Mediastinoscopy

CURRENT REVIEW

Medias tinoscopy A Reuiew of Anatomical Relationships and Complications

Eric D. Foster, M.D., Darrell D. Munro, M.D., and

Anthony R. C. Dobell, M.D.

ABSTRACT A review of anatomical relationships and complications of mediastinoscopy is presented. Knowledge of the anatomical structures encountered by the mediastinoscopist should include not only the major vessels, tracheobronchial lymph nodes, and mediastinal pleura, but, in addition, the cervical fasciae and veins, vagal nerves and their branches, cardiac plexus, bronchial arteries, and esophagus.

Emphasis is placed on the interrelationship of the involved anatomy and observed complications of mediastinoscopy. A review of fourteen mediastinoscopy series published from 1968 to 1970 reveals 3 deaths and 60 complications among 3,742 patients. Mediastinoscopy is not as benign a procedure as its more enthusiastic proponents imply.

Instruction in the use of graduated mediastinoscopes and knowledge of average tracheal measurements are urged. In this study, of 36 adult cadaver dissections the average length of the trachea from cricoid to carina was 12.3 cm. With the sternal notch as a reference point, the average trachea length to the carina, azygos vein, and left recurrent laryngeal nerve ranged from 5.2 to 6.9 cm.

urgical entry into the superior mediastinum as a therapeutic measure has been practiced for more than seventy years. Successful drainage of S a superior mediastinal abscess was reported first in 1899 [13]. The

technique of mediastinostomy in caring for superior mediastinitis was advanced by the Viennese, particularly von Hacker and Marschik. The method of von Hacker [29] to reach the retroesophageal space by entering the neck

From the Cardiovascular and Thoracic Surgical Service, Royal Victoria Hospital, and McGill University, Montreal, Que., Canada.

The authors gratefully acknowledge the aid of D. G. Osmond, M.D., Professor of Anatomy, and S. C. Harvey, M.D., Curator of Anatomy, both of McGill University, in preparing the dis- cussions pertaining to anatomy in this paper.

Address reprint requests to Dr. Munro, 10 Surgical, Royal Victoria Hospital, 687 Pine Ave. W.. Montreal 112, Que., Canada.

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FOSTER, MUNRO, AND DOBELL

at the anterior border of the sternocleidomastoid muscle and passing medial to the vessels within the carotid sheath was demonstrated to be clearly superior to techniques of passing lateral to the vessels or between the carotid artery and internal jugular vein. During World War I, Marschik [lS, 191 successfully employed mediastinostomy in more than 100 soldiers with neck or mediastinal wounds. In subsequent years, few modifications were made in mediastinostomy technique although reports of its use were frequent until after World War 11.

Despite this legacy of surgical knowledge, entry into the superior mediastinum as a diagnostic measure was not developed until the decade following 1950 and has been practiced widely only for the past ten years. The need for such a diagnostic technique has always been present. The difficulties in establishing the diagnosis or extent of disease in many patients with intrathoracic disorders is well known. The clinical status of these patients re- mains an enigma despite a thorough history and physical examination, blood and sputum analysis, examination of pleural exudates, roentgenographic studies, and bronchoscopy. In the past, thoracotomy to obtain a biopsy of lung or hilar tissue for study was often considered as the next step. In 1949, Daniels [8] suggested a diagnostic method much less drastic than thoracotomy, namely, scalene lymph node biopsy. By taking the scalene nodes and any others found as the subclavian and internal jugular veins were followed into the superior mediastinum, Daniels proposed that a possible diagnosis of pulmonary disease could be obtained, since these nodes were samples of the lung’s lymphatic drainage. Harken and his co-workers [12] in 1954 further developed the technique of biopsying lymph nodes from the lung’s lymphatic drainage channels; they suggested that the introduction of a Jack- son laryngoscope through a lateral supraclavicular incision down into the paratracheal region would facilitate exploration of the superior mediastinum. Aside from the technical difficulties and complications inherent in Daniels’ or Harken’s procedure, the most obvious criticism of both these methods is that the clinician is forced to decide which side of the patient to perform them on; often he is compelled to do bilateral biopsies.

