Stroke

Localization and Severity of Weakness

The upper motor neurons of the corticospinal tracts originate in the cerebral cortex, decussate (i.e., cross sides) in the brainstem, and terminate on lower motor neurons and interneurons in the spinal cord ( Fig. 37.7 ). Due to this crossing, lesions above the decussation cause contralateral motor deficits. In cortical strokes affecting upper motor neurons, the location of the injury determines which body parts are weak, as well as the degree of weakness. Given the large topographic distribution of the motor cortex and different vascular territories that supply it, a substantially large stroke in the motor cortex may cause weakness in only a relatively small area of the body. In contrast, a very small stroke in the internal capsule may cause complete hemiplegia, due to the compact nature of the corticospinal tract in this area. If a stroke in the brainstem causes unilateral weakness, it is typically accompanied by other signs of brainstem dysfunction.

The severity of unilateral weakness may vary from severe hemiplegia to subtle hemiparesis. On examination, hemiparesis may be accompanied by pronator drift, slowing of rapid alternating movements, or decreased arm swing during gait. Pronator drift is assessed by asking the patient to extend the arms at the shoulder while keeping the elbows straight with the palms facing up in a supinated position, as if carrying a tray. The patient is then asked to close the eyes and maintain the arms in this position. In pronator drift, the affected arm will slowly drift down and the hand may pronate. Assessing rapid alternating movements involves asking the patient to perform a series of repetitive movements as quickly though dexterously as possible. Movements include alternating supination and pronation of the forearm to tap the plantar and palmar surfaces of the hands against the thighs, touching each of the fingers to the thumb in succession in a repeating fashion, or tapping the floor by repeatedly flexing and extending the ankles. The weak limb will perform these movements with decreased speed and dexterity in comparison to the unaffected limb. Decreased arm swing can be observed when the patient is asked to ambulate; the affected arm does not swing as much as the unaffected arm.

Characterization of Weakness: Flaccid or Spastic

Tone is the resistance of muscle to stretch; the maintenance of normal tone requires intact central and peripheral nervous systems (see Chapter 35 ). Acutely following a stroke, weakness is usually flaccid, or hypotonic. For infants and young children, the flaccid weakness manifests symptomatically as decreased or absent spontaneous movement of the affected limbs, while passive movements of the affected limbs are met with little to no resistance. Such deficits in older children and adolescents are noticeable to both the patient and observers alike, and muscle group testing can further localize specific areas of weakness.

With time, patients with weakness from stroke typically develop increased tone, or spasticity, as well as clonus in the affected limbs. Spasticity generally involves antigravity muscles, primarily the arm flexors and leg extensors. As a result, the arms become flexed and pronated, while the legs become extended and adducted, with plantar flexion of the foot and inversion of the ankle. If the hand is affected, cortical thumbing, consisting of adduction and flexion of the thumb, may occur. Testing for spasticity involves moving the relaxed affected extremity several times through its range of motion and assessing for freedom of movement. The extremity is then suddenly stretched through that range of motion at a higher velocity, at which point, if there is spasticity, tone will notably increase and the limb will “catch,” a finding referred to as the clasp-knife response .

In addition to developing spasticity, patients with stroke affecting the corticospinal tracts develop brisk and hyperactive deep tendon reflexes due to the interruption of descending inhibitory upper motor neuron pathways and increased activity of the γ neuron reflex loop (see Chapter 35 ). Hyperactive reflexes are often accompanied by pathologic clonus, consisting of repetitive, rhythmic muscle contractions in response to tendon percussion or stretch of that muscle. Healthy neonates may have several beats of physiologic clonus; clonus in older infants or in children, adolescents, or adults is generally considered pathologic. Greater than 10 beats upon elicitation is considered sustained clonus and is indicative of more severe hypertonia. Pathologic spread of reflexes , in which antagonist or nearby adjacent muscle groups contract along with the muscle whose stretch reflex is being tested, is an additional sign of hypertonia. Other specific pathologic reflexes may be present if the relevant portion of the corticospinal tract is affected. Plantarflexion of the great toe is the physiologic response to stroking the foot in an arc from the heel, along the lateral aspect of the plantar surface, and across the ball of the foot to the great toe. Patients with an upper motor neuron lesion affecting control of the leg and foot will demonstrate the Babinski response, in which the great toe dorsiflexes rather than plantarflexes. The Hoffmann sign is elicited when the examiner flicks the fingernail of the patient’s middle finger rapidly downward; if present, the index finger and the thumb involuntarily flex.

