Appendix C: Circulation of the Brain

Introduction

• The Blood Supply of the Brain Can Be Divided into Arterial Territories

• The Cerebral Vessels Have Unique Physiological Responses

• A Stroke Is the Result of Disease Involving Blood Vessels

• Clinical Vascular Syndromes May Follow Vessel Occlusion, Hypoperfusion, or Hemorrhage

  • Infarction Can Occur in the Middle Cerebral Artery Territory

  • Infarction Can Occur in the Anterior Cerebral Artery Territory

  • Infarction Can Occur in the Posterior Cerebral Artery Territory

  • The Anterior Choroidal and Penetrating Arteries Can Become Occluded

  • The Carotid Artery Can Become Occluded

  • The Brain Stem and Cerebellum Are Supplied by Branches of the Vertebral and Basilar Arteries

  • Infarcts Affecting Predominantly Medial or Lateral Brain Stem Structures Produce Characteristic Syndromes

  • Infarction Can Be Restricted to the Cerebellum

  • Infarction Can Affect the Spinal Cord

  • Diffuse Hypoperfusion Can Cause Ischemia or Infarction

  • Cerebrovascular Disease Can Cause Dementia

  • The Rupture of Microaneurysms Causes Intraparenchymal Stroke

  • The Rupture of Saccular Aneurysms Causes Subarachnoid Hemorrhage

• Stroke Alters the Vascular Physiology of the Brain

The brain is highly vulnerable to disturbance of its blood supply. Anoxia lasting only seconds causes neurological symptoms; when it lasts minutes it can cause irreversible neuronal damage. Blood flow to the central nervous system must efficiently deliver oxygen, glucose, and other nutrients and remove carbon dioxide, lactic acid, and other metabolites. The cerebral vasculature has special anatomical and physiological features that protect the brain. However, when these mechanisms fail, the result is a stroke. Broadly defined, the term stroke, or cerebrovascular accident, refers to the neurological symptoms or signs that result from diseases involving blood vessels. These are usually focal and acute.

The Blood Supply of the Brain Can Be Divided into Arterial Territories

Each cerebral hemisphere is supplied by an internal carotid artery, which arises from the common carotid artery beneath the angle of the jaw, enters the cranium through the carotid foramen, traverses the cavernous sinus (giving off the ophthalmic artery), penetrates the dura, and then divides into the anterior and middle cerebral arteries (Figure C–1).

The large surface branches of the anterior cerebral artery supply the cortex and white matter of the inferior frontal lobe, the medial surface of the frontal and parietal lobes, and the anterior corpus callosum (Figure C–2). Smaller penetrating branches—including the so-called recurrent artery of Heubner —supply the deeper cerebrum and diencephalon, including limbic structures, the head of the caudate, and the anterior limb of the internal capsule.