CT: THE JOURNAL OF COMPUTED TOMOGRAPHY 1987: 11:303-306 303

INFERIOR PULMONARY LIGAMENT LYMPHADENOPATHY: DEMONSTRATION BY COMPUTED TOMOGRAPHY

GORDON CROSS, MD AND JOHN H. WOODRING, MD

Inferior pulmonary ligument lymphadenopathy is common in bronchogenic carcinoma and may also occur in Jymphoma and potentially in any condi- tion which may cause intrathoracic lymphadenop- athy. Despite the apparent frequency with which inferior pulmonary ligament lymphadenopathy oc- curs, we have been unable to find a description of the computed tomographic findings of this condi- tion. In a patient with lymphoma, we found inferior pulmonary ligament lymphadenopathy by com- puted tomography as an oval, elongated soft-tissue density arising within the inferior pulmonary liga- ment and still attached to the mediastinum by a piece of the normal ligament. We believe that this appearance should be sufficient for the correct computed tomographic diagnosis of inferior pul- monary ligament lymphndenopathy.

KEY WORDS:

Inferior pulmonary ligament; Computed tomography of thorax; Lymphadenopathy; Lymphoma; Bronchogenic carcinoma

INTRODUCTION The inferior pulmonary ligament (IPL) is formed as apposing layers of mediastinal (parietal) pleura, which reflect anteriorly and posteriorly over the

From the Department of Diagnostic Radiology, Albert B. Chandler Medical Center, University of Kentucky, Lexington, Kentucky.

Address reprint requests to John H. Woodring, MD, Depart- ment of Diagnostic Radiology, Albert B. Chandler Medical Cen- ter, University of Kentucky, 800 Rose St., Lexington, Kentucky 40536-0084.

Received October 1986.

0 1987 by Elsevier Science Publishing Co., Inc. 52 Vanderbilt Avenue, New York, NY 10017 0149-936X187/$3.50

hilum, meet medially and inferiorly to the inferior pulmonary vein (l-4). The IPL is triangular in shape with its apex at the hilum, the lateral margin at the inferior pulmonary vein, the medial margin against the mediastinum, and the base directed in- feriorly toward the diaphragm (l-4). On the right the IPL is attached to the mediastinum along the inferior vena cava and azygos vein; on the left the IPL in attached to the mediastinum along the esophagus and descending thoracic aorta (1, 2). Al- though the IPL is an extraparenchymal structure, the IPL is engulfed by the lower lobe (1) forming a cleavage plane in the parenchyma of the lower lobe, referred to as the intersublobar septum, which separates the medial basal segment from the posterior basal segment (2). The IPL extends a variable distance inferiorly from the hilum. It may end in a free edge (incomplete form) or may ex- tend to the diaphragm resulting in an area devoid of parietal pleura on the top of the diaphragm termed the “bare area” (complete form) (2). This variation may occur from side to side in a given individual (2).

Despite its extremely thin nature, the IPL does contain a number of normal structures, including lymphatics, lymph nodes, bronchial veins, and small arteries which are branches of the esophageal arterial plexus (1, 5). Mass lesions arising within the IPL have been infrequently reported in the lit- erature concerning diagnostic imaging. Godwin et al. (2) mention that the IPL may contain the stom- ach in hiatus hernia, and Ishikawa et al. (6) report that paraesophageal venous varices in patients with portal hypertension may be found as a lobular vas- cular mass within the IPL. Stocker and Malczak (5) also mention that the enlarged systemic arteries feeding intralobar pulmonary sequestration course through the IPL. Rost Jr. and Proto (1) caution that since the IPL is engulfed by the lower lobe, disease

304 CROSS AND WOODRING CT: THE JOURNAL OF COMPUTED TOMOGRAPHY VOL. 11 NO. 3

C

FIGURE I. (A) CT of the thorax at the level of the basilar segments of the lower lobes. Window width 1166, win- dow center -618. Inferior pulmonary ligament lymph- adenopathy is seen as.an oval soft-tissue density [arrowJ within the right inferior pulmonary ligament (arrow- head). The remaining normal right inferior pulmonary ligament (arrowhead) is attached to the mediastinum be- hind the inferior vena cava [vc). Note normal left inferior

pulmonary ligament (two arrowheads) and how the mass density in the right inferior pulmonary ligament conforms to the position and orientation of the normal ligament. N- enlarged right superior diaphragmatic nodes. (B) Same image as in A, window width 349, window center - 15. Arrow indicates right inferior pulmonary ligament lymphadenopathy, N indicates enlarged right superior diaphragmatic nodes. [C) 1 cm lower, window width