Types of Aphasias

The examination of a patient with suspected aphasia must consider age and developmental stage, as the evaluation requires pre-existent language production and comprehension, as well as the ability to follow commands, such as the repetition of words. Aphasias can be broadly divided into expressive (nonfluent) and receptive (fluent) and can be further categorized based on the ability to repeat words or phrases ( Table 37.6 ).

The prototypical expressive aphasia is Broca aphasia , the evaluation of which typically reveals a frustrated patient who is able to comprehend language while being unable to speak or repeat phrases. In the most severe form, the patient is mute, whereas in the milder forms the patient may produce speech with frequent paraphasic errors (e.g., responding “pan” when asked to name a pen). An additional expressive aphasia is transcortical motor aphasia , in which a patient retains the ability to comprehend and repeat speech but is unable to produce spontaneous speech.

The prototypical receptive aphasia is Wernicke aphasia , in which comprehension of language is impaired but prosody or fluency of speech is preserved. The content of speech is often nonsensical and the words are often malformed; however, since the patient cannot understand their own nonsensical speech, frustration or concern with the deficit is absent. With pure Wernicke aphasia repetition is impaired. An additional expressive aphasia in which repetition is preserved is transcortical sensory aphasia .

Additional aphasia syndromes include global aphasia , in which both production and comprehension are impaired; mixed transcortical aphasia , in which both receptive and expressive language are impaired but the repetition of words is preserved; and conduction aphasia , in which the comprehension and production of speech are preserved but the repetition of words is impaired.

Brainstem Syndromes

The brainstem contains many critical gray and white matter structures, such as the corticospinal tracts, the dorsal columns and spinothalamic tracts, cranial nerve nuclei, connections with the cerebellum, the reticular activating system, and ascending neurotransmitter-specific projection pathways. The vascular supply of the brainstem corresponds to its three levels, with the midbrain supplied by the superior cerebellar arteries (with the exception of the superior midbrain that is supplied by the posterior cerebral arteries), the pons supplied by the anterior inferior cerebellar arteries, and the medulla supplied by the posterior inferior cerebellar arteries. These three arteries arise from the vertebrobasilar system. Given the dense organization of these structures and the nature of their blood supply, symptoms of brainstem stroke are varied and localization is often challenging. Presenting symptoms, such as nausea or vertigo, are often vague and may mimic migraine, benign positional paroxysmal vertigo, seizure, or other sometimes less emergent diagnoses, leading to diagnostic delays and significant morbidity and mortality.

Table 37.7 describes classic brainstem syndromes . The hallmark of a brainstem stroke is crossed paresis , which consists of facial weakness ipsilateral to the stroke with contralateral limb hemiparesis. This pattern of findings is due to the notion that all cranial nerves, with the exception of cranial nerve IV, project ipsilaterally and the corticospinal tracts do not cross the midline until the cervicomedullary junction, rostral to the brainstem. Depending on whether a brainstem lesion is located more medially or dorsolaterally determines the nature of symptoms: medial brainstem strokes are primarily motor, whereas dorsolateral brainstem strokes are predominantly sensory. Dorsolateral brainstem strokes may also affect the cerebellar peduncles, leading to deficits in coordination and movement precision. Ventral pontine stroke from a basilar artery thrombosis or embolism may present with locked-in syndrome , in which the patient is awake and conscious but unable to move or communicate except for blinking and vertical eye movements. Locked-in syndrome must be distinguished from coma by determining the level of consciousness.

