Arnold-Chiari Malformation

Arnold-Chiari malformation, sometimes referred to as 'Chiari malformation' or ACM, is a congenital anomaly of the brain in which the cerebellar tonsils are elongated and pushed down through the opening of the base of the skull (see foramen magnum), blocking the flow of cerebrospinal fluid (CSF). The brainstem, cranial nerves, and the lower portion of the cerebellum may be stretched or compressed. Therefore, any of the functions controlled by these areas may be affected. The blockage of CSF flow may also cause a syrinx to form (syringomyelia).

In infants, the most common symptoms are stridor and swallowing difficulties. In older children, upper limb weakness and breathing difficulties may occur. Patients may experience no symptoms or remain asymptomatic until early adulthood, at which point they will often experience severe headaches and neck pain. Fatigue, dizziness, vertigo, neuropathic pain, visual disturbances, difficulty swallowing, ringing in the ears, impaired fine motor skills, muscle weakness, and palpitations are other common symptoms. Because of the complex combination of symptoms and the lack of experience with ACM1 had by many, even outstanding neurologists and neurosurgeons, many patients are frequently misdiagnosed.

Some patients may go an entire lifetime without having noticeable symptoms. Or, symptoms can be minimal, then turn severe suddenly due to head trauma which alters the condition of the spine, brain, or cerebellar tonsils and begins to cause more difficulties. Once these "onset of symptoms" occurs, the most frequent treatment is decompression surgery, in which a neurosurgeon seeks to open the base of the skull and through various methods unrestrict CSF flow to the spine.

Arnold-Chiari Malformation II occurs in almost all children born with both spina bifida and hydrocephalus, but ACM I is typically seen in children and adults without spina bifida. The scale of severity is rates I - IV, with IV being the most severe.

History
An Austrian pathologist, Professor Hans Chiari, first described these hindbrain malformations in the 1890s. A colleague of Professor Chiari, Dr. Arnold, later contributed to the definition of the condition, and students of Dr. Arnold suggested the term "Arnold-Chiari malformation" to henceforth refer to the condition.