J Korean Radiol Soc 1997; 36 : 7?? - 786

Mediastinal Interfaces and Lines : Clinical Significance and Radiographic-CT Correlation

1

Kyung SOO Lee, M.D., Yookyung Kim, M.D. , Boo Kyung Han, M.D. Hye Kyung Yoon, M.D., Dulζ WooRo, Ph.D., Yeon Hyeon Choe, M.D.

Hong Sik Byun, M.D., In Wool‘ Choo, M.D., Bokyung Kim Han, M.D.

Mediastinal interfaces on a chest radiograph result from contact between medias­tinal structures and the adjacent lung, while mediastinallines result from contact be­tween the two lungs across the midline. A variation ofmediastinal interface is medias­tinal stripe, a narrow band produced by contact ofboth sides of a mediastinal structure with the lungs. Alterations in mediastinal interfaces and lines may be due to variations in normal anatomy, or may reflect the presence of abnormalities within the medias­tinum. Familiarity with the various normal mediastinal interfaces and lines, and the changes that occur with disease is important for the interpretation of the chest radio­graph and in the diagnosis of mediastinal abnormalities. The purpose of this pictorial essay is to illustrate the most important normal and abnormal interfaces and lines and also to correlate radiographic and CT findings.

Index Words : Mediastinum Mediastinum, abnormalities Mediastinum, CT Mediastinum, radiography

Contact of the lung with the various mediastinal structures provides many kinds of mediastinal interfaces and lines. A chest radiograph, by showing normal and abnormal mediastinal interfaces and lines, reflects the anatomic status of a patient mediastinum and gives information on further diagnostic work-up. By showing cross-sectional images of the mediastinum and lung, CT can visualize and explain the formation of normal and abnormal mediastinal interfaces and lines.

There are two true mediastinal lines : the anterior and posterior junction lines; man y kinds of medias­tinal interfaces can be shown on normal and abnormal chest radiographs. In this exhibit, we will first de­scribe the mediastinal lines, then the mediastinal interfaces. Only those mediastinal interfaces that are clinically important will be addressed. They will be subdivided into those in the supraazygous, in­fraazygous , supraaortic and infraaortic areas, as de­scribed by Heitzman et al (1) and will be described in thatorder.

IDepartment ofRadiology , Sumsung Medical Center Received December 26 , 1996; Accepted February 4, 1997 Address reprint requests to: Kyung Soo Lee, M.D., Department of Radiology, Samsung Medical Center I 50 Irwon-Dong, Kangnam-Ku, Seoul 135-230, Korea

Tel : 82-2-3410-251 L 25 16 FAX: 82-2-34 10-2559

Mediastinal Li nes

AnteriorJunctionalline The anteromedial right and left lungs approach the

midline and forms the anterior junctionalline. If the lungs do not meet each other closely to form a line, a bandlike stripe is formed (Fig. 1). Above and below the junctional line, the right and left lungs contact the retromanubrial anterior mediastinal fat rather than contralaterallung, thus forming an interface instead of forming a true line. This interface, above and below the true junctionalline was called superior (V-shaped configuration) and inferior (inverted V-shaped con­figuration) recess of anterior junctional reflection by Proto (2, 3) (Fig. L 2). The interfaces of the superior and inferior recess usually shows medial convexity (Fig. 1, 2)

Effacement and distortion of the anterior junctional line or lateral convexity ofthe interface ofthe superior and inferior recess suggests the possibility of medias­tinal abnormality (Fig. 3). Anterior junctionalline may be displaced and visualized prominently when a lobe or lung is atelectatic and contralateral lobe or lung herniates through the anterior mediastinum (Fig. 4).

