Carotid Insufficiency Case File

Carotid Insufficiency Case File

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

CASE 37

A 59-year-old man complains of numbness of his right arm and slurred speech for a 4-h duration. On examination, he has a blood pressure of 150/90 mmHg and a normal body temperature. His heart has a regular rate and rhythm. Auscultation of the neck reveals a blowing sound bilaterally.

⯈ What is the most likely diagnosis?

⯈ What is the most likely anatomical mechanism for this condition?

ANSWER TO CASE 37:

Carotid Insufficiency

Summary: A 59-year-old hypertensive man complains of a 4-h history of numbness of his right arm and slurred speech. He has carotid bruits bilaterally.

• Most likely diagnosis: Transient ischemic attack

• Most likely anatomical mechanism: Left carotid insufficiency leading to ischemia of the left cerebral hemisphere

CLINICAL CORRELATION

This 59-year-old man has a 4-h history of right arm numbness and slurred speech. This suggests ischemia of the left cerebral hemisphere including the speech area. If the deficits were to resolve before 24 h, it would be called a transient ischemic attack. If the deficits were to continue beyond 24 h, it would be called a cerebrovascular accident, or stroke. The two major types of strokes are ischemic and hemorrhagic. Differentiating between the two is important because fibrinolytic therapy (medication that dissolves blood clots) would be contraindicated with hemorrhagic strokes. Ischemic strokes can be caused by atherosclerosis or emboli. In this patient, the bruits identified on the carotid arteries are likely due to increased rate and turbulence of blood flow through the stenotic vessels. Immediate management of this patient would include administration of an antiplatelet medication such as aspirin and/or clopidogrel. An emergency computer tomographic (CT) scan of the head can help to differentiate between ischemic and hemorrhagic stroke, and fibrinolytic therapy can be considered if a cerebral hemorrhage is not found. After stabilization of the patient, carotid endarterectomy surgery may be indicated.

APPROACH TO:

The Neck: Vasculature

OBJECTIVES

1. Be able to review the somatotopic organization of sensory and motor regions in the brain

2. Be able to list the branches of the common carotid artery and the vascular supply to the brain and identify the sites most susceptible to formation of atherosclerotic plaques

3. Be able to describe structures in the anterior triangle of the neck that relate to the carotid artery and sheath

DEFINITIONS

AUSCULTATION: Procedure of listening to the body during the physical examination, generally through a stethoscope

BRUITS: An abnormal sound heard through the stethoscope, generally a “whoosh”

SOMATOTOPIC: An orderly mapping of the body surface onto an internal organ, usually a region of the brain

ANSA CERVICALIS: A loop formed superficially in the carotid sheath by branches of cervical spinal nerves innervating the strap muscles

DISCUSSION

The major structural features of the brain include the cerebrum and the cerebellum. The cerebrum is involved in the major functions of sensory perception, motor control, and the associational processing that integrates the two. The cerebellum is primarily involved in motor control. The surface or cortex of the cerebrum is folded into a number of ridges (gyri) separated by valleys (sulci) of different depths. The brain is divided into lobes named for the overlying cranial bones: frontal, temporal, parietal, and occipital. The central sulcus separates the frontal from the parietal lobes. The precentral gyrus controls voluntary motion, whereas the postcentral gyrus is the site of somatosensory perception.

The sensory and motor areas are arranged according to a somatotopic organization. The lower extremity is represented medially along the gyrus; the upper extremity, more laterally; and the head and neck, most laterally. The tracts going to and from the sensory and motor areas cross in the lower brain and spinal cord to control the opposite side of the body. Another important region is the motor speech area (Broca area), which is a small gyrus in the anterior parietal cortex of the left brain, called the operculum, just superior to the temporal lobe. These basic organizational features are important because they help physicians identify the region of the brain damaged by a stroke or hemorrhage. Thus, numbness or paralysis of the right upper extremity indicates damage on the left side of the brain, which will frequently involve the motor speech area.

The blood supply to the brain is from the common carotid and the vertebral arteries (Figure 37-1). The two ascend separately through the neck. The vertebral artery ascends through the transverse foramina of the cervical vertebrae without giving off any major branches. It then curves medially to ascend through the foramen magnum. The paired vertebral arteries fuse to form the basilar artery. The common carotid bifurcates at about the level of the hyoid bone (vertebrae C3 and C4). The external carotid ascends to provide branches to structures outside the cranium. The internal carotid ascends without major branches to enter the cranium through the carotid canal. After a relatively tortuous course through the sphenoid bone and the cavernous sinus, the internal carotid emerges into the middle cranial fossa. In the region of the sella turcica and surrounding the pituitary stalk, the vertebral and carotid circulations anastomose through a complex structure called the circle of Willis, which is formed posteriorly by the bifurcation of the basilar into left and right posterior cerebral arteries. It forms anteriorly with the internal

Figure 37-1. Branches of the external carotid artery: 1 = superior thyroid, 2 = lingual, 3 = facial, 4 = ascending pharyngeal, 5 = occipital, 6 = posterior auricular, 7 = maxillary, 8 = superficial temporal, 9 = internal carotid. (Reproduced, with permission, from the University of Texas Health Science Center, Houston Medical School.)

carotids, which bifurcate into the anterior and middle cerebral arteries. The left and right anterior cerebrals anastomose through the anterior communicating branch. The middle cerebral and posterior cerebral arteries anastomose through the posterior communicating branch.

