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).