Chapter 29 - Cranial and spinal trauma
Head trauma is a common cause of disability in this country, with vehicular accidents representing the major cause. Of those who die from vehicular accidents, 75% die from the primary and secondary effects of trauma on the vital centers of the central nervous system. Of those who survive major head trauma, defects in CNS functioning (due to tissue damage) or irritative phenomena (such as seizures) may result. There can be residual symptoms of more minor head injury (such as concussion), although generally good prognosis is the rule. Furthermore, surprisingly good recovery is possible even from severe head injury if the person survives the days and weeks after trauma.
This chapter deals mainly with evaluation of the person with suspected or proven head injury. As a preamble, some basic principles and definitions should be discussed.
The major effects of trauma on the brain can be divided into two categories: primary and secondary (or late) effects. The primary effects are those that are caused directly by the head trauma and include concussion, contusion, and laceration of the central nervous system.
Concussion is a reversible state of diffuse cerebral dysfunction associated with a transient alteration in consciousness. Most often there is a brief period of loss of consciousness. However, patients may be only severely stunned or dazed. Typically, there is loss of memory for recent events (retrograde amnesia), and this may extend for some seconds or minutes prior to the injury and, rarely, with more severe impact, for days or more. A variable period of inability to learn new material (anterograde amnesia) typically follows recovery of consciousness and may be dense enough to leave the patient with no memory of early post injury events. Rarely, some patients tell of being "unconscious" for weeks to as long as several months following head injury. In fact, they were not unconscious but were unable to remember ongoing events. The retrograde amnesia is presumed to be caused by a mechanical distortion of neurons, probably in the temporal lobes, which consolidate the memory trace. The anterograde amnesia is presumed to be the result of distortion of the mesial temporal-limbic circuits known to be necessary for learning.
The underlying pathophysiology of concussion appears to be a shearing effect. Rapid displacement of the head, in either acceleration or deceleration injury, causes a swirling of the cerebrum within the cranium, and shearing forces play most markedly at the junctions between brain tissues of different density. Rotational injuries may be particularly damaging, since the brain stem torques quite easily while there is a lot of inertia against the rotation of the cerebral cortex. This results in torsion of the nerve fibers in the core of the brain (i.e., the reticular activating system). Another major zone of diffuse axonal injury is the interface between gray and white matter. It is here and in the core of the rostral brain stem that microscopic evidence of ruptured axons can be found pathologically. It is not surprising that the patient's resistance to future concussion tends to decline with repeated concussions or that repeated concussion, such as boxers experience, may lead to dementia.
Penetrating injuries of the cranium, such as bullet wounds, frequently cause only focal cerebral dysfunction without loss of consciousness because no cranial displacement and brain shearing occur.
Contusions of the brain are bruises usually associated with more severe trauma than necessary for concussion. They are most prominent at the summits of gyri, the cerebral poles (particularly the frontal poles and the anterior temporal lobe), and portions of the brain stem. All these regions lie close to the bony and dural surfaces of the cranial cavity. They may directly underlie the site of the blow to the cranium or may be opposite the site of impact (contrecoup). The contusions can usually be seen acutely on CT scan (which shows extravasated blood) as small petechiae in the brain parenchyma. The breakdown products of this blood may be seen for years on MRI scanning.
Laceration of the brain usually follows cranial trauma severe enough to cause fracture of the skull and penetrating injury to the brain by skull fragments or foreign objects. However, fracture of the skull need not be associated with laceration or contusion or major concussion. On the other hand, laceration may on occasion occur with severe shearing forces unassociated with fracture. Usually some form of hemorrhage (intracerebral, subdural, epidural) is associated with laceration.
The secondary effects of cranial trauma that may further compromise brain function are edema, hypoxia, hemorrhage, infection and epilepsy. Edema may be the result of diffuse shearing of capillary, glial, and neuronal membranes or may be secondary to local contusion or laceration. Edema can generate local pressure that can compromise both arterial and venous cerebral blood flow, causing ischemia and more edema. This may precipitate a vicious cycle sometimes impossible to reverse. The mass effect of edema, focal or diffuse, can cause rostrocaudal brain stem deterioration (possibly with herniation), a major cause of delayed death from head trauma (see Chap. 17). Brain dysfunction and destruction are aggravated by hypoxia, the result of compromised respiratory function caused by the following: (1) injury to the chest, (2) aspiration pneumonia in the unconscious patient, (3) respiratory center depression from rostrocaudal deterioration or direct damage to the medulla, (4) pulmonary edema secondary to hypothalamic-septal damage, or (5) status epilepticus. Blood loss from multiple injuries and, as mentioned, brain edema further compromise delivery of oxygen to the brain.
