Journ al of the Korean Radiological Society, 1995: 32( 4) : 595 -605 Lobar Atelectasis : Typical and Atypical Radiographic and CT Findings1 Kyung 500 Lee, M.D., Joong Mo Ahn, M.D., Jung-Gi 1m, M.D.2, Nestor L. Müller, M.D., PhD.3 The characteristic radiographic and CT findings of lobar atelectasis are well known. However, lobar atelectasis is a dynamic process, and atypical presen­ tations may occur due to a number of different causes. Familiarity with the vari­ ous typical and atypical radiographic findings of lobaratelectasis is important for correct diagnosis. The aim of this manuscript is toillustrate the spectrum of radiographic findings of lobar atelectasis and to correlate the radiographic findings with the CT findings. The review will illustrate examples of typical and atypicallobar atelectasis, including combined lobar atelectasis, peripherallobar atelectasis, migrating lobar atelectasis, rounded atelectasis involving the entire lobeand lobaratelectasis mimicking paravertebral and mediastinal masses. Index Words: Lung, collapse Lung, CT Lung , radiography made based on findings of the chest radiograph. Com­ INTRODUCTION puted tomography (CT) can be helpful in the assess­ ment of patients with lobar atelectasis, partic 비 arly Volume loss leads to anatomic alterations within the when the radiographic findings are atypical (4-7). CT is atelectatic lobe as well as compensatory changes in also often performed in order to determine the underly­ adjacent structures as they attempt to occupy the space ing cause for the atelectasis. left by the atelectatic lobe (1 - 3). Considerable volume The aims of this manuscript are to illustrate the vari­ loss is required in order to increase the opacity of the 。 us forms of typical and atypical lobar atelectasis on lung. More sensitive findings of atelectasis include dis­ chest radiographs and to correlate the radiographic placement of the interlobar fissures, hila, mediastinum findings of lobar atelectasis with those seen on CT. and bronchi. The presence and conspicuity of the vari­ ous findings is influenced by the severity of atelectasis, Right Upper Lobar Atelectasis type of atelectasis, condition of the underlying lung, as Right upper lobe (RUL) atelectasis results in ove­ well as the presence of extrap 비 monary abnormal ities rinflation of the right middle lobe and shift of the minor such as pleural thickening. Awareness of the various fissure superiorly and medially (Table 1). It also results direct and indirect signs of lobar atelectasis and of in compensatory overinflation of the right lower lobe atypical presentations is important in order to make the (RLL) with shift of the major fissure anteriorly, su­ correct diagnosis. periorly and medially (Fig. 1). The Golden ’s S sign The diagnosis of lobar atelectasis can usually be denotes a centrally located mass with associated lobar atelectasis. The mass should be large enough to be 'DeparlmenlofDiagnoslic Imaging , Samsung Medical Cenler (KSL, JMA) borderforming with the adjacent hyperexpanded lung 2DepartmenlolRadiology , CollegeolMedicine, Seoul Nalional Universily (JG I) (Fig. 1). With complete atelectasis, the RUL is either 3Departmenl 01 Radiology , Universily 01 Brilish Col umbia and Vancouver Hospi­ tal and Health Sciences Cenlre (NLM) pancaked medialiy, simulating mediastinal widening Recipient 01 a Certilicate 01 Merit award lor a scientilic exhibitatthe1994 RSNA or a mediastinal mass (Fig. 2) , or superiorly simulating scienlilic assemb ly and Bronse Medal Award lor a Scienlilic Exhibilatthe 1994 an apical pleural cap Korean Radiological Sociely Meeling On the lateral chest radiograph , an ill - defined Received March 5, 1995; Accepted April17 , 1995 Address reprinl requesls 10 :Kyung Soo Lee, M.D., Deparlmenl 01 Diagnoslic opacity anterior to the trachea and obliteration 01 the Imaging , Samsung Medical Cenler , # 50 Irwon-Dong , Kangnam-Ku , Seoul anterior margin olthe ascending aorta may sometimes 135-230, Korea. Tel. 82- 2- 341 0- 2511 ,2516 Fax. 82- 2-3410- 2559 be the only lindings (1 -3) . 595 - Journ al of th e Korean Radiologica l Soc iety. 1995; 32(4) : 595- 605 The minor fissure changes its position more dra­ aight. concave. or convex (4- 7) matically than does the major fissure. With elevation of the minor fissure. the middle lobe shifts up laterally Left Upper Lobar Atelectasis alongside the atelectatic upper lobe. At CT the middle With LUL atelectasis. the direction of movement is and upper lobes can be seen side- by- side anterior to anterosuperior rather than directly superior as in RUL the major fissure with the superior segment of the atelectasis (Table 2). The left p 비 monary artery. which lower lobe posterior to the fissure (Fig. 1). The major courses over the left main bronchus. restrains the fissure maintains its previous contour. whether str- bronchus and limits the superior migration of the a b Fig. 1. Typical right upper lobar atelectasis a. Chest radiograph shows right upper lung zone opacity marginated laterally by the elevated right minor fissure. b. Conventional (10 mm collimation) CT scan demonstrates atelectatic right upper lobe marginated laterally by right minor fissure (arrowheads) and posteriorly by right m 러。 