Morphological basis of radiological shadows chest radiographs'Band shadows' were identified in the excised lungs and these were correlated with in vivo radio-graphs and with the morphological

J. clin. Path., 1976, 29, 610-620

Morphological basis of radiological band shadows on

chest radiographsAMANDA HERBERT, GERARD SLAVIN, LOUIS KREEL, BRENDA SANDIN,AND CHRISTINE BATEMAN

From the Departments of Histopathology and Radiology, Northwick Park Hospital and Clinical ResearchCentre, Harrow, Middx.

SYNOPSIS Lungs of unselected cadavers were fixed at necropsy using a formalin vapour technique.'Band shadows' were identified in the excised lungs and these were correlated with in vivo radio-graphs and with the morphological changes in the lung. Persistent shadows were produced bypulmonary infarction, subsegmental atelectasis, and septal fibrosis singly and in combination.Potentially transient shadows were seen in association with atelectasis and pulmonary oedema.

Band shadows are linear intrapulmonary shadowsseen on chest radiographs that may be up to severalmillimetres in width and 30-70 mm in length. Theymay be transient, such as the horizontal linearshadows often seen above the diaphragm in post-operative and postpartum chest radiographs whichare not seen in subsequent films, or they may persiston sequential chest radiographs over a long period.

It is possible to infer the origin of certain bandshadows during life, for example by the demonstra-tion of an obstructive bronchial lesion proximal tothe band shadow caused by an atelectatic segment oflung, or by observing the evolution of a solid infarctshadow into a thin band on sequential chest radio-graphs in a patient with arteriographic evidence ofpulmonary embolism. However, much of the radio-logical evidence for the origin of band shadows hasbeen circumstantial and not based on anatomicalstudy.

There are, moreover, difficulties in the retro-spective diagnosis of band shadows by the examina-tion of lungs at necropsy: the pathologist is usuallynot informed of changes in the chest radiographs,and examination of uninflated lungs may be inade-quate to demonstrate foci of atelectasis or smallscars. Examination of lungs distended with liquidformalin may demonstrate macroscopic lesions, butsmall lesions can be overlooked or not examinedhistologically unless the pathologist is aware of theirradiological significance. Transient band shadowsoccur as incidental non-fatal episodes and present afurther problem: only close co-operation of radio-

Received for publication 26 November 1975

logist and pathologist, with postmortem radio-graphic examination of lungs, ensures that suchtransient lesions are recognized and examined.A direct comparison of radiological and patho-

logical findings was carried out by Fleischner et al(1941). Their heroic method demanded the sus-pension of the body by a rope and pulley system.Postmortem chest radiographs of the suspendedcadaver were then taken and the lungs were examinedpathologically after instillation of formalin. Theyshowed that infarct scars could produce linearshadows and they also verified the concept of 'plateatelectasis' underlying transient horizontal linearshadows above the diaphragm. The development ofa method of routine radiography of inflated, excisedlungs permits correlations more easily (Wright et al,1974). In this paper we report the pathologicalfeatures of lungs bearing radiological band shadowsinvestigated by this technique.

Material and methods

The lungs of unselected cadavers were examined atnecropsy. Lungs were removed complete with mainbronchi and were inflated by formalin vapour usingintermittent positive pressure ventilation (Wrightet al, 1974). Anteroposterior and lateral radiographswere taken of the fixed lungs. The lungs were thensliced to a thickness of 10-15 mm and further radio-graphs were taken of the slices. Histological blockswere selected by the pathologist in association withthe radiologist after inspection of the lungs and bothin vivo and necropsy radiographs. The exact loca-tions of the blocks were marked on the lung slice

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Morphologictl basis of radiological band shadows on chest radiographs

radiographs. Multiple sections were cut through theblocks as required and direct correlations were madebetween histological sections, postmortem radio-graphs, and chest radiographs taken duringlife. Bandshows identified only on the necropsy radiographswere also directly correlated with the histology. Inthis way some potentially reversible lesions presentat the time of death were examined.

Results

The pathological lesions underlying 10 band shadowsin nine patients are described in detail below andsummarized in the table. In six cases persistent bandshadows were followed from in vivo films to necropsyradiographs. Four were caused by long-standinglesions and two by acute, potentially reversiblelesions. In four cases band shadows present onnecropsy radiographs were not identified on previousin-vivo chest radiographs: two were caused byacute potentially reversible lesions and two by long-standing lesions.