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PosteriorJunctional Li ne The posteromedial upper right and left lungs ap­

proach the midline in front ofthe spine and behind the esophagus to form the posterior junctionalline usually above the azygos and aortic arches (Fig. 2) . As in the anterior junctional reflection, the interface, above and below the true junctionalline is called superior and in­ferior recess of posterior junctional reflection. Pos­terior junctional line rarely forms below the azygos and aortic arch, usually anterior to the esophagus and posterior to the descending aorta w hen the postero me­dial right and left lungs meet each other (2, 4). Air wit­hin the lumen of the esophagus along with air in the posteromediallungs may delineate the esophageal wal­ls such that a band-like density denoting esophageal wall may be observed.

Kyung Soo Lee, et a/: Mediastinal Interfaces and Lines

Posterior junctional line may be distorted by me­diastinal disease and especially by esophageal abnor­mality.

Mediastinallnterfaces

Supraazygous Area

Superior Vena Cava I nterface The superior vena cava (SVC) usually indents the lat­

eral right lung and forms an interface on poserior­anterior (PA) radiograph. This interface merges with the border of the right atrium. The great vessels (right subclavian artery) ofthe aortic arch become ectatic and tortuous as the patients get old , further displacing the interface laterally. In this case, differentiation of SVC interface from atelectasis of the right upper lobe and

Fig. 1. Chest radiograph demonstrat­ing anterior junctionalline and rec­esses (arrows) and posterior junc­tional line and recesses (arrow­heads). Anterior junctional line is oblique from right to left whereas posterior junctional line is vertical. Anterior junctionalline is inferior to posterior junctional line which is most frequently seen in supraaortic area. Fig. 2. Chest radiograph showing su­perior recesses of anterior junctional complex (arrowheads) rather than line. When two superior recesses meet together anteriorly, they form anterior junctionalline (arrows).

B

Fig. 3. Lateral convexity of superior recess of anterior junctional complex d ue to anterior mediastinal mass. A. Chest radiograph shows widening of superior mediastinum. Lateral convexity of superior recess of anterior junctional complex (arrow) is seen right lateral to sternal shadow (arrowhead). B. Enhanced conventional (lO-mm collimation) CT scan obtained at level of aortic arch demonstrates anterior mediastinal mass (tu berculous lymphadenitis), with lateral displacement of anterior lung

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J Korean Radi이 Soc 1997; 36 :777-786

media와inal abnormality is difficult. Imperceptible tap­ering of the interface superior to the clavicle (due to horizontal course of the innominate vein rather than vertical at this leveI) and arcuate course ofthe interface on lodortic view are useful signs favoring the diagnosis of SVC interface (Fig. 5) rather than abnormalities in the right upper lobe or the mediastinum (1)

Right Paratracheal Stripe Contact of the tracheal wall (sometimes along with

areolar tissue, fat and smalllymph nodes) with air both

in the right lung and in tracheallumen produces right paratracheal stripe. The stripe is usually not more than 4 mm in thickness (1 , 2)

Localized thickening of the stripe and change in its thickness on serial examinations are important signs that indicate abnormalities in paratracheal area (Fig. 6).

Azygos (Tracheobronchial angle) Node vs. AzygosVein A mass in the right tracheobronchial angle, extend­

ing cephalad from azygos arch, is usually due to lymph

Fig. 4. Lateral displacement ofanterior junctionalline after right lung transplantation. A. Chest radiograph shows right displacement of anterior junctionalline (arrows). Note hyperlucency of native left lung and increased density oftransplanted right lung. B. Thin-section {1. 5-mm co떼o이에11…lima line (arrow) to t산theri핑ghthemi야t산ho야rax. Na따t디ive터hωungi성smo야re hyperlucκcent than transplanted lung .

A B c Fig. S. Lateral displacement ofsuperior vena cava interface due to tortuous right innominate artery A. Chest radiograph demonstrates right lateral displacement of superior vena cava interface with lateral convexity (arrows). B. Follow-up lodortic view in same patient shows smooth arc of superior vena cava interface (arrows) heading laterally to axil­laryarea. c. Enhanced conventional (lO-mm collimation) CT scans obtained at levels of thoracic inlet shows tortuous riQht innominate artery (arrows) which causes displacement ofright innominate vein and superior vena cava (curved arrows) to right side.

