E. Lee Murray, MD

DEVELOPMENTAL DISORDERS

There are innumerable developmental disorders; this chapter does not address disorders that primarily affect children, because of the adult focus of this book. Instead, we focus here on developmental or genetic disorders that are likely to come to the attention of the hospital neurologist.

Chiari Malformations

Chiari malformations are a family of disorders affecting the brainstem, upper cervical spinal cord, and craniocervical junction. In hospital practice, only Chiari type 1 is commonly encountered; the other types are rarer and/or usually diagnosed in childhood.

The types are:

•Chiari-1: Cerebellar tonsils extending below the foramen magnum

•Chiari-2: Cerebellar tonsils and vermis extending below the foramen magnum, with myelomeningocele

•Chiari-3: Cerebellum and brainstem protrude through the foramen magnum, as can the 4th ventricle; may be associated with occipital encephalocele

•Chiari-4: Cerebellar hypoplasia, without displacement of the tonsils

PRESENTATION of Chiari-1 is varied. This is often a diagnosis made after magnetic resonance imaging (MRI) is performed for symptoms unrelated to the finding. Chiari has been theorized to be implicated in a variety of disorders for which it has no consistent responsibility, such as fibromyalgia and chronic fatigue syndrome. When Chiari-1 has neurologic symptoms, presentation is usually with headache, which is often worse with movement of the head and neck, cough, or Valsalva maneuver. Neurologic deficits may include cerebellar ataxia, myelopathy, nystagmus, dysarthria, or dysphagia.

DIAGNOSIS is considered when a relatively young patient, usually young adult, has cerebellar and/or corticospinal findings, especially when there are other bulbar deficits. MRI brain shows the anatomical change, with the degree of cerebellar displacement and craniocervical compression appropriate to the symptoms. Mild Chiari-1 unrelated to the presentation is common, and other causes of the symptoms need to be considered. If Chiari is diagnosed, MRI of the spine should be considered to look for syringomyelia.

MANAGEMENT depends on the severity. If symptoms are minimal, only symptomatic treatment is needed. Neurologic deficits should prompt consideration of neurosurgical consultation. Suboccipital decompression can be performed, but more extensive surgery is sometimes needed.

The role of the neurologist is usually to determine whether a newly diagnosed Chiari seen on MRI explains the symptoms and needs further evaluation or treatment. Often, the finding is incidental, and the search for a cause of the neurologic complaints should continue.

Syringomyelia and Syringobulbia

Syringomyelia is a fluid-filled cavity within the spinal cord, and syringobulbia is a similar cavity in the brainstem. Many of these are associated with Chiari malformations or other developmental abnormalities.

PRESENTATION depends on the anatomy:

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