Clinical applications of radionuclide lung scanning in infants and children

Pediatric bronchiectasis: correlation of HRCT, ventilation and perfusion scintigraphy, and pulmonary function testing

Bronchiectasis in children, although occurring with diminished frequency, continues as a major challenge for the pediatric pulmonologist. The method of choice for the diagnosis of the condition is high-resolution computed tomography (HRCT). The aim of the present study was to correlate the relationship(s) of HRCT, lung function, ventilation lung scintigraphy (VLS), and perfusion lung scintigraphy (PLS) in children with bronchiectasis. Sixteen children ranging in age from 4-18 years with clinical and chest X-ray evidence of bronchiectasis were enrolled in the study. The degree of bronchiectasis was assessed by HRCT scores, decrease in attenuation on expiratory scans, VLS, and PLS. HRCT scores for bronchiectasis and decreased lung attenuation showed a strong correlation with PLS (rho = 0.82; P < 0.001) and with VLS (rho = 0.72; P < 0.01). There was a moderate negative correlation between FEV(1) and HRCT bronchiectasis scores (rho = -0.53; P = 0.02), decreased lung attenuation score (rho = -0.64; P = 0.007), and atelectasis score (rho = -0.54; P = 0.03). In conclusion, HRCT provides a complete and precise assessment of children with bronchiectasis. Ventilation/perfusion scans and lung functions are additive tools to understand the complexity of the disease process and to improve diagnosis and therapeutic strategies.

[Magnetic resonance imaging and lung perfusion scintigraphy in tetralogy of Fallot following surgery]

OBJECTIVE

To evaluate pulmonary arteries in patients with tetralogy of Fallot following surgery with quantified lung perfusion scintigraphy and magnetic resonance imaging.

MATERIAL AND METHODS

From January 1985 to December 1999, 47 patients who underwent surgery between 1985 and 1999 were studied. To obtain values of normality, 45 infants with no pulmonary artery disease were assessed with lung perfusion scintigraphy (right lung flow: 54-61%, left lung flow: 38.7-46%) and magnetic resonance imaging axial view (right/left pulmonary artery branch diameter ratio: 1-1.1). Patients with stenosis underwent catheterization.

RESULTS

Group 1: 27 patients with normal parameters. Group 2: nine patients with left pulmonary branch stenosis and irregularities in all parameters; left/right branch diameter ratio 0.51 and left lung perfusion 26.3 +/- 7.9%, r correlation ratio 65%, p < 0.005, left branch pressure gradient 34.4 +/- 17.9 mm Hg, rate-gradient r 89%, p < 0.001. Group 3: five patients with right pulmonary branch stenosis and irregularities in all parameters; right/left branch diameter ratio 0.52, reduced right lung perfusion 32 +/- 11%, with a stenotic branch gradient of 40 +/- 19 mm Hg., rate/gradient ratio r 72%, p < 0.005; gradient/perfusion ratio r 82%, p < 0.003. Group 4: Six patients with bilateral stenosis, reduced diameter in the stenotic area with normal perfusion in both lungs and bilateral gradient. Eighteen patients with stenosis underwent re-operation, with favorable outcome in 14.

CONCLUSION

Magnetic resonance imaging and quantified lung perfusion scintigraphy provide useful information in the follow-up of tetralogy of Fallot.

Ventilation and perfusion scanning in children

Ventilation and perfusion scintigraphy (VQ scans) provide a relatively non-invasive evaluation of lung function. They indicate the relative blood flow to each lung and allow a quantitative assessment of the perfusion of each lung segment. They can detect areas of abnormal aeration and demonstrate air trapping. However, VQ scanning gives relatively poor anatomical detail of the lungs and so is commonly used in conjunction with other radiological modalities, most notably the chest X-ray. VQ scans have been utilized for a large range of pathological conditions including congenital cardiac and lung abnormalities, suspected pulmonary emboli, the assessment of childhood diseases, including cystic fibrosis, bronchopulmonary dysplasia and asthma.

The anatomy of left bronchus syndrome

This explanation of the previously described left bronchus syndrome (Ashour et al., 1990, Thorax, 45:210-212) is based on a prospective study of 17 additional cases with unilateral lung destruction. It is likely that the anatomic peculiarities of the left main bronchus predispose the left lung to more frequent bronchial obstruction and hemodynamic changes than the right. Broncho-pulmonary shunt formation and retrograde filling of the pulmonary artery most likely lead to increased oxygen tension and impaired lymph flow in the entire lung, thus spreading tuberculosis in the lung and ultimately leading to left lung destruction.

