Книги по МРТ КТ на английском языке / PLUM AND POSNER S DIAGNOSIS OF STUPOR AND COM-1

cerebellar angiomas or are receiving anticoagulant drugs. In elderly patients, amyloid angiopathy may be the culprit.159 On rare occasions, a cerebellar hemorrhage may follow a supratentorial craniotomy.160 Among our own 28 patients,161 five had posterior fossa arteriovenous vascular malformations, one had thrombocytopenic purpura, three were normotensive but receiving anticoagulants, and the remainder, who ranged between 39 and 83 years of age, had hypertensive vascular disease. Hemorrhages in hypertensive patients arise in the neighborhood of the dentate nuclei; those coming from angiomas tend to lie more superficially. Both types usually rupture into the subarachnoid space or fourth ventricle and cause coma chiefly by compressing the brainstem.

Fisher’s paper in 1965162 did much to stimulate efforts at clinical diagnosis and encouraged attempts at successful treatment. Subsequent reports from several large centers have increasingly emphasized that early diagnosis is critical for satisfactory treatment of cerebellar hemorrhage, and that once patients become stuporous or comatose, surgical drainage is a near-hopeless exercise.156 The most common initial symptoms of cerebellar hemorrhage are headaches (most often occipital), nausea and vomiting, dizziness or vertiginous sensations, unsteadiness or an inability to walk, dysarthria, and, less often, drowsiness. Messert and associates described two patients who had unilateral eyelid closure contralateral to the cere-

bellar hemorrhage, apparently as an attempt to prevent diplopia.163 Patient 4–3, below, is a typical example.

Patient 4–3

A 55-year-old man with hypertension and a history of poor medication compliance had sudden onset of severe occipital headache and nausea when sitting down with his family to Christmas dinner. He noticed that he was uncoordinated when he tried to carve the turkey. When he arrived in the hospital emergency department he was unable to sit or stand unaided, and had severe bilateral ataxia in both upper extremities. He was a bit drowsy but had full eye movements with end gaze nystagmus to either side. There was no weakness or change in muscle tone, but tendon reflexes were brisk, and toes were downgoing. He was sent for a CT scan, but by the time the scan was finished the CT technician could no longer arouse him.

The CT scan showed a 5-cm egg-shaped hemorrhage into the left cerebellar hemisphere, compressing the fourth ventricle, with hydrocephalus. By the time the patient returned to the emergency department he had no oculocephalic responses, and breathing was ataxic. Shortly afterward, he had a respiratory arrest and died before the neurosurgical team could take him to the operating room.

Table 4–9 lists the most frequent early physical signs as recorded in a series of 72 patients.164

As Patient 4–3 illustrates, deterioration from alertness or drowsiness to stupor often comes over a few minutes, and even brief delays to carry out radiographic procedures can prove fatal. Mutism, a finding encountered in children after operations that split the inferior vermis of the cerebellum, occasionally occurs in adults with cerebellar hemorrhage.165 Although usually not tested during the rush of the initial examination, cognitive dysfunction, including impairment of executive functions, difficulty with spatial cognition, and language deficits, as well as affective disorders including blunting of affect or disinhibited or inappropriate behavior, called the ‘‘cerebellar cognitive affective syndrome,’’166 are sometimes present (see also page 306, Chapter 6). Similar abnormalities may persist if there is damage to the posterior hemisphere of the cerebellum, even following successful treatment of cerebellar mass lesions.167

All patients who present to the emergency room with acute cerebellar signs, particularly when associated with headache and vomiting, require an urgent CT. The scan identifies the hemorrhage and permits assessment of the degree of compression of the fourth ventricle and whether there is any complicating hydrocephalus. Our experience with acute cerebellar hemorrhage points to a gradation in severity that can be divided roughly into four relatively distinct clinical patterns. The least serious form occurs with small hemorrhages, usually less than 1.5 to 2 cm in diameter by CT, and includes self-limited, acute unilateral cerebellar dysfunction accompanied by headache. Without imaging, this disorder undoubtedly would go undiagnosed. With larger hematomas, occipital headache is more prominent and signs of cerebellar or oculomotor dysfunction develop gradually or episodically over 1 to several days. There may be some associated drowsiness or lethargy. Patients with this degree of impairment have been reported to recover spontaneously, particularly from hemorrhages measuring less than 3 cm in diameter by CT. However, the condition requires extremely careful observation until one is sure that there is no progression due to edema formation, as patients almost always do poorly if one waits until coma develops to initiate sur-

