Anatomy of an Abnormality
Chiari malformations (CMs) are structural defects appearing where the brain and spinal cord connect. There is an estimated one Chiari malformation for every 1,000 births amongst the general population. The advancement of imaging test technology may be the reason Chiari malformation diagnoses have been on the rise. Normally, the cerebellum (brain section which controls coordination and motion) rests in the indented area at the base of the skull (posterior fossa). The posterior fossa lies just above the foramen magnum; a funnel-like opening at the base of the skull where the spinal cord attaches to the brain. When the cerebellum forms below the foramen magnum, it is called a Chiari malformation.
Development of Structural Defects
CMs can develop when the space provided for the cerebellum is smaller than normal. Less space causes the brainstem to be pushed downward on the foramen magnum as well as the upper spinal canal. The downward pressure can lead to the blockage of cerebrospinal fluid (colorless liquid which cushions the brain and spinal cord) to and from the brain.
The cause of these abnormalities is unknown. They are deemed congenital (primary) conditions (diagnosed at birth), but are also known to be acquired (secondary) later in life when injury, infection or exposure to harmful substances calls for excessive amounts of fluid to be drained from the spine. It is widely accepted that the structural defects occur during fetal development due to several factors, such as genetic syndromes, lack of proper nutrition in the maternal diet and exposure to harmful substances during pregnancy.
Classifications of CMs
Classification depends on the condition’s severity as well as the affected sections of the brain and spinal cord. Classifications include:
Type I – Type I is the only classification that is secondary (can be acquired) and is typically discovered during examinations for other conditions during adolescence or early adulthood. This condition is characterized as having an undeveloped or improperly formed posterior fossa and upper spinal area.
Type II – A Type II CM is the most common. They are known as “Classic“ Chiari malformations where extensions of the rear part of the brain shift downward through the bottom of the skull. Downward displacement of the medulla as well as cerebellar and brain stem tissue into the spinal canal may cause several complications. Conditions such as spina bifida, hydrocephalus, myelomeningocele and other skull and spine-related birth defects share associated symptoms with Type II malformations.
Type III – High mortality rates, severe neurological defects and life-threatening complications are associated with this condition where portions of the cerebellum and/or brainstem protrude through a deficit in the rear of the head or neck.
Type IV – In Type IV CMs, the brain fails to develop fully or normally. This is the most severe and rare case.
Diagnosis and Treatment
Oftentimes, diagnoses of Chiari malformations are made when other congenital defects are present at birth. Diagnosis is often made after symptoms become apparent and tests (X-ray, MRI, CT scans) have been performed. A child’s medical history and developmental milestones are important in helping to diagnose a malformation.
Treatment is dependent on the exact type of malformation and any symptoms experienced. In many cases with infants, progressions of symptoms are rapid and severe, causing urgent or emergency actions to be taken. Malformations which cause no symptoms should not be treated.
Surgery can be performed to locally decompress bone, the dura (membrane covering brain and spinal cord) and the tissues of the spinal canal, or to resect a portion of cerebellar tissue. The goals of surgery are to optimally decompress nerve tissue and restore the normal flow of cerebrospinal fluid around and behind the cerebellum.
Reassurance of Excellent and Professional Care
The physicians of IGEA Brain, Spine & Orthopedics, P.A. are no strangers to neurosurgery and are board-certified specialists who work in the treatment of brain disorders. They aim to provide comprehensive neurosurgical care with the use of state-of-the-art technology. For answers to your questions about Chiari malformations, call 866-467-1770.