Neurosurgery for Hydrocephalus 

Hydrocephalus was first described by Hippocrates. Hydrocephalus was not treated effectively until the mid 20th century, when the development of appropriate shunting materials and techniques occurred. Interestingly, at the beginning of the 20th century, doctors (including urologists) attempted to introduce scopes into the ventricular system. Attempts were also made to remove the choroid plexus, which generates much of the cerebrospinal fluid (CSF), in an attempt to treat hydrocephalus. Today, the focus of hydrocephalus research is on pathophysiology, valve design in shunting, and minimally invasive techniques of treatment.

An image depicting hydrocephalus can be seen below.

Hydrocephalus is the abnormal rise in CSF volume and, usually, pressure, that results from an imbalance of CSF production and absorption.

Frequency

The overall incidence of hydrocephalus is unknown. When cases of spina bifida are included, congenital hydrocephalus occurs in 2-5 births per 1000 births. Incidence of acquired types of hydrocephalus is unknown.

Tanaka et al concluded that the incidence of idiopathic normal pressure hydrocephalus was 1.4% in their study of an elderly Japanese population.^[1]

The etiology of hydrocephalus in congenital cases is unknown. Very few cases (< 2%) are inherited (X-linked hydrocephalus). The most common causes of hydrocephalus in acquired cases are tumor obstruction, trauma, intracranial hemorrhage, and infection.

Hydrocephalus can be subdivided into the following 3 forms:

• Disorders of CSF production: This is the rarest form of hydrocephalus. Choroid plexus papillomas and choroid plexus carcinomas can secrete CSF in excess of its absorption.
• Disorders of CSF circulation: This form of hydrocephalus results from obstruction of the pathways of CSF circulation. This can occur at the ventricles or arachnoid villi. Tumors, hemorrhages, congenital malformations (such as aqueductal stenosis), and infections can cause obstruction at either point in the pathways.
• Disorders of CSF absorption: Conditions, such as the superior vena cava syndrome and sinus thrombosis, can interfere with CSF absorption. Some forms of hydrocephalus cannot be classified clearly. This group includes normal pressure hydrocephalus and pseudotumor cerebri.

The various types of hydrocephalus can present differently in different age groups.

Acute hydrocephalus typically presents with headache, gait disturbance, vomiting, and visual changes. In infants, irritability or poor head control can be early signs of hydrocephalus. When the third ventricle dilates, the patient can present with Parinaud syndrome (upgaze palsy with a normal vertical Doll response) or the setting sun sign (Parinaud syndrome with lid retraction and increased tonic downgaze). Occasionally, a focal deficit, such as sixth nerve palsy, can be the presenting sign. Papilledema is often present, although it may lag behind symptomatology. Infants present with bulging fontanelles, dilated scalp veins, and an increasing head circumference. When advanced, hydrocephalus presents with brainstem signs, coma, and hemodynamic instability.

Normal pressure hydrocephalus has a very distinct symptomatology. The patient is older and presents with progressive gait apraxia, incontinence, and dementia. This triad of symptoms defines normal pressure hydrocephalus.

Most cases of symptomatic hydrocephalus need to be treated before permanent neurologic deficits result or neurologic deficits progress.

When an etiologic factor is known, hydrocephalus can be treated with temporary measures while the underlying condition is treated. Examples of temporary treatment measures are ventriculostomy until a posterior fossa tumor is resected or lumbar punctures in a neonate with intraventricular hemorrhage until the blood is absorbed and normal cerebrospinal fluid (CSF) absorption resumes.

See Intraoperative details for a discussion of relevant anatomy.

Few cases of hydrocephalus should not be treated. Cases in which treatment should not be implemented include the following:

• The patient in whom a successful surgery would not affect the outcome (eg, a child with hydranencephaly)
• In ventriculomegaly of senescence, the patient who does not have the symptom triad
• Ex vacuo hydrocephalus is merely the replacement of lost cerebral tissue with cerebrospinal fluid. Because no imbalance in fluid production and absorption exists, this technically is not hydrocephalus.
• Arrested hydrocephalus is defined as a rare condition in which the neurologic status of the patient is stable in the presence of stable ventriculomegaly. The diagnosis must be made extremely carefully because children can present with very subtle neurological deterioration (eg, slipping school performance) that is difficult to document.
• Benign hydrocephalus of infancy is found in neonates and young infants. The children are asymptomatic, and head growth is normal. CT scan shows mildly enlarged ventricles and subarachnoid spaces.