]ULY 1987

processes within the IPL may appear to be within the lung parenchyma by plain chest radiographs and that the correct distinction between IPL pathol- ogy and intraparenchymal pathology may be possi- ble only by computed tomography (CT). They illus- trate one example of pulmonary venous varices and esophageal leiomyoma each residing within the IPL (1). Still, to our knowledge, one of the most impor- tant causes for a mass density within the IPL-en- largement of the IPL lymph nodes-has not been mentioned or illustrated in the imaging literature. We recently examined a patient with extensive su- praclavicular, axillary, and intrathoracic lymphad- enopathy from lymphoma whose CT examination revealed lymphadenopathy in wish to report the findings in feel should be characteristic of thy by CT.

the right IPL. We this case which we IPL lymphadenopa-

CASE REPORT

The patient is a 78-year-old woman who was ad- mitted to the hospital complaining of a swollen left breast of two months duration. Physical examina- tion revealed a markedly enlarged, firm left breast with marked skin edema and nipple retraction. There was palpable lymphadenopathy in the left axilla. A surgical biopsy of the left axillary lymph nodes produced tissue which revealed malignant lymphoma, large noncleaved cell type. A CT scan of the thorax, performed as part of her staging eval- uation, revealed marked edema and skin thickening of the left breast, and definite lymphadenopathy in- volving both supraclavicular, left axillary, right par- atracheal, right tracheobronchial, right intrapulmo- nary, subcarinal, right superior diaphragmatic, and right inferior pulmonary ligament lymph node

1166, window center -618. Note oval, elongated density within right inferior pulmonary ligament (arrow) abutting posterior aspect of inferior vena cava (vc). Compare with position and orientation of normal left inferior pulmonary ligament (arrowheads). (D) Same image as in C, window width 349, window center -- 15. Arrow indicates right in- ferior pulmonary ligament lymphadenopathy abutting posterior aspect of inferior vena cava (vc). Arrowhead in- dicates normal left inferior pulmonary ligament. (E) 1 cm lower, window width 1166, window center -618. The right inferior pulmonary ligament lymphadenopathy blends imperceptibly into the right hemidiaphragm (ar- row]. Compare position and orientation of normal left in- ferior pulmonary ligament (arrowheads). (F) Same image as in E, window width 349, window center -15. The right inferior pulmonary ligament lymphadenopathy blends imperceptibly into the right hemidiaphragm (ar- row). Compare with normal left inferior pulmonary liga- ment (arrowheads).

INFERIOR PULMONARY LYMPHADENOPATHY 305

groups. The IPL lymphadenopathy was identified by CT as an oval, elongated soft tissue density aris- ing in the right IPL within the intersublobar septum behind the inferior vena cava, below the right hilum, and just above the right hemidiaphragm (Figure 1 A-F). Abdominal CT revealed splenic and mesenteric involvement; a bone marrow biopsy re- vealed bone marrow involvement by the lymphoma also. The patient was subsequently treated with cy- toxan, oncovin, prednisone, bleomycin, adriamycin, and matulane (COP-BLAM) chemotherapy and went into apparent remission. Six months later she had recurrent disease with lymphomatous meningitis. The patient and her family declined further ther- apy; she was placed in a nursing home for suppor- tive therapy.

DISCUSSION

In the past, the inferior pulmonary ligament lymph nodes have been considered by some authors to be part of the intrapulmonary lymph node group be- cause they may receive lymphatic drainage from the basilar segments of the lower lobes (1). However, the IPL lymph nodes are extraparenchymal, extra- pleural, and in continuity with the mediastinal nodes. The new American Thoracic Society classi- fication of intrathoracic lymph nodes has attempted to define specific nodal stations in terms of well- recognized anatomic landmarks that can be identi- fied both before and during thoracotomy (7). The IPL lymph nodes have been reclassified as a distinct nodal station (nodal station 9, defined as right or left pulmonary ligament nodes) (7). The IPL lymph nodes are most commonly enlarged by metastatic diseases from bronchogenic carcinoma (8); how- ever, as our case illustrates, lymphoma may also be a cause of IPL lymphadenopathy. We have been un- able to find any other reported causes of IPL lymph- adenopathy, but it is potentially possible that other conditions such as sarcoidosis, primary tuberculo- sis, and primary fungal infections could also cause IPL lymphadenopathy. It would be expected then, that the CT demonstration of IPL lymphadenopathy would not be specific for malignant disease.