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Kyung Soo Lee. et a/: Mediastinal Interfaces and Lines

Fig. 6. Obliteration ofright paratracheal stripe due to Castleman’s disease. A. Chest radiograph shows semilunar shaped soft tissue lesion in supraazygos area with obliteration of right paratracheal stnpe. B. Enhanced conventional (lO-mm collima디on) CT scan obtained at level of aortopulmonary window shows highly enhancing mass in pretracheal and retrocaval area, which turned out to be Castleman’s disease

A B

Fig. 7. Prominent azygos arch due to azygos continuation ofinferior vena cava. A. Chest radiograph shows prominent azygos arch (arrow). This arch extends inferiorly at area of tracheobronchial angle whereas azygos nodes extends superiorly from tracheobronchial angle. Additionally, right paratracheal stripe is clearly visualized superior to azygos arch. B. Tl -weighted (TR/TE; 720/16msec) MR image shows dilated azygos vein (arrows), which was direc t1y connected to inferior vena cava.

node enlargement (Fig. 6) whereas a mass beneath the arch is due to dilated azygos arch (Fig. 7) (1 , 2). In ad­dition, azygos arch is always situated lateral to the azygos node, thus deviating the SVC laterally (since azygos arch drains into the SVC) with extensive aden­opathy in the right tracheobronchial angle (2).

Infraazygous Area

Azygoesophageal Recess Interface The azygoesophageal recess refers to the posteromed­

ial right lower lobe of the lung, which lies lateral and

posterior to the esophagus and in front of the spine and the ascending portion of the azygos vein (5 , 6). It is bounded cephalad by the azygos arch and caudad by the diaphragm. Contact of the lung in the azygoes­ophageal recess with the mediastinum produces azy­goesophageal recess interface. The azygos vein usually borders the recess. The esophagus or mediastinal fat sometimes borders the recess especially in caudallevel. On chest radiograph, the interface is usually straight in young adults . As age increases, it tends to be shown as a smooth arc with convexity to the left. Sigmoid shape

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J Korean Radiol Soc 1997; 36 : 7?? - 786

with midline cross may be noted in an aged person (5). Right-sided and downward displacement of the

interface beneath the carina may be observed with subcarinal adenopathy (usually more than 2.5 cm in di­ameter) (5 , 7) and bronchogenic cyst in subcarinal area Lymphadenopathy less than 2.5 cm in diameter usually does not displace the interface. With left atrial enlarge­ment, obliteration of the interface at T8- 1O level may be observed (5) . Focal right-sided bulging of the interface is observed with abnormality in the esophagus (Fig. 8). Dilatation of the esophagus (due to achalasia, previous esophageal surgery , or distal

A

esophageal obstruction) or azygos vein (congenital or acquired) (Fig. 7) and esophageal hiatal hernia may cause the interface to be displaced laterally. Posterior herniation of the right lung may occur when the left lung loses its volume extensively. The herniation usually occurs between the esophagus anteriorly and the azygos vein or the vertebral body posteriorly.

Supraaortic Area

Aortopulmonary Interface Contact of the anteromedial left lung with left

anterior mediastinum (main pulmonary artery and

Fig. 8. Right lateral displacement of azygoesophageal recess interface due to esophageal cancer. A. Chest radiograph shows focal area ofright lateral displacement of azygoesophageal recess interface (arrow), B. Enhanced conventional (lO-mm collimation) CT scan obtained at ventricular level reveals circumferential thickening of esphageal wall with right lateral displacement oflung in azygoesophageal recess (arrow).

Fig. 9. Left lateral displacement of aortopulmonary interface due to left anterior mediastinal mass. A. Chest radiograph demonstrates left lateral displacement of aortopulmonary interface due to soft tissue mass lesion in left suprahilar area. pulmonary vessels are seen in mass lesion with so-called positive hilum overlay sign B. Enhanced conventional (lO-mm collimation) CT scan reveals low attenuation soft tissue lesion containing calcification. Lesion turns out to be lymphangioma.

