aneurysm

The ACOMM Aneurysm: Balloons and Blood

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In order to understand the anterior communicating artery, we have to first appreciate the anatomy of the anterior cerebral arteries. The anterior cerebral arteries are one of the two terminal branches of each internal carotid artery (the other being the middle cerebral artery). Each anterior cerebral artery has several sections from A1 to A5.

Each A1 segment branches into an A2 segment and into the anterior communicating artery. The anterior communicating artery connects each anterior cerebral arteries’ A1 segment together to form a circle (see schematic below).

The anterior communicating artery is one of the most common sites for intracranial aneurysm formation. Patients at risk for developing aneurysms include those with atherosclerosis, those with a family history of intracranial aneurysms, those with a history of hypertension or collagen vascular disease, and those with polycystic kidney disease. Smokers are also at a higher risk of developing aneurysms.

Basilar Tip Schematic Drawing
Anterior communicating artery aneurysms form when the lining of the vessel wall is thinned and the muscular layer of the blood vessel (tunica media) becomes weakened.

This thinning allows turbulent blood flow to form out-pouchings in the vessel wall. Typically these out-pouchings occur at points where blood vessels branch.

Signs and Symptoms

Anterior communicating artery aneurysms commonly present after a subarachnoid hemorrhage, which can cause a variety of signs and symptoms. The most common being a severe headache, although cranial nerve dysfunction, stroke, coma, and death can also occur.

Less commonly, aneurysms in this location can compress the optic chiasm or optic nerves leading to problems with vision.

How Do You Diagnose Aneurysms

Anterior cerebral artery aneurysms are most commonly diagnosed after a subarachnoid hemorrhage when a patient presents with the "worst headache of their life". The best imaging methods for diagnosing these aneurysms are CT angiograms (see image below), MR angiograms, and formal cerebral angiograms.

Treatment

Like other intracranial aneurysms, anterior communicating artery aneurysms may be clipped or coiled. Clipping of an aneurysm involves an open surgical procedure where the surgeon dissects down to the aneurysm and places a clip across its neck. This excludes it from the circulation and prevents it from rupturing.

Anterior Communicating Artery Aneurysm CT Angiogram

Aneurysms may also be treated from inside the blood vessel. In this procedure a catheter is threaded from the femoral artery in the groin up towards the location of the aneurysm. Small metallic coils are placed within the dome of the aneurysm, which also excludes it from the normal circulation.

Regardless of how the aneurysm is treated – either with clipping or coiling – the end result is that the aneurysm is excluded from the normal circulation. This prevents it from rupturing.

The merits of clipping versus coiling are still under debate. Ultimately, the treatment depends on the size and location of the aneurysm, as well as other medical problems that the patient may have.

The Highlights…

Anterior communicating artery aneurysms are the most common intracranial aneurysm. They typically present after rupturing into the subarachnoid space and/or adjacent frontal lobes. They are diagnosed using CT angiograms or formal cerebral angiography. Treatment is with clipping and/or coiling.

Related Readings

Not Satisfied? More Reading on the Subject…

  • Bederson JB, Awad IA, Wiebers DO, et al. Recommendations for the management of patients with unruptured intracranial aneurysms. Stroke 2000;31:2742-2750.
    • li>Hunt WE, Hess RM. Surgical Risk as Related to Time of Intervention in the Repair of Intracranial Aneurysms. Journal of Neurosurgery 1968; 28:14-20.
  • Brisman JL, Song JK, Newell DW. Cerebral Aneurysms. NEJM 2006; 355:928-939.
  • Kumar V, Abbas AK, Fausto N. Robbins and Cotran Pathologic Basis of Disease. Seventh Edition. Philadelphia: Elsevier Saunders, 2004.
  • Frontera JA. Decision Making in Neurocritical Care. First Edition. New York: Thieme, 2009.
  • Greenberg MS. Handbook of Neurosurgery. Sixth Edition. New York: Thieme, 2006. Chapter 25.

The Anterior Choroidal Artery: Small but Mighty

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The anterior choroidal arteries are small, but vital blood vessels in the brain. They are branches of the internal carotid arteries. They arise proximal to the splitting of the internal carotid into the anterior and middle cerebral arteries.

The anterior choroidal arteries deliver blood to vital brain structures. These structures include the posterior limbs of the internal capsules, portions of the thalami, optic tracts, middle third of the cerebral peduncles, portions of the temporal lobes (ie: parts of the pyriform cortex, uncus, and amygdala), substantia nigra, portions of the globus pallidus, as well as the choroid plexus in the lateral ventricles.

The anterior choroidal artery forms connections (anastamoses) with the posterior lateral choroidal arteries. Cerebral angiograms are the best way to visualize the anterior choroidal arteries.

Importance in Disease

Blockage of the anterior choroidal artery can cause a stroke. The most common symptoms of an anterior choroidal stroke are hemiparesis (weakness on the opposite side of the body), hemianesthesia (decreased sensation on the opposite side of the body), and a homonymous hemianopsia (loss of a portion of the visual field of both eyes). High blood pressure is the most common underlying factor in people with anterior choroidal artery strokes.

The hemiparesis is a result of damage to the posterior limb and genu of the internal capsule. The posterior limb contains the corticospinal tracts, which send information about movement from the brain to the spinal cord.

The hemianesthesia is a result of damage to the ventral posterolateral nucleus of the thalamus. This nucleus contains neurons that receive information from the spinal cord about sensation from the body. This symptom is less common than weakness, and occurs in roughly half of patients with an anterior choroidal stroke.

Cerebral angiogram showing anterior choroidal artery.

The final symptom, homonymous hemianopsia, is caused by damage to the optic tracts and lateral geniculate nucleus of the thalamus. Patients lose the ability to see objects on the left or right side (depending on which anterior choroidal artery is involved) in both eyes. This is an even more uncommon symptom, which occurs in less than 10% of patients with an anterior choroidal artery stroke.

Strokes of the anterior choroidal artery rarely cause all three symptoms. This is because the brain tissue served by the anterior choroidals also receives blood flow from other arteries.

Aneurysms of the anterior choroidal arteries are rare and will not be discussed in this article.

Overview

The anterior choroidal arteries are paired structures that arise from the internal carotid arteries. They supply blood to many important structures within the brain. Stroke is the most common pathological disease related to this blood vessel and frequently causes weakness of the opposite side of the body. High blood pressure is the most common underlying disease seen in people who have a stroke in this vascular distribution.

Other Stuff Worth Looking At…

References and Resources

  • Pezzella FR, Vadalà R. Anterior choroidal artery territory infarction. Front Neurol Neurosci. 2012;30:123-7. Epub 2012 Feb 14.
  • Bruno A, Graff-Radford NR, Biller J, et al. Anterior choroidal artery territory infarction: a small vessel disease. Stroke. 1989 May;20(5):616-9.
  • Baehr M, Frotscher M. Duus’ Topical Diagnosis in Neurology: Anatomy, Physiology, Signs, Symptoms. Fourth Edition. Stuttgart: Thieme, 2005.
  • Nolte J. The Human Brain: An Introduction to its Functional Anatomy. Sixth Edition. Philadelphia: Mosby, 2008.
  • Baskaya MK, Coscarella E, Gomez F, et al. Surgical and angiographic anatomy of the posterior communicating and anterior choroidal arteries. Neuroanatomy (2004) v3:38-42.