Increased intracranial pressure ICP), mostly due to edema but added to by any intracranial bleeding, is a major cause of secondary injury. High pressure decreases the perfusion pressure in brain blood vessels (since the perfusion pressure is the mean arterial pressure minus the intracranial pressure). If this is too low, there will be further damage to neural tissue due to ischemia, which will result in further edema and an even greater increase in pressure. The treatment of this increase in ICP can be by lowering intracranial pressure. Evacuation of cerebrospinal fluid (via an intraventricular catheter), or dehydration of the brain (via diuretics and hyperosmotic agents) can lower pressure. Hyperventilation, which constricts intracranial arteries, can lower pressure, but will decrease blood flow. This has been shown to be detrimental. Recently, it has been shown that raising arterial pressure can improve outcome, presumably by increasing perfusion pressure.
Intracranial hemorrhage, arterial or venous, intra- or extracerebral, is a frequent sequela of cranial trauma and may be great enough to cause rostrocaudal deterioration of neural function and death if not recognized and attended to immediately. Rostrocaudal deterioration, if rapid, may itself cause hemorrhage by downward stretching and tearing of the paramedian penetrating arteries of the midbrain and pons. These so-called Duret hemorrhages usually occur when the clinical course of deterioration has reached the midbrain and upper pons (see Chap. 17 ). It is imperative to terminate rostrocaudal changes at the diencephalic or early midbrain level because Duret hemorrhages in most cases herald irreversible deterioration and death or, at the least, severe permanent brain disability.
Subdural and epidural hematomas deserve some comment because both can be treated via surgical intervention, which can be curative if undertaken prior to irreversible brain damage. Both epidural and subdural hematoma are extracerebral. For this reason, and because they are soft masses, there tends to be relatively little effect on the underlying and compressed cerebral hemispheres. However, due to distortion of the brain itself, secondary rostrocaudal distortion of the brain stem is the process that usually gives rise to the major clinical signs (Fig. 29-1): depression of consciousness (reticular formation), hemiparesis (cerebral peduncles), eye signs (third and sixth nerves), and respiratory pattern abnormalities. The process of deterioration often goes through defined stages, which are discussed in Chap. 17 . Herniation, the process of squeezing brain tissue from one intracranial compartment into another, is often the terminal event since this produces permanent damage in the region of herniation.
Epidural hematomas are most often arterial. They are usually the result of transection of the middle meningeal artery by a skull fracture that passes through the middle meningeal groove. It must be emphasized, however, that fracture is not necessary since the skull has elasticity that may permit the blow to rupture the artery which is pinned between the dura matter and the skull. Because of the location of the middle meningeal artery, the clots typically lie over the lateral hemisphere (temporal and/or parietal lobes). Since the epidural hematoma is under arterial pressure, it typically continues to grow unless evacuated. However, because the dura is adhered to the inside of the skull, and since the clot is between these layers, the growth of the clot is over hours. The typical middle meningeal artery epidural hematoma is associated with a syndrome that appears within hours of the injury. Classically, trauma is associated with a concussive loss of consciousness. The patient may awaken from this to achieve a good level of consciousness (lucid interval) only to lose consciousness again from brain stem distortion caused by the clot growth. If the bleeding is very severe there is no lucid interval. The patient does not have time to awaken from the concussion before compressive brain stem deterioration begins. Surgical evacuation is critical. Less often epidural collections may be the results of tears in the venous sinuses or leakage from the diploic veins. These hemorrhages may occur over any portion of the hemispheres or in the posterior fossa and are much slower.
Subdural hematomas are typically due to disruption of veins that are bridging from the brain to the venous dural sinuses. The hemorrhage is presumed to arise from angular forces that cause the dura to move (along with the skull to which it is tightly adhered) in relationship to the cerebral hemispheres which tend to lag behind in such rotational injuries. The bridging veins tend to shear where they enter the dura after passing through the thin subdural space between the dura and arachnoid. Subdural hemorrhage is more likely to occur in older individuals presumably because the veins bridging the enlarged subdural space are stretched. Because the blood is under very low pressure (being from veins) the hematoma tends to collect slowly, causing signs and symptoms that develop over days to months. Head trauma that can be so minor that it is not remembered may result in a subdural hematoma under these circumstances. Therapeutic anticoagulation predisposes to subdural hematoma and also intracerebral hemorrhage.