Seizures

Seizures are a common presenting symptom in pediatric stroke, occurring in the majority of neonates and ∼30% of older children. Children who have had a stroke are also at risk for developing epilepsy, sometimes years after a stroke; in some cases, seizures may be refractory to treatment and may lead to adverse neurodevelopmental outcomes.

While seizures in neonatal AIS are common, symptoms can be subtle. Pauses in breathing or even true apneic spells may not be noticed if not accompanied by cyanosis or unless continuous cardiorespiratory monitoring is in place; myoclonic activity may be confused for benign neonatal movements. Electroencephalogram can assist in determining whether a particular event of concern is seizure-related. Perinatal stroke is a risk factor for infantile spasms , a rare and potentially devastating epileptic syndrome characterized by developmental delays, a specific electroencephalographic pattern termed hypsarrhythmia , and frequent seizures. The seizures— epileptic spasms —consist of an abrupt, brief contraction followed by a more sustained but less intense tonic contraction lasting no more than several seconds. The spasms involve the muscles of the neck, trunk, and extremities. Spasms may be flexor, extensor, or mixed and occur in clusters typically after waking from sleep. Infantile spasms are considered a relative neurologic emergency, as treatment must be initiated soon after diagnosis to mitigate neurocognitive deterioration. Infantile spasms typically present months after stroke and are thought to be due to maladaptive changes in regulatory GABAergic pathways of brain development.

Disorders of Consciousness

Pediatric stroke may present with diffuse neurologic features such as alteration in consciousness or coma. Disorders of consciousness may arise from bilateral cerebral hemispheric, bi-thalamic, or brainstem infarctions; however, disordered consciousness may also be due to increased intracranial pressure from a large unilateral infarction leading to herniation and brainstem compression, in which case the Cushing triad of hypertension, bradycardia, and abnormal respiration may indicate the need for emergent intervention. Lastly, disordered consciousness may be secondary to prolonged seizures or the effects of medications given to control seizures.

Clinical Presentation and Mimics

Neonatal AIS is the most common type of perinatal stroke, and focal motor seizures are the most frequent presenting symptom, occurring in up to 90% of affected term newborns. Other presenting symptoms include encephalopathy in ∼66% of affected neonates, feeding difficulties, apnea, and tone abnormalities. Lateralized findings, most typically motor weakness or decreased tone, may be present, though their absence does not exclude cerebral infarction. Furthermore, diminished extremity movement on the side of a focal seizure may represent postictal paralysis rather than paresis from upper motor neuron injury caused by cerebral infarction. Preterm neonates with AIS are commonly asymptomatic and may be incidentally diagnosed on routine screening cerebral ultrasound. Preterm infants with AIS most frequently present with respiratory difficulties, though seizures, feeding difficulty, and abnormal tone may occur as well. Presenting features for neonates with AIS are summarized in Table 37.10 . Neonates with hemorrhagic stroke and with CSVT present similarly, with a combination of encephalopathy, seizures, feeding and respiratory difficulties, and focal neurologic deficits. Neonates with hemorrhagic stroke may also have a bulging fontanelle or widening of the cranial suture lines.

Seizures are the most common presentation of neonatal stroke, and are also the most common stroke mimic. Neonatal seizures may occur in the setting of hypoxic ischemic encephalopathy (HIE), cerebral malformations, meningitis, sepsis, acute metabolic derangements, inborn errors of metabolism, kernicterus, neonatal abstinence syndrome, and genetic epilepsy syndromes. The timing of seizures, as well as associated findings, can assist in distinguishing etiology: Neonates with seizures secondary to stroke typically have seizure onset after 24 hours of life, have focal motor activity, and remain lucid interictally. In contrast, neonates with HIE typically have seizures within the first 12 hours of life, have an associated antenatal event such as fetal distress or perinatal asphyxia, and have encephalopathy of varying degrees. Neonates with meningitis or sepsis often have associated temperature and hemodynamic instability and may have metabolic derangements and acid-base disturbances. Neonates with inborn errors of metabolism often have hypoglycemia and acid-base disturbances, can have hyperammonemia depending on the metabolic disorder, and may have progressive encephalopathy.

