Neurologic Disorders



Neurologic Disorders






INTRODUCTION

The neurologic system, the body’s communications network, coordinates and organizes the functions of all body systems. This intricate network has three main divisions:



  • central nervous system (CNS): the control center, made up of the brain, the brain stem, and the spinal cord


  • peripheral nervous system: motor and sensory nerves that connect the CNS to remote body parts and relay and receive messages from them


  • autonomic nervous system (part of the peripheral nervous system): regulates involuntary functioning of the internal organs and vascular system.


FUNDAMENTAL UNIT

The fundamental unit of the nervous system is the neuron, a highly specialized conductor cell that receives and transmits electrochemical nerve impulses. Its structure contains delicate, threadlike nerve fibers that extend from the central cell body and transmit signals: axons, which carry impulses away from the cell body, and dendrites, which carry impulses to it. Most neurons have multiple dendrites but only one axon. Sensory (afferent) neurons transmit impulses from special receptors to the spinal cord or the brain, motor (efferent) neurons transmit impulses from the CNS to regulate activity of muscles or glands, and interneurons (connecting or association neurons) shuttle signals through complex pathways between sensory and motor neurons. Interneurons account for 99% of all the neurons in the nervous system and include most of the neurons in the brain. (See Parts of a neuron.)


INTRICATE CONTROL SYSTEM

This intricate network of interlocking receptors and transmitters forms, together with the brain and spinal cord, a dynamic control system — a living computer — that controls and regulates every mental and physical function. From birth to death, this astonishing system efficiently organizes the body’s affairs — controlling the smallest action, thought, or feeling; monitoring communication and instinct for survival; and allowing introspection, wonder, abstract thought, and awareness of one’s own intelligence. The brain, the primary center of the CNS, is the large soft mass of nervous tissue housed in the cranium and protected and supported by the meninges and skull bones.

The fragile brain, brain stem, and spinal cord are protected by bone (the skull and vertebrae), cushioning cerebrospinal fluid (CSF), and three protective membranes, called meninges:



  • The dura mater, or outer sheath, is made of tough white fibrous tissue.


  • The arachnoid membrane, the middle layer, is delicate and lacelike.


  • The pia mater, the inner meningeal layer, is made of fine blood vessels held together by connective tissue. It’s thin and transparent and clings to the brain and spinal cord surfaces, carrying branches of the cerebral arteries deep into the brain’s fissures and sulci.

Between the dura mater and the arachnoid membrane is the subdural space; between the pia mater and the arachnoid membrane is the subarachnoid space. The subarachnoid space and the brain’s four ventricles contain CSF, a clear liquid containing water and traces of organic materials (especially protein), glucose, and minerals.

CSF is formed from blood in capillary networks called choroid plexus, which are located primarily in the brain’s lateral ventricles. This fluid is eventually reabsorbed into the venous blood through the arachnoid villi, in dural sinuses on the brain’s surface.

The cerebrum, the largest portion of the brain, is the nerve center that controls sensory and motor activities and intelligence. The outer layer of the cerebrum, the cerebral cortex, consists of neuron cell bodies (gray matter); the inner layers consist of axons (white matter) and basal ganglia, which control motor coordination and steadiness. The cerebral surface is deeply convoluted, furrowed with elevations (gyri) and depressions (sulci). A longitudinal fissure divides the cerebrum into two hemispheres connected by a wide band of nerve fibers called the corpus callosum, through which the hemispheres share information. The hemispheres don’t share equally; one always dominates, giving one side control over the other. Because motor impulses descending from the brain through the pyramidal tract cross in the medulla, the right hemisphere controls the left side of the body; the left hemisphere, the right side of the body. Several fissures divide the cerebrum into lobes, each of which is associated with specific functions. (See A look at the lobes, page 154.)

The thalamus, a relay center below the corpus callosum, further organizes cerebral function by transmitting impulses to and from appropriate areas of the cerebrum. In addition to its primary relay function, it’s responsible for primitive emotional responses, such as fear, and for distinguishing pleasant stimuli from unpleasant ones.


The hypothalamus, which lies beneath the thalamus, is an autonomic center that has connections with the brain, spinal cord, autonomic nervous system, and pituitary gland. It regulates temperature control, appetite, blood pressure, breathing, sleep patterns, and peripheral nerve discharges that occur with behavioral and emotional expression. It also has partial control of pituitary gland secretion and stress reaction.


THE BASE OF THE BRAIN

Beneath the cerebrum, at the base of the brain, is the cerebellum. It’s responsible for smooth muscle movements, coordinating sensory impulses with muscle activity, and maintaining muscle tone and equilibrium.