gical treatment. The most characteristic and therapeutically important syndrome of cerebellar hemorrhages occurs in individuals who develop acute or subacute occipital headache, vomiting, and progressive neurologic impairment including ipsilateral ataxia, nausea, vertigo, and nystagmus. Parenchymal brainstem signs, such as gaze paresis or facial weakness on the side of the hematoma, or pyramidal motor signs develop as a result of brainstem compression, and hence usually are not seen until after drowsiness or obtundation is apparent. The appearance of impairment of consciousness mandates emergency intervention and surgical decompression that can be lifesaving. About one-fifth of patients with cerebellar hemorrhage develop early pontine compression with sudden loss of consciousness, respiratory irregularity, pinpoint pupils, absent oculovestibular responses, and quadriplegia; the picture is clinically indistinguishable from primary pontine hemorrhage and is almost always fatal.

Kirollos and colleagues have proposed a protocol based on CT and the patient’s clinical state to help determine which patients are candidates for surgical intervention and to predict prognosis (Figure 4–8). The degree of fourth ventricular compression is divided into three grades depending on whether the fourth ventricle is normal (grade 1), is compressed (grade 2), or is completely effaced (grade 3). Grade 1 or 2 patients who are fully conscious are carefully observed for deterioration of level of consciousness. If grade 1 patients have impaired consciousness, a ventricular drain is placed. If grade 2 patients have impaired consciousness with hydrocephalus, a ventricular drain is placed. In grade 3 patients and grade 2 patients who have impaired consciousness without hydrocephalus, the hematoma is evacuated. No grade 3 patients with a Glasgow Coma Score less than 8 experienced a good outcome.156

Clinical predictors of neurologic deterioration are a systolic blood pressure over 200 mm Hg, pinpoint pupils, and abnormal corneal or oculocephalic reflexes. Imaging predictors are hemorrhage extending into the vermis, a hematoma greater than 3 cm in diameter, brainstem distortion, interventricular hemorrhage, upward herniation, or acute hydrocephalus. Hemorrhages in the vermis and acute hydrocephalus on admission independently predict deterioration.164

Cerebellar Infarction

Cerebellar infarction can act as a mass lesion if there is cerebellar edema. In these cases, as in cerebellar hemorrhage, the mass effect can cause stupor or coma by compression of the brainstem and death by herniation. Cerebellar infarction represents 2% of strokes.168,169 Most victims are men. Hypertension, atrial fibrillation, hypercholesterolemia, and diabetes are important risk factors in the elderly168; verte-

bral artery dissection should be considered in younger patients.169 Marijuana use has been implicated in a few patients.170 The neurologic symptoms are similar to those of cerebellar hemorrhage, but they progress more slowly, as they are typically due to edema that develops gradually over 2 to 3 days after the onset of the infarct, rather than acutely (Table 4–10).

The onset is characteristically marked by acute or subacute dizziness, vertigo, unsteadiness, and, less often, dull headache. Most of the

patients examined within hours of onset are ataxic, have nystagmus with gaze in either direction but predominantly toward the infarct, and have dysmetria ipsilateral to the infarct. Dysarthria and dysphagia are present in some patients and presumably reflect associated lateral medullary infarction. Only a minority of patients are lethargic, stuporous, or comatose

on admission, which suggests additional injury to the brainstem.168

Initial CT rules out a cerebellar hemorrhage, but it is often difficult to demonstrate an infarct. Even if a hypodense lesion is not seen, asymmetric compression of the fourth ventricle may indicate the development of acute edema. A diffusion-weighted MRI is usually positive on initial examination.

In most instances, further progression, if it is to occur, develops by the third day and may progress to coma within 24 hours.171 Progression is characterized by more intense ipsilateral dysmetria followed by increasing drowsiness leading to stupor, and then miotic and poorly reactive pupils, conjugate gaze paralysis ipsilateral to the lesion, ipsilateral peripheral facial paralysis, and extensor plantar responses. Once the symptoms appear, unless surgical decompression is conducted promptly, the illness progresses rapidly to coma, quadriplegia, and death.