Risk Factors of Neonatal Stroke

For neonatal AIS, the low recurrence rate of <2% suggests the pathophysiology is related to a process unique to the perinatal state. The left hemisphere is the most commonly involved area, with exclusive involvement of the middle cerebral artery territory in up to 90% of perinatal AIS strokes ( Fig. 37.11 ), though the location of stroke varies based on gestational age ( Table 37.11 ). Risk factors for neonatal AIS can be broadly categorized as maternal, fetal, and placental ( Table 37.12 ). Placentally derived emboli may lodge in cerebral vessels. Congenital heart defects involving right-to-left shunts through septal defects increase the risk of embolic stroke. Congenital defects of coagulation (factor VIII, protein C, protein S, antithrombin III deficiency, and others) or sepsis-induced disseminated intravascular coagulation may also result in neonatal embolic stroke. Fetal head trauma during labor and delivery that results in endothelial damage to cerebral vessels occasionally leads to thrombosis and resultant focal ischemia of the brain. Polycythemia and hypotension can each lead to intravascular stasis and abnormalities in flow, resulting in cerebrovascular thrombosis in neonates. Meningitis and encephalitis cause diffuse or localized thrombosis as a result of vascular inflammation, leading to hemostasis and thrombosis. Lastly, specific neonatal cardiac conditions requiring extracorporeal membrane oxygenation (ECMO) may predispose the neonate to AIS. Many have an unknown etiology.

Neonatal hemorrhagic stroke or intraparenchymal hemorrhage (IPH), in the absence of intraventricular hemorrhage (IVH), occurs most commonly in full-term infants. Hemorrhage into the parenchyma of the cerebral hemispheres can be caused by head trauma, vascular malformation ( Fig. 37.12 ), coagulopathy, thrombocytopenia, tumor, or infarction. A common cause of prenatal, intrapartum, and postnatal hemorrhage is alloimmune thrombocytopenia, caused by acquired antiplatelet antibodies when a mother becomes sensitized to paternal antigens on fetal platelets. Maternal immune thrombocytopenia may also affect the fetus, producing thrombocytopenia in utero; however, the incidence of neonatal cerebral hemorrhage is much lower in immune thrombocytopenia than in alloimmune thrombocytopenia. Vitamin K–deficient bleeding should be considered as a cause of intracranial hemorrhage for breast-fed full-term neonates or for neonates who were not administered parenteral vitamin K shortly after birth. In the absence of recognized coagulation or anatomic abnormalities, cerebral hemispheric IPH may also be due to hemorrhagic conversion of a previous infarction.

In premature infants, IPH most often occurs in conjunction with severe IVH ( Fig. 37.13 ). Hemorrhage from the friable, unsupported germinal matrix leads to accumulation of intraventricular blood, and often ventricular distention. These events, in turn, cause impairment of blood flow in the medullary veins located in the periventricular white matter, preventing blood drainage into the greater cerebral venous system. Eventually, the periventricular venous congestion leads to ischemia and a resultant venous infarction. If there continues to be difficulty with cerebrospinal fluid production and reabsorption dynamics, the infant may develop posthemorrhagic hydrocephalus and in some instances may need cerebrospinal fluid diversion procedures.

Risk factors for neonatal CSVT include thrombophilia, infection, dehydration, polycythemia, congenital heart disease, and ECMO ( Table 37.13 ). The lesions associated with cerebral venous thrombosis include thrombosis in the deep or superficial veins, venous infarction, and hemorrhage ( Fig. 37.14 ). The hemorrhage that typically accompanies CSVT is a result of the increased venous and capillary hydrostatic pressure due to the presence of the clot causing extravasation of fluid and red blood cells.

Evaluation and Management