Pulmonary Embolism Case File

Pulmonary Embolism Case File

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

CASE 14

A 65-year-old woman diagnosed with uterine cancer underwent surgery to remove her uterus (total abdominal hysterectomy) 2 days previously. She was doing well until today, when she developed shortness of breath, and she describes a sharp pain in the right side of her chest on inspiration. Physical examination revealed a respiratory rate of 28 breaths/min and a heart rate of 110 beats/min. Auscultation of the lungs demonstrates no wheezing or crackles. She appears anxious.

⯈ What is the most likely diagnosis?

⯈ What is the most likely location of the primary disease?

ANSWER TO CASE 14:

Pulmonary Embolism

Summary: Two days ago, a 65-year-old woman underwent a total abdominal hysterectomy because of endometrial cancer. She developed acute-onset dyspnea with pleuritic chest pain. She has tachypnea and tachycardia and appears anxious. Rales (crackles) are not present on pulmonary examination.

• Most likely diagnosis: Pulmonary embolism

• Most likely location of the primary disease: Deep-vein thrombosis (DVT) of the pelvis or lower limb

CLINICAL CORRELATION

This woman has multiple risk factors for DVT or blood clot formation within the large veins. These factors include the patient’s age, likely minimal physical exercise, and bedrest after a major operative gynecological procedure for a cancerous lesion. Postoperative orthopedic patients are similarly at risk. Deep-vein thrombi are typically asymptomatic but may cause lower-limb swelling and pain. When pelvic or lower limb veins are involved, clot material can break free (embolize) and travel through the inferior vena cava (IVC) to and through the right side of the heart, whence they are pumped to the lungs, where they will lodge in branches of the pulmonary arteries. These emboli effectively block blood flow beyond this point and prevent this unoxygenated blood from reaching the alveoli, where it is to be oxygenated. The size and number of emboli produced will determine the amount of lung tissue that will be infarcted because of lack of oxygen. The most common symptom of pulmonary embolism is dyspnea, and patients are often anxious, with tachycardia and pleuritic chest pain at inspiration. The next step would be an arterial blood-gas study to assess oxygen status. A chest radiograph and ventilation-perfusion scan are performed to directly determine whether an embolus is present. If present, intravenous anticoagulants such as heparin are beneficial. Large or untreated emboli can cause death. One particularly devastating type, the “saddle embolus,” lodges in the pulmonary trunk at the bifurcation of the right and left pulmonary arteries, thus blocking blood flow to both lungs, leading to cardiovascular collapse and death.

APPROACH TO:

Pulmonary Vasculature

OBJECTIVES

1. Be able to describe the origin, branching pattern, and anatomical relations of the pulmonary arteries and veins

2. Be able to describe the origin of the bronchial arteries, structures supplied, and sites of anastomosis with the pulmonary circulation

DEFINITIONS

TOTAL HYSTERECTOMY: Complete surgical removal of the uterus, that is, the body and the cervix. A subtotal hysterectomy consists in removal of the uterine corpus (body) but not of the cervix.

PULMONARY EMBOLISM: Obstruction or occlusion of pulmonary arteries by emboli typically arising from thrombi of veins in the lower limbs or the pelvis.

INFARCTION: Tissue necrosis due to the sudden decrease in the blood supply as the result of an embolus, thrombus, or external pressure.

RALES: “Crackles” heard when listening to the lung fields with a stethoscope, usually indicative of excess fluid in the lungs as with pneumonia or pulmonary edema.

DISCUSSION

The pulmonary trunk, which carries unoxygenated blood, arises from the conus arteriosus portion of the right ventricle. At the level of the sternal angle, the trunk divides into right and left pulmonary arteries (see Figure 14-1). The right pulmonary artery passes laterally, posterior to the ascending aorta and SVC, to reach the hilum of the right lung. The left pulmonary artery passes anterior to the descending thoracic aorta to reach the hilum of the left lung. The pulmonary arteries are the most superior vessels in the hilum of each lung, and the branch to the superior lobe of each lung typically arises outside the lung hilum. Each artery courses through the lung tissue adjacent to bronchial and bronchiolar airway structures, where they

Figure 14-1. Superior mediastinum and relations of the pulmonary vessels. (Reproduced, with permission, from Way LW, ed. Current Surgical Diagnosis and Treatment, 7th ed. East Norwalk, CT: Appleton & Lange, 1985.)

branch out and are named for these airway structures. Thus each artery will divide into lobar and then segmental branches to the lung lobes and their bronchopulmonary segments, respectively. The bronchioles and the adjacent arteries branch further down to the level of the terminal bronchiole, which supplies a lobule, the smallest anatomical unit of lung tissue.

