Berry Aneurysm Case File

Berry Aneurysm Case File

Eugene C. Toy, MD, Lawrence M. Ross, MD, PhD, Han Zhang, MD, Cristo Papasakelariou, MD, FACOG

CASE 46

A 43-year-old man was washing his car when he suddenly complained of a severe headache and then slumped to the ground. His son, who witnessed the episode, stated that his father grabbed his head with both hands and cried out in pain as he was falling. The son said that his father had no medical problems and exercised regularly. On examination in the emergency department, the patient was lethargic but responsive to deep pain stimuli. His pupils were dilated bilaterally and sluggishly reactive to light. CT scan of the head showed a significant intracranial hemorrhage. An angiogram demonstrated leakage of dye from the junction of the right internal carotid artery and the circle of Willis.

⯈ What is the most likely diagnosis?

⯈ What is the clinical anatomy for this event?

ANSWER TO CASE 46:

Berry Aneurysm

Summary: An otherwise healthy 43-year-old man suddenly complained of a severe headache and lost consciousness. He is lethargic, responsive to deep pain, and has bilaterally dilated and sluggishly reactive pupils. CT imaging showed a significant intracranial hemorrhage, and an angiogram demonstrated leakage of dye from the junction of the right internal carotid artery and the circle of Willis.

• Most likely diagnosis: Ruptured berry aneurysm

• Clinical anatomy for this event: Weakness of the intracranial arterial junction

CLINICAL CORRELATION

This otherwise healthy 43-year-old man had an acute and significant cerebral event. He had a severe headache quickly followed by loss of consciousness. There was no motor activity to suggest an epileptic seizure. Further, his comatose state ruled out self-limited etiologies such as syncope due to a vasovagal reaction. Cerebral imaging confirms intracranial hemorrhage. The possibilities include an arteriovenous malformation (a tangle of vessels that sometimes rupture) or a hemorrhagic stroke. An arteriogram shows leakage of dye from the junction of the internal carotid artery and the circle of Willis, strongly suggesting a berry aneurysm. The blood supply to the brain is derived from the paired internal carotid and the paired vertebral arteries. Occlusion of even one of these vessels would cause severe damage were it not for the anastomosis between these four vessels known as the circle of Willis. However, there is inherent weakness at the junction of the arteries, and an outpouching of the arterial wall, a berry aneurysm, may occur and ultimately rupture. The best treatment for such a ruptured aneurysm is surgical clip ligation. Medications such as calcium channel blockers are useful for preventing coexisting arterial vasospasm.

APPROACH TO:

Vascular Supply of Brain

OBJECTIVES

1. Be able to describe the course of the internal carotid and vertebral arteries

2. Be able to list the major intracranial branches of the internal carotid and the basilar arteries

3. Be able to identify the components of the circle of Willis

DEFINITIONS

ANGIOGRAPHY: Radiographic technique in which contrast medium is injected into the arterial system. X-ray images may be taken at regular intervals to follow the dye from the arterial supply through the venous drainage. Recent advances in MRI have made it possible to examine blood flow without injection of contrast medium.

ANEURYSM: Disruption within the wall of an artery that fills with blood and inflates the muscular coat. The resulting dilation can exert pressure on surrounding structures and ultimately may rupture, leading to a rapid loss of blood pressure.

SYNCOPE: Episode of fainting; a loss of consciousness not related to sleeping.

DISCUSSION

The arterial blood supply to the brain is derived from the paired internal carotid and paired vertebral arteries. The internal carotid arteries arise from the bifurcation of the common carotid arteries at about the level of the superior border of the thyroid cartilage. They are described as being the direct continuation of the common carotids, having no branches in the neck, and ascending to the base of the skull, where they enter the carotid canal. The internal carotid arteries pass anteriorly and medially through the cavernous sinus to enter the cranial cavity and divide into its terminal branches, the anterior cerebral artery and the middle cerebral artery. The two anterior cerebral arteries join through the anterior communicating branch. The posterior communicating branch joins the middle cerebral with the posterior cerebral arteries.