It remained for another European, Eric Carlens [4] of Sweden, to re- fine a suitable surgical technique for entry into the superior mediastinum for diagnostic purposes. As with von Hacker, Carlens proposed that a more medial approach would be preferable to the lateral techniques of Daniels and Harken. In 1959 Carlens introduced the mediastinoscope, a specially designed instrument which could be passed into the superior mediastinum through a suprasternal incision, allowing the biopsy of tissue from both paratracheal regions and the subcarinal areas. Although evoking immediate clinical interest in Europe, the Carlens technique of mediastinoscopy has gained widespread use in North America only in the past five years.

The purpose of this paper is to provide a review of the anatomical relationships and complications of mediastinoscopy. In few other diagnostic

274 THE ANNALS OF THORACIC SURGERY

CURRENT REVIEW: Mediastinoscopy

procedures are a technique’s anatomical relationships and observed complications so conjoined.

Anatomy of Medias t in oscop y In preparation for discussing the anatomical relationships of medias-

tinoscopy, 36 adult cadavers were studied. The group consisted of 31 fixed specimens from the dissecting room and 5 fresh postmortem specimens. None had any pathological process distorting the superior mediastinal anatomy.

The technique of mediastinoscopy has changed little since it was first described by Carlens [4]; only a rCsumC is presented here insofar as it will aid the subsequent anatomical discussion. The patient lies supine on the operating table with his head slightly extended and rotated to one side. Un- der general anesthesia and with the patient intubated, a 3 to 4 cm. transverse skin incision is made 2 cm. above the suprasternal notch between the anterior borders of the sternocleidomastoid muscles. The incision is carried down in the midline to the anterior surface of the trachea, retracting the sternohyoid and sternothyroid muscles laterally. Using blunt dissection, preferably with a finger, a tissue cleavage plane is developed down into the superior mediastinum anterior to the trachea and posterior to the major vessels. The mediastinoscope is introduced into the dissection plane, and biopsy of paratracheal and subcarinal tissues is performed.

To reach the anterior surface of the trachea through the suprasternal mediastinoscopy incision, three layers of cervical fascia must be divided. In order, from skin to trachea, these are: (1) the superficial fascia of the neck investing the platysma muscle; (2) the deep cervical fascia; and (3) the pretracheal fascia. Whereas the superficial fascia of the neck is thin and barely discernible, the deep cervical fascia is thick and can be demonstrated anteriorly as it invests the sternocleidomastoid, sternohyoid, and sternothyroid muscles. Neither the superficial fascia nor the deep cervical fascia passes into the superior mediastinum, although the deep layer of the deep cervical fascia is attached to the posterior aspect of the manubrium associated with the ori- gins of the sternohyoid and sternothyroid muscles. The superficial layer of the deep cervical fascia is attached to the anterior aspect of the manubrium; the slitlike space between the two layers of the deep cervical fascia and ex- tending 2 to 3 cm. above the suprasternal notch is termed the suprasternal space. The thin pretracheal fascia invests the thyroid gland; of prime interest to the mediastinoscopist is the fact that this fascia does pass into the superior mediastinum as an investment for the inferior thyroid veins. The importance of incising the pretracheal fascia is clear when it is understood that efforts to enter the superior mediastinum without doing so will lead the unwary examiner anteriorly to the major vessels of the superior mediastinum rather than posteriorly to these structures.

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/eft bmchim&fic

FIG. 1. Relationship of the mediastinoscope to medsastinal structures as viewed from the right of a cadaver dissection with right lung, parietal pleura, and a portion of the anterior chest wall removed.

Neck veins of varying size may be encountered as the mediastinoscopy incision is fashioned from skin to trachea. The anterior jugular veins pass along the anterior borders of the sternohyoid muscles invested by deep cervical fascia; often they are joined across the midline by the jugular arch lying within the suprasternal space. Deep to these jugular vessels lie the inferior thyroid veins invested by pretracheal fascia. There may be a single inferior thyroid vein or a venous plexus covering the anterior tracheal surface below the thyroid isthmus, either of which will drain to the left brachiocephalic (innominate) vein.

The thyroidea ima is a small and inconstant artery arising from either the aorta, right common carotid, subclavian, or internal thoracic arteries. It ascends in front of the trachea to the thyroid isthmus; often, if there is an

&rachiocepha/ic arfery FIG. 2. Relationship of the mediastinoscope to medrastinal

/eft common mrotidartey structures as viewed from the left side of a cadaver dissection with left lung, parietal pleura, and a portion of the anterior chest wall removed.

