Clinical Radiology (1981) 32, 2 7 1 - 2 7 5 0 0 0 9 - 9 2 6 0 / 8 1 / 0 0 3 5 0 2 7 1 5 0 2 . 0 0 © 1981 Royal College o f Radiologists

The Luftsichel: An Old Sign in Upper Lobe Collapse MICHAEL WEBBER and PETER DAVIES

The Department of Radiology, City Hospital, Nottingham

The Luftsichel is a paramediastinal translucency due to interposition of the apex of the lower lobe between the mediastinum and the shrunken upper lobe. It occurs more commonly on the left than the right. It is so common on the left that it should be regarded as the typical appearance. It is to be distinguished from media- stinal hernia.

The appearances of upper lobe collapse have been well established for 35 years, since the description by Robbins and Hale (1945), with subsequent amplifi- cation by Lubert and Krause (1961), and the current views are summarised by Felson (1973) in his book.

The appearances differ on the two sides, because the right lung is divided into three lobes and the left into two. On the right the horizontal fissure and superior part of the oblique fissure move upwards, and the lobe collapses upwards and medially. On the left the collapsing lobe moves fowards and medially.

The radiographic signs of collapse are of three kinds:

1. Direct signs are increased opacity of the lobe and movement of the associated fissures.

2. Indirect signs are those associated with move- ment of other structures in the thorax: eleva- tion of the hemidiaphragm, contraction of the hemithorax, hilar displacement and over- inflation of the normal lung.

3. The third kind of sign is the 'silhouette sign'.

We have seen a crescentic translucency adjacent to the left superior mediastinum which renders the aortic knuckle clearly visible. Many people interpret this as mediastinal herniation. This translucency, the Luftsichel, was described by Dahm (1942), but we have found no reference to it in English or American journals.

METHODS

The films of 44 cases of upper lobe collapse were examined. All were secondary to carcinoma of the bronchus. In all cases postero-anterior and lateral films were available and in some cases there were penetrated postero-antelior films or tomograms. The films were examined for the presence of a Luftsichel and the presence or absence was recorded separately for the two sides. The films of left upper

lobe collapse with a Luftsichel were examined for the following signs:

1. Whether the Luftsichel showed a sharp lateral border.

2a. Absence of the silhouette of the aortic knuckle.

2b. If aortic knuckle was discernible, whether of normal or reduced size.

3a. Radiolucency of the apex of the hemithorax. 3b. If the apex of the hemithorax was radiolucent

whether it was continuous with the LuftsicheL 4. If the apex was opaque, whether a sharply

defined lower border was present.

The cases were tabulated as those that definitely showed a Luftsichel and those that did not. There were six cases in which we could not decide if a Luftsichel was present and these are recorded as doubtful (Table 1).

Table 1 - F requency of cases o f upper lobe collapse on each side in which a Luftsichel was present, absent, or in which we could no t decide on its presence

Right upper Left upper Total lobe collapse lobe collapse

Luftsichel 5 19 24 present

Doub t fu l 3 3 6 Luftsichel 9 5 14

absent

Total 17 27 44

RESULTS

Figs 1 and 2 show the appearances usually described as typical of left upper lobe collapse, and Fig. 3 the appearances of right upper lobe collapse. Figs 4 and 5 show the Luftsichel on the left and right.

272 C L I N I C A L R A D I O L O G Y

Fig. 1 - The appearances usually described in left upper lobe collapse. The lobe has collapsed to abou t half its volume. The left hear t border, h i lum and aortic knuckle are obscured.

Fig. 2 - A mediast inal wedge is well seen, as is the posterior aspect o f the collapsed lobe. Note the ascending aorta out- l ined on the right side o f the chest behind the s ternum.

Fig. 3 - Collapse of the right upper lobe showing a wedge- shaped opacity adjacent to the medias t inum. Note the normal aortic knuckle.

Fig. 4 - The Luftsichel. The signs are identical to those of Fig. 1 except for the presence o f air-containing lung above the aortic arch. Note the unders ide o f the aortic arch is no t seen, and the left upper lobe b ronchus is occluded.

T H E L U F T S I C H E L IN U P P E R L O B E C O L L A P S E 273

Fig. 5 - The Luftsichel on the right. The proximal part of the hilum cannot be seen. The arteries to the lower lobe start suddenly at the lower border of the collapsed lobe.

