Archives of Disease in Childhood, 1982, 57, 696-701

Investigating the small lung: which imagingprocedure?I GORDON AND P HELMS

Department ofPaediatric Radiology and Respiratory Unit, Hospital for Sick Children, London

SUMMARY Ventilationandperfusion radionuclide lung scans, using krypton 8im and technetium-99mmacroaggregates, were performed together with a variety of other imaging proceduresin 18 children aged between 1 week and 13 years in whom radiology had shown a small lung.Radionuclide scans provided an assessment of regional ventilation and perfusion unobtainable byother means, and 4 main categories of disturbed function could be seen in the radiological smalllung-namely, absence of ventilation and perfusion, absent perfusion with preserved ventilation,generalised or segmental decreases in ventilation, and perfusion and segmental perfusion defects inareas of decreased ventilation. The clinical history and other imaging procedures, includingfluoroscopy and penetrated mediastinal views, enabled a firm diagnosis to be made in each of these18 patients. In 3 main pulmonary arteries were absent, 2 had lung aplasia, 2 had lobar aplasia, 9had varying degrees of pulmonary hypoplasia (two with additional sequestrated segments), 1 hadlobar emphysema, and 1 had post-infective lung mal-development (MacLeod's syndrome).

The child with a radiological small lung poses twomain questions for the clinician. Is this finding a

manifestation of a congenital abnormality, or has itbeen acquired? Is there any treatment which could bebeneficial and allow for a better functional result as

lung growth and development progress? The range

of possible imaging procedures is wide, none iswithout risk, and the risks relating to radiationdosage must be considered. The aim is to avoid overinvestigating the child but at the same timemaintain a high degree of confidence in explainingthe radiological appearances. The purpose of thisstudy was to assess the role of 81m krypton (Kr)ventilation (V) and technetium-99m (99mTc) micro-sphere perfusion (0) lung scans in suchcircumstances. There is little discomfort for thechild, a lower radiation dose is used than inother second-line imaging procedures, and theinvestigation can be performed without co-operationfrom the patient, so making it suitable for youngchildren.' -2

Patients and methods

Eighteen children aged between 1 week and 13 years

with unilateral lung disease of unknown aetiologyhad Kr, V, and 99mTc 0 lung scans as part of a

variety of other imaging procedures which includedfluoroscopy, bronchography, and angiography

(Table). The results of the V/(2 scans and otherimaging investigations were discussed at regularclinico-radiological meetings with the cliniciansresponsible for the children's management, at whichtime decisions about further investigation andmanagement were also made. Fluoroscopy wascarried out in the supine position with a variable kVusing an image intensifier.

Results

The disturbances found on V/( scanning could beplaced in 4 categories-namely complete absenceof ventilation and perfusion in one lung, complete

I absence of perfusion with preserved ventilation inone lung, decreases both of ventilation and perfusionin one lung either generalised or segmental innature, and segmental perfusion defects in hypo-

I ventilated lungs. In each case a diagnosis could bemade from the clinical history together with theimaging results. Cases 1, 2, and 3 were shown tohave absent main pulmonary arteries, Cases 4 and 5had total lung aplasia, Cases 6 and 7 had lobaraplasia, Cases 8-16 had varying degrees ofpulmonary hypoplasia (two with additionalsequestrated segments), Case 17 had lobaremphysema, and Case 18 had predominantlyunilateral post-infective lung mal-development(MacLeod's syndrome)3 (Table).

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Table Details ofpatientsCase Age Admission diagnosis Fluoroscopy Barium Pulmonary Other Final diagnosis