&daVhn artery

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inferior thyroid venous plexus, there will be an associated arterial plexus lying on the anterior tracheal wall.

Once a suitable channel has been developed by blunt dissection into the superior mediastinum along the anterior aspect of the trachea posterior to the major vessels, the mediastinoscope can be introduced. Figure 1 depicts the relationships of the mediastinoscope to the mediastinal structures as viewed from the right side of a cadaver dissection in which the right lung, parietal pleura, and a portion of the anterior chest wall have been removed. Figure 2 presents the relationships as viewed from the left side with the lung, parietal pleura, and a section of the anterior chest wall removed. That the mediastinoscope and major vessels in the superior mediastinum have an

’ intimate relationship deserves emphasis. Figure 3 depicts a right anterior view of this relationship in a cadaver dissection with the anterior chest wall, lungs, pleura, and heart removed.

A

/f main &ronchus

B FIG. 3. Photograph ( A ) and artist’s drawing (B) showing relationship of mediastinoscope t o malor vessels in the superior mediastinum ns seen in a right anterior view of a cadaver dissection with the anterior chest wall, lungs, pleura, and heart removed.

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As the mediastinoscope passes behind the suprasternal notch, its anterior surface comes into contact with the posterior aspect of the brachiocephalic (innominate) artery. The left common carotid artery lies anterior and to the left of the instrument, while the left subclavian artery is posterior and to the left (see Fig. 2). Crossing obliquely in front of these three arteries from left to right is the left brachiocephalic vein, which joins the right brachiocephalic vein anterior to the right side of the mediastinoscope, behind the junction of the first right costal cartilage and the sternum (see Fig. 1). As the mediastinoscope is advanced, it passes behind the arch of the aorta with the superior vena cava maintaining a relationship to the right and anterior to the instrument (see Fig. 3). T o reach the subcarinal area or to pass onto the primary bronchi, the tip of the mediastinoscope nearly always con- tacts the pulmonary artery or its divisions (see Figs. 1-3).

On the right side, arching across the mediastinoscopist’s dissection field, is the azygos vein (see Fig. 1). This vessel passes from the posterior chest wall over the right primary bronchus or the right upper lobe bronchus to drain into the superior vena cava. Often lying between the vein and bronchus wall is the azygos lymph node, which is one of the superior tracheobronchial nodes: it is much sought after for biopsy.

The bronchial arteries are highly variable in number and course; however, a right bronchial artery may bear a close relationship to the mediastinoscopy dissection at the tracheal bifurcation. The degree of right bronchial artery variability is made apparent by reports such as that of Na- than and his co-workers [21], who found, in contrast to other investigators, that in 60 cadaver dissections this vessel always originated from a right aortic intercostal artery and passed along the posterior aspect of the right primary bronchus. Caudwell and associates [6] found that in 13 of 150 bodies a right bronchial artery passed anterior to the trachea or tracheal division. In the present series of 36 dissections, a right bronchial artery was noted originating from the aorta and passing anterior to the tracheal bifurcation and right primary bronchus in 2 patients.

While the phrenic nerves are beyond the range of the usual mediastinoscopy exploration, the vagi, or their branches, are included within the area of dissection (see Figs. 1, 2). On the right side, after the vagus crosses the anterior aspect of the subclavian artery, its recurrent laryngeal branch loops under that vessel and returns to the neck. The right vagus nerve de- scends into the thorax interposed between the mediastinal pleura and the right side of the trachea; its course is an oblique one, traveling anterior to posterior until it runs behind the right pulmonary hilus (see Fig. 1). The left vagus enters the thorax between the left common carotid and left subclavian arteries behind the left brachiocephalic vein; it crosses the aortic arch, gives off the left recurrent laryngeal branch, and passes behind the left pulmonary hilus (see Fig. 2). The left recurrent laryngeal nerve winds under the arch of the aorta, comes to lie in close approximation to the trachea’s left side


CURRENT REVIEW: Medimtinoscopy

near the left tracheobronchial junction, passes posteriorly to the tracheo- esophageal groove, and ascends to the neck.