As the small pulmonary artery branches reach the respiratory bronchioles, they form the extensive capillary network around and between the alveoli. The thin capillary endothelium, basal lamina, and type I pneumocytes form the blood-gas barrier through which gaseous exchange occurs.

Oxygenated blood drains from the capillary bed to pulmonary veins within the thin connective tissue septae between lobules. In this location, they receive blood from adjacent lobules. As the pulmonary veins unite to form increasingly larger veins, they remain separated from the pulmonary artery and airway structures; they are found at the periphery of lung tissue subdivisions such as the bronchopulmonary segments and lobes. These larger veins will drain adjacent segments or lobes. Eventually, two pulmonary veins exit the hilum of each lung anteriorly and inferiorly to the entering pulmonary arteries. Thus four pulmonary veins drain oxygenated blood into the left atrium, typically two from each lung.

The bronchi, bronchioles, and related structures, the connective tissue stroma and the visceral pleura, receive their blood supply from bronchial arteries. These are typically branches of the thoracic aorta but may arise from intercostal arteries. Anastomoses between the pulmonary and bronchial arteries occur within the bronchial walls and the visceral pleura. Bronchial veins from the right and left lungs typically drain to the azygous and accessory hemiazygous veins, respectively, but carry only small amounts of blood. The pulmonary vein carries most of the blood supplied by the bronchial arteries.

COMPREHENSION QUESTIONS

14.1 As a surgeon exploring the thorax, you will be able to identify the right pulmonary artery in which of the following locations?

A. Anterior to the ascending aorta and the SVC

B. Anterior to the ascending aorta and posterior to the SVC

C. Posterior to the descending aorta and the SVC

D. Posterior to the ascending aorta and the SVC

E. Posterior to the ascending aorta and anterior to the SVC

14.2 As a radiologist examining a contrast study of the pulmonary vessels, you will note how many pulmonary veins entering the left atrium?

A. Two

B. Three

C. Four

D. Five

E. Six

14.3 A 44-year-old woman who has a DVT of the lower extremity suddenly gasps and collapses. She is found to be hypotensive. Resuscitative measures are attempted without success. Which of the following is the most likely diagnosis?

A. Myocardial infarction

B. Saddle embolus

C. Right peripheral pulmonary embolus

D. Embolic stroke

ANSWERS

14.1 D. The right pulmonary passes posteriorly to the ascending aorta and the SVC.

14.2 C. Four pulmonary veins that carry oxygenated blood drain into the left atrium.

14.3 B. The patient likely developed a saddle embolus that occluded blood flow to both pulmonary arteries and, in effect, stopped the circulatory system.

ANATOMY PEARLS

⯈ Pulmonary arteries carry unoxygenated blood, accompany airway structures, and follow their branching patterns

⯈ Pulmonary veins, which carry oxygenated blood, course separately from the arteries and airways at the periphery of lung tissue subdivisions.

⯈ The blood-gas barrier is composed of the capillary endothelium, basal lamina, and type I pneumocytes.

⯈ Bronchial arteries typically arise from the thoracic aorta and supply the airway structures and stromal tissue.

References

Gilmore AM, MacPherson BR, Ross LM. Atlas of Anatomy, 2nd ed New York, NY: Thieme Medical Publishers; 2012:88, 124−126. 

Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy, 7th ed. Baltimore, MD: Lippincott Williams & Wilkins; 2014:116−117, 124−125. 

Netter FH. Atlas of Human Anatomy, 6th ed. Philadelphia, PA: Saunders; 2014: plates 202−204.

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