The brain stem houses cell bodies for most of the cranial nerves and includes the midbrain, the pons, and the medulla oblongata. With the thalamus and the hypothalamus, it makes up a nerve network called the reticular formation, which acts as an arousal mechanism and controls wakefulness. It also relays nerve impulses between the spinal cord and other parts of the brain. The midbrain is the reflex center for the third and fourth cranial nerves and mediates pupillary reflexes and eye movements. The pons helps regulate respirations; it’s also the reflex center for the fifth through eighth cranial nerves and mediates chewing, taste, saliva secretion, hearing, and equilibrium. The medulla oblongata affects cardiac, respiratory, and vasomotor functions.


BLOODLINE TO THE BRAIN

Four major arteries — two vertebral and two carotid — supply the brain with oxygenated blood. These arteries originate in or near the aortic arch. The two vertebral arteries (branches of the subclavian) converge to become the basilar artery, which supplies the posterior brain. The common carotids branch into the two internal carotids, which divide further to supply the anterior brain and the middle brain. These arteries interconnect through the circle of Willis, at the base of the brain. This anastomosis usually ensures continual circulation to the brain.


THE SPINAL CORD: CONDUCTOR PATHWAY

Extending downward from the brain through the vertebrae, to the level of approximately the second lumbar vertebra, is the spinal cord, a two-way conductor pathway between the brain stem and the peripheral nervous system. The spinal cord is also the reflex center for activities that don’t require brain control, such as deep tendon reflexes, the jerking reaction elicited by tapping with a reflex hammer.


A cross section of the spinal cord shows an internal H-shaped mass of gray matter divided into horns, which consist primarily of neuron cell bodies. (See Cross section of the spinal cord, page 155.) Cell bodies in the posterior, or dorsal, horn primarily relay sensations; those in the anterior, or ventral, horn are needed for voluntary or reflex motor activity. The white matter surrounding the outer part of these horns consists of myelinated nerve fibers grouped functionally in vertical columns, called tracts. The sensory, or ascending, tracts carry sensory impulses up the spinal cord to the brain; the motor, or descending, tracts carry motor impulses down the spinal cord. The brain’s motor impulses reach a descending tract and continue through the peripheral nervous system via upper motor neurons. These neurons originate in the brain and form two major systems:



  • The pyramidal system (corticospinal tract) is responsible for fine, skilled movements of skeletal muscle. An impulse in this system originates
    in the frontal lobe’s motor cortex and travels downward to the pyramids of the medulla, where it crosses to the opposite side of the spinal cord.


  • The extrapyramidal system (extracorticospinal tract) controls gross motor movements. An impulse traveling in this system originates in the frontal lobe’s motor cortex and is mediated by basal ganglia, the thalamus, cerebellum, and reticular formation before descending to the spinal cord.



OUTLYING AREAS

Messages transmitted through the spinal cord reach outlying areas through the peripheral nervous system, which originates in 31 pairs of segmentally arranged spinal nerves attached to the spinal cord. Spinal nerves are numbered according to their point of origin in the cord:



  • 8 cervical: C1 to C8


  • 12 thoracic: T1 to T12


  • 5 lumbar: L1 to L5


  • 5 sacral: S1 to S5


  • 1 coccygeal.

On the cross section of the spinal cord, you’ll see that these spinal nerves are attached to the spinal cord by two roots:



  • The anterior, or ventral, root consists of motor fibers that relay impulses from the cord to glands and muscles.



  • The posterior, or dorsal, root consists of sensory fibers that relay sensory information from receptors to the cord. The posterior root has an enlarged area — the posterior root ganglion — which is made up of sensory neuron cell bodies.


After leaving the vertebral column, each spinal nerve separates into rami (branches), distributed peripherally, with extensive but organized overlapping. This overlapping reduces the chance of lost sensory or motor function from interruption of a single spinal nerve.


TWO FUNCTIONAL SYSTEMS



  • The somatic (voluntary) nervous system is activated by will but can also function independently. It’s responsible for all conscious and higher mental processes and for subconscious and reflex actions such as shivering.


  • The autonomic (involuntary) nervous system regulates unconscious processes to control involuntary body functions, such as digestion, respiration, and cardiovascular function. It’s usually divided into two competing systems: The sympathetic nervous system controls energy expenditure, especially in stressful situations, by releasing adrenergic catecholamines. The parasympathetic nervous system helps conserve energy by releasing the cholinergic neurohormone acetylcholine. These systems balance each other to support homeostasis under normal conditions.


ASSESSING NEUROLOGIC FUNCTION

A complete neurologic assessment helps confirm the diagnosis when a neurologic disorder is suspected. It establishes a clinical baseline and can offer lifesaving clues to rapid deterioration. Neurologic assessment includes:



  • Patient history: In addition to the usual information, try to elicit the patient’s and his family’s perception of the disorder. Use the patient interview to make observations that help evaluate mental status and behavior.