On the left side a Luftsichel was definitely present in 19 of 27 cases (70.4%). The signs were present in these 19 cases as follows:

1. The Luftsichel showed a sharp lateral border in 13 (68.4%).

2a. The margin of the aortic knuckle was obscured in 14 (73.7%).

2b. The aortic knuckle was of normal size in seven (36.8%).

3a. The apex of the hemithorax was radiolucent in five (26.3%).

3b. The radiolucency was continuous with the Luftsichel in four (21%).

4. Where the apex was opaque, ttle opacity showed a sharply defined crescentic lower border in five (26.3%).

There was no set of signs that was more common than any other set. The appearances changed with posture in one patient (Fig. 7). Although the Luftsichel is present in both positions, when the patient is erect the border of the aortic knuckle is sharp, and when supine, the border is obscured. This is an example of the silhouette sign changing with position.

The Luftsichel was seen more often on the left, 19 out of 27 cases (70.4%), than on the right, five out of 17 cases (29.4%) (Table 1).

(a) (b)

Fig. 6 - (a) Left upper lobe collapse. The lobe is perhaps half its normal volume. The aerated lower lobe is seen above the upper lobe. Note the sudden appearance of the lower lobe vessels. Note also the absence of the silhouette of part of the aortic arch. (b) Lateral film showing lower lobe above the upper lobe.

20 ̧

274 C L I N I C A L R A D I O L O G Y

(a) (b) Fig. 7 - (a) Erect PA film. There is a faint translucency adjacent to the dearly visible aortic knuckle. The translucency extends up to the apex. Note again the sudden appearance of the lower lobe vessels. (b) Supine AP. The Luftsichel is now seen, the aortic knuckle is obscured, and the apical translucency has disappeared. The differences are due to the upper lobe failing backwards in the recumbent position.

DISCUSSION There is no description of the Luftsichel in the

English literature. The appearance has been recog- nised at the City Hospital for some years but we have been surprised at how often it is a t t r ibuted to media- stinal hernia or displacement. The case illustrated in Fig. 6 in which the apex of the lower lobe is above the upper lobe shows how much relative movement of the two lobes can occur with litt le shift of the mediastinum.

The relation of this appearance to the silhouette sign is of considerable interest. In the standard description of left upper lope collapse the aortic knuckle is said to be obscured and it is implied that there is uniform opacity in the upper part of the left hemithorax. The Luftsichel is a translucency in this uniform opacity and yet the silhouette of the aortic knuckle was found to be unsharp in more than 70% of our cases. This implies contact of the collapsed lobe with it. This contact may change with changing posit ion as shown in Fig. 7 and the sharpness of the silhouette changes with it.

The silhouette sign is impor tant in localising pulmonary lesions (Foote and Meredith, 1979). Foote and Meredith (1979) at tr ibute its description to Hodson (1956) although he did not give it its name and since he was referring to small lesions did not

Fig. 7c - Nine centimetre tomogram. The Luftsichel is clearly outlined. Its medial margin is continuous with the posterior pleural reflection, and its lateral border forms the medial border of the upper lobe.

THE LUFTSICHEL IN UPPER LOBE COLLAPSE 275

distinguish between consolidation and collapse. We think that in lobar lesions it is important to distin- guish between the two conditions and this is usually done by estimating volume loss on the postero- anterior and lateral films. The Luftsichel is, however, an additional sign present on the postero-anterior film which indicates collapse rather than consolidation.

The silhouette sign was named by Felson and Felson in 1950 but it had been recognised before this (Robbins and Hale, 1945) and Felson (1973) states that H. K. Dunham observed it in 1935. I f the upper lobe collapses to become very thin, obli teration of the left heart border may be the only evidence of collapse (Felson, 1973).

The absence of the proximal part of the left pulmonary artery where it lies in the upper lobe is another example of the silhouette sign and we believe the sudden appearance of the vessels to the lower lobe, apparently disconnected from the heart, as they enter the aerated lung (Fig. 5) is as important a sign as obli teration of the cardiac border.

