Sunday, March 14, 2021

Thoracic Outlet Syndrome Case File

Posted By: Medical Group - 3/14/2021 Post Author : Medical Group Post Date : Sunday, March 14, 2021 Post Time : 3/14/2021
Thoracic Outlet Syndrome Case File
Eugene C. Toy, MD, Lawrence M. Ross, MD, PhD, Han Zhang, MD, Cristo Papasakelariou, MD, FACOG

CASE 58
A 48-year-old handyman complains of difficulty working due to increasing numbness, weakness, and pain in his right arm and hand. The paresthesias and weakness worsen when he lifts his arm over his head to perform tasks such as painting or hammering. The numbness also sometimes wakes him up at night and is worst on the volar side of his fourth and fifth fingers. He has also noticed that his right hand and fingers sometimes seem paler and colder than his left hand and fingers. He denies any history of trauma to the shoulder or arm and of any medical problems. On exam, some muscle wasting is evident in his right hand. Phalen’s and Tinel’s signs are negative. He is unable to complete the elevated arm stress test (EAST) or Roos test (the musculoskeletal shoulder flexibility or “hands up” test) because of heaviness and fatigue in his right arm. (In this test, the patient opens and closes his hands for 3 min while his arms are externally rotated and abducted to 90° with elbows flexed at 90°.)

 What is the most likely diagnosis?
 What anatomical structures are most likely affected?
 What are the common causes?


ANSWER TO CASE 58:

Thoracic Outlet Syndrome
Summary: A 48-year-old man has pain, paresthesias, and weakness in his right arm and hand worsened with arm abduction and at night. He also has signs of poor circulation in his right hand (pallor and coolness). On exam, EAST is positive, and muscle wasting is present in the right hand.

• Most likely diagnosis: Thoracic outlet syndrome

• Anatomical structures likely affected: Neural (brachial plexus branches), arterial (subclavian artery), and venous (subclavian vein) structures

• Common causes: Often associated with a cervical rib, but can also be caused by anomalous ligaments, hypertrophy of the anterior scalene muscle, or cervical trauma


CLINICAL CORRELATION
This man complains of neurological symptoms (numbness and tingling) as well as signs of arterial insufficiency (pallor, coolness) in his right arm and hand, suggesting compromise, or in this case compression, of neural and arterial structures–branches of the brachial plexus and the subclavian artery. (The subclavian vein can also be involved, producing venous signs such as swelling and edema.) The signs and symptoms are worsened with use, when more demand is placed on these structures; or with position, when the structures are further compressed. These structures run through the thoracic outlet, between the clavicle and the first rib. The brachial plexus and subclavian artery also run between the anterior and middle scalene muscles. (The subclavian vein is anterior to the anterior scalene, which is why it is less commonly involved.) The EAST as well as Adson’s test and the costoclavicular maneuver can be helpful in detecting thoracic outlet syndrome but are not completely diagnostic. X-rays, MRI, and EMG can also be useful in demonstrating compression. Depending on the severity, treatment can range from stretching and physical therapy to surgery.


APPROACH TO:
Thoracic Outlet

OBJECTIVES
1. Be able to describe the anatomy of the thoracic outlet and the structures that exit through this opening
2. Be able to describe those adjacent structure(s) at risk from any pathologic process or structure at or near the thoracic outlet

DEFINITIONS
CERVICAL RIB: An abnormal extra rib (often bilateral) articulating with the C7 vertebra, and stretching structures exiting the thoracic outlet or that are nearby


DISCUSSION
While the superior opening of the thoracic cage is often called the thoracic outlet by clinicians, anatomists refer to this opening as the superior thoracic aperture. It is bounded anteriorly by the superior margin of the manubrium of the sternum, laterally by the first rib and its cartilages, and posteriorly by the body of the T1 vertebra.

The superior thoracic aperture serves as a route for structures to enter and exit the thorax. Structures that descend from the neck to enter the thorax are the esophagus, trachea, internal thoracic artery, subclavian and internal jugular veins, the vagus, the phrenic and cardiac nerves, and the sympathetic trunk. Structures exiting the thorax through the superior aperture are the apex of the two lungs and the cervical pleura, the subclavian artery, and the recurrent laryngeal nerves (see Figure 58-1).

Important anatomical and clinical structures near the superior thoracic aperture are the anterior scalene muscles, which insert on the first rib; and the subclavian vein and artery, which are related anteriorly and posteriorly to insertion of the anterior scalene muscle. Just superior to the subclavian artery is the lower portion of the brachial plexus; the plexus is the major nerve supply to the upper limb. The plexus emerges from between the anterior and middle scalene muscles. Thus both the blood-and-nerve supply to the upper limb lies in or anatomically very close to the superior thoracic aperture.

Thoracic Outlet Syndrome anatomy

Figure 58-1. Superior mediastinum and root of the neck. [Reproduced, with permission, from Lindner HH. Clinical Anatomy. East Norwalk, CT: Appleton & Lange, 1989:226 (Figure 17-6)].


COMPREHENSION QUESTIONS
58.1 Which of the following structures defines the lateral boundary of the superior thoracic aperture?
    A. Clavicle
    B. Rib 1
    C. Rib 2
    D. Manubrium
    E. Disk between T3 and T4

58.2 You are in anatomy lab and ask a fellow medical student about the course of the right subclavian artery. Your colleague answers that this structure lies immediately posterior to the
    A. Clavicle
    B. Anterior scalene muscle
    C. Middle scalene muscle
    D. Posterior scalene muscle
    E. Sternocleidomastoid muscle

58.3 You demonstrate the relationship between the brachial plexus and the superior thoracic aperture during the dissection. What portion of the plexus lies closest to the aperture?
    A. C5 root
    B. C6 root
    C. Superior trunk
    D. Middle trunk
    E. Inferior trunk


ANSWERS
58.1 B. Rib 1 forms the lateral boundary of the superior thoracic aperture. The superior margin of the manubrium and the body of T1 form the anterior and posterior boundaries, respectively.

58.2 B. The subclavian artery, on both sides, lies immediately posterior to the anterior scalene muscle. The subclavian vein lies immediately anterior to this muscle.

58.3 E. The most inferior portion of the brachial plexus listed is the inferior trunk. The other portions of the plexus are more superior.


ANATOMY PEARLS
 The boundaries of the superior thoracic aperture lie from anterior to posterior: superior border of the manubrium, first ribs and cartilages, and the body of T1.
 The subclavian vein and artery lie anterior and posterior, respectively, to the insertion of the anterior scalene muscle as they cross the first rib, and groove it slightly.
 The superior thoracic aperture is tilted inferiorly anterior, allowing the cervical pleura or cupula and lung apex to project superiorly into the neck.
 The most common cause of thoracic outlet syndrome is pressure from a cervical rib.

References

Gilroy AM, MacPherson BR, Ross LM. Atlas of Anatomy, 2nd ed. New York, NY: Thieme Medical Publishers; 2012:55, 59, 65−66, 74, 89, 99, 593−595, 607−608. 

Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy, 7th ed. Baltimore, MD: Lippincott Williams & Wilkins; 2014:72−79, 85, 160−168, 721−725, 1012−1017. 

Netter FH. Atlas of Human Anatomy, 6th ed. Philadelphia, PA: Saunders; 2014: plates 186, 195, 203.

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