  • Physical examination: Pay particular attention to obvious abnormalities that may signal serious neurologic problems; for example, fluid draining from the nose or ears. Check for these significant symptoms:



    • headaches, especially if they’re more severe in the morning, wake the patient, or the pain is unusually intense



    • change in visual acuity, especially sudden change


    • numbness or tingling in one or more extremities


    • clumsiness or complete loss of function in an extremity


    • mood swings or personality changes


    • any new onset of seizures or change in seizure activity.


  • Neurologic examination: Determine cerebral, cerebellar, motor, sensory, and cranial nerve function.

Obviously, there isn’t always time for a complete neurologic examination during bedside assessment. It’s therefore necessary to select priorities; for example, typical bedside assessment focuses on level of consciousness, pupillary response, motor function, reflexes, sensory functions, and vital signs. However, when time permits, a complete neurologic examination can provide valuable information regarding total neurologic function.


ASSESSING MENTAL STATUS, INTELLECT, AND BEHAVIOR

Mental status and behavior are good indicators of cerebral function, and they’re easy to assess. Note the patient’s appearance, mannerisms, posture, facial expression, grooming, and tone of voice. Check for orientation to time, place, and person and for memory of recent and past events. To test intellect, ask the patient to count backward from 100 by 7s, to read aloud, or to interpret a common proverb, and see how well he understands and follows commands. To assesses executive function, ask the patient to follow a series of commands. If you make such checks frequently, vary the questions to avoid a programmed response.


ASSESSING LEVEL OF CONSCIOUSNESS

Level of consciousness (LOC) is a valuable indicator of neurologic function. It can vary from alertness (response to verbal stimulus) to coma (failure to respond even to painful stimulus). Document the patient’s exact response to the stimulus; for example, write, “Patient pulled away in response to nail bed pressure,” rather than a simple adjective like “stuporous.”

The Glasgow Coma Scale (GCS), which assesses eye opening as well as verbal and motor responses, provides a quick, standardized account of neurologic status. In this test, each response receives a numerical value. (See Glasgow Coma Scale.) For instance, if the patient readily responds verbally and is oriented to time, place, and person, he scores a 5; if he’s completely unable to respond verbally, he scores a 1. If the patient is intubated or has a tracheostomy, assess and score accordingly, such as 5/T (‘T’ meaning tracheostomy). A score of 15 for all three parts is normal; 7 or less indicates coma; 3 — the lowest score possible — generally (but not always) indicates brain death. Although the GCS is useful, it isn’t a substitute for a complete neurologic assessment.


ASSESSING MOTOR FUNCTION

The inability to perform the following simple tests, or the presence of tics, tremors, or other abnormalities during such testing, suggests cerebellar dysfunction.



  • Ask the patient to touch his nose with each index finger, alternating hands. Repeat this test with his eyes closed.


  • Instruct the patient to tap the index finger and thumb of each hand together rapidly.


  • Have the patient draw a figure eight in the air with his foot.


  • To test tandem walk, ask the patient to walk heel to toe in a straight line.


  • To test balance, perform the Romberg test: Ask the patient to stand with feet together, eyes closed, and arms outstretched without losing balance.

Motor function is a good indicator of LOC and can also point to central or peripheral nervous system damage. During all tests of motor function, watch for differences between right and left side functions.



  • To check gait, ask the patient to walk while you observe posture, balance, and coordination of leg movement and arm swing.


  • To check muscle tone, palpate muscles at rest and in response to passive flexion. Look for flaccidity, spasticity, and rigidity. Measure muscle size, and look for involuntary movements, such as rapid jerks, tremors, or contractions.


  • To evaluate muscle strength, have the patient grip your hands and squeeze. Then ask him to push against your palm with his foot. Compare muscle strength on each side, using a 5-point scale (5 is normal strength, 0 is complete paralysis). Also test the patient’s ability to extend and flex the neck, elbows, wrists, fingers, toes, hips, and knees; to extend the spine; to contract and relax the abdominal muscles; and to rotate the shoulders.


  • Rate reflexes on a 4-point scale (4 is clonus, 0 is absent reflex). Before testing reflexes, make sure that the patient is comfortable and relaxed. Then, to test superficial reflexes, stroke the skin of the abdominal, gluteal, plantar, and scrotal
    regions with a moderately sharp object that won’t puncture the skin. (Don’t use the same pin to test another patient.) A normal response to this stimulus is flexion. To test deep reflexes, use a reflex hammer to briskly tap the biceps, the triceps, and the brachioradialis, patellar, and Achilles tendon regions. A normal response is rapid extension and contraction.



ASSESSING SENSORY FUNCTION

Impaired or absent sensation in the trunk or extremities can point to brain, spinal cord, or peripheral nerve damage. Determining the extent of sensory dysfunction is important because it helps locate neurologic damage. For instance, localized dysfunction indicates local peripheral nerve damage, dysfunction over a single dermatome (an area served by 1 of the 31 pairs of spinal nerves) indicates damage to the nerve’s dorsal root, and dysfunction extending over more than one dermatome suggests brain or spinal cord damage.