Only the evaluation of clinical signs can determine whether the swelling is resolving or the enlarging mass must be surgically treated

(by ventricular shunt or extirpation of infarcted tissue).171,172 The principles of management of

a patient with a space-occupying cerebellar infarct are similar to those in cerebellar hemorrhage. If the patient remains awake, he or she is observed carefully. If consciousness is impaired and there is some degree of acute hydrocephalus on scan, ventriculostomy may relieve the compression. However, if there is no acute hydrocephalus, or if the patient fails to improve after ventriculostomy, craniotomy with removal of infarcted tissue is necessary to relieve brainstem compression. Survival may follow prompt surgery, but patients may have distressing neurologic residua if they survive.

Cerebellar Abscess

About 10% of all brain abscesses occur in the cerebellum.173 Cerebellar abscesses represent about 2% of all intracranial infections. Most arise from chronic ear infections,174 but some occur after trauma (head injury or neurosurgery) and others are hematogenous in origin. If untreated, they enlarge, compress the brainstem, and cause herniation and death. If successfully recognized and treated, the outcome is usually good. The clinical symptoms of a cerebellar abscess differ little from those of other cerebellar masses (Table 4–11).

Headache and vomiting are very common. Patients may or may not be febrile or have nu-

*Data from Shaw and Russell.175 {Data from Nadvi et al.173

chal rigidity.175 If the patient does not have an obvious source of infection, is not febrile, and has a supple neck, a cerebellar abscess is often mistaken for a tumor, the correct diagnosis being made only by surgery. About one-half of patients have a depressed level of consciousness.173 The diagnosis is made by imaging, scans revealing a mass with a contrast-enhancing rim and usually an impressive amount of edema. Restricted diffusion on diffusion-weighted MRI helps distinguish the abscess from tumor or hematoma. Hydrocephalus is a common complication. The treatment is surgical, either primary excision176 or aspiration.177 The outcome is better when patients with hydrocephalus are treated with CSF diversion or drainage.173

are uncommon.179 The symptoms of cerebellar tumors are the same as those of any cerebellar mass, but because their growth is relatively slow, they rarely cause significant alterations of consciousness unless there is a sudden hemorrhage in the tumor. Patients present with headache, dizziness, and ataxia. Because the symptoms are rarely acute, MRI scanning can usually be obtained. The contrast-enhanced image will not only identify the enhancing cerebellar tumor, but will also inform the physician whether there are other metastatic lesions and whether hydrocephalus is present. The treatment of a single metastasis in the cerebellum is generally surgical or, in some instances, by radiosurgery.128 Multiple metastases are treated with radiation therapy.

Cerebellar Tumor

Most cerebellar tumors of adults are metastases.178 The common cerebellar primary tumors of children, medulloblastoma and pilocytic astrocytoma, are rare in adults. Cerebellar hemangioblastomas may occur in adults, but they

Pontine Hemorrhage

Although pontine hemorrhage compresses the brainstem, it causes damage as much by tissue destruction as by mass effect (Figure 4–9). Hemorrhage into the pons typically produces

the characteristic pattern of sudden onset of unconsciousness with tiny but reactive pupils (although it may require a magnifying glass or the plus 20 lens of the ophthalmoscope to visualize the light response). Most patients have impairment of oculocephalic responses, and eyes may show skew deviation, ocular bobbing, or one of its variants. Patients may have decerebrate rigidity, or they may demonstrate flaccid quadriplegia. We have seen one patient in whom a hematoma that dissected along the medial longitudinal fasciculus, and caused initial vertical and adduction ophthalmoparesis, was followed about an hour later by loss of consciousness (see Patient 2–1). However, in most patients, the onset of coma is so sudden that

there is not even a history of a complaint of headache.180

SUPRATENTORIAL DESTRUCTIVE LESIONS CAUSING COMA

The most common supratentorial destructive lesions causing coma result from either anoxia or ischemia, although the damage may occur due to trauma, infection, or the associated immune response. To cause coma, a supratentorial lesion must either involve bilateral cortical or subcortical structures multifocally or diffusely or affect the thalamus bilaterally. Following recovery from the initial insult, the

coma is usually short lived, the patient either awakening, entering a persistent vegetative state within a few days or weeks, or dying (see Chapter 9).

VASCULAR CAUSES

OF SUPRATENTORIAL

DESTRUCTIVE LESIONS

Diffuse anoxia and ischemia, including carbon monoxide poisoning and multiple cerebral emboli from fat embolism181 or cardiac surgery,182 are discussed in detail in Chapter 5. We will concentrate here on focal ischemic lesions that can cause coma.

