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Syracuse, NY
Dr. Obeid is Clinical Professor of Medicine, State University of New York, Upstate Medical University.
Correspondence to: Anis I. Obeid, MD, Clinical Professor of Medicine, State University of New York, Upstate Medical University, Syracuse, NY 13210
Surgical resection is the main therapeutic procedure in the management of most cases of lung cancer. However, the feasibility of surgery as well as the choice of the proper surgical approach in the individual patient depend, among other conditions, on an accurate assessment of the extent of the tumor invasion of local structures, a process known as staging.1 Staging includes the assessment of the presence and extent of local spread of the tumor to adjacent structures such as the pleura, pericardium, chest wall, and blood vessels, as well as metastasis to mediastinal lymph nodes and distant organs. Lymph node involvement and distant metastases are outside the area of our interest in this editorial.
The advent of CT scanning some 30 years ago marked a major advance, beyond the standard radiographic procedures such as chest radiography, toward a more accurate staging of the disease. Ongoing technical advances in CT scanning (eg, spiral CT scanning and multidetector CT scanning) as well as the availability of faster and more powerful computers led to an increase in the accuracy and speed with which information can be gathered and processed.23 Three-dimensional reconstruction of the images is expected to add further refinement and accuracy to the radiographic staging of lung cancer. Positron emission tomography and single photon emission CT scanning are imaging modalities that reflect the metabolic activity in the areas of interest, which is usually higher in tumor tissue and, therefore, may indicate tumor presence in these "hot" areas.45 MRI is another imaging modality that may have a big role as it continues to evolve.
Yet, despite these major advances, many difficulties remain with respect to the ability of these techniques to accurately differentiate between resectable (T3) and nonresectable (T4) lung tumors. The main problem lies with the difficulty in differentiating between the actual invasion of neighboring structures by tumor cells and simple contact by contiguity or adhesion by fibrosis and inflammation. Tumors that abut the thoracic aorta pose a major problem, since the surgical decision depends on the presence or absence of the actual invasion of the wall of the aorta by tumor cells. Definitive resolution of this question thus far was only possible with the findings at surgery. Clearly, if another noninvasive modality can be utilized to improve the diagnostic accuracy of the presence or absence of aortic invasion by lung cancer, it would contribute significantly to the proper management of these patients.
Transesophageal echocardiography (TEE) is a technique that utilizes the esophagus as an imaging widow on the heart and great vessels. It involves the introduction of an upper endoscope fitted with an ultrasound transducer with a high power of resolution. Since intravascular catheters are not introduced, it is considered to be noninvasive. The close proximity of the esophagus to the heart and major blood vessels in the chest with no air or bone interference increases the clarity and the resolution of the echo images. In addition, TEE allows the interrogation of structures that are difficult to accurately assess from the transthoracic windows. These structures include the thoracic aorta. Thus, from a humble beginning in 1976 when Frazin and coworkers6 attached a single ultrasound transducer to a string, which was then swallowed to obtain M-mode images, TEE emerged as one of the indispensable tools in the practice of cardiology.67 TEE lent itself to intraoperative monitoring of different cardiac lesions and the assessment of surgical results,8 such that it has become part of the required training for cardiologists and cardiac anesthesiologists. Outside of the operating room, TEE is the procedure of choice in the evaluation of diseases of the heart valves (natural and prosthetic), cardiac tumors, vegetations, clots (particularly in the left atrial appendage), congenital defects, and critically ill patients when the thoracic window does not yield diagnostic quality images.91011121314 It is also the procedure of choice in the diagnosis of most diseases that affect the thoracic aorta. Such diseases include dissecting aneurysm, aortic hematoma, traumatic laceration, atherosclerosis with or without intimal ulceration, mobile atheroma, or clot formation.15161718 We now have a report proposing the use of TEE in the assessment of a novel lesion that may affect the thoracic aorta.