(years) swallow angiogram

1 0.3 Parenchymal lung disease + + Absent pulmonary artery2 6.2 Collapse left lower lobe + + + Absent pulmonary artery3 5.0 Asthma + + + Absent pulmonary artery4 0.1 Pleural effusion + Lung aplasia5 0.1 Pneumonia + + Lung aplasia6 12.6 Hypoplastic lung + + Bronchography Lobar aplasia7 0.1 Incidental finding + + Lobar aplasia8 0-3 Pneumonia + Lung hypoplasia9 2.3 Incidental finding + + Lung hypoplasia10 0.7 Pneumonia + Lung hypoplasia1 1 0.7 Recurrent infection + Lung hypoplasia12 0-3 Lobar emphysema + + Lung hypoplasia13 0.2 Diaphragmatic hernia + + + Ultrasound Lung hypoplasia14 0.2 Unexplained tachycardia/ + + + Lung hypoplasia

tachypnoea15 0.2 Coarctation of aorta + + + Coarctation, lung hypoplasia,

sequestrated segment16 0.1 Diaphragmatic hernia + + Ultrasound+ Lung hypoplasia,

liver scan sequestrated segment17 0-4 Lobar emphysema + Lobar emphysema18 4-0 Recurrent infection + + MacLeod's syndrome

+ Examination carried out.

Complete absence of V/Q in one lung. Three childrenwere found to have a non-functioning lung on V/(scanning. Chest radiographs in 2 of them showedopaque hemithoraces with mediastinal shift to theaffected side strongly suggesting a diagnosis ofpulmonary aplasia. This diagnosis was establishedwhen penetrated mediastinal radiographs showedabsent main stem bronchi on the affected side. Theremaining child had an aerated small lung on chestradiography, and fluoroscopy showed paradoxicalmovement of a raised hemidiaphragm. A mainbronchus was also seen and a diagnosis of severepulmonary hypoplasia was made (Fig. 1).

Complete absence of Q in a ventilated lung. Threechildren showed decreased V on the side of the smalllung with total absence of (.2 The chest radiographsshowed small lungs with mediastinal displacement tothe affected side. This pattern was caused by acongenital absence of the pulmonary artery and wasconfirmed at pulmonary angiography in each case(Fig. 2).Decreased V/Q in one lung. In 13 childrenpronounced decreases in both V and 0 wereobserved in one lung. The chest radiographs showedsmall hemithoraces containing aerated lung withmediastinal displacement to the affected side (Fig.3). These abnormalities were present in 9 of the 13children. V/02 scans showed loss of the normalanatomical landmarks on the oblique projectionswhich suggested a diagnosis of pulmonary hypo-plasia. One child was found to have air trapping onthe affected side during fluoroscopy with patchyareas of poor V and 0 in the opposite lung. Thesefindings, together with a history of severe lower

respiratory tract infection in early childhood,suggested the diagnosis of unilateral post-infectivelung mal-development (MacLeod's syndrome).3

..

Fig. 1 Chest radiograph shows mediastinal displacementto the right with a raised right hemidiaphragm. Aeratedright lung is noted in the small hemithorax. Radionuclidescan demonstrates homogeneous V/Q in the left lungwith virtually no activity in the right.

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Fig. 2 Chest radiograph shows asmall left hemithorax containinga small hypertransradiant leftlung. The V' scan shows decreasedoverall ventilation of the left lungwhile the Q scan shows absence ofperfusion; the right lung appears tobe normally ventilated andperfused. The pulmonaryangiogram showed an absent leftpulmonary artery.

Fig. 3 Chest radiograph shows a small right lung with mediastinal displacement to the right; the hemidiaphragmsappear to be normal. The V scan shows a well ventilated left lung with overall poor ventilation of the right. The Qscan shows a poorly perfused right lung with a segmental defect at the base medially (arrow). Aortogram showssystemic supply to the non-perfused area at the right base (arrow) confirming the diagnosis of a sequestrated segmentin the hypoplastic right lung. There is an increased incidence of sequestrated segments in hypoplastic lungs.

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In 2 of the 3 remaining children the decreasedV/(2 was noted to be mainly in the region of theupper lobe suggesting aplasia of a single lobe. Oneof these children had severe exercise limitation withmarked expiratory airflow obstruction not reversiblewith bronchodilators. Because of this finding andthe limited abnormality demonstrated on V/(scanning, bronchoscopy and bronchography wereperformed. These studies demonstrated a fixedstenosis of the lower trachea, complete absence of aright upper lobe bronchus, and a long segmenttracheomalacia in the left main bronchus (Fig. 4).The remaining child had a segmental V/(2 defect inthe region of the lingula. Fluoroscopy revealed afixed hyperinflated area in the left lung with airtrapping, the chest radiograph showed mediastinaldisplacement to the right; lobar emphysema wasdiagnosed and confirmed at thoracotomy.