Carotid Ischemic Lesions

Unilateral hemispheric infarcts due to carotid or middle cerebral occlusion may cause a quiet, apathetic, or even confused appearance, as the remaining cognitive systems in the patient’s functional hemisphere attempt to deal with the sudden change in cognitive perspective on the world. This appearance is also seen in patients during a Wada test, when a barbiturate is injected into one carotid artery to determine the lateralization of language function prior to surgery. The appearance of the patient may be deceptive to the uninitiated examiner; acute loss of language with a dominant hemisphere lesion may make the patient unresponsive to verbal command, and acute lesions of the nondominant hemisphere often cause an ‘‘eyeopening apraxia,’’ in which the patient keeps his or her eyes closed, even though awake. However, a careful neurologic examination demonstrates that despite the appearance of reduced

responsiveness, true coma rarely occurs in such cases.183

In the rare cases where unilateral carotid occlusion does cause loss of consciousness, there

is nearly always an underlying vascular abnormality that explains the observation.184,185 For

example, there may be pre-existing vascular anomaly or occlusion of the contralateral carotid artery, so that both cerebral hemispheres may be supplied, across the anterior communicating artery, by one carotid. In the absence of such a situation, unilateral carotid occlusion does not cause acute loss of consciousness.

Patients with large hemispheric infarcts are nearly always hemiplegic at onset, and if in the dominant hemisphere, aphasic as well. The lesion can be differentiated from a cerebral hemorrhage by CT scan that, in the case of infarct, may initially appear normal or show only slight edema with loss of gray-white matter distinction (Figure 4–10). MRI scans, however, show marked hyperintensity on the diffusionweighted image, indicating ischemia. Symptoms may be relieved by early use of thrombolytic agents,186 but only if the stroke is identified and treated within a few hours of onset. There are currently no neuroprotective agents that have demonstrated effectiveness. Patients with massive infarcts should be given good supportive care to ensure adequate blood flow, oxygen, and nutrients to the brain, but hyperglyce-

mia should be avoided as it worsens the outcome.187,188 These patients are best treated in

a stroke unit189; they should be watched carefully for the development of brain edema and increased ICP.

Although impairment of consciousness is rare as an immediate result of carotid occlusion, it may occur 2 to 4 days after acute infarction in the carotid territory, as edema of the infarcted hemisphere causes compression of the other

hemisphere and the diencephalon, and may even result in uncal or central herniation.186,190

This problem is presaged by increasing lethargy and pupillary changes suggesting either central or uncal herniation. Many patients who survive the initial infarct succumb during this period. The swelling does not respond to corticosteroids as it is cytotoxic in origin. It may be diminished transiently with mannitol or hypertonic saline,191 but these agents soon equilibrate across the blood-brain barrier and cease

to draw fluid out of the brain, if they ever did192,193 (see Chapter 7). Surgical resection of the infarcted tissue may improve survival,194,195

but this approach often results in a severely impaired outcome. Decompressive craniotomy (removing bone overlying the damaged hemisphere) may increase survival, but many of the patients have a poor neurologic outcome.196

Distal Basilar Occlusion

Distal basilar occlusion typically presents with a characteristic set of findings (the ‘‘top of the basilar syndrome’’) that can include impairment

of consciousness.197 The basilar arteries give rise to the posterior cerebral arteries, which perfuse the caudal medial part of the hemispheres. The posterior cerebral arteries also give rise to posterior choroidal arteries, which perfuse the caudal part of the hippocampal formation, the globus pallidus, and the lateral

Figure 4–10. Development of cerebral edema and herniation in a patient with a left middle cerebral artery infarct. A 90-year-old woman with hypertension and diabetes had sudden onset of global aphasia, right hemiparesis, and left gaze preference. (A) A diffusion-weighted magnetic resonance imaging scan and

(B) an apparent diffusion coefficient (ADC) map, which identify the area of acute infarction as including both the anterior and middle cerebral artery territories. The initial computed tomography scan (C, D) identified a dense

left middle cerebral artery (arrow), indicating thrombosis, and swelling of the sulci on the left compared to the right, consistent with the region of restricted diffusion shown on the ADC map. By 48 hours after admission, there was massive left cerebral edema, with the medial temporal lobe herniation compressing the brainstem (arrow E) and subfalcine herniation of the left cingulate gyrus (arrow in F) and massive midline shift and compression of the left lateral ventricle. The patient died shortly after this scan.

