From the Guidelines
A stroke or hemorrhage in the external capsule can lead to significant morbidity, including contralateral hemiparesis, sensory deficits, dysarthria, language deficits, and cognitive impairments, with the severity of these deficits varying based on the size of the bleed. The external capsule is a thin layer of white matter in the brain located between the putamen and claustrum, containing association fibers connecting different cortical areas and projection fibers from the thalamus to the cerebral cortex 1. Given its location, a bleed or stroke in this area can have profound effects on motor and sensory function, as well as higher-order cognitive processes.
Clinical Presentation
- Contralateral hemiparesis (weakness on the opposite side of the body) is a common presentation due to the involvement of motor fibers.
- Sensory deficits can occur, affecting touch, pain, temperature, and proprioception.
- Dysarthria (slurred speech) may be present, particularly if the dominant hemisphere is affected.
- Language deficits, such as aphasia, can occur if the lesion encroaches upon language pathways.
- Cognitive impairments, including attention, memory, and executive function deficits, might also be present depending on the extent of the lesion.
Prognosis and Recovery
The prognosis for recovery depends on the extent of damage, with smaller, isolated external capsule lesions generally having better outcomes than larger bleeds affecting multiple structures. The proximity of the external capsule to critical areas such as the internal capsule, basal ganglia, and insular cortex means that bleeds often extend beyond just the external capsule, creating a complex clinical picture. Management and treatment strategies, such as those outlined in guidelines for acute ischemic stroke, including the use of aspirin within 48 hours of symptom onset as supported by high-quality evidence from studies like IST and CAST 1, can significantly impact morbidity and mortality.
Management Considerations
- Early administration of aspirin (160-300 mg) within 48 hours of ischemic stroke onset can result in fewer deaths and more patients with a good functional outcome at 30 days, as evidenced by the Cochrane systematic review of four trials assessing the effect of early aspirin administration in patients with acute stroke 1.
- The risk of nonfatal major extracranial hemorrhage is increased with aspirin use, but the overall benefit in reducing mortality and improving functional outcomes in acute ischemic stroke patients supports its use in appropriate candidates.
From the Research
External Capsule and Associated Deficits
The external capsule is a structure in the brain that can be affected by stroke or bleeding, leading to various deficits.
- The external capsule is involved in motor function, sensation, and speech, and damage to this area can result in corresponding deficits 2.
- Motor deficits are common in external capsule strokes, and can include faciobrachial, faciobrachiocrural, or brachiocrural paresis 2.
- Hypesthesia, or abnormal sensation, can also occur, particularly with regard to light touching 2.
- Speech disturbances, such as dysarthria or transient speech arrest, can be present in some cases 2.
Etiology and Prognosis
- The main etiologies of external capsule strokes are small artery disease and artery-to-artery embolism, often due to atherosclerotic carotid artery disease 2.
- The prognosis for external capsule strokes is generally good, with most patients experiencing a favorable outcome 2.
- However, it is essential to note that the clinical presentation and outcome of external capsule strokes can vary depending on the individual case and the underlying cause of the stroke 2.