Ligament Pulmonar.pdf

VOL.87

Radiology

NO.6

DECEMBER 1966

a monthly journal devoted to clinical radiology and allied sciences PUBLISHED BY THE RADIOLOGICAL SOCIETY OF NORTH AMERICA, INC.

Roentgen Significance of the Pulmonary Liqament' JACK G. RABINOWITZ, M.D., and BERNARD S. WOLF, M.D.

H E INFERIOR pulmonary ligament is unfamiliar to most radiologists because it blends with the mediastinum and is not visualized on the normal chest roentgenogram. The thoracic surgeon, however, encounters this structure during operative procedures involving the lower part of the thorax. Although the ligament does not affect the normally functioning lung, it does exert a restrictive influence under certain pathological circumstances and can affect the resultant roentgen appearance of the chest. In these instances, the ligament itself may become visible. It is the purpose of this paper to clarify the anatomy of this structure and its appearance in various disease states.

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ANATOMY

The inferior pulmonary ligament (5) consists of a double serosal sheath connecting the visceral pleura on the medial surface of the lower lobe of each lung to the parietal pleura covering the mediastinum (Fig. 1). It extends downward in a sheet-like manner from the inferior margin of the pulmonary hilus to the diaphragm and loosely attaches the medial surface of the lung to the mediastinum. The ligament forms a barrier between the anterior and posterior parts of the mediastinal portion of the pleural cavity below the root of the lung. When the lung is displaced laterally away

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Fig. 1. Diagrammatic view of the left side of the mediastinum. The pulmonary ligament (L) extends downward and backward from the hilus to the dome of the diaphragm. It has been cut along its attachment to the lung. The side drawings are cross sections through various levels of the hemithorax to demonstrate the relationship of the visceral and mediastinal pleurae (dotted lines) to the lung and the pulmonary ligament at several levels. Above the hilus (A), the visceral and mediastinal pleurae are completely separated and the lung lies free within the thorax. The pleura that surrounds the hilus (B) is connected to both the visceral and mediastinal portions. The pulmonary ligament (C, D) is composed of a double layer of pleura that bridges the visceral and mediastinal pleurae and attaches the lung to the mediastinum.

from the mediastinum, the pulmonary ligament is stretched and assumes a triangular configuration (Fig. 2). It has, therefore, been referred to as the triangular ligament.

1 From the Department of Radiology, The Mount Sinai Hospital, New York, N. Y. in July 1966. RADIOLOGY 87: 1013-1020, December 1966.

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bounded posteriorly by the descending aorta. The right ligament is related anteriorly to the inferior vena cava and posteriorly to the azygos vein. The lateral border is attached to the medial surface of the lower lobe. As the ligament courses downward from the hilus, it curves in a posterior direction (Fig. 1) . The lower border of the ligament, therefore, pursues a slightly oblique course running posteriorly and laterally from the mediastinum to the medial surface of the base of the lower lobe. The two sheets of pleura which comprise the ligament enclose a network of connective and elastic tissue. At the hilus, this network blends intimately with the connective tissue surrounding the pulmonary vessels, the bronchi, and the esophagus. Within it, lymph nodes are occasionally found. ROENTGENOGRAPHIC FEATURES

Fig. 2. Schematic drawings to demonstrate the triangular configuration of the pulmonary ligament (L). The lung is shown retracted away from the mediastinum so that the ligament is stretched out as a sheet. The dotted lines represent the retrocardiac extension of the ligament. In the first drawing, the ligament is fully developed and its inferior margin is attached to the diaphragm. In the second drawing, the ligament fails to reach the diaphragm and ends inferiorly in a free falciform border. Fig. 3. Schematic cross section of the chest shows the relationship of the pulmonary ligaments to the mediastinal structures. Pulmonary ligament, L; aorta, A; esophagus, E; inferior vena cava, IVC; azygos vein, A V.

The apex of the triangle is situated at the inferior margin of the root of the lung immediately below the inferior pulmonary vein. The lower margin or base of the ligament is usually continuous with the pleura over the diaphragm, leaving a linear bare area on the diaphragm between the two leaves of the ligament. In some cases, the ligament does not reach the diaphragm and terminates in a free falciform border (Fig. 2). The medial border of the pulmonary ligament arises from the pleura over the mediastinum immediately posterior to the heart on each side (Fig. 3). The left ligament lies adjacent to the esophagus and is

