Brief Summary
This video by Dr. Srinivas Medical Concepts provides a detailed overview of stroke syndromes, focusing on both cortical and brainstem strokes. It explains the vascular anatomy of the brain, emphasizing the Circle of Willis and the distinction between anterior and posterior circulation strokes. The video covers specific stroke syndromes related to the middle cerebral artery (MCA), anterior cerebral artery (ACA), and posterior cerebral artery (PCA), as well as internal capsule involvement. Additionally, it discusses various brainstem syndromes, including those affecting the midbrain, pons, and medulla oblongata, and introduces the "rule of four" as a helpful tool for understanding brainstem strokes.
- Vascular anatomy and the Circle of Willis are crucial for understanding stroke syndromes.
- Anterior circulation strokes (MCA, ACA) are generally less dangerous than posterior circulation strokes (brainstem).
- The "rule of four" simplifies the understanding of brainstem strokes by categorizing structures and cranial nerves involved.
Introduction to Stroke and Vascular Anatomy
The video introduces stroke as an abrupt onset of neurological deficit due to a focal vascular cause. Understanding stroke syndromes requires knowledge of vascular anatomy, specifically the Circle of Willis, which is an anastomosis between the vertebrobasilar system and the internal carotid artery system. The brain is divided into cortical and brainstem regions, each supplied by different arteries.
Anterior vs. Posterior Circulation Strokes
The brain's circulation is divided into anterior and posterior. The vertebrobasilar system supplies the brainstem, and strokes in this area are called posterior circulation strokes. The internal carotid artery supplies the cortex via the middle cerebral artery (MCA) and anterior cerebral artery (ACA), and strokes here are anterior circulation strokes. Anterior circulation strokes are more common and generally less dangerous than posterior circulation strokes, which can affect vital brainstem structures.
Cortical Syndromes: Middle Cerebral Artery (MCA)
MCA strokes are divided into superior and inferior divisions. Superior division strokes on the left side can cause Broca's aphasia and right hemiplegia. Inferior division strokes on the left can cause Wernicke's aphasia without hemiplegia. Stem occlusions of the MCA can result in hemiplegia, hemianesthesia, global aphasia, and gaze palsy, where the eyes look towards the side of the lesion and hemiplegia occurs on the opposite side.
Cortical Syndromes: Anterior Cerebral Artery (ACA)
ACA strokes primarily affect the medial part of the frontal lobe, leading to leg weakness and primitive reflexes. Patients may also exhibit behavioral changes and, if the left ACA is involved, transcortical motor aphasia. Key signs of ACA involvement include leg weakness, primitive reflex emergence, behavioral changes, and transcortical motor aphasia.
Cortical Syndromes: Posterior Cerebral Artery (PCA)
PCA strokes affect the midbrain, temporal lobe, and occipital cortex. Temporal lobe involvement can cause memory disturbances, while occipital cortex involvement can lead to cortical blindness (Anton syndrome) and visual agnosia. Lesions affecting the splenium of the corpus callosum can result in alexia without agraphia, where patients can write but cannot read what they have written.
Internal Capsule Strokes
The internal capsule is supplied by the MCA (upper part) and ACA (lower part). The anterior limb contains thalamic radiations, the genu contains corticobulbar fibers, and the posterior limb contains corticospinal fibers. Strokes in the anterior cerebral artery territory of the internal capsule can cause faciobrachial monoplegia. Involvement of the entire anterior choroidal artery territory can cause hemiplegia, hemianesthesia, and homonymous hemianopia. Small lesions in the internal capsule can produce dense hemiplegia due to the close proximity of corticobulbar and corticospinal fibers.
Brainstem Syndromes: Midbrain
Midbrain syndromes include Nothnagel syndrome (cerebellar ataxia), Benedict syndrome (tremors), Claude syndrome (combination of Nothnagel and Benedict), and Weber syndrome (third nerve palsy with hemiplegia). Parinaud syndrome involves selective upward gaze palsy. Third nerve involvement can be differentiated by nuclear involvement (bilateral ptosis) versus nerve involvement (unilateral ptosis). Extrinsic compression of the third nerve causes pupil dilation, while intrinsic pathology affects the center of the nerve.
Brainstem Syndromes: Pons
Pons syndromes include Foville syndrome (sixth nerve nuclear involvement causing horizontal gaze palsy, seventh nerve palsy, and contralateral hemiplegia) and Millard-Gubler syndrome (sixth nerve palsy, seventh nerve palsy, and hemiplegia). Locked-in syndrome involves pontine infarcts affecting horizontal gaze and corticobulbar/corticospinal tracts, resulting in quadriplegia with preserved vertical eye movements. One-and-a-half syndrome involves a combination of PPRF and medial longitudinal fasciculus (MLF) lesions, causing impaired horizontal eye movements and nystagmus.
Brainstem Syndromes: Medulla Oblongata
Medulla oblongata syndromes include medial medullary syndrome (posterior column and twelfth nerve involvement) and lateral medullary syndrome (Wallenberg syndrome). Wallenberg syndrome involves the spinal nucleus of the fifth nerve (facial sensory loss), spinothalamic tract (contralateral pain and temperature loss), sympathetic tract (Horner's syndrome), spinocerebellar tract (ataxia), tenth nerve (palatal palsy, dysphagia), and vestibular nuclei (vertigo). Wallenberg syndrome does not typically cause hemiplegia.
The Rule of Four for Brainstem Strokes
The "rule of four" simplifies brainstem stroke localization. It includes four midline structures starting with "M" (motor/corticospinal tract, medial lemniscus, motor nucleus of cranial nerves, medial longitudinal fasciculus) and four sideways structures starting with "S" (spinothalamic tract, sympathetic tract, sensory nucleus of the fifth nerve, spinocerebellar tract). There are four cranial nerves in the medulla (9, 10, 11, 12), four in the pons (5, 6, 7, 8), and two in the midbrain (3, 4). Cranial nerves that divide 12 into equal parts (3, 4, 6, 12) are located in the midline, while those that do not (5, 7, 8, 9, 10, 11) are located sideways.