In assessing sensory function, always test both sides of symmetrical areas — for instance, both arms, not just one. Reassure the patient that the test won’t be painful.



  • Superficial pain perception: Lightly press the point of an open safety pin against the patient’s skin. Don’t press hard enough to scratch the skin. Discard pin after use.


  • Thermal sensitivity: The patient tells what he feels when you place a test tube filled with hot water and one filled with cold water against his skin.


  • Tactile sensitivity: Ask the patient to close his eyes and tell you what he feels when touched lightly on hands, wrists, arms, thighs, lower legs, feet, and trunk with a wisp of cotton.


  • Sensitivity to vibration: Place the base of a vibrating tuning fork against the patient’s wrists, elbows, knees, or other bony prominences. Hold it in place, and ask the patient to tell you when it stops vibrating.


  • Position sense: Hold the lateral medial portion of the patient’s fingers and toes and move them up, down, and to the side. Ask the patient to tell you the direction of movement.


  • Discriminatory sensation: Ask the patient to close his eyes and identify familiar textures (velvet or burlap) or objects placed in his hand or numbers and letters traced on his palm.



  • Two-point discrimination: Using calipers or other sharp objects, touch the patient in two different places simultaneously. Ask if he can feel one or two points. Record how many millimeters of separation are required for the patient to feel two points.


ASSESSING CRANIAL NERVE FUNCTION

By using the simple tests that follow, you can reliably localize cranial nerve dysfunction.



  • Olfactory nerve (I): Have the patient close his eyes and, using each nostril separately, try to identify common nonirritating smells, such as cinnamon, coffee, or peppermint.


  • Optic nerve (II): Examine the patient’s eyes with an ophthalmoscope, and have him read a Snellen eye chart or a newspaper. To test peripheral vision, ask him to cover one eye and fix his other eye on a point directly in front of him. Then, ask if he can see you wiggle your finger in the four quadrants; you’d expect him to see your finger in all four.


  • Oculomotor nerve (III): Compare the size and shape of the patient’s pupils and the equality of pupillary response to a small light in a darkened room. Shine the light from a lateral position, not directly in front of the patient’s eyes.


  • Trochlear nerve (IV) and abducens nerve (VI): To assess for conjugate and lateral eye movement, ask the patient to follow your finger with his eyes as you slowly move it from his far left to his far right.


  • Trigeminal nerve (V): To test all three portions of this cranial nerve, test facial sensation by stroking the patient’s jaws, cheeks, and forehead with a cotton swab, the point of a pin, or test tubes filled with hot or cold water. Because testing for a blink reflex is irritating to the patient, it’s not commonly done. If you must test for this response (it may be decreased in patients who wear contact lenses), touch the cornea lightly with a wisp of cotton or tissue, and avoid repeating the test, if possible. To test for jaw jerk, ask the patient to hold his mouth slightly open; then tap the middle of his chin lightly with a reflex hammer. The jaw should jerk closed.


  • Facial nerve (VII): To test upper and lower facial motor function, ask the patient to raise his eyebrows, close his eyes, wrinkle his forehead, and show his teeth. To test sense of taste, ask him to identify the taste of salty, sour, sweet, and bitter substances, which you have placed on his tongue.


  • Acoustic nerve (VIII): Ask the patient to identify common sounds such as a ticking clock. With a tuning fork, test for air and bone conduction.


  • Glossopharyngeal nerve (IX): To test gag reflex, touch a tongue blade to each side of the patient’s pharynx.


  • Vagus nerve (X): Observe ability to swallow, and watch for symmetrical movements of soft palate when the patient says, “Ah.”


  • Spinal accessory nerve (XI): To test shoulder muscle strength, palpate the patient’s shoulders, and ask him to shrug against a resistance.


  • Hypoglossal nerve (XII): To test tongue movement, ask the patient to stick out his tongue. Inspect it for tremor, atrophy, or lateral deviation. To test for strength, ask the patient to move his tongue from side to side while you hold a tongue blade against it.


TESTING FOR A FIRM DIAGNOSIS

A firm diagnosis of many neurologic disorders usually requires a wide range of diagnostic tests — both noninvasive and invasive. Noninvasive tests are done first and may include the following:



  • Skull X-ray identifies skull malformations, fractures, erosion, or thickening. Changes in landmarks may indicate a space-occupying lesion.


  • Computed tomography (CT) scan produces three-dimensional images that can identify hemorrhage, intracranial tumors, malformation, and cerebral atrophy, edema, calcification, and infarction. If a contrast medium is used, the procedure is invasive.