GROUP 1 BAND SHADOWS ASSOCIATED WITH

PULMONARY INFARCTION

Case IE.P., a 79-year-old woman, a diabetic of 30 years'duration, was admitted for amputation of a gangre-nous toe. On admission the chest radiograph showedan oblique band shadow 70 x 20 mm above theright hemidiaphragm (fig 1) which persisted fourweeks later when a further left basal band shadowappeared after a presumed pulmonary embolism.She was treated with anticoagulants but collapsedand died 16 days later.At necropsy there was a recent myocardial infarct

and thrombosis of the left circumflex coronary

artery. There was thrombosis of multiple veins in themuscles of the right calf. The combined weight ofthe unfixed lungs was 995 g.Radiographs of the vapour-fixed lungs showed an

oblique band shadow in the posterior lower lobeof the right lung corresponding to the persistentshadow in the in vivo chest radiograph. There were

smaller band shadows lying anteriorly in thelingula, and below this there was a wedge of con-solidated lung.The lesions underlying the right basal band

shadow, seen on the whole inflated lung as con-tracted subpleural scarring (fig 2), consisted of twoadjoining brown scars. Posteriorly, a rectangularscar extended from the lateral pleural surface, whichwas smooth and indented, and anteriorly there wasscarring at the costodiaphragmatic angle with deepindrawing of the pleura (fig 3). The histology of bothlesions showed fibrotic scars associated with throm-

Fig I Case 1. Oblique linear band shadow is seen atright base in in vivo chest radiograph.

Group Band Shadows Case No. Aetiological Factor

I Associated with pulmonary infarction I Organized infarction; atelectasis2 Recent infarction; bronchiolitis; atelectasis3 Organized infarction4 Organized infarction; atelectasis

It Associated with atelectasis 5 (a) Atelectasis(b) Bronchiolitis; atelectasis

6 Bronchiolitis; atelectasisIII Associated with interstitial septal oedema and/or fibrosis 7 Septal oedema (D-line)

8 Septal fibrosisIV Associated with multiple factors 9 Atelectasis; infarction; secondary carcinoma

Table Aetiologicalfactors in band shadows

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612 Amanda Herbert, Gerard Slavin, Louis Kreel, Brenda Sandin, and Christine Bateman

bosed and recanalized pulmonary arteries (fig 4).The alveolar architecture was lost and the residualelastic fibres showed the 'tangled hair' pattern typicalof old infarcts (Castleman, 1940). Adjacent to theanterior scar a wedge of simple atelectasis exaggera-ted the deep indrawing of the pleura at the uppermargin of the scar (fig 3).On slicing the left upper lobe, linear scars were

not seen. There was a solid fibrotic lesion in thelingula with an irregular though not indrawn pleuralsurface. Microscopy of this area showed an organizedpneumonia. The alveolar architecture was main-taimed with intra-alveolar fibrosis. No evidence ofinfarction or atelectasis was seen. Linear scars werenot seen on the radiographs of the sliced lungs andthe linear shadowing seen in life was not explained.In addition to the fibrotic scarring both lungs showedsevere intra-alveolar oedema and there were freshemboli in segmental branches of the pulmonaryarteries.Case 2M.J., a 75-year-old woman, was admitted with acutemyocardial infarction. Five days later she developedan arrhythmia and died.Necropsy confirmed an anterior myocardial

infarct with thrombosis of the anterior descendingFig 2 Case 1. Inflated right lung showing scarring with coronary artery. The combined weight of the unfixedindrawing ofpleura in the lower lobe. lungs was 750 g.

Fig 3 Case 1. Infarctscar at the costo-

0fi.>ta* * 4 diaphragmatic angle.7te|,..-g°S't't. Z ........with linear atelectasis.r.<,,w . f - ~~which accentuates

pleural retraction.Haematoxylin and

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Fig 4 Case 1. Thrombosed artery showing recanalizationElastic van Gieson x 195.

Fig 5 Case 2. Radiograph of lung slice shows a bandshadow (arrow) in the posterior basal segment of lung.

