Terms that appear in Chiari malformation scan reports, clinic letters and research papers, in plain English.
- Arnold-Chiari malformation
- An older name for Chiari malformation, properly used for Chiari II, the type that occurs with spina bifida.
- Aseptic meningitis
- Inflammation of the membranes around the brain without infection, causing headache, neck stiffness and fever. It can follow surgery in which the dura is opened.
- Brainstem
- The lowest part of the brain, connecting it to the spinal cord. It controls breathing, swallowing and other basic functions.
- Central sleep apnea
- Pauses in breathing during sleep because the brain stops signaling the breathing muscles, as opposed to a blocked airway.
- Cerebellar tonsils
- Two rounded lobes at the bottom of the cerebellum, just above the foramen magnum. In Chiari malformation they extend below it.
- Cerebellum
- The part of the brain at the back of the skull that controls balance and coordination.
- Cerebrospinal fluid (CSF)
- The clear fluid that surrounds and cushions the brain and spinal cord, moving between the head and the spine with each heartbeat.
- Cine MRI (CSF flow study)
- An MRI technique that shows cerebrospinal fluid moving with each heartbeat, used to see whether flow is blocked at the foramen magnum.
- Clivoaxial angle
- An angle measured on imaging between the base of the skull and the second vertebra. An abnormal angle may predict instability at the junction of the skull and spine.
- Cough headache
- A headache brought on within seconds by coughing, sneezing or straining. At the back of the head and lasting under five minutes, it is the characteristic headache of Chiari I.
- Craniocervical instability
- Abnormal movement between the skull and the top two vertebrae of the neck. It is sometimes treated by fusing the joint.
- Craniocervical junction
- The region where the skull meets the spine, including the foramen magnum and the first two vertebrae.
- CSF leak
- Escape of cerebrospinal fluid through a defect in the dura, either spontaneously in the spine or after surgery.
- Dura
- The tough outer membrane covering the brain and spinal cord.
- Dura-splitting decompression
- A version of decompression in which only the outer layer of the dura is divided, so the membrane can expand without being opened.
- Duraplasty
- Opening the dura and sewing in a patch to enlarge it. The patch can be made from the patient's own tissue or from a manufactured material.
- Encephalocele
- A sac containing brain tissue that protrudes through a defect in the skull, as in Chiari III.
- Foramen magnum
- The large opening at the base of the skull through which the brainstem continues into the spinal cord.
- Hydrocephalus
- Build-up of cerebrospinal fluid in the fluid spaces of the brain, raising pressure. It is common with Chiari II.
- Idiopathic intracranial hypertension (IIH)
- Raised pressure of the fluid around the brain without a visible cause. It can push the tonsils down and mimic Chiari I.
- Myelomeningocele
- The most severe form of spina bifida, in which the spinal cord and its coverings are exposed through an opening in the back at birth. Chiari II occurs with it.
- Nystagmus
- Involuntary jerking movements of the eyes, a sign of cerebellar or brainstem involvement.
- Obex
- A landmark on the back of the lower brainstem. Its position below the foramen magnum distinguishes Chiari 1.5 from Chiari I.
- Occipital bone
- The bone forming the back and base of the skull, around the foramen magnum.
- Occipital neuralgia
- Sharp, shooting pain along the nerves at the back of the head, often tender at a specific point.
- Posterior fossa
- The compartment at the back and base of the skull that holds the cerebellum and brainstem. In Chiari I it is too small for its contents.
- Posterior fossa decompression
- The standard operation for Chiari I. Bone is removed at the back of the skull, and usually the back of the first vertebra, to enlarge the space around the cerebellum. Also called foramen magnum decompression.
- Primary cough headache
- A headache brought on by coughing or straining with no structural cause. It closely resembles the Chiari headache.
- Pseudomeningocele
- A collection of cerebrospinal fluid under the skin after surgery, caused by fluid escaping through the dura.
- Scoliosis
- A sideways curve of the spine. In children it can be the first sign of a syrinx caused by Chiari I.
- Spontaneous intracranial hypotension
- Low pressure of the fluid around the brain, usually from a leak in the spine. It can pull the tonsils down and mimic Chiari I; the headache is worse when upright.
- Syringomyelia
- The presence of a syrinx in the spinal cord. With Chiari I it results from obstructed fluid flow at the foramen magnum.
- Syrinx
- A fluid-filled cavity inside the spinal cord.
- Tentorium
- A sheet of dura that separates the cerebellum from the rest of the brain above it.
- Tonsil reduction
- Shrinking the cerebellar tonsils with heat (coagulation) or partly removing them during decompression surgery.
- Tonsillar descent
- How far the cerebellar tonsils lie below the foramen magnum, measured in millimeters on MRI. At least 5 mm, or 3 mm with crowding, defines Chiari I.
- Tonsillar ectopia
- Cerebellar tonsils lying lower than normal. Another term for tonsillar descent.