The pulmonary ligament exerts an important effect on the configuration and position of the lung in the presence of a pneumothorax. If the pneumothorax is not under tension, the lung does not collapse concentrically. Whereas the upper pole tends to collapse around the hilus, the lower lobe usually collapses so that its outer border remains parallel to the mediastinum (4). The lower surface of the lung maintains its position adjacent to the diaphragm or separated slightly from it. The lower lobe, therefore, tends to retain its usual shape. This is a result of the attachment of the lower third of the lung to the mediastinum by the pulmonary ligament. Variation in the separation of the lower margin of the lung from the diaphragm depends upon the extent of the attachment of the ligament to the lung and diaphragm. If the ligament does not reach the diaphragm, the inferior free border of the ligament may be visualized as a falciform shadow extending from the mediastinum to the inferior part of the partly collapsed lower lobe (Fig. 4). The crescentic margin may lie parallel to the diaphragm or it may rise obliquely as it extends laterally. A slight oblique projection may demonstrate

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Fig. 4. A. Erect film of the chest in a slight right anterior oblique position demonstrates a total spontaneous pneumothorax on the left. The upper lobe (upper arrow) is collapsed around the hilus whereas the lower lobe (seen through the cardiac shadow) is parallel to the mediastinum. Immediately above the medial portion of the diaphragm, the inferior border of the pulmonary ligament (lower arrow) is seen as a linear density extending between the mediastinum and the collapsed lower lobe. B. Erect film of the chest in another patient with pleural metastasis and effusion. A large left-sided hydropneumothorax is present. The left upper lobe is maintained in a fixed position by apical adhesions and is only partially collapsed. The lower lobe (white arrows) is collapsed toward the mediastinum. The free falciform border of the pulmonary ligament (black arrow) is a linear density extending between lower lobe and mediastinum.

the border of the ligament more clearly. In a similar manner, the ligament also affects the pattern of lower lobe atelectasis (Figs. 5 and 6). In partial atelectasis of the lower lobe, the long fissure remains in contact with the lateral chest wall as the lobe contracts posteriorly and medially toward the posterior costophrenic sinus. When the atelectasis is more complete, the long fissure loses contact with the chest wall as the lobe flattens against the posteroinferior mediastinum. The lobe must collapse against the mediastinum since it is fixed to it by the pulmonary ligament. The collapsed lobe is seen in the lateral projection as a posteriorly placed triangular density (Fig. 6, B) (2) with a wedge-shaped anterior extension pointed toward the mediastinum. This extension is produced in part by the pulmonary ligament and its attachment to the lung.

The pulmonary ligament often influences the distribution of fluid within the pleural space (Fig. 7). This space is divided by the ligament into anterior and posterior compartments. When fluid is localized to the posterior compartment (Fig. 8), it is bounded by the ligament anteriorly, the adjacent lung laterally, and the posterior mediastinum medially. When the patient is erect, the fluid-filled posterior compartment assumes a triangular configuration with its apex at the hilus and its lateral margin straight or somewhat convex. The postero-anterior projection shows a density within the cardiac silhouette (Fig. 8, A) or sometimes extending beyond the heart. The lateral border may be shown more dearly in a slight oblique projection; right anterior oblique for the left side and vice versa. In the supine position, fluid in this compartment may simulate widening

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Fig. 5. Cross section of the chest demonstrating left lower lobe atelectasis (A). The collapsed lobe is attached to the mediastinum by means of the pulmonary ligament (L) along its entire length and therefore is forced to rotate about this attachment posteriorly and medially.

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ther laterally and the diaphragm is completelyobscured. Fluid in the anterior compartment of the mediastinal pleural space is usually associated with fluid elsewhere in the pleural cavity and is therefore difficult to recognize. Occasionally, such a collection of fluid produces an increase in the density of the right side of the heart and replaces the normal right atrial contour with a straightened oblique line continuous with the cardiac silhouette but representing the lateral margin of the fluid (Fig. 9). Droplets of opaque solution instilled into the pleural cavity, such as Lipiodol, may collect anterior to the ligament and outline its position (Fig. 10). When the pulmonary ligament is transected, as during a transthoracic hiatal hernia repair, the distinction between anterior and posterior pleural compartments is lost and these will communicate with the mediastinum

Fig. 6. An eight-year-old boy with atelectasis of the left lower lobe. A. Postero-anterior chest film shows a triangular density behind the heart. The heart and mediastinum are displaced toward the left. B. On the lateral exposure the long fissure (single posterior arrow) is displaced backward, exposing the mediastinal attachments (arrows) of the lower lobe extending anteriorly.

