Stephen J. Schueler, M.D.

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Subarachnoid Bleed Anatomy

To better understand subarachnoid hemorrhage, it helps to understand the anatomy of the brain.

The arachnoid is one of three layers of tissue that cover the brain. Bleeding from blood vessels underneath the arachnoid is called a subarachnoid hemorrhage.

Brain Anatomy
The brain is well protected by:

  • The scalp
  • The skull
  • The dura
    • A tough 3-layer sheath that surrounds the brain and spinal cord
    • Layers include the dura mater (strongest layer), arachnoid mater (middle layer), and pia mater (closest to the brain)

The brain is a complicated structure containing many parts. These include:
  • The cerebrum:
    • Made up of two cerebral hemispheres that are connected in the middle
    • It is the largest part of the brain
    • Each area of the cerebrum performs an important function, such as language or movement
    • Higher thought (cognition) comes from the frontal cortex (front portion of the cerebrum)
    • Outside of the cerebrum are blood vessels
    • There are fluid-filled cavities and channels inside the brain
  • The cerebellum:
    • Located in the lower, back part of the skull
    • Controls movement and coordination
  • The brainstem and pituitary gland:
    • Responsible for involuntary functions such as breathing, body temperature, and blood pressure regulation
    • Pituitary gland is the "master gland" that controls other endocrine glands in the body, such as the thyroid and adrenal glands
    • Pineal gland
  • The cranial nerves:
    • Twelve large nerves exit the bottom of the brain to supply function to the senses such as hearing, vision, and taste
  • The cerebral blood vessels:
    • A complicated system that supplies oxygenated blood and nutrients to the brain

The blood supply to the brain is divided into two main parts:
  • Anterior cerebral circulation:
    • The front of the brain is supplied by the paired carotid arteries in the neck.
  • Posterior cerebral circulation:
    • The back portion of the brain is supplied by the paired vertebral arteries in the spine.

Anatomy examples:
  • Carotid artery branches shown on arteriogram
  • Cerebral arteries viewed in cross-section through middle of brain
  • Cerebral arteries viewed from bottom of brain
  • Cerebral arteries on enhanced CT scan
  • Cerebral arteries on arteriogram

Last Updated: Jan 5, 2011 References
Authors: Stephen J. Schueler, MD; John H. Beckett, MD; D. Scott Gettings, MD
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PubMed Subarachnoid Bleed References
  1. Ashley WW Jr, Chicoine MR. Subarachnoid hemorrhage caused by posterior inferior cerebellar artery aneurysm with an anomalous course of the atlantoaxial segment of the vertebral artery. Case report and review of literature. J Neurosurg. 2005 Aug;103(2):356-60. [16175868]
  2. Edlow JA. Diagnosis of subarachnoid hemorrhage. Neurocrit Care. 2005;2(2):99-109. [16159051]
  3. Rosen DS, Macdonald RL. Subarachnoid hemorrhage grading scales: a systematic review. Neurocrit Care. 2005;2(2):110-8. [16159052]
  4. Salary M, Quigley MR, Wilberger JE Jr. Relation among aneurysm size, amount of subarachnoid blood, and clinical outcome. J Neurosurg. 2007 Jul;107(1):13-7. [17639867]
  5. Stiefel MF, Heuer GG, Abrahams JM, Bloom S, Smith MJ, Maloney-Wilensky E, Grady MS, LeRoux PD. The effect of nimodipine on cerebral oxygenation in patients with poor-grade subarachnoid hemorrhage. J Neurosurg. 2004 Oct;101(4):594-9. [15481712]
  6. Toussaint LG 3rd, Friedman JA, Wijdicks EF, Piepgras DG, Pichelmann MA, McIver JI, McClelland RL, Nichols DA, Meyer FB, Atkinson JL. Influence of aspirin on outcome following aneurysmal subarachnoid hemorrhage. J Neurosurg. 2004 Dec;101(6):921-5. [15597751]
  7. van Gijn J, Kerr RS, Rinkel GJ. Subarachnoid haemorrhage. Lancet. 2007 Jan 27;369(9558):306-18. [17258671]
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