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artery and aortic arch cephalad), behind the anterior junctionalline and in front ofthe left subclavian artery interface, produces aortopulmonary interface. This interface extends cephalad from the main pulmonary artery along the aortic arch through the aortic knob The interface may be convex or straight along the main pulmonary artery (lower portion of the interface) whereas it may appear straight or concave medially through the aortic knob (upper portion) (1).

If the interface projects lateral to the aortic knob, mediastinal abnormality should be considered (Fig. 9).

Kyung Soo Lee. et a/: Mediastinal Interfaces and Lines

Presence of a left superior vena cava, left vertical vein or double aortic arch may distort the interface (Fig. 10).

Small projection from the left lateral aspect of the aortic knob, caused by the left superior intercostal vein, is called aortic nipple (Fig. 11). More than 4.5 mm in size of this nipple is abnormal (Fig. 12) and is caused by obstruction mostly of the superior vena cava and rarely ofthe inferior vena cava.

Left Subclavian Artery I nterface Contact between the ascending first part of the left

Fig. 10. Lateral displacement of aortopulmonary interface due to left sided superior vena cava. A. Chest radiograph shows lateral displacement of aortopulmonary interface (arrow). AIso note cardiomegaly and redistri­bution ofpulmonary vascularity due to pulmonary venous hypertension. B. Enhanced conventional (lO-mm collimation) CT scans obtained at thoracic inlet demonstrates left sided superior vena cava (arrow) with left lateral displacement of adjacent let lung.

A B

Fig. 11. Normal sized aortic nipple in a 31-year-old man. A. Chest radiograph shows smalllateral projection (arrow) from aortic kno b. B. Mediastinal window ofthin-section (l.O-mm collimation) CT scan obtained at level of aortic arch shows superior intercostal vein (arrow) directing anteriorly from accessory hemiazygos vein.

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J Korean Radiol Soc 1997; 36 : 777 -786

A

Fig. 12. Enlarged aortic nipple due to superior vena cava obstruction. A. Chest radiograph shows enlarged aortic nipple (arrow). 8. Enhanced conventional (lO-mm collimation) CT scan obtained at ventricular level demonstrates dilated hemiazygos vein (arrow) d ue to obstruction of superior vena cava caused by indwelling catheter. This dilated vein drains into left superior in­tercostal vein with resultant enlarged aortic nipple

A B Fig. 13. Aberrant right subclavian artery in a 51-year-old woman. A. Chest radiograph shows unusual interface (arrows) arising from superior portion of aortic knob and directing right superiorly. Tubular density overlapped with tracheal air shadow may represent aberrant artery perse. 8. Enhanced conventional (10-mm collimation) CT scan obtained at level of great vessels reveals aberrant right subclavian ar­tery (arrow) in retroesophageal area. This vessel appears as retrotracheal rectangular density in chest radiograph.

subclavian artery and anteromedial portion of the left upper lobe produces an interface in supraaortic area. The interface extends upward in curved fashion from the aortic arch . Focal obliteration of the interface suggests the possibility ofmediastinal abnormality.

Aberrant right subclavian artery may be identified in the supraaortic area. A linear interface extending from the aortic knob to the right can be observed on frontal ‘ radiograph (Fig 13). Additional findings are a stripe through the tracheal air column denoting the

vessel per se and mass effect to the right lung in medial aspect of the clavicle on frontal radiograph. On lateral radiograph, the vessel may cause a retrotracheal opacity or indentation of the posterior wall of the tra­chea (8) .

Left Paratracheall nterface Left paratracheal interface represents contact of the

lung with left paratracheal mediastinal fat (94%), proximal 1 - 2 cm of the lateral wall of the left common

%

Kyung Soo Lee. et a/: Mediastinal Interfaces and Lines

A

Fig. 14. Lateral convexity of aortopulmonary window interface due to lymph node enlargement. A. Chest radiograph shows lateral convexity of aortopulmonary window interface (arrows). B. Enhanced conventional (lO-mm collimation) CT scan obtained at carinal level shows 떠larged lymph node (arrow) displacing left lung laterally.