In this issue of CHEST (see page 438), Schröder and coworkers present their findings in using TEE for the evaluation of possible tumor invasion of the wall of the thoracic aorta in patients with cancer of the left lung. They collected their material from patients who had been admitted to a large referral center over a 10-year period (from 1993 to 2003). Of 5,000 patients who were admitted to the hospital during that period of time, their report is based on 201 patients who had left lung cancer abutting the thoracic aorta. The tumor was located in the left upper lobe in 93 patients, the left lower lobe in 61 patients, and the left main bronchus in 47 patients. All of the 201 patients underwent staging with conventional CT scanning, and 6 patients underwent MRI as well. The CT scans were performed at the main center as well as at affiliated clinics, and the data were based on an analysis of the reported results. TEE was performed in all patients using available commercial equipment and a 5-MHz probe within 2 weeks after the CT scans were performed. The monoplane probe was used in 139 patients, the biplane probe was used in 47 patients, and the multiplane probe was used in 15 patients. There were no complications. The authors considered that the signs were positive for invasion of the aortic wall by echocardiography when the two distinct lines of reflection that are normally generated by the aortic wall and the adjoining pleura lost their distinction and became obliterated. Additionally, the respiratory movement of the consolidated lung along the border with the aorta is lost with tumor invasion. Disappearance of the pleural reflection alone (outer line) indicates pleural invasion that does not extend to the aortic wall. Confirmation of the findings by CT scan and TEE was possible in 96 cases at surgery and in 1 case at autopsy. The other 114 patients were not considered to be surgical candidates due to advanced state of the disease (80 patients), advanced respiratory insufficiency (18 patients), and patient refusal of surgery (16 patients).
For the entire group, TEE findings were considered to be positive for aortic invasion in 61 patients, negative in 129 patients, and inconclusive in 11 patients, while CT scan findings were considered to be positive in 14 patients, negative in 12 patients, and inconclusive in 66 patients. In 109 patients, there was no comment at all with respect to aortic invasion by CT scanning. Of more interest are the data from the 97 patients with confirmation of a pathologic condition. Of the 12 patients with definite aortic invasion at surgery, 10 patients were correctly staged by TEE, 1 patient was understaged, and the staging for 1 patient was inconclusive. In contrast, CT scanning allowed correct staging in only 2 patients, 1 patient was understaged, and the staging in 9 patients was inconclusive. Of the 85 patients without aortic invasion at surgery, 79 patients were correctly identified by TEE, 2 were overcalled, and the staging in 4 patients was inconclusive. For the same group, only 4 patients received correct diagnoses by CT scanning, 6 patients were overstaged, and the staging in 75 patients was inconclusive. The authors correctly concluded that TEE is far superior to conventional CT scanning in the evaluation of the involvement of the thoracic aorta in cancer of the left lung.
This is an extremely interesting study that provides useful information in a small subset of patients in which the difference between the contiguity and invasion of the thoracic aorta by lung cancer has a direct impact on the choice of therapy. Perhaps the most pertinent finding is the ability of TEE to exclude aortic invasion with a high degree of certainty and thus to avoid denying surgery to a defined group of patients. The group of patients with a positive identification of aortic invasion by TEE is, I think, too small (12 patients) for a definitive decision. The study obviously does not deal with newer and more advanced radiologic or metabolic scanning procedures, nor with MRI.
This is, to my knowledge, the first large-scale study of its kind and should pave the way for more experience with larger groups of patients in order to further refine the techniques and define the echocardiographic criteria for aortic invasion by lung cancer. Questions of lateral resolution are expected to arise in some cases, depending on the point of contact between the tumor and the aorta, and the blind spot at which the aorta is obscured by tracheobronchial interference. Other questions arise with respect to the capacity of TEE to accurately differentiate between inflammation and tumor invasion, and the possible interference of aortic atheromas and calcium deposits with the accurate resolution of the diagnostic criteria set by the authors. These reservations not withstanding, the ease with which TEE is performed, the quickness of the procedure, the mobility of the equipment, and the relatively low cost make the view from the rear window, as suggested by the authors, an attractive alternative, or an addition, to what is currently available. I hope it stands the test of time.
References
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