The carotids are susceptible to occlusion as a result of atherosclerotic disease. The most common sites of occlusion are bifurcation of the internal and external carotids and bifurcation of the anterior and middle cerebral arteries. Occasionally, small pieces of an atherosclerotic plaque will break off (embolize) and obstruct a smaller artery. The middle cerebral artery and its branches are most commonly affected by this process. This artery ascends through the Sylvian fissure along the superior border of the temporal lobe. A major branch runs lateral to medial in the central sulcus. As a consequence, many strokes produce deficits in movement and sensation of the face and upper extremities and in language. More severe damage may also affect the lower extremity.

The carotid arteries are palpated in the anterior triangle of the neck. The sternocleidomastoid muscle (SCM) separates the superficial neck into anterior and posterior triangles. The anterior triangle is further divided by the omohyoid and digastric muscles into four additional triangles: submental, submandibular, muscular, and carotid. The common carotid artery ascends in the neck deep to the contents of the muscular triangle. These muscles are the sternothyroid, sternohyoid, and superior belly of omohyoid. It then goes through the carotid triangle, which is bordered by the superior belly of omohyoid, posterior belly of digastric, and sternocleidomastoid muscles. The common carotid bifurcates at the level of the hyoid bone (C3), and the internal carotid continues posteriorly. The carotids are contained within the carotid sheath. This fascial membrane originates from the other three layers of deep fascia that are in the neck: superficial layer of deep fascia, prevertebral fascia, and pretracheal/buccopharyngeal fascia. Also contained in the carotid sheath are the internal jugular vein and the vagus nerve (CN X). The vein is larger than the artery and lies more superficially. Several other cranial nerves have a structural relation to the carotid sheath. These include the glossopharyngeal (CN IX) and spinal accessory (CN XI) nerves, which exit with the vagus through the jugular foramen. The sinus branch of the glossopharyngeal nerve courses within the sheath to innervate the carotid body and sinus. The hypoglossal nerve (CN XII) passes deep to the carotid sheath as it projects anteriorly into the submandibular triangle. The sympathetic trunk lies deep to the carotid sheath on the surface of the prevertebral muscles. The superior and inferior roots of the ansa cervicalis, from spinal nerves C2 through C4, typically form the loop within the anterior surface of the carotid sheath before giving off branches to the infrahyoid muscles.

COMPREHENSION QUESTIONS

37.1 A 47-year-old man complains of right arm weakness and difficulty speaking (expressive aphasia). Which of the following arteries is most likely affected?

    A. Vertebral

    B. Posterior cerebral

    C. Middle cerebral

    D. Anterior cerebral

37.2 While performing a carotid endarterectomy in a 55-year-old man who has carotid artery occlusion, and on approach to the internal carotid artery, a surgeon severs a nerve embedded in the carotid sheath. Which nerve was severed?

    A. Superior laryngeal

    B. Vagus

    C. Sympathetic trunk

    D. Ansa cervicalis

    E. Recurrent laryngeal

37.3 A 44-year-old man falls from a tree and develops a severe scalp hematoma. The superficial temporal artery continues to bleed internally because the man takes warfarin sodium (Coumadin) for an artificial heart valve. Which of the following arteries may be ligated to control the bleeding?

    A. Internal carotid

    B. External carotid

    C. Occipital

    D. Maxillary

ANSWERS

37.1 C. The middle cerebral artery supplies the temporal and parietal regions that contain the Broca area (the speech center).

37.2 D. The ansa cervicalis is a branch of the cervical plexus that innervates the infrahyoid strap muscles. The superior root generally descends within the carotid sheath superficially to the internal jugular vein. Therefore, this nerve is at risk during surgical approaches to the internal carotid artery.

37.3 B. The external carotid artery divides into two branches: the maxillary artery and the superficial temporal artery.

ANATOMY PEARL

⯈ The brain is divided into lobes named for the overlying cranial bones: frontal, temporal, parietal, and occipital.

⯈ The blood supply to the brain is from the common carotid and the vertebral arteries

⯈ The carotid arteries are palpated in the anterior triangle of the neck.

⯈ The vertebral and carotid circulations anastomose through a complex structure called the circle of Willis.

References

Gilroy AM, MacPherson BR, Ross LM. Atlas of Anatomy. 2nd ed. New York, NY: Thieme Medical Publishers, 2012:516−517, 636−637. 

Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy, 7th ed. Baltimore, MD: Lippincott Williams & Wilkins; 2014:882−885, 887−888, 1001. 

Netter FH. Atlas of Human Anatomy, 6th ed. Philadelphia, PA: Saunders; 2014: plates 106, 137, 140, 142−143.

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