The vertebral arteries are the first branches of the subclavian arteries in the root of the neck. They ascend through the transverse foramina of vertebrae C6 through C1, enter the cranial cavity through the foramen magnum, and unite to form the basilar artery near the junction of the pons and medulla (Figure 46-1).

Figure 46-1. The circle of Willis. (Reproduced, with permission, from Chusid JG. Correlative Neuroanatomy and Functional Neurology, 19th ed. East Norwalk, CT: Appleton & Lange, 1985.)

At the superior border of the pons, the basilar artery divides into the posterior cerebral arteries. The chief intracranial branches of the vertebral arteries are the posterior inferior cerebellar arteries. Before its terminal bifurcation, the chief branches of the basilar artery are the anterior inferior cerebellar arteries, superior cerebellar arteries, and several pontine branches.

The cerebral arterial circle (of Willis) is the major anastomosis of the cerebral vasculature. This allows for perfusion of the brain even with arterial occlusion of one or more major arteries (such as carotid insufficiency). If the occlusion develops slowly, the anastomotic vessels will expand to compensate. However, the anastomosis may not be able to compensate if the occlusion develops rapidly, as with trauma. Blockage of one cerebral artery will have characteristic effects based on the region of the brain supplied by the vessel (Figure 46-2). The anterior cerebral artery supplies the medial surface of the cerebrum. The middle cerebral artery supplies the lateral surfaces, and the posterior cerebral artery supplies the inferior surface. The middle

Figure 46-2. Arterial supply of the cerebral cortex. (Reproduced, with permission, from Lindner HH. Clinical Anatomy. East Norwalk, CT: Appleton & Lange, 1989:32.)

cerebral artery is occluded most often, presumably because it follows the same trajectory as the internal carotid.

COMPREHENSION QUESTIONS

46.1 A 53-year-old man is being examined for carotid bruits. The physician wants to auscultate the internal carotid artery. At what level does the carotid artery usually bifurcate into the internal and external carotid arteries?

    A. At the level of the cricoid cartilage

    B. At the level of the thyroid cartilage

    C. At the level of sternal notch

    D. At the level of the C8 vertebra

46.2 A 64-year-old man is diagnosed with an acute stroke. His main deficit is a partial loss of his visual field. The neurologist diagnoses a lesion of the occipital lobe. Which of the following arteries is likely to be involved?

    A. Internal carotid

    B. External carotid

    C. Middle cerebral

    D. Posterior cerebral

46.3 A 35-year-old man complains of the worst headache of his life, grabs onto the back of his neck, and then slumps onto the floor. At the hospital, his CT findings are consistent with a subarachnoid hemorrhage. Which of the following is the most likely etiology?

    A. Carotid artery occlusion

    B. Vertebrobasilar artery occlusion

    C. Middle meningeal artery laceration

    D. Rupture of a berry aneurysm

ANSWERS

46.1 B. The carotid artery bifurcates at the level of the thyroid cartilage.

46.2 D. The occipital lobes are supplied by the posterior cerebral arteries, which are terminal branches of the basilar artery.

46.3 D. The most common causes of subarachnoid hemorrhage are rupture of a berry aneurysm in the circle of Willis and bleeding from an arteriovenous malformation.

ANATOMY PEARL

⯈ The internal carotid arteries have no branches in the neck.

⯈ The terminal branches of the internal carotid arteries are the anterior and middle cerebral arteries.

⯈ The blood supply to the cerebellum is derived from the vertebrobasilar arterial system.

⯈ The circle of Willis allows anastomosis of the arterial blood supply of the brain.

⯈ The major arterial blood supply of the brain is from the internal carotid and vertebral arteries.

References

Gilroy AM, MacPherson BR, Ross LM. Atlas of Anatomy, 2nd ed. New York, NY: Thieme Medical Publishers; 2012:636−637. 

Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy, 7th ed. Baltimore, MD: Lippincott Williams & Wilkins; 2014:882−885, 887−888. 

Netter FH. Atlas of Human Anatomy, 6th ed. Philadelphia, PA: Saunders; 2014: plates 138−142.

HomeCase FilesBerry Aneurysm Case File