TYPES OF CHIARI
Chiari type I, the most common, affects both children and adults. Because the back of the skull is too small or deformed, a crowding of the brainstem, cerebellum, and tonsils occurs. As the tonsils push out of the skull, they block CSF flow. Chiari I may cause a fluid-filled cyst (syrinx) in the spinal cord.
Chiari type 0, a newly identified form of Chiari, describes the absence (or a “zero” herniation) of the tonsils below the foramen magnum. Yet Chiari 0 includes the presence of both symptoms and a syrinx in the spinal cord. This new type is under study and controversial.
Chiari type II is present at birth and affects infants. It occurs with the birth defect myelomeningocele, a form of spina bifida. When the spinal canal does not close before birth, some of the spinal cord protrudes like a sac from the baby’s back. Both the brainstem and tonsils are pulled down into the spinal canal to block CSF flow in the brain and causing hydrocephalus. This type is correctly called Arnold-Chiari malformation.
Chiari type III affects infants and is a rare but severe herniation that involves the cerebellum. It can develop with the birth defect encephalocele, a fluid-filled sac at the back of the baby’s neck.
Chiari type IV affects infants. This rare and often fatal malformation occurs when the cerebellum does not develop properly.
In the late 19th century, Austrian pathologist Hans Chiari described seemingly related anomalies of the hindbrain, the so-called Chiari malformations I, II and III. Later, other investigators added a fourth (Chiari IV) malformation. The scale of severity is rated I – IV, with IV being the most severe. Types III and IV are very rare
The malformation is named for Austrian pathologist Hans Chiari. A type II CM is also known as an Arnold–Chiari malformation in honor of Chiari and German pathologist Julius Arnold.
Click link for more history https://pdfs.semanticscholar.org/79dd/127d31820d612600c0b032225437295d86c3.pdf
Chiari malformation is the most frequently used term for this set of conditions. The use of the term Arnold–Chiari malformation has fallen somewhat out of favor over time, although it is used to refer to the type II malformation. Current sources use “Chiari malformation” to describe four specific types of the condition, reserving the term “Arnold-Chiari” for type II only. Some sources still use “Arnold-Chiari” for all four types.
OTHER CONDITIONS ASSOCIATED WITH CM
Hydrocephalus is an excessive buildup of CSF in the brain. A CM can block the normal flow of this fluid and cause pressure within the head that can result in mental defects and/or an enlarged or misshapen skull. Severe hydrocephalus, if left untreated, can be fatal. The disorder can occur with any type of Chiari malformation, but is most commonly associated with Type II.
Spina bifida is the incomplete closing of the backbone and membranes around the spinal cord. In babies with spina bifida, the bones around the spinal cord do not form properly, causing defects in the lower spine. While most children with this birth defect have such a mild form that they have no neurological problems, individuals with Type II Chiari malformation usually have myelomeningocele, and a baby’s spinal cord remains open in one area of the back and lower spine. The membranes and spinal cord protrude through the opening in the spine, creating a sac on the baby’s back. This can cause a number of neurological impairments such as muscle weakness, paralysis, and scoliosis.
Syringomyelia is a disorder in which a CSF-filled tubular cyst, or syrinx, forms within the spinal cord’s central canal. The growing syrinx destroys the center of the spinal cord, resulting in pain, weakness, and stiffness in the back, shoulders, arms, or legs. Other symptoms may include a loss of the ability to feel extremes of hot or cold, especially in the hands. Some individuals also have severe arm and neck pain.
Tethered cord syndrome occurs when a child’s spinal cord abnormally attaches to the tissues around the bottom of the spine. This means the spinal cord cannot move freely within the spinal canal. As a child grows, the disorder worsens, and can result in permanent damage to the nerves that control the muscles in the lower body and legs. Children who have a myelomeningocele have an increased risk of developing a tethered cord later in life.
Spinal curvature is common among individuals with syringomyelia or CM Type I. The spine either may bend to the left or right (scoliosis) or may bend forward (kyphosis).
Connective tissue disorders such as Ehlers-Danlos syndrome and Marfan syndrome are sometimes associated with CM.