Because subdural venous bleeding is slow to accumulate, gradual shifting of the brain occurs and brain stem distortion can be better accommodated in contrast to the acute brain stem distortions and severe dysfunction caused by epidural and acute subdural hemorrhages. Mild depression of consciousness, difficulty with cognitive function, and chronic headache (from meningeal stretching and increased intracranial pressure) may be the presenting picture. Acute deterioration may occur when the capacity to adapt for the expanding mass is exceeded. In this case there may be a picture of rostrocaudal deterioration of brain function that is superimposed on chronic complaints. The acute deterioration may be caused by fresh bleeding into the subdural hematoma from friable vessels that formed on the surface of the hematoma during the process of organized encapsulation of the clot. In many patients the symptoms of subdural hematoma wax and wane over hours or days. These symptoms may include headache, depression of consciousness, confusion and signs of focal cortical dysfunction (based on the region that is affected). The blood products in close proximity to the brain may also result in seizures.
Acute subdural hematomas are seen less frequently. They are usually associated with head trauma severe enough to cause skull fracture and cerebral contusion or laceration. Epidural hematoma and intracerebral hematoma are frequently associated. The mortality is extremely high and the residual dysfunction of survivors is severe.
Arterial dissection may affect the carotid or vertebral arteries. This is usually associated with a tear in the intimal lining of the artery and an accumulation of blood in the media. Stroke may result from blockage of the artery or its branches or from artery-to-artery emboli arising from the site of vessel damage. The weakened artery may also rupture (often into the subarachnoid space) with potentially catastrophic results.
Open injuries of the skull may result in intracranial infection and may take the form of diffuse sepsis of the brain coverings (meningitis) or local collections of purulence (cerebral, subdural, and epidural abscess, see Chap. 25 ). Infection of dural sinuses may lead to stasis, occlusion, and infarction (see Chap. 27).
The early recognition of posttraumatic meningitis or its prophylaxis in situations with which it is highly associated is critical. Unrecognized and untreated meningitis is a likely cause of death. This is most likely to occur in the unconscious patient. Depressed fractures that tear the dura and lie under or near scalp laceration are particularly prone to infection. Fractures through sinuses (sphenoid, ethmoid, and frontal sinuses) are frequently associated with dural tears and subsequent meningitis or intracerebral abscess. If such fractures lack dural tear, they may be associated with extradural buildup of purulence (epidural abscess). Fracture of the cribriform plate or petrous bone may tear the dura and create a communication between the subarachnoid space and the nasal cavity or external auditory cavities. The former may be recognized by leakage of CSF through the nose (rhinorrhea) and the latter by leakage from the ear (otorrhea). This leakage is a potential direct passage for bacteria to travel from the exterior to the subarachnoid space. Any fluid collected from the nose can be tested for the presence of glucose (which is high in CSF but not in nasal secretions). These leaks may persist long after recovery from trauma because CSF pressure presumably keeps them open and may cause recurrent meningitis if not repaired.
Epilepsy may be a sequela of head injury. Seizures, frequently focal motor or focal with secondary generalization, occur in the first week after nonmissile trauma in approximately 5% of patients, but they herald chronic epilepsy in only about 25% of those so involved. Seizures appearing weeks to years following injury are much more likely to represent a chronic and recurring disorder. Approximately 5% of persons with nonmissile injuries develop seizures after one week, and the presence of more than 24 hours of anterograde amnesia, a dural tear, or seizures within the first week following injury increases the likelihood that these late seizures will be recurrent. Seizures are also more frequent following penetrating injuries or those patients with cortical laceration. Current evidence suggests that the use of anticonvulsants, which are often given in the initial post-injury period, does not alter the risk of later development of epilepsy. Therefore, most authorities recommend against long term anticonvulsants unless the patient proves to have later onset seizures. These "late onset" seizures appear to correlate with glial scarring and the presence of blood products in the brain. The most common time to develop them is 6-18 months after the trauma and patients are likely to require long-term anticonvulsants.