r fissure (arrow). Due to central mass. the medial major fissure shows convex border (Golden ’ sSsign) a b Fig . 2. Right upper lobar atelectasis simulating rightsuperior mediastinal mass a. Chest radiograph shows semilunar opacity abutting right superior mediastinum b. Conventional (10 mm collimation) enhanced CT scan at level of distal trachea shows atelectatic right upper lobe with mucoid impac­ tion in dilated bronchi. Atelectatic upper lobe is sharply marginated laterally by the minor fissure -「 % J Kyun g Soo Lee, et al: Lobar Atelectasis atelectatic lobe (8). For this reason, the superior seg­ On OT scans, the atelectatic LUL forms a homo­ ment of the LLL expands upward toward the apex of the geneous 이객 city based on the anterior chest wall and left hemithorax. Therefore atelectasis of the left upper the mediastinum. The posterior margin has a V lobe is associated with increased opacity in the shaped contour from the lung apex to the hilum, where suprahilar region on the PA radiograph. As atelectasis the apex of the V merges with the hilar vessels and progresses, it leads to increased opacity with poorly bronchi. It is these hilar structures, which are relatively defined margins in the perihilar region (Fig. 3a) fixed in position , that tether the major fissure into the On the lateral radiograph, the lateral portion of the V - shape (Fig. 3c). The superior segment of the LLL is major fissure is displaced forward and is placed tan­ pulled forward along both the medial and laterallimbs gentially resulting in a sharp interface (Fig. 3b) of the V. The part of the superior segment that follows Table 1. Ancillary Radiographic Findings of Atelectasis of Right Upper Lobe Findings Fissural reorientation Elevated right minor fissure on PA radiograph , minor and major fissure marginate the atelectatic lobe on lateral view Hilum Right hilum elevated to or above the left hilum Mediastinum Tracheal deviation to ipsilateral side, mediastinal shift is less prominent than with lower lobe atelectasis Diaphragm Elevated, diaphragmatic tenting Bronchus Lateral position of bronchus intermedius on PA radiograph, larger lumen of RUL bronchus due to horizontal reorientation on lateral view Table 2. Ancillary Radiographic Findings of Atelectasis of Left Upper Lobe Findings Fissural reorientation Anterior displacement of major fissure on lateral radiograph Hilum Elevation of left hilum both on PA and lateral radiographs Mediastinum Anterior right lung herniation, producing prominent anterior margin of ascending aorta on lateral view Diaphragm Elevation with peak-I ike contour Bronchus Transverse orientation of left main bronchus resulting in enlarged orifice on lateral radiograph in place of smaller lumen of LUL bronchus 1 ’ a b c Fig. 3. Typicalleft upper lobar atelectasis a. Chest radiograph shows ill-defined opacity in left hilar area. The hyperexpanded superior segment ofthe left lower lobe leads to a lu­ cency between the mediastinum and atelectatic left upper lobe, the so-called Luftsichel (air-crescent) (arrows) b. Lateral radiograph shows anterior displacement of left major fissure. Anterior border of ascending aorta (arrows) is well visualized. c. Conventional (10 mm collimation) CT scan at level of aortic arch shows V-shaped posterior margin of atelectatic left upper lobe. Su­ perior segment of left lower lobe is p 비 led forward along both medial and laterallimbs of V. - 597 - Journal of the Korean Radiological Society, 1995 : 32 (4) : 595 - 605 the medial limb forms a tongue of lung between the Occasionally the atelectatic lobe may have sharp mediastinum and the atelectatic LUl. This tongue is margins on the PA radiograph simulating a hilar mass visible on PA radiographs and has been called the (Fig. 4 , 5). With marked LUL atelectasis, the contour of Luftsichel (air- crescent) or periaortic lucency (7) (Fig. the major fissure interface may appear continuous with 3c). Less commonly, the major fissure may have a that of the normal epipericardial fat on the lateral straight border rather than a V - shaped contour (Fig. 4) radiograph (Fig. 5). Fig. 4. Complete atelectasis 01 left upper lobe. a. Chest radiograph shows mass-like lesion in left hilar area. b. Thin-section (1.5collimation) CT scan 。 btained at level 01 carina shows atelectatic left upper lobe. Left upper lobe, being re­