Congenital malformations - Edocr

72 PART II CENTRAL NERVOUS SYSTEM MALFORMATIONS
CLINICAL PRESENTATION
The Chiari I malformation is rarely diagnosed in
the neonatal period unless it is associated with a
broader malformation syndrome that leads to
neuroimaging. Patients with an isolated Chiari I
typically appear normal in early infancy and the
diagnosis is not established until early adult life. At
the time of diagnosis, it is sometimes recognized,
however, that patients have had lifelong symptoms
including headache and clumsiness. When
the diagnosis is established, the most common
presenting symptoms are headache and neck pain,
although a wide variety of signs and symptoms
can be observed. 5 Symptoms in Chiari I are generally
felt to be the result of direct cerebellar
compromise, compression of the brain stem and
cranial nerves, and syrinx-associated central cord
syndrome. In addition to head and neck pain,
other symptoms that can be observed include
blurred vision or photophobia, dizziness, tinnitus,
decreased hearing, dysphagia, numbness, and
weakness. Some patients present with apnea, possibly
related to respiratory center dysfunction, or
to vocal cord paralysis, and these patients may be
at increased risk for postoperative complications.
When the diagnosis of a Chiari I malformation is
suspected, it can be confirmed by MRI (Fig. 10-1).
It has been estimated that approximately
57% of pediatric patients with a Chiari I are
asymptomatic. Of those who have symptoms,
63% have pain, 26% numbness, 19% weakness,
16% incoordination, 18% cranial nerve abnormalities,
28% central cord signs, and 13% cerebellar
signs. 6 Scoliosis is an important finding as
it is indicative of the presence of syringomyelia. 7
The Chiari type II malformation (or
Arnold-Chiari malformation) has associated
myelomeningocele in all cases and essentially
never occurs in its absence. Less than 20% of
Chiari II malformations produce symptoms and,
when they do, they usually occur prior to
3 months of age. The Chiari II malformation is the
leading cause of death in infants with spina bifida
under the age of 2 years. 8 Symptoms begin
to appear following closure of the spinal defect
Figure 10-1. Sagittal MRI of a patient with a
Chiari I malformation showing the herniation of
the cerebellar tonsils through an enlarged
foramen magnum. (Used with permission from
Alexander G. Bassuk, MD, PhD, Dept. of Pediatrics,
Northwestern University University’s
Feinberg School of Medicine.)
and are the result of brain stem dysfunction resulting
from the small posterior fossa with downward
displacement of the hindbrain into the
cervical canal, obstructing the flow of CSF into
the fourth ventricle. The lower cranial nerves are
compressed as they exit the cranium and are at
risk for necrosis. Symptomatic infants present
with dysphonia, stridor, difficulty in swallowing,
and vocal cord dysfunction. Sleep apnea is common
and glossopharyngeal dysfunction leads to
an increased risk of aspiration. Vagal nerve dysfunction
results in respiratory compromise and
sudden death. There is no correlation between
the level of the myelomeningocele and the risk
of a symptomatic Chiari II malformation.
ASSOCIATED MALFORMATIONS
AND SYNDROMES
There are no anomalies commonly associated with
Chiari I malformations. Hydrocephalus occurs in
less than 10% of cases. Other CNS anomalies are