Fig 5

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Amanda Herbert, Gerard Slavin, Louis Kreel, Brenda Sandin, and Christine Bateman

Radiographs of the inflated lung showed a smallband shadow in the posterior basal segment measur-ing 32 x 2 mm. The band shadow ran verticallyand was associated with pleural retraction (fig 5).The appearances were consistent with a healed basalpulmonary infarct. This small band shadow was notseen on review of in vivo chest radiographs.On slicing the lung there was a small contracted

haemorrhagic lesion at the costodiaphragmaticangle of the right posterior base of the lower lobe.Sections showed an acute pulmonary infarct under-going organization. There was also acute purulentbronchiolitis. The infarction involved the costo-diaphragmatic angle and also a thin subpleural stripof the lateral costal cortex which showed markedatelectasis. It was this subpleural extension of theinfarct which produced the linear shadow seen onthe radiograph. The degree of parenchymal collapseseen in this lesion was unusual for an acute pul-monary infarct and may have been due to theassociated bronchiolitis.

Case 3H.C., a 92-year-old man, with an untreated carci-noma of bladder, developed terminal acute pyelone-phritis and bronchopneumonia.At necropsy the combined weight of the unfixed

lungs was 1055 g.Radiographs of the inflated lungs showed a short

line shadow 21 x 2 mm, with ill-defined marginsand retraction of the adjacent pleural surface, onthe anterior aspect of the middle lobe. Bilateral basalpulmonary oedema and scattered bronchopneumonicshadowing were also present, and several 1 cmmetastases were seen in the left lower lobe.On slicing the lungs there was basal oedema and

bronchopneumonia with scattered fresh emboli insegmental pulmonary arteries. There was a smallfibrotic scar in the anterior middle lobe correspond-ing to the band shadow. Histological sectionsshowed scarring and fibrosis with the fragmentedelastica of an old infarct, and surrounding compen-satory emphysema.

Case 4H.A., a 68-year-old man, died with widespreadmetastases from carcinoma of the bladder.At necropsy the lungs weighed 770 g.Radiographs of the excised inflated lungs showed

multiple interstitial oedema lines, but there was alsoa vertical-oblique band shadow lying postero-medially at the base of the right lower lobe, measu-ring 83 x 3 mm. There was retraction of thepleural surface of the lung. Multiple subpleuralmetastases were also visible. The band shadow wasnot visible on the in vivo chest radiographs.

On slicing the lungs there were multiple sub-pleural and parenchymal metastases. The lesionproducing the band shadow was a contracted scarextending between opposing pleural surfaces poster-iorly at the base of the right lower lobe with indraw-ing of the pleura. Histological sections showed asmall organized infarct with recanalized arterieslying beneath the indrawn pleura. Extending fromthe scar to the opposite pleura was a band ofsimple atelectasis.

GROUP 2 BAND SHADOWS ASSOCIATEDWITH ATELECTASIS ALONECase 5S.G., an 82-year-old man, whose chest radiographshad previously been normal, was admitted for atransurethral resection for prostatic carcinoma.Chest radiography showed a short thick bandshadow measuring 28 x 2 mm across the leftcostophrenic angle. He was readmitted three monthslater with bronchopneumonia and died five dayslater.At necropsy there was cerebral atrophy, old

cerebral infarction, and prostatic adenocarcinoma.The combined weight of the unfixed lungs was880 g.Radiographs of the inflated lungs showed a short

band shadow 22 x 1 mm in the anterior part ofthe inferior segment of the lingula, which also hada vertical component forming an inverted T (fig 6).On the lateral view there was marked pleuralretraction which indented the pleura for 32 mm andwas 21 mm wide at the pleural surface. There wasalso a short oblique band shadow at the right base(28 x 1-5 mm).On slicing both lungs focal emphysema, acute

bronchiolitis, and pulmonary oedema were found.The left lung showed atelectasis in the inferiorsegment of the lingula over which the pleuralsurface was smooth and deeply indented althoughthe distal tip of the lingula was expanded normally(fig 7). Vertical blocks were taken of the inferiorlingula to include the entire lesion as well as proxi-mal and distal lung (fig 8). The lung parenchymashowed simple atelectasis with moderate elasticthickening of the alveolar walls (fig 9). The bronchiand pulmonary arteries proximal and distal to thelesion were quite normal. There was no fresh orrecanalized thrombus: no cause for the atelectasiswas found.The right lung showed a firm, linear lesion at the

lateral costodiaphragmatic angle of the lower lobe.Microscopy showed a zone of atelectasis with focalpleural and septal fibrosis. A proximal bronchiolewas plugged with pus, suggesting that the atelectasiswas of recent origin due to bronchiolar obstruction.

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Fig 6 Case 5. Radiograph of the inflated, unsliced lungwith a band shadow forming an inverted T in the lingula.

