Chapter 55 Raised intracranial pressure
Raised intracranial pressure (RICP) may be caused by space-occupying lesions including intracranial tumors, obstructed circulation and readsorption of cerebrospinal fluid (CSF) resulting in hydrocephalus, or pseudotumor cerebri syndromes. These conditions generate frequent clinical questions in the eye clinic. For example, patients in primary eye care may have physical signs which point toward RICP and which require urgent neurologic evaluation; other specialists frequently request ophthalmic assessment when there is known or suspected RICP and patients with treated RICP need to be followed carefully to be sure that vision remains stable.
Headache is the most common symptom of a brain tumor causing RICP by the time of hospital admission, but is a rare presenting symptom. Because headache is such a common symptom it accounts for many referrals because of concerns about the possibility of RICP. Brain tumor headaches may be intermittent, non-specific, and indistinguishable from tension headaches. A number of features are suggestive of RICP:
Brain tumors cause RICP by a variety of mechanisms. They may grow so large, so quickly that they cause stretching of pain-sensitive intracranial structures by a direct mass effect or by an effect on the microvasculature leading to cerebral edema. Tumors may also cause RICP by producing large cysts. Smaller tumors, particularly those in the posterior fossa, may cause headaches by obstructing cerebrospinal fluid circulation and producing hydrocephalus. Headaches with migrainous features are rarely due to an underlying tumor. Occipital tumors may produce occipital seizures, similar in some respects to migraine.
RICP may lead to gradual deterioration in cognition, intermittent drowsiness, and eventually coma. Progressive herniation of the medial temporal lobe across the tentorium causes an ipsilateral third nerve palsy; herniation of the cerebellar tonsils through the foramen magnum leads to coma and death.
Infants and younger children may present with vague symptoms including poor feeding, mood changes, lethargy, irritability, and somnolence. Other symptoms include failure to thrive, behavioral disturbances, drowsiness, posturing, and seizures. Physical findings may include bulging fontanelles, rapid growth of head circumference, and distended scalp veins. In older children and teenagers, abnormal signs may be confined to the eyes.
Abnormalities may include supranuclear vertical gaze palsies in pretectal syndromes, horizontal gaze palsies and nystagmus in posterior fossa masses, and skew deviation in a pretectal syndrome. Single infranuclear cranial nerve palsies may be a false localizing sign of raised pressure, especially sixth or fourth nerve palsy; third nerve palsy may be due to uncal herniation. Childhood comitant esotropia with a deviation larger for distance than near may originate from central nervous system (CNS) lesions. Tumors involving the anterior visual pathways (e.g. optic pathway glioma and craniopharyngioma) may present with a sensory deviation in one eye with advanced visual loss and optic atrophy combined with RICP.
Acute papilledema does not usually reduce vision (apart from blindspot enlargement), but as secondary atrophy develops, peripheral field loss may develop with preserved central acuity. Acuity is only lost after major field loss, and is not usually recoverable. Monitoring visual field (VF) is mandatory. Monitoring disk swelling alone is not sufficient.
Hydrocephalus is RICP associated with dilated lateral ventricles. This is due to an imbalance between secretion of CSF in the choroid plexus within the lateral ventricles, and reabsorbtion from the arachnoid villi in the subarachnoid space. Causes are classified as:
Hydrocephalus may be congenital or acquired. Congenital hydrocephalus is one of the most frequent congenital abnormalities of the CNS and a common complication of spina bifida and neural tube defects. Other causes include cerebral aqueduct stenosis, Chiari malformation, and Dandy-Walker syndrome. Common causes of acquired hydrocephalus include meningitis and intraventricular hemorrhage in preterm infants.
The features of hydrocephalus depend on the age of the child and whether the RICP is acute in onset. When the cranial sutures have not closed, there is a progressive increase in skull growth with separation of the sutures. The fontanel is tense and scalp veins are dilated due to compression of the cortical veins and sinuses. If the ventricles are greatly enlarged, the skull may transilluminate. There may be failure to thrive and developmental delay. Papilledema is uncommon but the “setting-sun” sign – upper-lid retraction and downwardly deviated eyes due to upgaze paresis – may be seen in infants. In later childhood, papilledema is typically present often accompanied by unilateral or bilateral sixth nerve paresis and upgaze impairment.
Ventriculo-peritoneal shunt insertion is the most commonly performed pediatric neurosurgical procedure. In a series from the United States, 69 000 discharges and 36 000 procedures related to shunts were performed in 1995. The population with hydrocephalus has grown considerably since that study due to improved survival of very premature infants. The morbidity due to complications remains significant. In one UK series, there was a 11% mortality rate during a 10-year follow-up study of 155 children.1