  • Magnetic resonance imaging (MRI) views the CNS in greater detail than a CT scan and is the procedure of choice for detecting multiple sclerosis; intraluminal clots and blood flow in arteriovenous malformations and aneurysms; brain stem, posterior fossa, and spinal cord lesions; early cerebral infarction; and brain tumors. A noniodinated contrast medium may be used to enhance lesions. Advances in MRI allow visualization of cerebral arteries and venous sinuses without administration of a contrast medium.


  • EEG detects abnormal electrical activity in the brain (for example, from a seizure, metabolic disorder, or drug overdose).


  • Ultrasonography detects carotid lesions or changes in carotid blood flow and velocity. High-frequency sound waves reflect back the velocity of blood flow, which is then reported as a graphic recording of a waveform.


  • Evoked potentials evaluate the visual, auditory, and somatosensory nerve pathways by measuring the brain’s electrical response to stimulation of the sensory organs or peripheral nerves.

Invasive tests may include the following:



  • In lumbar puncture, a needle is inserted into the subarachnoid space of the spinal cord,
    usually between L3 and L4 (or L4 and L5). This allows aspiration of CSF for analysis to detect infection or hemorrhage; to determine cell count and glucose, protein, and globulin levels; and to measure CSF pressure. Lumbar puncture is usually contraindicated in hydrocephalus and in increased intracranial pressure (ICP) because a quick pressure reduction may cause brain herniation. (See What happens in increased ICP.)





  • Myelography follows a lumbar puncture and CSF removal. In this procedure, a radiologic dye is instilled and X-rays show spinal abnormalities and determine spinal cord compression related to back pain or extremity weakness.


  • In cerebral arteriography, also known as angiography, a catheter is inserted into an artery — usually the femoral artery — and is threaded up to the carotid artery. Then a radiopaque dye is injected, allowing X-ray visualization of the cerebral vasculature. Sometimes the catheter is threaded directly into the brachial or carotid artery. This test can show cerebrovascular abnormalities and spasms plus arterial changes due to a tumor, arteriosclerosis, hemorrhage, an aneurysm, or blockage. A patient undergoing this procedure is at risk for a stroke and for increased ICP.


  • Digital subtraction angiography visualizes cerebral vessels using contrast medium administered I.V., after which computer-assisted precontrast and postcontrast images are compared. The first image is “subtracted” from the second, which highlights the cerebral vessels.


  • Brain scan measures gamma rays produced by a radioisotope injected I.V. Uptake and distribution of the isotope in the brain highlights intracranial masses, vascular lesions, and other problems.


  • ICP monitoring can be a direct, invasive method of identifying trends in ICP. A subarachnoid screw and an intraventricular catheter convert CSF pressure readings into waveforms that are displayed digitally on an oscilloscope monitor. Another method uses a fiber-optic catheter inserted in the subdural space; with this indirect method, pressure changes are reported digitally or in waveform.


  • Electromyography detects lower motor neuron disorders, neuromuscular disorders, and nerve damage. A needle inserted into selected muscles at rest and during voluntary contraction picks up nerve impulses and measures nerve conduction time.


  • Magnetic resonance spectroscopy provides a measure of brain chemistry. It can be used to monitor biochemical changes in tumors, epilepsy, metabolic disorders, infection, and neurodegenerative diseases.


CONGENITAL ANOMALIES


Cerebral palsy

The most common cause of crippling in children, cerebral palsy (CP) is a group of neuromuscular disorders resulting from prenatal, perinatal, or postnatal CNS damage. Although nonprogressive, these disorders may become more obvious as an affected infant grows older. Three major types of CP occur — spastic, athetoid, and ataxic — sometimes in mixed forms. Motor impairment may be minimal (sometimes apparent only during physical activities such as running) or severely disabling. Associated defects, such as seizures, speech disorders, and mental retardation, are common. The prognosis varies; in cases of mild impairment, proper treatment may make a near-normal life possible.


CAUSES AND INCIDENCE

See Causes of cerebral palsy for a more detailed description of the causes of CP. Incidence is slightly higher in premature neonates (anoxia plays the greatest role in contributing to CP) and in neonates who are small for their gestational age. CP is slightly more common in males than in females. For every 1,000 births, 2 to 4 neonates are affected.

Spastic cerebral palsy is the most common type of CP, affecting about 50% of CP patients. Athetoid cerebral palsy affects about 20% of CP patients, ataxic cerebral palsy accounts for another 10% of these patients, and the remaining 20% of patients are mixed, with a combination of symptoms.



SIGNS AND SYMPTOMS

Spastic cerebral palsy is characterized by hyperactive deep tendon reflexes, increased stretch reflexes, rapid alternating muscle contraction and relaxation, muscle weakness, underdevelopment of affected limbs, muscle contraction in response to manipulation, and a tendency to contractures. Typically, a child with spastic CP walks on his toes with a scissors gait, crossing one foot in front of the other.