Before any useful or reliable neurologic examination can be performed on a patient with acute head injury, the following other essential systems must be evaluated.
- An adequate airway and adequate oxygenation must be assured. This can usually be tested by a brief physical examination and/or chest x-ray and by arterial blood gas measurements. Hypoxia is commonly associated with head injury in the immediate post-trauma period because of the frequency of lung contusion and/or emesis with aspiration of gastric contents. The hypoxic patient's neurologic status can often be dramatically improved by establishing adequate oxygenation.
- Blood pressure and pulse should be noted. Adequate blood volume and pressure are also necessary for adequate cerebral oxygenation. Beware - shock is not due to reversible cerebral injury. Shock must be assumed to be from noncerebral causes such as hypovolemia (i.e., from a hidden site of hemorrhage), cardiac failure, or sepsis. Shock that can be produced by cerebral injury is manifest by a loss of peripheral vasomotor tone that is mediated by the medulla. Shock from medullary failure is seldom seen even in the agonal patient.
- Body core temperature should be noted. Hypothermia secondary to exposure can cause marked neurologic changes. Hypothermia decreases CNS metabolism and tends to decrease the level of consciousness, reflexes, and nearly all motor responses.
- Baseline blood studies should be done (blood count, electrolytes, and glucose) when the patient is first seen. If the patient is unconscious and a known diabetic, a bolus of intravenous 50% glucose (after 100 mg of thiamine) should be administered after the blood glucose is drawn. Immediate treatment of hypoglycemia (quite possible in the diabetic who is unable to eat because of trauma) is necessary to minimize brain damage.
Along with assuring an adequate airway, oxygenation, perfusion, and a normal body temperature, a brief history of the trauma can be extremely helpful. Progression or nonprogression of the patient's level of consciousness from the time of trauma to the time s/he is being seen by the examiner should be documented if possible. Was the patient immediately unconscious? For how long? Was s/he awake and talking or walking after the trauma? this is a story often seen in expanding hematomas (especially epidural). Did any witnesses observe seizure activity? Did the patient strike their head and then become unconscious, or did s/he first become unconscious and then strike their head?
If available, a brief history may also be important. Was the patient taking any medication, alcohol, or other drugs? Did the patient have a preexisting illness, seizure disorder, or history of syncope?
The most sensitive and reliable clinical parameter of brain function is the patient's level of consciousness (mediated primarily by the ascending reticular formation of the brain stem, see Chap. 17). On the initial and all subsequent examinations, the level of consciousness should be clearly described and recorded. Confusing and ambiguous terms such as "stupor", "lethargy", and "coma" should be avoided unless defined. Decreasing levels of consciousness often follow a logical progression and can be documented in a stepwise pattern (Table 29-1). The "Glasgow coma score" is a rapid and reproducible tool that may allow comparison of function over time and different observers.
After early childhood, the skull is a nonexpanding bony encasement for the brain. The only direction in which an expanding supratentorial mass can force the brain is through the tentorial opening into the posterior fossa. The midbrain with its segment of reticular activating system normally occupies this tentorial opening. As a supratentorial mass enlarges, it causes transtentorial herniation of the mesial portion of the ipsilateral temporal lobe with compression of the brain stem and reticular activating system (Fig. 29-1). A decrease in the level of consciousness may be the first sign that this is happening.
Posterior fossa masses usually expand toward the foramen magnum. They can produce foramen magnum impaction by forcing the cerebellar tonsils into the upper cervical spinal canal. This may produce compression of the medulla with sudden apnea and death from asphyxiation.
Direct involvement of the brain stem may occur at several levels. In trauma to the back of the head, the midbrain may be concussed by the rigid leading edge of the tentorium. With a severe linear occipital trauma, especially if a fracture occurs, vertebral arterial compromise may occur with subsequent pontomedullary dysfunction. Either of these can be fatal.
The examination should focus on determining brain stem function and should include evaluation of respiration, pupillary response, vestibulo-ocular response and motor response (see also Chap. 17).
- Respiratory pattern. Normal breathing progresses to hyperventilation ("central neurogenic hyperventilation") as the midbrain is compressed, and then to an irregular respiratory pattern or apnea as the medulla is compressed (see Chap. 1).
- Pupillary response. Equally responsive pupils progress to midposition without response to light as the upper midbrain (the region of the third cranial nerve nucleus and descending sympathetic pathway) is compressed. No further change is seen even with increased transtentorial herniation and descending brain stem compression (see Chap. 4).