Case 6J.D., a 59-year-old man, had a carcinoma of therectum treated by abdominoperineal resection. Twoyears later he developed metastases in the liver,brain and lung. He deteriorated rapidly and diedwithin two months. Chest radiography showed a

short horizontal band shadow in the left midzone(31 x 2 mm) towards the periphery (fig 10).At necropsy widespread metastatic adenocarci-

noma was confirmed. The combined weight of theunfixed lungs was 1315 g.

Radiographs of inflated lungs showed bilateralbasal pulmonary oedema which rose above thelesser fissure on the right side. Multiple 'B' and 'D'lines of interstitial pulmonary oedema were also

noted as well as multiple nodular metastases. Ashort horizontal band shadow was present at theperiphery of the left mid-zone on the posterior sliceof the left lung.When sliced, the lungs showed extensive cavita-

ting metastases. In the posterolateral cortex of theleft lower lobe there was a firm linear lesion with adeeply indrawn pleural margin (fig 11). Histologyshowed a wedge of acute atelectasis associated withbronchiolitis and bronchopneumonia. There was nofibrosis or scarring and no evidence of infarction orpulmonary embolism.

GROUP 3 BAND SHADOWS ASSOCIATEDWITH OEDEMA OR FIBROSIS OF THEINTRALOBAR CONNECTIVE TISSUENumerous cases were seen in which interstitialoedema was sufficiently severe to produce broadband shadows not conforming to Kerley's A, B, orC lines. These are illustrated by one case.

Case 7E.H., a 25-year-old woman, had had chronicmyeloid leukaemia for two years. One year beforedeath she had a splenectomy and in the last monthof life developed a 'blast' crisis with terminalpseudomonas septicaemia and shock. Numerous'band shadows' were seen in the right midzone andbase (fig 12).At necropsy there was very little remaining haemo-

poietic tissue. Pseudomonas species was culturedfrom the brain and cerebrospinal fluid. The com-bined weight of the unfixed lungs was 1500 g.Radiographs of the formalin-inflated lungs clearly

Fig 7 Case S.Inferior segmentof lingula witha depressed scarand markedindrawing of thepleura

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7 9 10Fig 8 Case 5. Sections taken at the levels marked in fig 7, showing atelectasis: the bronchovascular bundlesupplying the afrcted lung is normal. EVG x 2.

demonstrated numerous Kerley B lines, but inaddition the thick band-like shadows were alsoidentified (fig 13).

Matching histological sections showed that theselatter lines were due to broad markedly oedematous

septa running from the pleural surface and branch-ing to form an irregular network between veins andbronchovascular bundles (fig 14). Some of the septacontained distended lymphatics. There was focal, butextensive, intra-alveolar oedema.

SASaA Fig 9 Case 5. Detailof section 9infig 8,showing longstanding

pPr>e ' atelectasis withmaintained alveolararchitecture and nofibrosis. EVG x 30.

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Fig 10. Case 6. Horizontal band shadow in the leftmid-zone.

Fibrosis of connective tissue septa was seen incase 8.

Case 8

F.B., a 65-year-old man, was treated with inter-mittent chemotherapy for nine months before hedied from multiple myeloma. One month beforedeath he developed increasing back pain, necessita-

ting radiotherapy. He developed bilateral basalbronchopneumonia and died in acute renal failure.The chest radiographs during his terminal illnessshowed a short, thick horizontal band shadowacross the left costophrenic angle which appearedas a long, thin band, 85 x 2 mm, in the posteriorsegment of the left lower lobe on the lateral view.Necropsy confirmed multiple myeloma with

'myeloma kidney'. There was a dense localizedpleural thickening of the diaphragmatic pleura whichbound the lung to the diaphragm.

Frontal radiographs of the inflated lungs showeda short horizontal band at the periphery of the leftbase merging with markedly thickened basal pleura.In the lateral film it appeared as a long linear shadowjust above markedly indented pleura below whichthere was a dense area of thickening.The lung slices showed a fibrotic septum running

obliquely from grossly thickened pleura for 25 mminto the lung. Histology showed that the fibroticseptum and pleura both consisted of mature collagenwith no cellular infiltrate (fig 15). There was noinfarction or atelectasis. The adjacent lung paren-chyma appeared normal.