In athetoid cerebral palsy, involuntary movements — grimacing, wormlike writhing, dystonia, and sharp jerks — impair voluntary movement. Usually, these involuntary movements affect the arms more severely than the
legs; involuntary facial movements may make speech difficult. These athetoid movements become more severe during stress, decrease with relaxation, and disappear entirely during sleep.

Ataxic cerebral palsy is characterized by disturbed balance, incoordination (especially of the arms), hypoactive reflexes, nystagmus, muscle weakness, tremor, lack of leg movement during infancy, and a wide-based gait as the child begins to walk. Ataxia makes sudden or fine movements almost impossible.

Some children with CP display a combination of these clinical features. In most, impaired motor function makes eating (especially swallowing) difficult and retards growth and development. Up to 40% of these children are mentally retarded, about 25% have seizure disorders, and about 80% have impaired speech. Many also have dental abnormalities, vision and hearing defects, and reading disabilities.






Hydrocephalus

Hydrocephalus is an excessive accumulation of cerebrospinal fluid (CSF) within the ventricular spaces of the brain. In infants, hydrocephalus enlarges the head; in infants and adults, resulting compression can damage brain tissue. With early detection and surgical intervention, the prognosis improves but remains guarded. Even after surgery, such complications as mental retardation, impaired motor function, and vision loss can persist. Without surgery, the prognosis is poor: Mortality may result from increased intracranial pressure (ICP); infants may also die prematurely of infection and malnutrition.


CAUSES AND INCIDENCE

Hydrocephalus may result from an obstruction in CSF flow (noncommunicating hydrocephalus) or from faulty absorption of CSF (communicating hydrocephalus). (See Normal circulation of CSF.)

In noncommunicating hydrocephalus, the obstruction occurs most frequently between the third and fourth ventricles, at the aqueduct of Sylvius, but it can also occur at the outlets of the fourth ventricle (foramina of Luschka and Magendie) or, rarely, at the foramen of Monro. This obstruction may result from faulty fetal development, infection (syphilis, granulomatous diseases, meningitis), a tumor, cerebral aneurysm, or a blood clot (after intracranial hemorrhage).

In communicating hydrocephalus, faulty absorption of CSF may result from surgery to repair a myelomeningocele, adhesions between meninges at the base of the brain, or meningeal hemorrhage. Rarely, a tumor in the choroid plexus causes overproduction of CSF, producing hydrocephalus.

Hydrocephalus occurs most commonly in neonates but can also occur in adults as a result of injury or disease. It affects 1 of every 1,000 people.



SIGNS AND SYMPTOMS

In infants, the unmistakable sign of hydrocephalus is rapidly increasing head circumference, clearly disproportionate to the infant’s growth. Other characteristic changes
include widening and bulging of the fontanels; distended scalp veins; thin, shiny, and fragile-looking scalp skin; and underdeveloped neck muscles. In severe hydrocephalus, the roof of the orbit is depressed, the eyes are displaced downward, and the sclerae are prominent. Sclera seen above the iris is called the setting-sun sign. A high-pitched, shrill cry; abnormal muscle tone of the legs; irritability; anorexia; and projectile vomiting commonly occur. In adults and older children, indicators of hydrocephalus include decreased level of consciousness (LOC), ataxia, incontinence, loss of coordination, and impaired intellect.






Cerebral aneurysm

Cerebral aneurysm is a localized dilation of a cerebral artery that typically results from a congenital weakness in the arterial wall. Its most common form is the berry aneurysm, a saclike outpouching in a cerebral artery. Cerebral aneurysms may arise at an arterial junction in the circle of Willis, the circular anastomosis forming the major cerebral arteries at the base of the brain. Cerebral aneurysms can rupture and cause subarachnoid hemorrhage. (See How a cerebral aneurysm forms.)

The prognosis is guarded. Probably half the patients with subarachnoid hemorrhages die immediately; of those who survive untreated, 35% die from the effects of hemorrhage; another 15% die later from recurring hemorrhage. New treatments are improving the prognosis, however.


CAUSES AND INCIDENCE

Cerebral aneurysm may result from a congenital defect, a degenerative process, or a combination. For example, hypertension and atherosclerosis may disrupt blood flow and exert pressure against a congenitally weak arterial wall, stretching it like an overblown balloon and making it likely to rupture. After such rupture, blood spills into the space normally occupied by cerebrospinal fluid (CSF), resulting in subarachnoid hemorrhage. Blood may also spill into the brain tissue and form a clot, which can result in potentially fatal increased intracranial pressure (ICP) and brain-tissue damage.

Incidence is slightly higher in women than in men, especially those in their late 40s or early to mid-50s, but cerebral aneurysm may occur at any age, in both women and men.