- Oculocephalic reflex. This reflex should normally be inhibited in the conscious person and disinhibited in the person with depressed consciousness. It can be elicited by briskly turning the patient's head. Of course, if there is a possibility of neck trauma, this should be avoided (caloric testing can be done without neck movement). A disinhibited response is common in patients who are unconscious but whose brain stem is functioning. In this case, the patient's eyes appear to be fixed on an imaginary point as the head is turned (i.e., they move opposite to head movement). If the reflex is absent, the eyes do not move in the head, staying fixed in place. The movements of adduction first disappear with upper midbrain (third-nerve) compression, and the movements of abduction disappear when the compression progresses to involve the pons (sixth nerve). With downward movement of the brain stem caused by expansion of the supratentorial contents, loss of abduction (lateral rectus function) may occur before parenchymal involvement of the pons. This is caused by stretching of the sixth nerve against the edge of the petrous bone (see Chap. 4).
- Motor response. Normal motor strength and tone progress to intermittent decorticate or decerebrate posturing as the midbrain is compressed. The progression is then to flaccid areflexia as the pons and medulla are compressed. Decerebrate posturing is manifested by leg extension along with arm extension and internal rotation that can occur spontaneously or following any noxious stimulation (such as tickling the nose). Since this is a reflex that is generated in the caudal brain stem (particularly by the vestibular nuclei), the finding of decerebrate posturing suggests that the rostral brain stem is being compromised. Decorticate posturing is similar but leg extension is accompanied by arm flexion and internal rotation. To produce this type of posturing, descending cortical motor impulses must be interrupted. This interruption must be above the level of the midbrain, leaving the rubrospinal and vestibulospinal motor systems intact and facilitated (see Chap. 8).
Cerebral hemisphere dysfunction after head trauma, unlike brain stem dysfunction, is not clearly correlated with changes in the level of consciousness. Large cerebral hemisphere lesions can be found in persons who are alert, particularly if the trauma did not cause direct brain stem damage and the lesion does not act as an expanding mass and cause transtentorial herniation.
In trauma, two basic mechanisms are responsible for focal cerebral hemisphere deficits:
- Direct compression of the brain by a mass lesion (hematoma, edematous brain tissue) or by cortical or subcortical brain contusion. Common findings associated with compression or contusion are:
- a. Contralateral motor weakness with frontal lesions
- b. Receptive aphasia of varying degree with left temporoparietal lesions
- c. Contralateral loss of sensation with parietal lesions
- d. Contralateral visual field deficits with temporal, parietal, or occipital lesions
- a. Progressive ipsilateral third cranial nerve dysfunction (Fig. 29-1). This is caused by direct peripheral third-nerve compression by the herniated uncus at the tentorial incisure. The pupil fully dilates and the extraocular muscle movements of the eye controlled by the third nerve become paralyzed on that side.
- b. Hemiparesis is also seen with the third cranial nerve deficit. If the paresis is ipsilateral to the pupillary dilatation, it is caused by a shifting of the brain and brain stem away from the extracerebral lesion (usually hemorrhage) with pressure of the contralateral cerebral peduncle against the rigid tentorial edge (Kernohan's notch - Fig. 29-2). If the paresis is contralateral, it is caused by direct compression or destruction of the cerebral hemisphere and descending fiber tract.
Lesions that produce cerebral hemisphere deficits also act as expanding masses and produce transtentorial herniation. Persons with head trauma who show signs of cerebral hemisphere dysfunction usually have alterations in their level of consciousness that frequently are the result of herniation compression of the brain stem. However, direct traumatic injury to the brain stem may also cause depression of consciousness, particularly following severe trauma. Cranial nerve dysfunction usually belies the presence of direct brain stem involvement, whereas depression of consciousness usually precedes cranial dysfunction with supratentorial expanding lesions. The exception is low temporal lesions, where the third nerve may be involved early (see also Chap. 17).
An assumption that should be made in the initial evaluation of an unconscious trauma patient is that s/he has an unstable neck fracture until proved otherwise by x-ray. Head and neck movements should be minimized during the examination. If moved or turned, the head and body should remain as a unit, en bloc.
The initial evaluation of a person with head trauma to this point has included checking the following:
- Respiratory airway patency, oxygenation (arterial blood gases) and perfusion (blood pressure and pulse), and body temperature.