The autonomic nervous system’s cardiac plexus consists of a superficial and a deep part lying, respectively, in the concavity of the aortic arch in front of the pulmonary artery and on the anterior aspect of the trachea near its bifurcation (Fig. 4). The cardiac plexus receives sympathetic and para-

--supenor cervica/ ganghon

.,syqoafbefic trunk

mYd/e cervica/ gangkon

vogus nerve I .

FIG. 4. Autonomic nervous system fibers forming cardiac plexus. The lower portion of the figure shows the superficial cardiac plexus.

VOL. 13, NO. 3, MARCH, 1972 279


sympathetic fibers of both cervical and thoracic origin. The small superficial part of the plexus usually receives only two branches directly, the left superior cervical cardiac branch of the sympathetic nerve and the left inferior cervical cardiac branch of the vagus. The larger deep portion of the cardiac plexus receives all other sympathetic and vagus cardiac branches in its loca- tion on the front of the tracheal bifurcation. From the cardiac plexus, sub- sidiary plexuses are distributed onto the heart, especially along the coronary arteries.

Throughout its course in the superior mediastinum, the esophagus lies posterior to the trachea and away from the mediastinoscopy dissection field except in the subcarinal region, where it may become vulnerable (cf. Fig. 3).

Biopsy of the tracheobronchial lymph nodes is usually the prime objec- tive of the operator. These nodes include some of the largest found in the body. Five interconnecting groups of nodes form a channel draining lymph from the lungs to the thoracic or right lymphatic duct. In order, from lungs to ducts, the five main groups are: (1) pulmonary, in the lung substance on the larger branches of the principal bronchi; (2) bronchopulmonary, in the hilus of each lung; (3) inferior tracheobronchial (subcarinal), in the angle between the two primary bronchi; (4) superior tracheobronchial, in the angles between the lower part of the trachea and bronchi; and (5) paratracheal, at the sides of the thoracic part of the trachea. Members of the last three groups of nodes can be reached by the mediastinoscope.

The mediastinal pleura, which was removed in the dissection preparing Figures 1 and 2, lies in close approximation to the trachea, particularly on the right side. The right pleural space can be entered inadvertently during mediastinoscopy. The right side of the thoracic portion of the trachea over most of its course is separated from the mediastinal pleura only by the right vagus nerve and its branches, or by paratracheal lymph nodes. At the prox- imal and distal ends of the thoracic trachea the brachiocephalic artery and the azygos vein, respectively, lie between the mediastinal pleura and the right tracheal wall (see Fig. 1). The left side of the trachea is more widely separated from the pleura by the paratracheal lymph nodes, left recurrent laryngeal nerve, aortic arch, left common carotid artery, left subclavian artery, left phrenic nerve, and left vagus nerve (see Fig. 2).

Distances within the superior mediastinum can be deceiving, especially to the inexperienced mediastinoscopist. Table 1 summarizes lengths to three important structures within the mediastinoscopy dissection field as found in the 36 cadavers studied in this series. The point on the trachea immedi- ately posterior to the suprasternal notch was chosen arbitrarily as a reference point. In all cases the body’s chest wall was in the end-expiration state, the head and neck in much the same position as that of a patient undergoing mediastinoscopy. The average trachea length from cricoid to carina found in this series was 12.3 cm.; other investigators have reported average tracheal lengths of 11.0 and 11.8 cm. [II, 201.



'TABLE 1. TRACHEAL MEASUREMENTS IN 36 ADULT HUMAN CADAVERS

Tracheal Length (cm.) Sternal

Sternal Notch to L. Cadaver Sternal Notch Recurrent Height No. of Cricoid to Notch to Azygos Laryngeal (cm.) Studies Carina to Carina Vein Nervea

Fixed dissection room cadavers 140-149 8 11.3 6.0 4.6 4.5 150-159 1 1 12.1 6.8 5.2 5.1 160-169 7 12.7 7.4 5.7 5.7 170-1 79 5 13.7 7.8 5.7 5.7

158 31 12.3 6.9 5.2 5.2

142-176 9.8-15.4 5.0-9.1 4.0-6.4 3.5-6.5

Totals & averages

Range

Fresh postmortem cadavers Totals & averages

Range 164 5 12.1 6.6 6.3 6.2

158-178 11.9-12.9 6.0-6.9 5.5-6.5 5.4-6.5 -"Length on trachea from posterior to suprasternal notch to point where left recurrent laryngeal nerve loops under aortic arch and is closely approximated to left side of trachea's distal end.

