HYDROCEPHALUS
 |
Symptomatic
hydrocephalus is subdivided into obstructive and nonobstructive etiologies.
Obstructive hydrocephalus is due to blockage of CSF flow by a congenital
malformation, such as aqueductal stenosis or suprasellar arachnoid cyst, or by
an acquired condition, such as a ventricular tumor that obstructs flow (Plate 1-15).
Communicating hydrocephalus was originally defined before modern imaging
modalities by the ability to recover dye initially injected into the lateral
ventricle from the lumbar thecal space. Communicating, or nonobstructive
hydrocephalus, is due to impaired CSF absorption through the arachnoid villi
and occurs most commonly secondary to intraventricular or subarachnoid
hemorrhage, trauma, meningitis, or leptomeningeal tumor spread.
When
symptomatic hydrocephalus occurs in infants and young children, progressive
macrocephaly occurs because the cranial sutures are not yet fused. Head
circumference measurement and assessment of the fontanel and cranial suture
closure are routine components of the neurologic examination (see Plate 1-16).
Other causes of macrocephaly in infants are benign external hydrocephalus and
extra-axial fluid collections. Benign external hydrocephalus usually occurs in
the setting of familial macrocephaly, is asymptomatic except for the
excessively large head circumference, and has a characteristic imaging pattern
of frontal extra-axial collections without any suggestion of mass effect. The
infant has a normal neurologic examination without other symptoms or signs of
elevated intracranial pressure. Extra-axial fluid collections associated with
elevated intracranial pressure have other etiologies, including meningitis and
subdural hematomas from abusive head trauma and rare metabolic disorders.
Elevated intracranial pressure in infants, including from advanced symptomatic
hydrocephalus or extra-axial fluid collections, is often characterized by
lethargy, irritability, poor oral intake, engorged scalp veins, a full fontanel,
and downward deviation of the eyes, referred to as “sunset eyes.”
Imaging
with CT or MRI can facilitate the diagnosis and management of patients with
suspected hydrocephalus. Patients with suspected elevated intracranial pressure
from hydrocephalus need imaging with CT or MRI before any intervention that
might change the CSF dynamics, such as a lumbar puncture. Current MRI sequences
can suggest points of blockage or demonstrate flow through the aqueduct of
Sylvius. The coronal brain section shown in the illustration indicates that the
hydrocephalus, in this instance, is caused either by obstruction of an outflow
pathway distal to the third ventricle or is a form of communicating
hydrocephalus, in which case the fourth ventricle would also be dilated. Symptomatic
hydrocephalus in older children and adults is similarly divided into
obstructive and non-obstructive etiologies, and this guides management
decisions. Clinically, patients with symptomatic hydrocephalus
are often lethargic, with headache, emesis, and other features of elevated
intracranial pressure, including papilledema and cranial nerve palsies. Idiopathic
intracranial hypertension, or pseudotumor cerebri, is characterized by
elevated intracranial pressure without ventriculomegaly. Patients typically
pre- sent with headache, vision loss, and diplopia and may require urgent
intervention to minimize vision loss.
Normal-pressure
hydrocephalus (NPH) is a well-described syndrome in adults that is
associated with neurologic symptoms and signs without markedly elevated
intracranial pressure. Initial symptoms are progressive dementia, gait
disorders, and urinary incontinence. Brain imaging shows ventricular dilation,
and the condition must be differentiated from ventricular dilation secondary to
brain atrophy. A high-volume lumbar puncture can be diagnostic, although other
clinicians prefer to use an isotope cisternogram to trace the CSF circulation
(remove cisternogram images). In carefully selected patients with NPH, symptoms
improve or esolve after the CSF shunt insertion (see Plate
1-16).