- Brain stem function. - The level of consciousness is the most important
- Cerebral hemisphere function.
- Cervical spinal stability. - A lateral cervical spine x-ray showing all seven cervical vertebrae is necessary for identification of cervical spine fracture and/or instability.
In the evaluation of an unconscious person, a history of minor head trauma with a disproportionate loss of consciousness should alert the examiner to the possibility of a pre-existing reason for the clinical findings. Other possible causes are:
- Metabolic: endogenous or exogenous, such as hypoxia, hypoglycemia, sepsis, hepatic or renal failure, and medication overdose (see Chap. 17).
- A pre-existing seizure disorder, with coma appearing due to a postictal state.
- Other neurologic disease: subarachnoid hemorrhage, vascular occlusive disease, brain tumor, or chronic subdural hematoma.
If a history strongly suggests any of these, the head trauma may be only an incidental factor in producing the neurologic picture.
Papilledema is evidence for increased intracranial pressure. Thirty minutes to several hours of increased pressure are required before papilledema becomes clinically apparent.
Papilledema as viewed through the ophthalmoscope may have several causes, however, the principal one is impedance of normal venous return. The central retinal veins drain through the optic disk and optic nerve before communicating with the ophthalmic veins that drain into the cavernous sinus, located inside the cranium. The optic nerve is surrounded by a sleeve of dura, which is continuous with the sclera. Between this sleeve and the optic nerve is a space that communicates with the subarachnoid space. Increased intracranial pressure, which is reflected in the subarachnoid space, is therefore communicated into the optic nerve sleeve, compressing the optic nerve and thus impeding normal venous drainage. The secondary vascular stasis in the retinal veins would be expected to produce capillary leakage around the optic disk, which is probably the major cause of visible papilledema. Additionally, high pressure inside the head may be directly transmitted to the ophthalmic veins, although this pressure would be expected to result in flow into other anastomotic pathways.
Some patients do not develop papilledema even with marked elevations of their intracranial pressure. A lack of normal spinal fluid (subarachnoid space) communication along the optic nerve may explain this apparent anomaly. Elevated intraocular pressure (glaucoma) may also prevent papilledema.
Battle's sign is an ecchymotic discoloration over the mastoid bone behind the ear without local skin or scalp contusion. It indicates periosteal bleeding, which drains toward the exterior from a basilar fracture and usually does not develop for several hours following the trauma.
Hematotympanum is blood seen through the tympanic membrane in the middle ear. This finding as well as blood draining from the external ear indicates either a skull fracture across the temporal bone (basilar fracture) or severe shearing of the contents of the middle ear. A conductive or sensorineural hearing loss may be associated.
The facial nerve (VII) passes through the temporal bone next to the middle ear and therefore if hematotympanum is noted, facial nerve function should be carefully tested. Peripheral facial nerve contusion or transection at the fracture line causes facial paralysis, which may develop many hours or days after the trauma.
Cerebrospinal fluid leakage may be noted from the nose or ears (as described earlier). This is not necessarily a bad prognostic sign for neurologic recovery but it does indicate a skull fracture. It should alert the examiner to the possible development of meningitis from retrograde passage of bacteria along the leakage tract.
The Cushing reflex is a dramatic elevation in blood pressure associated with bradycardia. It is seen with increased intracranial pressure or an expanding mass lesion in the posterior fossa. When pressure is placed on the lower brain stem, peripheral vasoconstriction ensues with an increase in blood pressure. This is presumed by some to be a homeostatic compensation for the decreased cerebral blood flow caused by increased intracranial pressure. The carotid sinus in turn causes reflex cardiac slowing by increasing vagal tone. More often than not, however, the carotid sinus reflex is inadequate to overcome the tachycardia that accompanies the central vasomotor response.
Computerized tomography (CT scan) has revolutionized the care of head-injured patients (see Chap. 11). Fractures, hemorrhage, and edema are revealed with facility, and surgical intervention is more rationally decided. Additionally, CT techniques can be used to investigate the possibility of arterial trauma, eliminating the need for more hazardous angiography, in most instances. MRI techniques are not usually used in acute trauma because of the slowness of the procedure and the susceptibility to movement and other artifact. It may be applicable to cases of chronic injury (see Chap. 11).