Complications of Mediastinoscopy In 1966 Jepsen [ 141 reported on the complications of mediastinoscopy

observed in his own patients and in sixteen other series published to that date; a total of 39 complications occurred in 4,134 patients undergoing mediastinoscopy. These are summarized in Table 2. No deaths were noted in Jepsen's survey. The complications listed represent a morbidity rate of 0.9%.

A review of more recently published data on the mortality and morbidity of mediastinoscopy is presented in Table 3; a total of 3 deaths and 60 complications are listed among 3,742 patients. Postoperative respiratory in- sufficiency in 2 patients and an operative cardiac arrest in 1 accounted for the 3 deaths, a mortality rate of 0.08%. The specific complications found in this review are enumerated in Table 4; they represent a morbidity rate of 1.6%.

Comment The reported incidences of mortality and morbidity with mediastinos-

copy have been low, despite the fact that the procedure is performed in a region of the body with a high concentration of vital structures. Carlens [5] and Clagett [7] have suggested that not all the deaths and complications associated with mediastinoscopy have been published.

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TABLE 2. COMPLICATIONS OF MEDIASTINOSCOPY OCCURRING IN 4,134 PATIENTS AS REPORTED BY JEPSEN IN 1966 I141

ComDlica tion No. of Patients ~~

Bleeding Moderate Necessitating mediastinostomy or thoracotomy From right pulmonary artery From azygos vein

Vocal cord paralysis Left vocal cord Right vocal cord Side not given

Pneumo thorax Pleural tear Pleural tear with hemothorax Tumor seeding in incision line Perforation of esophagus Myocardial infarction (postoperative) Bradycardia Mediastinal abscess Possible mediastinitis

Total

6 1 2 7 1 1 3 2 1 1 1 1

39

The intimate relationship afforded the mediastinoscopist to the vital structures of the superior mediastinum is reflected in the technique’s mortality and morbidity. T h e first to attest to this fact are those most experi- enced with the method, including its innovator, Carlens; they urge the

TABLE 3. MORTALITY AND COMPLICATIONS OF MEDIASTINOSCOPY AS REPORTED IN FOURTEEN SERIES PUBLISHED FROM 1968 T O 1970

No. of No. of Compli- Author & Year Patients Deaths cations

Benedict & Buhl [21, 1969 52 0 2 Bilgutay et al. [31, 1969 100 0 0 Carlens [51, 1968 1,500 0 3 Duvall et al. 191, 1968 100 0 3 Goldberg et al. 1101, 1970 200 0 12 Lincoln & Provan [161, 1970 48 0 5 MacVaugh & Danielson [171, 1968 32 0 0 Ostergaard & Klaft [221, 1969 29 1 0 11 Pearson [241, 1968 432 0 7 Pinkham & Torgerson [251, 1969 117 2 0 Ross et al. [261, 1970 124 0 2 Sarin lk Nohl-Oser [271, 1969 400 0 2 Trinkle et al. [281, 1970 300 1 8 Ward et al. 1301, 1969 46 0 5

Total 3,742 3 60



TABLE 4. COMPLICATIONS FOUND IN REVIEW OF FOURTEEN MEDIASTINOSCOPY SERIES PUBLISHED FROM 1968 TO 1970

Complication No. of Patients Bleeding

Moderate 15 Necessitating thoracotomy 4 From superior vena cava 1 From brachiocephalic artery 1 Wound hematoma 1

Left vocal cord 7 Side not given 4 Bilateral 1 Hoarseness, possible vocal cord paralysis 1

Pneumothorax 11 Pleural tear 3

1

Vocal cord paralysis

Tumor seeding in incision line Perforation of esophagus 1 Myocardial infarction (postoperative) Bradycardia Cardiac arrest (anesthetic error) Wound infection Left hemiparesis (transient)

Total 60

neophyte to study thoroughly the superior mediastinal anatomy in both dissection room and postmortem specimens. Close supervision during the clinical training of mediastinoscopists is essential; a patient must not be relegated to a lone, inexperienced operator for mediastinoscopy. The use of a graduated mediastinoscope is suggested as an aid in training for the safe performance of the procedure (Fig. 5). Use of such an instrument with the knowledge of average tracheal length and the distance from a reference point to such important structures as the carina, azygos vein, and left recurrent laryngeal nerve can bring some clarity to the technique’s anatomical relationships. Rarely, tissues which can be safely biopsied are out of the range of an 11 cm. mediastinoscope; routinely employing a longer instrument tends to lead the unwary operator where he has no business.