Segmental Q defect in a hypoventilated lung. A single

segmental ( defect was noted in 2 of the 9 childrenwith a small hypoventilated lung, raising theadditional differential diagnosis of pulmonaryemboli or sequestration in the affected lungs.Sequestration on the affected lung was confirmed inboth cases, one at surgery, the other on aorto-graphy (Fig. 3).

Discussion

In all these children the V/0 scans provided valuableinformation on the site and extent of theabnormalities of ventilation and perfusion in thelungs, and in 2 children with pulmonary hypoplasiathe scans led to the additional diagnosis of sequestra-tion. The importance of taking a clinical history andany relevant functional information into account wasdemonstrated in the child (Case 6) who was shownto have a more complex pattern of lung diseasethan had immediately been apparent (Fig. 4).

Fig. 4 (Case 6.) Chest radiograph shows abnormalities of the posterior aspect of the right 5th and 6th ribs with themediastinum shifted to the right; a small right lung can also be seen. The V scan shows a well ventilated left lung anda poorly ventilated right. The Q scan is similar in appearance to the V scan. Bronchogram demonstrates an absent rightupper lobe bronchus confirming the diagnosis of a congenital absence of the right upper lobe. The narrowing of thelower end of the trachea can also been seen.

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In children with only one functioning lung thedifferential diagnosis must include collapse/con-solidation, aplasia, or severe hypoplasia. In suchcases penetrated views of the mediastinum in orderto visualise the main stem bronchi, and chestfluoroscopy to assess the ventilatory function wereinvaluable. If no main bronchi or lung movementcould be detected the diagnosis of lung aplasia wasmade. If bronchi could be seen but no aerated lungobserved, a diagnosis of collapse or consolidationwas made. If collapse or consolidation is present, 42in the affected area may be partially preservedalthough V is absent (unpublished observations). Inthe 9 children with unilateral pulmonary hypoplasia,fluoroscopy showed a small aerated segment of lungon the affected side.

In adults, pulmonary emboli or bronchialcarcinoma are the most important causes of pureperfusion abnormalities. In young children however,the absence of perfusion is virtually diagnostic of acongenital absence of the pulmonary artery on theaffected side. This can be divided into 3 groups4:absent left pulmonary artery associated with a Fallottetralogy and increased incidence of right-sidedaortic arch,5 extracardiac anomalies,6 and an isolatedabsent pulmonary artery. Of the last group abouthalf are on the right and half on the left.7 In suchcases the V/4) scan is diagnostic, and cardiaccatheterisation may be carried out to evaluatepulmonary arterial pressure since pulmonary hyper-tension is liable to develop. If the chest radiographshows a large hypertransradiant lung on the side ofthe absent 42 then the possibility of an extrinsic masspressing on the pulmonary artery must also beconsidered.8

If a ventilated non-perfused segment isdemonstrated the differential diagnosis lies betweena single small pulmonary embolus, peripheralpulmonary artery stenosis (as seen in congenitalrubella), or a sequestrated segment. Not allsequestrated segments are in communication withthe bronchial tree as in our 2 cases,9 so the lung scanmay show a matched V/(22 defect. Aortography isnot only diagnostic but also important for thesurgeon to establish the source of the arterialsupply. Sequestration is more common in hypo-plastic lungs, as illustrated.

