Arnold-Chiari type II malformation
Incidence
Autosomal recessive or sporadic. It is common. Type II is almost always associated with spina bifida, and hydrocephalus and all their clinical problems.
Clinical Characteristics
An Arnold-Chiari Malformation (ACM) occurs when the brain forms incorrectly. This abnormality occurs very early in pregnancy, when the brain is still forming. This malformation involves the base, or bottom, of the brain, where the skull and the spine meet. This malformation results in some of the brain's structures being moved downward into the spinal canal. This pushing down of the brain into the spinal canal can lead to pressure on the lower parts of the brain and spinal cord. The symptoms found with this malformation are related to the damage done to the lower parts of the brain and spinal cord. ACM 2 symptoms are due to brain stem and cranial nerve damage. Most people who have this malformation have these symptoms in early childhood or in the newborn period. Symptoms include: swallowing difficulties: which result in poor eating, cyanosis (turning blue) during feeding, swallowed food coming out through the nose, prolonged feeding time, drooling, apneic spells (periods when the child does not breathe), stridor (difficulty taking a breath), aspiration (food entering the lungs), arm weakness, nystagmus (abnormal eye movements), weak or absent cry, progressive scoliosis, weakness of the muscles of the face. Untreated, ACM can lead to very serious consequences including paralysis. This form of the malformation may be accompanied by syringomyelia, hydrocephalus and spina bifida (myelomeningocele).
Precipitants
None
Provocation Tests
None
Diagnostic Procedures
MRI of the brain. Type II usually diagnosed at birth or infancy. It is characterized by a further downward displacement (herniaition) of the cerebellar tonsils and fourth ventricle at the foramen magnum into the cervical spinal cord. A kink in the medulla occurs in 55% of the cases of Type II which may cause brain stem or cervical cord compression. Type II is almost always associated with spina bifida, and hydrocephalus and all their clinical problems.