GROUP 4 BAND SHADOW PRODUCED BY A

COMPLEX COMPOSITE LESIONCase 9L.D., a 56-year-old woman, had a 30-year historyof asthma. She underwent an anterior resection forcarcinoma of the rectum in 1965 and a mastectomyfor carcinoma of the breast in 1966. In April 1973,

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after a hysterectomy, she began to develop increas-ingly severe dyspnoea associated with a malignantpleural effusion. She died after three months ofprogressive dyspnoea. Chest radiographs during herterminal illness showed a horizontal band shadowin the lingula associated with a left-sided pleuraleffusion.At necropsy no local recurrence of breast or rectal

carcinoma was found but there was extensiveperitoneal and subpleural tumour. The histologyshowed a carcinoma consistent with a breast origin.The combined weight of the lungs was 835 g.

Radiographs of the inflated lungs showed a bandshadow in the lingula, curving upwards towards the

Xjww9 pleura, associated with pleural retraction. At theperiphery of the anterior aspect of the lingula therewas a small area of consolidation. Small peripheraland subpleural metastases were present.When the lungs were sliced there were scattered

e multiple subpleural metastases. In the lingula thereFig 12 Case 7. In vivo chest radiograph shows was a firm band-like lesion associated with deepmid-zone and basal band shadows. indrawing between opposing pleural surfaces. Distal

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Fig 13 Case 7. Radiograph of lung slice showing broad band shadows.

Fig 14 Case 7. Histological section corresponding to fig 13 showing oedematous septa. H and E x 1.8.

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619Morphological basis of radiological band shadows on chest radiographs

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to this the tip of the lingula was partially collapsedand consolidated.

Sections of the band-like lesion showed that itconsisted of atelectatic lung between the pleuralsurfaces which were indrawn, fibrotic, and infiltratedwith carcinoma. The collapsed parenchyma showedthickened alveolar walls and very marked alveolarwall and vascular elastosis. The tip of the lingulawas partially collapsed. There was further pleuraltumour, but in addition there were small fibrotic focicontaining recanalized vessels, suggesting old infarc-tion. In many of the sections there were fresh pul-monary emboli and also small bronchi plugged withmucus.

Discussion

PERSISTENT BAND SHADOWSThese studies demonstrate that infarct scars may

produce persistent band shadows, as shown origin-ally by Fleischner et al (1941). Infarct scars arecontracted because the original lesion causes destruc-tion of lung parenchyma and there is reparativefibrosis which may also produce indrawing of thepleural surface. They are thus more likely to pro-

duce linear or band shadows than the scarring ofold pneumonia in which the alveolar architectureis maintained and organized intra-alveolar exudateleads to a solid scar without loss of tissue or distor-tion of the pleural profile.

In the cases described in this paper atelectasisplays an important role in the production of persist-

Fig 15 Case 8.A fibroticintralobarseptum runsobliquely fromthe denselyfibroticdiaphragmaticpleura. H andE x 3.7.

ent band shadows either alone or in concert withother factors. It may be prominently associated withinfarction (Fleischner et al, 1941; Fleischner, 1962).In case 1 atelectasis proximal to the infarct wasresponsible for the deep pleural indrawing noticedin the radiographs. Moreover, in cases 4 and 9 themain part of the band shadow itself was caused byatelectasis rather than the infarct scar itself. It isalso possible for chronic atelectasis unassociatedwith infarction, scarring or pulmonary embolism toproduce a persistent band shadow. In such cases thechronicity and irreversibility of the atelectasis maybe indicated by thickening of the alveolar walls inthe collapsed parenchyma (Spencer, 1968).

Intralobar septal fibrosis may also cause persistentband shadows resembling infarct scars on radio-logical examination. The origin of such fibrosis maybe postinflammatory.These observations stress that though pulmonary

infarcts may cause longstanding linear shadows,atelectasis and intralobar fibrosis are also importantcauses, and that frequently more than one lesion ispresent.

TRANSIENT BAND SHADOWSThe genesis of transient shadows is more difficult toelucidate because their natural history is resolution.However, study of postmortem radiographs showsmany band shadows present at death which areproduced by potentially reversible lesions. Byinference these could have been identified as tran-sient shadows on in vivo films if radiographs had



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been taken at the appropriate time. The commonestfinding was that acute interstitial pulmonary oedemamay produce such shadows. In the early stages ofoedema, fluid may collect in the intersegnental andinterlobular connective tissue septa and theremaybesmooth indentation of the pleural margins. Otherevidence of pulmonary oedema may be lacking, andunless it is realized that interstitial oedema canproduce band shadows, even in the absence ofclassical Kerley lines, they may be diagnosed radio-logically as infarcts or atelectasis. The appearanceof line shadows caused by interstitial oedema hasbeen described in detail in a previous paper (Kreelet al, 1975).