of the paravertebral shadow (6). In the lateral view, the fluid collection is projected en face, producing a hazy ill-defined density which may be difficult to recognize. In some cases, the dome of the diaphragm or the upper margin of an infrapulmonary effusion will be seen in this projection (Fig. 8, B); in others, the fluid collection in the posterior pleural compartment extends fur-

through the leaves of the cut ligament (Fig. 11). Fluid or exudate when present will often be found in the mediastinum and throughout the mediastinal pleural space (Fig. 12). A large hiatal hernia may protrude directly into the pulmonary ligament. The two leaves of the ligament are so separated that the base of the ligament

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Fig. 7. Cross sections of t he chest illustrating the effect of the pulmonary ligament (L) on the distribution of fluid (F) in thc paramediastinal pleural space. A. Fluid in the posterior paramediastinal pleural space on the left is adjacent to t.he aorta and spine. The aortic and paravertebral soft-tissue lines will be effaced in the frontal view. Fluid in the posterior compartment on the right side will have a similar appearance. B. Fluid in thc anterior mediastinal pleural space on the right side is behind and lateral to the right atrium. The mediastinal pleural margin or "stripe" adjacent to the esophagus and right border of the heart will be effaced. C. Fluid in the anterior mediastinal pleural space on the left is behind and lateral to t.hc left ventricle. The border of the ventricle will be obscured, but the border of the descending aorta will be seen.

Fig. 8. A 34-year-old woman several days postnephrectomy. Fluid is seen in the posterior mediastinal pleural space on the left. A. Postero-anterior erect :film shows a triangular density (upper and lower arrows) within the cardiac silhouette. The bronchovascular structures (middle arrow) are displaced medially. B. Lateral view discloses a faint increase in density overlying the lower dorsal spine. Normally, the lucency of the lower dorsal spine region should be greater than the upper. The apparent dome (arrow) of the left leaf of the diaphragm probably represents an infrapulmonary collection of fluid. Fig. 9. A 32-year-old woman with tuberculous infiltration in the right upper and middle lobes associated with an infrapulmonic pleural effusion. Fluid is also present in the anterior paramediastinal pleural space, producing an increased density on the right side of the heart shadow and a straightening of the right border of the cardiac silhouette (arrow).

becomes broadly continuous with the mediastinum (Figs. 13 and 14). The ligament may also be widened by invasion from without. A neoplasm of the lung may extend directly through the pleura into the ligament (Figs. 15 and 16). Radiologically, the appearance then suggests invasion of mediastinum (Fig. 16).

This can be misleading, since only the pulmonary ligament may be involved and the mediastinum free of neoplasm. In this latter instance, the lesion would still be resectable. DISCUSSION

Although the pulmonary ligament does

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Fig. 10. A film of the chest taken after Lipiodol injection into the pleural cavity for recurrent pneumothorax. A. A triangular collection of Lipiodol (arrows) is behind the right side of the heart, coating the surfaces of the pulmonary ligament. There has been some retraction of the right lung with displacement of the heart to the right. A large amount of opaque material is present around the right upper lobe. B. In the lateral film, the lower collection is band-like (arrows) and follows the course of the pulmonary ligament.

Fig. 11. Cross section of the chest showing loss of the pulmonary ligament after transthoracic mediastinal surgery. Postoperative fluid or exudate collects in the mediastinum and communicates with fluid in the continuous anterior and posterior pleural compartments. Fig. 13. Cross section of the chest demonstrates the manner in which a herniated portion of stomach (5) may extend into pulmonary ligament. (The peritoneal sac around the stomach is not shown.) Fig. 15. Cross section of the chest illustrates the manner in which a tumor (M) may invade and widen the pulmonary ligament (L), effacing the mediastinal pleural borders without significant invasion of the mediastinum.

not affect the normal function of the lung, it exerts a mechanical force in maintaining the normal configuration of the lower lobe. This was well appreciated in the days when pneumothorax was commonly used in the treatment of tuberculous cavities. In many instances, pneumothorax failed to collapse the lung because of the normal attachment of the pulmonary ligament. Therefore, attempts to compress cavities

within the mid or lower lung often proved futile (4). The fact that the mediastinal space is divided into anterior and posterior compartments by the ligament is of clinical importance when an empyema forms on one side of the ligament. If the ligament is complete, the infected fluid will often be localized to one of the pleural compartments. If the inferior margin of the Iiga-