A B Fig. 1 S. Preaortic interface in a 57-year-old man. A. Chest radiograph shows interface with white etching medial to left cardiac margin (arrows). B. Enhanced conventional (lO-mm collimation) CT scan obtained at subcarinal area demonstrates left lung (arrowhead) be­tween descending aorta and left pulmonary artery forming preaortic interface.

carotid artery (5 %), or the left tracheal wall perse (1 %) (9). This interface is observed in 31 % ofthe patients on chest radiographs. White (positive Mach band) left paratracheal interface can be distinguished from black (negative Mach band) left subclavian artery interface. In addition, the former is usually located medial to the latter. A variety of entities may alter the left para­tracheal interface.

Infraaortic Area

Aortopulmonary Window Interface Aortopulmonary window is the area of the medias-

tinum bounded superiorly by the aortic arch, inferiorly by the left pulmonary artery , medially by the trachea, left main bronchus, and esophagus, lat­erally by the mediastinal pleura, anteriorly by the as­cending aorta and posteriorly by the descending aorta (1 , 2). The aortopulmonary window contains fat, ductus ligament, left recurrent laryngeal nerve, nodes and left bronchial arteries.

Contact between the left lung and lateral closure of the aortopulmonary window (the mediastinal pleura) produce aortopulmonary window interface. This interface connects the aortic know with the left pul-

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J Korean Radi이 Soc 1997; 36: 777-786

monary artery . It is normally convex medially. Lateral convexity of the interface suggests abnormality in the aortopulmonary window (Fig. 14). Since the left recur­rent laryngeal nerve is located in the aortopulmonary window, careful observation should be given for alter­ation of the interface in a patient with left vocal cord palsy.

Preaortic Interface Contact of the posteromedial portion of the left

lower lobe with the mediastinum anterior to the descending thoracic aorta produces preaortic in-

A

terface. This interface is analogous to the azygoeso­phageal recess interface in the right side. Cephalad, the interface deviates laterally to be continuous with the aortic arch or ends vertically under the aortic knob. Caudad, it merges into the descending aorta smoothly at TlO level (Fig. 15).

Descending Aortic Interface Contact of the posteromedial left lower lobe with

descending thoracic aorta produces descending aortic interface. The interface is usually seen along its entire course. However, in about 9 % of subjects it may be

B

Fig. 16.0 bliteration of descending aortic interface due to contact between descending aorta and pulmonary artery. A. Chest radiograph shows obliteration of descending aortic interface just inferior to aortic knob (arrow). B. Enhanced conventional (lO-mm collimation) CT scan obtained at level of carina shows close contract between descending aorta and pulmonary artery.

Fig. 17. Focal obliteration of descending aortic interface due to paraesophageal varices due to liver cirrhosis A. Chest radiograph shows focal areas (arrows) of obliteration of descending aortic interface B. Enhanced conventional (lO-mm collimation) CT scans obtained at levels ofinferior vena cava and celiac axis area reveal ex­tensive collaterals with obliteration of descending aortic interface (arrow). Note smallliver and enlarged spleen.

%

Fig. 18. Obliteration of left paraspinal interface (arrows) due to plexiform neurofibromatosis in a 25-year-old man. AIso note multiple areas of mass lesion in right paratracheal and bilateral intercostal regions

oscured focally probably due to direct contact of the

aorta with pulmonary arteries (Fig 16), superior seg­

ment vessels, or other mediastinal structures (10).

Obliteration of descending aortic interface, along

with obliteration oflung markings in the adjacent lung

and opacity due to abnormality per se, suggests mediastinal abnormalities including mediastinal

adenopathy or mass, vascular ~isease ， pleural lesion, esophageallesions or lung cancer (Fig. 17).