The Luftsichel can be present while the silhouette of the 8ortic knuckle is obscured and the sharp margins ~J? the Luftsichel are seen above the aortic knuckle superiomediaUy; laterally the margin extends to just below the aortic knuckle. We have been able to consult only one paper which describes the Luftsichel (Burgel and Oleck, 1960) which states that Dahm (1942) was the first author to recognise this appearance and at t r ibuted it to the apex of the left lower lobe. Esser (1949) described a right-sided Luftsichel and Burgel and Oleck (1960) by freezing and sectioning a cadaver were able to confirm the radiological interpretat ion in a case of right-sided Luftsichel. Althought they stressed the rarity of the observation, we have found it sufficiently common in left upper lobe collapse for it to be regarded as the typical appearance.

The explanation of this appearance is not widely known and it is frequently at tr ibuted to a mediastinal herniation of the contralateral lung. The weak places of the mediastinum, those regions through which a hernia may occur, have been described in detailed papers (Nitsch, 1910; Barsony and Wald, 1936).

In the upper part of the mediastinum there are two such weak places:

1. Anterior mediastinum bounded anteriorly by sternum and posteriorly by the great vessels.

2. Posterior mediastinum superiorly, above the azygos arch at the T 3 - T 5 level between the vertebral bodies and the oesophagus.

By far the most common site of a hernia is in the anterior mediastinum: in such a situation the herniated lung lies anterior to the aortic arch, not in contact with it. A posterior hernia lies above and

behind the arch, also not in contact with it. Thus in neither case does it render the aortic arch visible on the postero-anterior film. If the hernia should move further from these positions to be adjacent to the aortic arch its borders would be below and lateral and it would be without borders on its medial and upper aspects. Case 7 clearly shows that the lucent area is closed superiorly and medially, and open inferiorly, which is the precise opposite of what would be expected in hernia.

The Luftsichel is a clearly translucent lower lobe. It has been given perfunctory at tent ion at best in the past, and yet i t is a common variant; from the cases we have observed it is encountered more often on the left than the usually described appearances. The more common occurrence on the left we attr ibute to the differing anatomy on the two sides.

Acknowledgements. We are grateful to Dr Alun Morris for providing cases and helpful discussion. Mr G. Gilbert prepared the prints and Mrs W. Georgiades and Miss S. Chamberlain typed the manuscript.

Note. Since this paper was accepted for publication we have seen a paper by Proto and Tocino (1980) which dra~s broadly the same conclusions from the appearance of the Luftsichel as we do.

REFERENCES Barsony, T. & Wald, B. (1936). Das Roentgenbild der oberen-

hinteren schwachen Stellen des Mediastinums. Der pr~/vertebrale retro6sophageale Lungenteil. Roentgen- praxis, 8, 88-95.

Bfirgel, E. & Oleck, H. G. (1960). Llber die rechtsseitige paramediastinale Luftsichel bei Oberlappenschrumpfung. Fortschritte auf dem Gebiete der R6ntgenstrahlen, 93, 160-163.

Dahm, M. (1942). Quoted by Biirgel & Oleck (1960). Fortschritte auf dem Gebiete der R6ntgenstrahlen, 66, 220.

Esser, C. (1949) Quoted by Btirgel & Oleck (1960). Fort- schritte auf dem Gebiete tier Rdntgenstrahlen, 71, 18.

Felson, B. (1973). Chest Roentgenology, W. B. Saunders Co., Philadelphia.

Felson, B. & Felson, H. (1950). Localisation of intra- thoracic lesions by means of the PA roentgenogram: the silhouette sign. Radiology, 55,326.

Foote, G. A. & Meredith, H. C. (1979). The silhouette sign and the inferior vena cava. Radiology, 133,583-585.

Hodson, C. J. (1965). The localisation of pulmonary collapse - consolidation. Journal o f the Faculty o f Radiologists, 8, 41-49.

Lubert, M. & Krause, G. R. (196J). Patterns of lobar collapse as observed radiographically. Radiology, 36,165-182.

Nitsch, G. (1910). Die 'Schwachen Stellen' des Mediastinums und ihre klinische Bedeutung bei pleuritischen Exsudat und Pneumothorax. Beitrage zur Klinik tier Tuberkulose, 18, 1-20.

Proto, A. V. & Tocino, I. (1980). Radiographic mani- festations of lobar collapse. Seminars in Roentgenology, 15, 117-173.

Robbins, L. L. & Hale, C. H. (1945). The roentgen appear- ance of lobar and segmental collapse of the lung. VI. Collapse of the upper lobes. Radiology, 45,347-355.