It has been suggested (Fleischner et al, 1941) thattransient horizontal linear shadows above thediaphragm are caused by acute focal atelectasisresulting from a variety of pathological processesinvolving depressed respiration and bronchial mucusretention. Recent studies stress the association ofacute focal atelectasis with the metabolic effects ofacute pulmonary embolism. In experimental pul-monary embolism there is a shift of ventilation fromunperfused to perfused lung (Robin, 1965). In hisdiscussion of the underlying mechanisms he suggeststhat loss of surfactant in unperfused lung may bethe basis of focal atelectasis in human pulmonaryembolism: an increase in pulmonary surface tension,preceding atelectasis, occurs after experimental pul-monary artery occlusion (Finley et al, 1964). Pul-monary embolism causes bronchoconstriction(Gurewich et al, 1965) and alveolar duct constriction(Nadel, 1965) due in part to humoral factors and inpart to local C02 alterations (Severinghaus et al,1961).We did not find foci of atelectasis associated with

acute pulmonary embolism in the absence of infarc-tion but cannot exclude the possibility that such focicould be re-expanded by the positive pressurerespiration which our technique involves, particu-larly if the atelectasis were caused by broncho-constriction rather than bronchial obstruction. Inthe observed cases where acute atelectasis producedpotentially reversible band shadows the cause wasmechanical obstruction of airways due to purulentbronchiolitis.The production of band shadows on chest radio-

graphs depends on the visualization of linear areas

contrasting with the radiolucent background ofairfilled lungs. This may be caused by subsegmentalcollapse and atelectasis, infarct scars, septal fibrosis,and oedema lines. However, the band produced byany mechanism may be manifest or exaggerated bypleural retraction so that the indrawn distortedpleural profile appears within the parenchyma whenviewed in the appropriate plane. The mechanism ofchanges seen in chest radiographs is frequentlyinferential and based on sequential in vivo films.There are relatively few direct correlative studiesbetween pathologists and radiologists. Simon (1971)has doubted the role of atelectasis and stressedvascular obstruction as the major aetiological factorin band shadows. This study indicates that atelectasisplays a significant role even in those cases where theprecipitating cause is a pulmonary vascular lesionand it may be the major or only lesion noted.

References

Castleman, B. (1940). Healed pulmonary infarcts. Arch.Path., 30, 130-142.

Finley, T. N., Tooley, W. H., Swenson, E. W., Gardner,R. E., and Clements, J. A. (1964). Pulmonary surfacetension in experimental atelectasis. Amer. Rev. resp. Dis.,89, 372-378.

Fleischner, F. G. (1962). Pulmonary embolism. Clin. Radiol.,13, 169-182.

Fleischner, F. G., Hampton, A. 0. and Castleman, B. (1941).Linear shadows in the lung. Amer. J. Roentgenol., 46,610-618.

Gurewich, V., Sasahara, A. A. and Stein, M. (1965). InPulmonary Embolic Disease, edited by A. A. Sasahara andM. Stein, pp. 162-169. Grune and Stratton, New York.

Kreel, L., Slavin, G., Herbert, A., and Sandin, B. (1975).Intralobar septal oedema: 'D' lines. Clin. Radiol., 26,209-221.

Nadel, J. A. (1965). In Pulmonary Embolic Disease, editedby A. A. Sasahara and M. Stein, pp. 153-161. Grune andStratton, New York.

Robin, E. D. (1965). In Pulmnonary E,nbolic Disease, editedby A. A. Sasahara and M. Stein, pp. 149-152. Grune andStratton, New York.

Severinghaus, J. W., Swenson, E. W., Finley, T. N., Lategola,M. T., and Williams, J. (1961). Unilateral hypoventilationproduced in dogs by occluding one pulmonary artery.J. appl. Physiol., 16, 53-60.

Simon, G. (1971). Principles of Chest X-ray Diagnosis, 3rdedition. Butterworths, London.

Spencer, H. (1968). Pathology of the Lung, 2nd edition.Pergamon Press, London.

Wright, B. M., Slavin, G., Kreel, L., Callan, K., and Sandin,B. (1974). Postmortem inflation and fixation of humanlungs. Thorax, 39, 189-194.

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Morphological basis of radiological shadows chest radiographs'Band shadows' were identified in the excised lungs and these were correlated with in vivo radio-graphs and with the morphological