SIGNS AND SYMPTOMS

Occasionally, rupture of a cerebral aneurysm causes premonitory symptoms that last several days, such as headache, nuchal rigidity, stiff back and legs, and intermittent nausea. Usually, however, onset is abrupt and without warning, causing a sudden severe headache, nausea, vomiting and, depending on the severity and location of bleeding, altered consciousness (including deep coma).

Bleeding causes meningeal irritation, resulting in nuchal rigidity, back and leg pain, fever, restlessness, irritability, occasional seizures, and blurred vision. Bleeding into the brain tissues causes hemiparesis, hemisensory defects, dysphagia, and visual defects. If the aneurysm is near the internal carotid artery, it compresses the oculomotor nerve and causes diplopia, ptosis, dilated pupil, and inability to rotate the eye.

The severity of symptoms varies considerably from patient to patient, depending on the site and amount of bleeding. To better describe their conditions, patients with ruptured cerebral aneurysms are grouped as follows:



  • Grade I (minimal bleed): Patient is alert with no neurologic deficit; he may have a slight headache and nuchal rigidity.


  • Grade II (mild bleed): Patient is alert, with a mild to severe headache, nuchal rigidity and, possibly, third-nerve palsy.


  • Grade III (moderate bleed): Patient is confused or drowsy, with nuchal rigidity and, possibly, a mild focal deficit.


  • Grade IV (severe bleed): Patient is stuporous, with nuchal rigidity and, possibly, mild to severe hemiparesis.


  • Grade V (moribund; commonly fatal): If nonfatal, patient is in deep coma or decerebrate.

Generally, cerebral aneurysm poses three major threats:



  • Death from increased ICP: Increased ICP may push the brain downward, impair brain stem function, and cut off blood supply to the part of the brain that supports vital functions.


  • Rebleed: Generally, after the initial bleeding episode, a clot forms and seals the rupture, which reinforces the wall of the aneurysm for 7 to 10 days. However, after the 7th day, fibrinolysis begins to dissolve the clot and increases the risk of rebleeding. Signs and symptoms are similar to those accompanying the initial hemorrhage. Rebleeds during the first 24 hours after initial hemorrhage aren’t uncommon, and they contribute to cerebral aneurysm’s high mortality.


  • Vasospasm: Why this occurs isn’t clearly understood. Usually, vasospasm occurs in blood vessels adjacent to the cerebral aneurysm, but it may extend to major vessels of the brain, causing ischemia and altered brain function.

Other complications of cerebral aneurysm include pulmonary embolism (a possible adverse effect of deep vein thrombosis or aneurysm treatment) and acute hydrocephalus, occurring as CSF accumulates in the cranial cavity because of blockage by blood or adhesions.





Arteriovenous malformations

Cerebral arteriovenous malformation (AVM) is a disorder of the blood vessels consisting of an abnormal connection between the arteries and the veins in the brain. It’s a congenital disorder commonly resulting in tangled masses of thinwalled, dilated blood vessels between arteries and veins that aren’t connected by capillaries. AVM primarily occurs in the posterior portion of the cerebral hemispheres. (See Where a cerebral AVM commonly occurs.) Adequate perfusion of brain tissue is prevented due to abnormal channels between the arterial and venous systems that allow mixing of oxygenated and unoxygenated blood. AVMs range in size from a few millimeters to large malformations that extend from the cerebral cortex to the ventricles. Patients typically present with multiple AVMs.

Complications of AVM include development of aneurysm and subsequent rupture, hemorrhage (intracerebral, subarachnoid, or subdural, depending on the location of the AVM), and hydrocephalus.


CAUSES AND INCIDENCE

Although some AVMs occur as a result of penetrating injuries such as trauma, most are present at birth. However, symptoms typically don’t occur until between ages 10 and 20. Very large AVMs may short-circuit blood flow enough to cause cardiac decompensation, in which the heart can’t pump enough blood to compensate for arteriovenous shunting in the brain. This typically occurs in infants and young children.

The vessels of an AVM are very thin and one or more arteries feed into it, causing it to appear dilated and tortuous. Typically, high-pressured arterial flow moves into the venous system through the connecting channels to increase venous pressure, engorging and dilating the venous structures. If the AVM is large enough, the shunting can deprive the surrounding tissue of adequate blood flow. Thin-walled vessels may ooze small amounts of blood — they may even
rupture — causing hemorrhage into the brain or subarachnoid space.


Cerebral AVMs occur in approximately 3 out of 10,000 people. Although the lesion is present at birth, symptoms may occur at any time. Twothirds of cases occur before age 40. Evidence suggests that AVMs run in families. Males and females are affected equally.



SIGNS AND SYMPTOMS

An AVM may be asymptomatic until complications occur; these may include rupture and a resulting sudden bleed in the brain, known as a hemorrhagic stroke. AVMs vary in size and location within the brain. Systolic bruit may be auscultated over the carotid artery, mastoid process, or orbit on examination.