Spinal tap is indicated only if there is a serious suspicion of bacterial meningitis. Helpful information is seldom obtained from the spinal tap in the evaluation of acute head trauma and it may be hazardous. Transtentorial or foramen magnum herniation can be precipitated or accelerated by a lumbar spinal tap in the setting of an expanding intracranial mass.
Almost all patients with significant head injury need to have an x-ray of their cervical spine to determine the presence or absence of bony fracture or displacement prior to any significant manipulation of the neck. This must include the cervicothoracic junction.
The spinal cord lies protected within the vertebral spinal canal, a channel lined by bone (vertebral bodies and laminae) and ligamentous structures (e.g., posterior longitudinal ligament and ligamentum flavum). The vertebral body laminae and facet fibrous attachments acting together with the preceding two ligaments form a semiflexible tubular structure that subserves maintenance of erect posture and protection of the spinal cord. Direct and indirect forces applied to the spine may cause injury to the spinal cord. Direct injuries that distort, fracture or crush the vertebral column may contuse or lacerate the spinal cord, which lies within the narrow spinal vertebral canal. Stab wounds entering through the interlaminar space may sever the spinal cord without bony injury.
Indirect distortion of the vertebral column is by far the most common cause of spinal cord injury. Acceleration-deceleration forces applied to the head or trunk cause distortion of the vertebral column and its contents. Not surprisingly, the most mobile portions of the vertebral column are the most prone to damaging distortion. These are the lower cervical and thoracolumbar junction regions. The rib cage of the thoracic spine makes it the least mobile and therefore the least likely to be distorted by indirect forces.
Flexion and extension distortions of the cervical spine are the most common cause of spinal cord injury. The vertebral bodies may be displaced anteriorly or posteriorly on themselves (listhesis) with or without ligamentous tears causing concussion, contusion, or laceration of the spinal cord. Severe flexion may stretch the spinal cord upward which in conjunction with the bony displacement mentioned earlier adds further injury. If the forces are great enough, or if there is a predisposing fragility of the spine as in the aged with cervical osteoarthritis, fractures may occur and bony fragments contribute to cord damage.
Acceleration and deceleration vehicular accidents are the most common causes of cervical and thoracolumbar spinal column distortion. Swimming pool diving accidents, associated with flexion or extension deceleration distortion of the cervical spine, are also frequent causes of spinal cord injury. The spinal cord may be damaged by direct compression or disruption (bone displacement or fracture, hematoma, extruded disk material, and ligamentous distortion), stretching, secondary edema following concussion, or secondary vascular occlusive and hemorrhagic phenomena. All degrees of cord dysfunction may result, from complete disruption with crush or lacerating injuries to minor symptoms with no objective losses from minor concussing forces.
A typical crush or contusing lesion typically damages the more fragile central gray matter of the cord with early preservation of the surrounding white matter and long-tract motor and sensory systems. This pattern may persist and, if the gray matter is the primary area of damage, functions below the injury may be preserved while there may be persistent problems at the level of injury ("central cord syndrome"). However, over a relatively short period of time the white matter pathways my be involved, possibly by edema or ischemia and by release of neurotoxic substances at the site of injury. Attempts are being made to determine ways to prevent the ensuing white-matter injury. Surgical decompression of the segments may be indicated in rare cases. Cooling of the spinal-cord cooling may decrease metabolic demands. Various drugs (antioxidants, vasodilators, etc) have at least some experimental support, but most have not been proven effective in humans. One possible exception is massive doses of corticosteroids, which were reported to make a tiny difference in outcome. However, reassessment of the data from this trial suggests minimal, if any benefit.
Any therapeutic approach in the acute event may be limited by the delay in getting the patient to an appropriate spinal cord trauma center. Prevention of further injury by immobilizing the spine at the site of the accident is important and may be the most effective acute treatment.
When paraplegia is established as a permanent baseline, rehabilitative efforts become of major importance. The average paraplegic can be rehabilitated to become an independent and productive member of society. The prognosis for the quadriplegic patient, if s/he survives for any length of time, is poor.
- Jennett, B. and Lindsay, K.: An Introduction to Neurosurgery, ed. 5. Oxford, Butterworth-Heinemann, 1994.
- Lindsay, K.W., Bone, I., Callander, R.: Neurology and Neurosurgery Illustrated, 2nd ed. New York, Churchill Livingstone, 1991.