If the affected lung showed pronounced V/0abnormalities, lack of the normal lobar landmarkson the oblique views, and a normally distributedV/0 in the contralateral lung without radiologicalevidence of acute lobar collapse/consolidation, thediagnosis of pulmonary hypoplasia could be made.This pattern of abnormality has also been found ininfants studied after successful repair of congenitaldiaphragmatic hernia on whom longitudinal studies

of lung function and V/(2 scans are in progress(unpublished observations). It was also possible inone child to demonstrate a congenital absence of alobar segment. In the single child with acquireddisease (MacLeod's syndrome)3 abnormalities werealso noted on the V/4) scan in the apparentlyradiologically normal lung which would perhaps beexpected as a more likely outcome of severepulmonary infection than a complete sparing of onelung. McKenzie et al.10 using a single radionuclide13 N and a 4 zone regional washout technique,together with other imaging techniques, foundMacLeod's syndrome to be a rare cause of unilateralpulmonary hypertransradiancy and argued the casein favour of investigating the child with a radiologicalhyperlucent hemithorax.We deliberately chose a descriptive approach to

our V/(2 scans with multiple views around the chestin order that the abnormalities could be localised atlobar, segmental, or subsegmental level. Thisapproach enables a direct comparison with theanatomical information provided on chest radio-graphy. V/( lung scans can be performed in childrenof any age; the radiation dose is lower than withmost other imaging techniques1 and a high level ofdiagnostic certainty can be achieved without havingto resort to more invasive methods. Most regionalnuclear medical centres have the necessary krypton81 generators. The ability to focus attention on theessential functional abnormalities suggests that V/4lung scans should be more widely applied in childrenand that they should be an early imaging investiga-tion. V/(} scans provide pathophysiological imagesunobtainable by any other method and, if taken inconjunction with the chest radiograph, allow a morecomplete understanding of the underlying disease.This technique also offers the possibility of followingfunctional lung growth in young children in whomestimates of lung function are difficult to obtain.Using these imaging techniques cardiac catheterisa-tion and angiography are not required for diagnosticpurposes but rather to outline the anatomy moreclearly if surgery is indicated.

We thank the physicians and surgeons at TheHospital for Sick Children who referred patients,and S E Coote for secretarial assistance. Krypton81m generators were supplied by the MedicalResearch Council's cyclotron at the HammersmithHospital, London.

P H was supported by the Medical Research Council.

References

Gordon I, Helms P, Fazio F. Clinical applications ofradionuclide lung scanning in infants and children. Br JRadiol 1981; 54: 576-85.

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2 Li D K, Treves S, Heyman S, Kirkpatrick J A, Jr,Lambrecht R M, Ruth T J, Wolf A P. Krypton 81m: abetter radiopharmaceutical for assessment of regionallung function in children. Radiology 1979; 130: 741-7.

3 MacLeod W M. Abnormal transradiancy of one lung.Thorax 1954; 9: 147-53.

4 Rees S. Arterial connections ofthe lung. Clin Radiol 1981;32: 1-15.

5 Emanuel R W, Pattinson J N. Absence of the leftpulmonary artery in Fallot's tetralogy. Br Heart J 1956;18: 289-95.

6 Pool P E, Vogel J H K, Blount S G, Jr. Congenitalunilateral absence of a pulmonary artery. The importanceof flow in pulmonary hypertension. Am J Cardiol 1962;10: 706-32.

7 Shakibi J G, Rastan H, Nazarian I, Paydar M, Aryanpour I,Siassi B. Isolated unilateral absence of the pulmonary

artery. Review of the world literature and guidelines forsurgical repair. Jpn Heart J 1978; 19: 439-51.

8 Alderson P 0, Gilday D L, Wagner H N, Jr. In: Atlas ofpediatric nuclear medicine. St Louis: Mosby, 1978:94-5.

9 Buntain W L, Woolley M M, Mahour G H, Isaacs H, Jr,Payne V, Jr. Pulmonary sequestration in children: atwenty five year experience. Surgery 1977; 81: 413-20.

10 McKenzie S A, Allison D J, Singh M P, Godfrey S.Unilateral hyperlucent lung. The case for investigation.Thorax 1980; 35: 745-50.

Correspondence to Dr I Gordon, Department ofPaediatric Radiology, Hospital for Sick Children,Great Ormond Street, London WCIN 3JH.Received 16 February 1982

British Paediatric Association

Annual meetings1983 12-16 April York University1984 10-14 April York University1985 16-20 April York University1986 15-19 April York University

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