Symptoms that occur prior to an AVM rupture are related to smaller and slower bleeding from the abnormal vessels, which are usually fragile because their structure is abnormal.

In more than half of patients with AVM, hemorrhage from the malformation is the first symptom. Depending on the location and the severity of the bleed, the hemorrhage can be profoundly disabling or fatal. The risk of bleeding from an AVM is approximately 2% to 4% per year.

The first symptoms often include headache, seizure, or other sudden neurologic problems, such as vision problems, weakness, inability to move a limb or a side of the body, lack of sensation in part of the body, or abnormal sensations, such as ringing and numbness. Symptoms are the same as for stroke. The individual with an AVM may complain of chronic mild headache, a sudden and severe headache, or a localized or general headache. The headache may resemble migraine and vomiting may occur. Seizures may result from focal neurologic deficits (depending on the location of the AVM) resulting from compression and diminished perfusion. Symptoms of intracranial (intracerebral, subarachnoid, or subdural) hemorrhage result. Muscle weakness and decreased sensation can occur in any part of the body. Mental status change can occur where the individual appears sleepy, stuporous, lethargic, confused, disoriented, or irritable. Additional symptoms may include stiff neck, speech or sense of smell impairment, dysfunctional movement, fainting, facial paralysis, eyelid drooping, tinnitus, dizziness, and decreased level of consciousness (LOC).

Intracerebral or subarachnoid hemorrhages are the most common first symptoms of
cerebral AVM. In some cases, symptoms may also occur due to lack of blood flow to an area of the brain (ischemia), compression or distortion of brain tissue by large AVMs, or abnormal brain development in the area of the malformation. Progressive loss of nerve cells in the brain may occur, caused by mechanical (pressure) and ischemic (lack of blood supply) factors.





PAROXYSMAL DISORDERS


Headache

The most common patient complaint, headache usually occurs as a symptom of an underlying disorder. Ninety percent of all headaches are vascular, muscle contraction, or a combination; 10% are due to underlying intracranial, systemic, or psychological disorders. Migraine headaches, probably the most intensively studied, are throbbing, vascular headaches that usually begin to appear in childhood or adolescence and recur throughout adulthood.


CAUSES AND INCIDENCE

Most chronic headaches result from tension (muscle contraction), which may be caused by emotional stress, fatigue, menstruation, or environmental stimuli (noise, crowds, or bright lights). Other possible causes include glaucoma; inflammation of the eyes or mucosa of the nasal or paranasal sinuses; diseases of the scalp, teeth, extracranial arteries, or external or middle ear; muscle spasms of the face, neck, or shoulders; and cervical arthritis. In addition, headaches may be caused by vasodilators (nitrates, alcohol, and histamine), systemic disease, hypoxia, hypertension, head trauma
and tumor, intracranial bleeding, abscess, or aneurysm.

The cause of migraine headache is unknown, but it’s associated with constriction and dilation of intracranial and extracranial arteries. Certain biochemical abnormalities are thought to occur during a migraine attack. These include local leakage of a vasodilator polypeptide called neurokinin through the dilated arteries and a decrease in the plasma level of serotonin.

Headache pain may emanate from the painsensitive structures of the skin, scalp, muscles, arteries, and veins; cranial nerves V, VII, IX, and X; or cervical nerves 1, 2, and 3. Intracranial mechanisms of headaches include traction or displacement of arteries, venous sinuses, or venous tributaries and inflammation or direct pressure on the cranial nerves with afferent pain fibers.

Affecting up to 10% of Americans, headaches are more common in females and have a strong familial incidence. Drops in estrogen level may precipitate migraine headaches.



SIGNS AND SYMPTOMS

Initially, migraine headaches usually produce unilateral, pulsating pain, which later becomes more generalized. They’re commonly preceded by a scintillating scotoma, hemianopsia, unilateral paresthesia, or speech disorders. The patient may experience irritability, anorexia, nausea, vomiting, and photophobia. (See Clinical features of migraine headaches, page 172.)

Both muscle contraction and traction-inflammatory vascular headaches produce a dull, persistent ache; tender spots on the head and neck; and a feeling of tightness around the head, with a characteristic “hatband” distribution. The pain is usually severe and unrelenting. If caused by intracranial bleeding, these headaches may result in mental changes and neurologic deficits, such as paresthesia and muscle weakness; narcotics may fail to relieve pain in these cases. If caused by a tumor, pain is most severe when the patient awakens.





Seizure disorder

Seizure disorder, also called epilepsy, is a condition of the brain marked by a susceptibility to recurrent seizures — paroxysmal events associated with abnormal electrical discharges of neurons in the brain.


CAUSES AND INCIDENCE

In about half the cases of seizure disorder, the cause is unknown. However, some possible causes of seizure disorder include:

Aug 27, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Neurologic Disorders
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