Clinical Cases - Superior Mediastinum & Lungs

During a routine physical exam for participation in interscholastic sports, the physician noted that E.S., a twelve-year-old boy, had a long continuous heart murmur at the second intercostal space near the left sternal border. A systolic thrill was also noted in the same region. When questioned, the patient's mother recalled that E.S. had periods of cyanosis and breathlessness as an infant, but that his previous pediatrician said that the murmur and the symptoms were nothing to be concerned about. E.S. also mentioned that he tires easily during physical activity. Chest films and Doppler ultrasound were ordered . The radiographs indicated slight left ventricular hypertrophy, and ultrasound revealed a patent ductus arteriosus. E.S. was scheduled for surgery to ligate the ductus arteriosus. The surgery resulted in successful ligation of the ductus arteriosus; however, E.S. experienced hoarseness when speaking following the procedure. Laryngoscopy revealed paralysis of the left vocal fold.

Questions to consider:

1. What is the ductus arteriosus, and where is it located?

   The ductus arteriosus is a fetal shunt between the pulmonary artery and the arch of the aorta.

2. What is the prenatal function of the ductus arteriosus, and what usually happens to it after birth?

   In the fetus, the ductus arteriosus allows oxygenated blood returning to the heart from the placenta to bypass the uninflated lungs and enter the systemic circulation. Following birth (usually within a few days), the ductus arteriosus functionally closes off and forms a fibrous cord called the ligamentum arteriosum. Complete anatomic closure of the ductus arteriosus may take up to 6 weeks. If the ductus arteriosus remains open, it forms a left-to-right shunt which carries some blood from the left side of the heart into the pulmonary trunk.

3. What are the eventual consequences if the ductus arteriosus is not closed? Should E.S.'s first pediatrician have been concerned?

   Initial consequences of a patent ductus arteriosus include cardiac failure and pulmonary edema in infants (accounting for the cyanosis and breathlessness experienced by E.S.); however, a patent ductus arteriosus is often compatible with survival to adulthood. Cardiac failure (which may be the reason for the slight left ventricular hypertrophy observed in E.S.) and bacterial endocarditis are common complications. If left untreated, pulmonary hypertension develops, resulting in hypertrophy of the right ventricle and eventually in a reversal of flow (to right-to-left), leading to cyanosis, clubbing of fingers and toes, and polycythemia due to systemic circulation of large amounts of deoxygenated blood, as well as right heart failure. Clearly, E.S.'s first pediatrician should have been more concerned about E.S.'s condition.

4. What likely caused paralysis of the left vocal fold?

   Paralysis of the left vocal fold resulted from damage to the left recurrent laryngeal nerve, which loops under the arch of the aorta adjacent to the ligamentum arteriosum (ductus arteriosus) after leaving the vagus nerve. The left recurrent laryngeal nerve innervates the muscles of the left larynx (the right recurrent laryngeal nerve, which loops similarly under the right subclavian artery, supplies the right larynx), with the exception of the left cricothyroid muscle, supplied by the superior laryngeal branch of the vagus. Surgeons must take great care in identifying and protecting the left recurrent laryngeal nerve when performing procedures in the region of the aortic arch.

5. Why would Doppler ultrasound be used to diagnose a patent ductus arteriosus?

   Doppler ultrasound permits the visualization of blood flow and can thus be used to identify a patent ductus arteriosus. This technique is preferable to traditional angiography, which may also be used, because it is noninvasive, involves no radiation, and is fairly inexpensive.

A twenty-three year old female presents to your clinic with complaints of being easily tired, pain in her lower extremities with weakness and cold feet, an inability to tolerate vigorous exercise, frequent headaches, and epistaxis (nosebleed). The patient reports these are not new symptoms, but have occurred over a number of years and have recently increased in their incidence. On physical exam you find: cool lower extremities with an absence of distal pulses and diminished femoral pulses, the blood pressure in the upper extremities is elevated (190/100), while the blood pressure in the lower extremities is 40/10; a systolic murmur is heard over the 5th left intercostal space which radiates to the interscapular region. A chest x-ray is performed and significant rib notching is noted along with a visible dilation of the aorta in the region of the aortic knob. The patient is diagnosed with coarctation of the aorta based on physical exam and findings.

Questions to consider:

1. What is this lesion?
   

   A narrowing of the descending aorta usually found immediately near the attachment of the ligamentum arteriosum, distal to the left subclavian artery.

2. Is there a difference in the findings of such a lesion as an adult or as a child?
   

   The most frequently occurring lesions are those which occur as an adult. These lesions are found in the postductal region of the aorta and the patients are frequently asymptomatic presenting only with headaches and epistaxis. The average life span for a patient with this type of lesion is 30-40 years.

3. What were the diagnostic clinical features of the case?
   

   The most important clinical finding was the difference in blood pressure in the upper versus lower extremity. This presented as diminished pulse in the lower extremities, coolness, fatigue and pain in the lower extremities (subsequent to anaerobic metabolism and lactic acid buildup). The higher blood pressure in the upper extremities was evident not only by the blood pressure itself, but also by the headaches and nosebleeds. The systolic murmur indicates a fluid overload or, in this case, stricture of the aorta and an inability to completely eject the volume through the aorta.

4. What single diagnostic finding was found on the chest X-ray?
   

   Pre- and post-coarctation dilation was seen in the region of the aortic knob. There was also rib notching, which reflects the erosion of bone by intercostal arteries that have become dilated and tortuous by the great volume of blood they are carrying as collateral blood flow.

5. Can you explain why a postductal (inferior) lesion is more compatible with long term survival versus a preductal lesion?
   

   A postductal lesion allows good collateral circulation from proximal to distal portions of the aorta via the anterior intercostals from internal thoracic artery anastomosing with posterior intercostal branches of descending aorta.
   
   A preductal lesion presents a life threatening situation early in infancy. The distal aorta is initially filled via a patent ductus arteriosus, but as the ductus closes blood flow to the distal aorta diminishes, and the infant's survival may be threatened.

6. What are the treatment options for a patient with this type of lesion?
   

   Surgical intervention, which includes resection of the coarctation and end-to-end anastomosis, patch aortoplasty or a bypass with a prosthetic graft. The treatment of choice for this patient would most likely be a bypass with a prosthetic graft.

7. What surgical complications would cause the greatest amount of concern?
   

   Significant hemorrhage secondary to damage to the dilated intercostal arteries. Because it is necessary to clamp the aorta for the procedure, paraplegia may result from diminished blood flow to the spinal cord.

References:

Moore's Clinical Anatomy 4th Edition pp. 142- 150.
Advanced Surgical Recall pp. 680-681.
Woodburne & Burkel p. 70; 207-8; 382.
Robbins Pathology p. 571-3, 575; 680-1.