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Fig. 12. Film of the chest taken during a barium swallow in a postoperative patient following transthoracic repair of a hiatal hernia. A homogeneous density (arrows) is in the left paramediastinal region, effacing the mediastinal pleural borders. This is produced by fluid in both the mediastinum and pleural space. The adjacent lung is partially compressed and consolidated, producing an air bronchogram. Fig. 14. A prone frontal :film obtained during a gastrointestinal examination reveals a large sliding hiatus hernia. The stomach extends out of the mediastinum to the left into the pulmonary ligament. A pleural reflection (arrow) extends in a crescentic manner from the superior aspect of the stomach to the mediastinum. Fig. 16. A 54-year-old woman with a persistent cough. A. A frontal :film of the chest demonstrates a mass lying within the medial aspect of the left lower lobe continuous with the mediastinal shadow. The inferior border of the mediastinum appears widened (lower arrow) and merges with the tumor. A mediastinal pleural reflection (upper arrow) is seen superiorly extending to the rnass. No pleural stripe is seen below this. B. Lateral :film demonstrates the mass posteriorly within the lower lobe. The circumference of the mass is well delineated with the exception of its anterior border. This portion presumably extends into the pulmonary ligament. At operation, there was no difficulty in resecting the tumor and lung after severing the mediastinal attachments of the pulmonary ligament.

ment does not reach the diaphragm at all points, however, exudate can flow under the free falciform border to the other compartment. The passageway under the ligament has been called the undefended space (3); surgical approach must then be adapted to drain both compartments.

The origm of the ligament is in close proximity to the inferior pulmonary vein. Consequently, trauma or unusual stress upon the ligament may in rare instances result in a tear of both the ligament and the vein, producing a massive hemothorax which may prove fatal. We have had

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occasion to observe one such case in which a massive hemothorax developed after a difficult labor. At postmortem examination, a tear of both the ligament and the inferior pulmonary vein was discovered. The anomalous branches from either the thoracic or abdominal aorta that supply an area of intralobar sequestration course through the pulmonary ligament. Three of the first 100 patients with intralobar sequestration operated upon died of hemorrhage (1) because this vessel was not under control before removal of the sequestered lung was attempted. It is important that the surgeon first expose the inferior pulmonary ligament carefully so that the feeding artery can be isolated. SUMMARY

The pulmonary ligament is a double serosal sheath that extends from the medial surface of the lower lobe to the mediastinum and from the hilus to the diaphragm. Along with the lung root, it serves to attach the lung to the mediastinum. When stretched to its maximum size, the ligament has a triangular appearance. In normal subjects, it is not visualized roentgenographically. Its location, however,

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influences the roentgen appearances of pneumothorax, mediastinal pleural effusions, and lower lobe collapse. In each of these conditions, a portion of the ligament may be visualized. In carcinoma of the lung, local extension between the pleural sheaths of the ligament may falsely suggest involvement of the mediastinum and therefore inoperability. ACKNOWLEDGMENT: The authors express their thanks to Drs. C. B. Rabin and M. G. Baron for their suggestions and review of the text.

Department of Radiology The Mount Sinai Hospital 11 E. lOOth Street New York, N. Y. 10029 REFERENCES 1. COOLEY, J. C.: Intralobar Bronchopulmonary Sequestration: A Report of Three Cases. Dis. of Chest 42: 95-99, July 1962. 2. LUBERT, M., AND KRAUSE, G. R.: Patterns of Lobar Collapse as Observed Radiographically. Radiology 56: 165-181, February 1951. 3. RABIN, C. B.: Personal communication. 4. SCHULZE, W.: Untersuchungen tiber das Ligamentum pulmonale. Deutsche Ztschr. f. Chir. 239: 127-149, 1933. 5. TESTUT, L., AND LATARJET, A.: Traite danatomie humaine. Vol. III. Paris, G. Doin & Cie, 9th ed., 1949. 6. TRACKLER, R. T., AND BRINKER, R. A.: Widening of the Left Paravertebral Pleural Line on Supine Chest Roentgenograms in Free Pleural Effusions. Am. J. Roentgenol. 96: 1027-1034, April 1966.

SUMMARIO IN INTERLINGUA

Signification Roentgenographic del Ligamenta Pulmonar

Le ligamento pulmonar es un duple vena serosal que se extende ab Ie superficie medial del lobo inferior usque ad le mediastino e ab le hilo usque ad le diaphragma. In cooperation con Ie radice pulmonar, illo servi a attachar le pulmon al mediastino. Quando le ligamento es tendite usque ad su dimensiones maximal, illo presenta un apparentia triangule. In subjectos normal, ilIo non es roentgenographicamente visualisabile. Tamen,

su location exerce un influentia super Ie apparentias de pneumothorace, de pleural effusiones mediastinal, e de collapso del lobo inferior. In cata-un de iste conditiones, un portion delligamento pote esser visualisate. In carcinoma pulmonar, extension local inter le venas pleural del ligamento pote suggerer falsemente un affection del mediastino e per consequente le inoperabilitate del caso.