Porth's Essentials of Pathophysiology, 4e

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Disorders of Brain Function

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reabsorption of CSF, or obstruction of CSF flow in the ventricular system. Pathophysiology. There are two types of hydroceph­ alus: communicating and noncommunicating. 4,7 Com­ municating hydrocephalus is caused by impaired reabsorption of CSF from the arachnoid villi into the venous system. Decreased absorption can result from a block in the CSF pathway to the arachnoid villi or a failure of the villi to transfer the CSF to the venous sys- tem. It can occur if too few villi are formed, if postinfec- tive (meningitis) scarring occludes them, or if the villi become obstructed with fragments of blood or infec- tious debris. Adenomas of the choroid plexus can cause an overproduction of CSF. This form of hydrocephalus is much less common than that resulting from decreased absorption of CSF. Noncommunicating or obstructive hydrocephalus occurswhenobstruction in the ventricular systemprevents the CSF from reaching the arachnoid villi. Cerebrospinal fluid flow can be obstructed due to congenital malforma- tions, tumors encroaching on the ventricular system, or inflammation or hemorrhage. Similar pathologic patterns occur with noncommunicating and communicating types of hydrocephalus. The cerebral hemispheres become enlarged, and the ventricular system beyond the point of obstruction becomes dilated 4 (Fig. 37-5). The sulci on the surface of the brain become effaced and shallow, and the white matter reduced in volume. Clinical Manifestations. In adults and children in whom the cranial sutures have fused, head enlargement does not occur. 4 Acute-onset hydrocephalus usually is marked by symptoms of increased ICP, including head- ache, vomiting, and papilledema or deviation in eye

movements due to pressure on the cranial nerves. 7 If the obstruction is not relieved, progression to herniation ensues. Signs and symptoms of hydrocephalus vary greatly, depending on age and rapidity of onset. When hydro- cephalus develops in utero or before the cranial sutures of the skull have fused in infancy, the ventricles expand beyond the point of obstruction, the cranial sutures separate, the head expands, and there is bulging of the fontanels. Because the skull is able to expand, signs of increased ICP may be absent, and intelligence spared. However, seizures are not uncommon, and in severe cases, optic nerve atrophy leads to blindness. Weakness and uncoordinated movement are common. Surgical placement of a shunt allows for diversion of excess CSF fluid, preventing extreme enlargement of the head and neurologic deficits. Diagnosis andTreatment. The most common diagnos- tic studies are computed tomographic (CT) and mag- netic resonance imaging (MRI). The usual treatment is a ventricular shunting procedure, which provides an alter- native route for return of CSF to the circulation. 7 Normal Pressure Hydrocephalus. An important type of communicating hydrocephalus that is seen in older adults is called normal-pressure hydrocephalus . 4,7 In normal-pressure hydrocephalus, there is ventricular enlargement with compression of cerebral tissue, but a normal CSF pressure. The signs and symptoms of normal-pressure hydrocephalus, which include memory changes, disturbances in gait, and urinary incontinence, usually have an insidious onset. The changes occur so slowly that they can be easily overlooked by the patient or his or her family or they may be attributed to the aging process. 7 The accepted treatment for normal-pressure hydrocephalus is a ventricular shunt. Traumatic Brain Injury The term “head injury” is used to describe all struc- tural damage to the head, including injury to the skull, brain, or both. The leading causes of head injury are motor vehicle accidents, bicycle crashes, battlefield trauma, sports injuries, falls, and assaults. 9,10 Head injury with concussion is becoming increasingly recog- nized as a significant medical problem with significant morbidity and sometimes devastating complications. 9 High-profile cases involving athletes and large num- bers of returning armed services personnel with battle- field injuries have brought concussions to the forefront of concern for school athletic personnel and health care professionals. The physical forces associated with head injury may result in skull fractures, brain injury, and vascular dam- age, all three of which can coexist. 1,4 Skull fractures are frequently accompanied by intracranial lesions, and the presence of skull fracture greatly increases the risk of an underlying subdural and/or epidural hemorrhage.

FIGURE 37-5. Hydrocephalus. Horizonatal section of the brain from a patient who died of a brain tumor that obstructed the aqueduct of Sylvius shows marked dilation of the lateral ventricles. (From Fuller GN, Goodman JC. Central nervous system. In: Rubin R, Strayer DS, eds. Rubin’s Pathology: Clinicopathologic Foundations of Medicine. 6th ed. Philadelphia, PA: Wolters Kluwer Health | Lippincott Williams & Wilkins; 2012:1302.)