The possibility of lacerating major vessels in the superior mediastinum and of entering the right pleural cavity during mediastinoscopy requires no further elucidation. Perhaps less familiar are the hazards that may be encountered with the rich venous plexus at the neck incision, the vagi and their branches, the cardiac plexus, the bronchial arteries, and the esophagus. Failure to achieve hemostasis as the incision is made through the anterior jugular and inferior thyroid venous plexuses may not only force a premature end to the procedure, but also may produce a significant wound hematoma. The vagi and their branches may be injured directly by being sectioned

VOL. 13, NO. 3, MARCH, 1972 283


FIG. 5. Mediastinoscopc with centi- meter gradations.

with the biopsy forceps, or they may be contused by the instruments; they also may be injured indirectly by compression from hematoma or edema in surrounding tissues resulting from the procedure. The network of autonomic nervous system fibers forming the cardiac plexus over the trachea’s distal end and bifurcation is vulnerable to the mediastinoscopist. Although the effect of manipulation within the cardiac plexus is not clear, it seems prudent that the patient’s electrocardiogram be monitored during the procedure. In 5 to 10% of patients a right bronchial artery is seen passing anteriorly across the trachea’s distal end and down the anterior aspect of the right primary bronchus; in this position, it may be lacerated easily. Esopha- geal perforation can occur during paratracheal and superior and inferior tracheobronchial lymph node dissections, particularly if tracheal deviation is present.

As a matter of technique, it is suggested that a pulse in the right upper extremity be monitored continuously during the procedure. The brachiocephalic artery may be compressed by the mediastinoscope, diminishing flow not only to the arm, but, of more importance, to the brain through the right common carotid and right vertebral arteries. Particular care should be ex- ercised with patients known to have significant arteriosclerotic disease of the carotid vessels. One patient with transient left hemiparesis resulting from mediastinoscopy has been reported 12281.

In their enthusiasm, advocates of mediastinoscopy commonly make the following statements: the procedure is a valuable addition to the techniques



of diagnosing intrathoracic disease; it provides an assessment of “biological operability” in patients with pulmonary neoplasm: mediastinoscopy is a simple and safe procedure. Mediastinoscopy has been shown to be a valuable diagnostic method, although its praise as a diagnostic technique must be kept in perspective in view of the possible life-threatening complications. Serious doubt is being raised by an increasing number of clinical surgeons concerning the value of mediastinoscopy in assessing operability in patients with pulmonary tumors. Konrad and Schulte [15] state that resection still is possible in more than 50% of patients having bronchogenic carcinoma with lymph node involvement and that follow-up of such patients reveals a five-year survival rate between 7 and 17%. Bell [l] cites a five-year survival rate of 6 to 22% in a small number of similar patients with metastatic disease in the mediastinal lymph nodes. Certainly a patient shown by mediastinoscopy to have metastatic involvement of the tracheobronchial lymph nodes should not be consigned automatically to a group beyond surgical aid and with no significant life expectancy.

The impression that mediastinoscopy is a simple and safe technique is false. In opposition to Palva’s [23] thinking that “one can begin on one’s own,” mediastinoscopy should not be performed by everyone with an interest in the technique but without adequate training. The first prerequisite of mediastinoscopy training is to instill the beginner with respect for the patient by emphasizing the basic surgical creed, “Above all else, do the patient no harm.” The second prerequisite should be a thorough knowledge of the procedure’s anatomical relationships and its complications and an un- derstanding of why these two factors are so closely conjoined.

Mediastinoscopy may be a valuable addition to the select group of diagnostic methods, led by a thorough history and physical examination, which have withstood the test of time. However, the procedure is not as benign, nor as revealing of information on which to base patient care, as its more enthusiastic proponents imply. Mediastinoscopy does represent progression in the development of diagnostic skills. It should not, however, be oversold. Those who use the procedure are obligated to respect its inherent dangers and develop a technique to minimize complications. With time and experience it will stabilize at its appropriate place in the spectrum of aids in the diagnosis and assessment of chest disease.

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