geniculate nucleus.198 In addition, thalamoperforating arteries originating from the basilar tip, posterior cerebral arteries, and posterior

communicating arteries supply the caudal part of the thalamus.199 Occlusion of the distal pos-

terior cerebral arteries causes bilateral blindness, paresis, and memory loss. Some patients

who are blind deny their condition (Anton’s syndrome). However, the infarction does not cause loss of consciousness. On the other hand, more proximal occlusion of the basilar artery that reduces perfusion of the junction of the midbrain with the posterior thalamus and

hypothalamus bilaterally can cause profound

coma.197,200–202

Isolated thalamic infarction can cause a wide variety of cognitive problems, depending on which feeding vessels are occluded (Table 4– 14). Castaigne and colleagues203 and others204 have provided a comprehensive analysis of clinical syndromes related to occlusion of each vessel (Table 4–12). Surprisingly, even bilateral thalamic injuries are typically not associated with a depressed level of consciousness unless there

is some involvement of the paramedian mesencephalon.205,206 Most such patients become

more responsive within a few days, although the prognosis for full recovery is poor.207

Venous Sinus Thrombosis

The venous drainage of the brain is susceptible to thrombosis in the same way as other venous circulations.208 Most often, this occurs during a hypercoagulable state, related either to dehy-

dration, infection, or childbirth, or associated with a systemic neoplasm.209,210 The throm-

bosis may begin in a draining cerebral vein, or it may involve mainly one or more of the dural sinuses. The most common of these conditions is thrombosis of the superior sagittal sinus.210 Such patients complain of a vertex headache, which is usually quite severe. There is increased ICP, which may be as high as 60 cm of water on lumbar puncture and often causes papilledema. The CSF pressure may be sufficiently high to impair brain perfusion. There is also an increase in venous back-pressure in the brain (due to poor venous drainage), and so the arteriovenous pressure gradient is further reduced, and cerebral perfusion is at risk. This causes local edema and sometimes frank infarction. For example, in sagittal sinus thrombosis, the impaired venous outflow from the paramedian walls of the cerebral hemisphere may result in bilateral lower extremity hyperreflexia and extensor plantar responses, and sometimes even paraparesis. Extravasation into the infarcted tissue, due to continued high

perfusion pressure, causes local hemorrhage, hemorrhagic CSF, and seizures.

Thrombosis of the lateral sinus causes pain in the region behind the ipsilateral ear. The thrombosis may be associated with mastoiditis, in which case the pain due to the sinus thrombosis may be overlooked. If the outflow through the other lateral sinus remains patent, there may be little or no change in CSF pressure. However, the lateral sinuses are often asymmetric, and if the dominant one is occluded, there may not be sufficient venous outflow from the intracranial space. This may cause impairment of CSF outflow as well, a condition that is sometimes known as ‘‘otitic hydrocephalus.’’ There typically is also venous stasis in the adjacent ventrolateral wall of the temporal lobe. Infarction in this area may produce little in the way of focal signs, but hemorrhage into the infarcted tissue may produce seizures.

Thrombosis of superficial cortical veins may be associated with local cortical dysfunction, but more often may present with seizures and focal headache.211 Thrombosis of deep cerebral veins, such as the internal cerebral veins or vein of Galen, or even in the straight sinus generally presents as a rapidly progressive syndrome with headache, nausea and vomiting,

and then impaired consciousness progressing to coma.212,213 Impaired blood flow in the thal-

amus and upper midbrain may lead to venous infarction, hemorrhage, and coma. Venous thrombosis associated with coma generally has a poor prognosis, whereas awake and alert patients usually do well.210

Venous occlusion is suggested when the pattern of infarction does not match an arterial distribution, especially if the infarct contains a region of hemorrhage. However, in many cases of venous sinus thrombosis, there will be little, if any, evidence of focal brain injury. In those cases, the main clues will often be elevated pressure with or without red cells in the CSF. Sometimes lack of blood flow in the venous sinus system will be apparent even on routine CT or MRI scan, although often it is not clearly evident. Either CT or MR venogram can easily make the diagnosis, but neither is a routine study, and unless the examining physician thinks of the diagnosis and asks for the study, the diagnosis may be overlooked. Although no controlled trials prove efficacy,214