The CT demonstration of IPL lymphadenopathy is important for several reasons. This may be most pertinent in patients with bronchogenic carcinoma. Despite obvious pitfalls in the preoperative staging of bronchogenic carcinoma by CT (81, CT does and will continue to play an important role in the stag- ing of bronchogenic carcinoma. Correct identifica- tion of IPL lymphadenopathy by CT during preop- erative evaluation of bronchogenic carcinoma does

306 CROSS AND WOODRING CT: THE JOURNAL OF COMPUTED TOMOGRAPHY VOL. 11 NO. 3

effect tumor staging and this may be important in patients whose cardiac or pulmonary function or type and extent of tumor involvement precludes op- erative intervention. Furthermore, it should be noted that IPL lymphadenopathy by itself does not preclude surgical intervention and potential resec- tion of the disease. Secondly, as Rost Jr. and Proto (1) caution, IPL disease engulfed by the lower lobe may be mistaken for intraparenchymal disease. Therefore, by CT, IPL lymphadenopathy might be mistaken for a pulmonary metastasis or second pri- mary tumor. The correct identification of IPL lymphadenopathy by CT could improve the preop- erative staging of bronchogenic carcinoma. The mis- identification of IPL lymphadenopathy as a sepa- rate, distinct intraparenchymal mass could suggest alternative diagnoses such as metastases to the lung from a tumor outside the thorax or a second pri- mary tumor in the lung, resulting in unnecessary evaluations for an extrathoracic malignancy or un- necessary needle biopsy of the IPL soft tissue mass to exclude a second primary. We believe that the findings of IPL lymphadenopathy as described in our case should be sufficiently characteristic to pro- vide a correct CT diagnosis.

REFERENCES 1.

2.

3.

4.

5.

Rost Jr. RC, Proto AV: Inferior pulmonary ligament: Computed tomographic appearance. Radiology 1983;148:479-83. Godwin JD, Vock P, Osborne DR: CT of the pulmonary liga- ment. AJR 1983;141:231-6. Cooper C, Moss AA, Buy J, Stark DD: CT appearance of the normal inferior pulmonary ligament. AJR 1983;141:23740. Friedman PJ: CT demonstration of tethering of the lung by the pulmonary ligament. J Comput Assist Tomogr 1985;9:947-8. Stocker JT, Malczak HT: A study of pulmonary ligament arter- ies relationship to intralobar pulmonary sequestration. Chest 1984;86:611-5.

Ishikawa T, Saeki M, Tsukune Y, Onove M, et al: Detection of paraesophageal varices by plain films. AJR 1985;144:701-4. Glazer HS, Aronberg DJ, Sage1 SS, Friedman PJ: CT demon- stration of calcified mediastinal lymph nodes: A guide to the new ATS classification. AJR 1986;147:17-20. McKenna Jr. RJ, Libshitz HI, Mountain CE, McMurtrey MJ: Roentgenographic evaluation of mediastinal nodes for preop- erative assessment in lung cancer. Chest 1985;88:206-10.

CONTINUING MEDICAL EDUCATION QUESTIONS

1. Which statements concerning the inferior pulmonary ligament are true? a. It is formed by visceral pleura. b. It is formed by mediastinal (parietal) pleura. c. It is an intraparenchymal structure. d. It is located beneath the hilum and extends from

the inferior pulmonary veins to the mediastinum. e. b and d above.

2. Which of the following normal structures may not be present within the inferior pulmonary ligament? a. Lymph nodes b. Bronchial veins c. Thoracic duct d. Small arterial branches of the esophageal arterial

plexus 3. Which of the following are potential causes for a mass

within the inferior pulmonary ligament? a. Enlarged nodes b. Hiatus hernia c. Paraesophageal varices d. Pulmonary venous varix e. All the above

4. Which of the following conditions may potentially be a cause for inferior pulmonary ligament lymphadenop- athy? a. Bronchogenic carcinoma metastasis b. Lymphoma c. Sarcoidosis d. Tuberculosis e. All of the above