp
* Intolerance to loud/confusing sounds
* Decreased sensation to touch in extremeties
* Decreased sensitivity to temperature
* Pain & tension along ear/eye/jawline
* Difficulty swallowing/lump in throat/sore throat/swollen lymph nodes
* Spontaneous vertigo
* Hand tremors
* Poor blood circulation/cold hands & feet
* Sinus/mucous problems
* Sleep apnea
* Pressure in ears
* Nausea
* Difficulty reading/focusing on text
* Depth perception problems
* Burning sensation in extremeties/shoulder blades
* Fluid-like sound in ears (like water running)
* Loss of sexual interest/lack of sensation in pelvic area
* Pulling sensation while sitting/standing
* Intense itchiness w/profuse sweating
* Gag reflex problems/lack of gag reflex
* Pressure/tightness in chest
* Loss of bladder control
* Frequent urination
* Dehydration/excessive thirst
* Dizziness
* Loss of smell/confusion with sense of smell
* Dry skin and lips
* Sudden/abrupt changes in blood pressure
* Hiccups (in higher frequency/severity)
* Low body temperature/sudden changes in body temperature
* Strangling feeling
* Floating sensation
As you may be able to tell, the variety of symptoms is astounding. This is one of the major causes of misdiagnosis and underdiagnosis. Also, many doctors are not well-educated about Chiari, especially about the most recent definitions and standards for diagnosis. Many neurologists are unaware of the condition or its severity. Many radiologists will note Chiari as an "incidental" finding if they are not well-informed. Also, even many neurosurgeons may not believe Chiari is the cause of the patient's symptoms. In particular, they may be using the former standard that the cerebellar tonsils must be at least 5mm below the foramen magnum. Doctors now know that the length of the herniation does not correlate with symptom severity. In order to get diagnosed and treated properly, it is best to go to a neurosurgeon with a great deal of experience with Chiari.
The treatment for Chiari is called a decompression surgery. This consists of a craniectomy, a laminectomy, and/or a duraplasty. A craniectomy is where they remove part of the base of the skull to enlarge the foramen magnum, which is the passageway between the skull and spine, to make more room for the flow of cerebro-spinal fluid. A laminectomy may also be done, where they remove the arch of one or more vertebra, also to open up the posterior fossa space and decrease crowding in the hindbrain area. Additionally, sometimes a duraplasty is done, in which the dura (the lining of the spinal cord) is opened and replaced with a patch, allowing for extra space for the flow of fluids.
For people with straight-forward cases of Chiari 1 malformation with no other conditions, this surgery is adequate treatment, and often allows for a full recovery. Post-surgically, patients still need to be very careful with their fragile necks, but symptoms often disappear completely.