Left Paraspinall nterface

Contact of the posteromedial left lower lobe of the

lung with left paraspinal soft tissue results in the left

paraspinal interface. Usually the interface begins at the

Kyung Soo Lee, et a/: Mediastinal Interfaces and Lines

level ofthe aortic knob and descends downward to the

left hemidiaphragm. Although the interface projects

medial to the descending aortic interface, this relation­

ship may be reversed occasionally. Left paraspinal

interface appears as white (positive Mach band)

whereas the descending aortic interface as black (nega­

tive Mach band). If the interface maintains white line

appearance parallel to the lateral margin of the ver­

tebral bodies , it indicates normal. Focal bulging ac­

companied by loss of the white appearance suggests

paraspinal mass lesion (Fig. 18).

References

1. Heitzman ER. The mediastinum. Radiologic correlations with

anatomy and pathology. 2nd ed. Berlin ’ Springer-Verlag, 1988 2. Proto AV. Mediastinal anatomy: emphasis on conventional

images with anatomic and computed tomographic correlations J Thorac Imag 1987 ; 2: 1-48

3. Proto AV, Simmons JD, Zylak CJ. The anterior junction anat­omy, Crit Rev Diagn Imaging 1983; 19: 111-173

4. Proto AV, Simmons JD, Zylak CJ. The posterior junction anat­omy. Crit Rev Diagn Imaging 1983; 20: 121-173

5. Cho WS, Lee KS, Kim IY, Lee BH. Normal and abnormal azygoesophageal recess: radiographic and CT correlation. J Kor

Rad Soc 1992; 28 : 545-552 (Korean) 6. Heitzman ER, Scrivani JV, Martino J, Moro J. The azygos vein

and its pleural ref1ections. Normal roentgen anatomy. Radiology

1971; 101 ‘ 249-258 7‘ Müler NL, Webb WR, Gamsu G. Subcarinal lymph node en­

largement: radiographic findings and CT correlation. AJR 1985

; 145: 15-19 8. Proto AV, Cuthbert NW, Raider L. Aberrant right subcla\'.ian

artery : further observations. AJR 1987; 148: 253-257 9. Proto AV, Corcoran HL, Ball JB. The left paratracheal ref1ec

tion. Radiology 1989; 171: 625-628 10. Takahashi K, Shinozaki T, Hyodo H, Ogawa C, Ohsawa T. Focal

obliteration of the descending aortic interface on normal frontal chest radiographs ’ correlation with CT findings . Radiology 1994

; 191: 685-690

대한방사선의학호I^I 199?; 36: ???-?86

종격동 공유면과 선 구조물:임상적 중요성 및 단순흉부촬영과 전산화단충촬영상의 상관관계l

1 삼성서울병원 진단방사선과

이경수·검유경·한부정·윤혜경·최연현·노덕우·변홍식·주인욱·검보경

단순흉부촬영상의 종격동 공유면 ( In terf ace)은 종격동 구조물과 주위의 폐와의 접촉에 의해서 기인하며 종

격동 선 구조물 (Line)은 양쪽 폐가 종격동의 중심에서 만날 때 형성된다. 종격동 공유면의 변형。1 종격동 띠

(Stripe) 인데 이는 종격동 구조물이 그 양쪽의 공기와 만나는 경우에 형성된다. 이러한 종격동 공유면과 선 구

조물의 변화는 정상 해부학의 변이나 종격동 내의 비정상 소견을 의미한다. 정상 종격동 공유면과 선 구조물 그

리고 이들의 변화에 익숙하면 단순흉부촬영의 해석에 도움이 되며 종격동 질환의 진단에도 중요하다. 이 임상화

보의 목적은 가장 중요한 정상， 혹은 비정상 종격동 공유연과 선 구조물을 보여 주고 이들의 단순흉부촬영과 전

산화단층촬영상의 상호관계를 기술하는데 있다.

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