Unilateral post-tuberculous lung destruction: the left bronchus syndrome

In a prospective study of 13 patients requiring pneumonectomy for unilateral post-tuberculous lung destruction the left side was found to be affected in 12. Review of a further 172 cases showed the left lung to have been destroyed in 109 (63%). It is suggested that this predominance of the left side is due to the anatomical characteristics of the left main bronchus and that disordered haemodynamics also appear to play a part.

Pulmonary sequelae in survivors of congenital diaphragmatic hernia

Nineteen survivors of congenital diaphragmatic hernia repair were compared with age and sex matched control children six to 11 years after repair. All subjects were examined clinically and underwent lung function testing. The patients also had individual lung volumes assessed radiographically and had radionuclide (krypton-81 m, technetium-99 m macroaggregates) ventilation-perfusion (V/Q) lung scans. Four patients had pectus excavatum and two had mild scoliosis. Spirometric measurements were lower in the patients than in the control subjects but only the differences in peak expiratory flow and flow at 50% of expired vital capacity were significant. The radiographic left lung volumes in patients surviving left diaphragmatic repair were larger than expected at 49.3% (SD 2%), suggesting alveolar overdistension. V/Q scans showed a mismatch in the ipsilateral lung, mean Q (40% (7%] being significantly lower than mean V (47% (6%)). In seven patients who had required ventilation for four days or more perfusion to the ipsilateral lung was significantly lower (34% (6%)) than values for the 12 patients ventilated for less than four days (43% (6%)). Survivors of right diaphragmatic repair had a better outcome in terms of relative radiographic lung volumes and V/Q distribution. More severely affected children are now surviving repair of congenital diaphragmatic herniation, with residual pulmonary abnormalities that could produce functional impairment in adult life.

The contribution of perfusion scintigraphy in the evaluation of children suffering from recurrent localized pneumonia

The value of perfusion scintigraphy as a screening test for children who have suffered from several episodes of recurrent localized pneumonia was evaluated in 32 patients aged 1-15 years. Perfusion studies were carried out using macroaggregated albumin (MAA) labeled with technetium 99m. In 9 patients (28%), large lobar or multisegmental perfusion defects were demonstrated. Their final diagnoses proved to be bronchiectasis (5 patients), bronchomalacia (2 cases), agenesis of a lobe (1 subject), and lobar sequestration (1 patient). In 23 children (72%), the perfusion scintigraphic patterns were normal or diffusely nonhomogeneous. All of these patients improved clinically on a 1- to 2.9-year follow-up. We conclude that a normal perfusion scintigraphy is a useful screening test for excluding structural lung abnormalities in pediatric patients with recurrent localized pneumonia. Children showing a pattern of lobar or multisegmental perfusion defects should be further investigated to rule out structural abnormalities as an underlying cause of disease.

Clinical applications of nuclear medicine

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Unusual ventilation-perfusion patterns in primary lung tuberculosis

We report two cases of primary lung tuberculosis in children with unusual perfusion ventilation scintigraphic patterns. In the first case, a mismatch in the right upper lobe suggests an elective compression of the bronchi by the mediastinal lymph nodes; in the second case, the total absence of ventilation and perfusion of the left lobe at scintigraphy illustrates the discrepancy sometimes encountered between chest x-ray and lung scintigraphy.

Regional ventilation in infancy. Reversal of adult pattern

There is evidence that in infants with unilateral lung disease, oxygenation improves when the good lung is uppermost--the reverse of the situation in adults. We performed krypton-81m ventilation scanning in 18 infants and very young children (11 days to 27 months old) with and without abnormal chest radiographs. Scanning was performed with the subject supine, in the left decubitus posture (right lung uppermost), and in the right decubitus posture (right lung dependent). Fractional ventilation to the right lung fell when that lung was dependent and rose when it was uppermost (P less than 0.001). This pattern was seen regardless of the appearance of the chest radiograph. The distribution of ventilation away from dependent lung regions represents a reversal of the adult pattern, which may be due to differences between infants and adults in lung mechanics and diaphragmatic function. This study adds further weight to the argument that infants and very young children with unilateral lung disease should be positioned with their normal lung uppermost to optimize gas exchange. It also offers a rational explanation for the observation that infants with unilateral gas trapping can be successfully treated by placing them so that the diseased lung is dependent.

The analytical sensitivity of Tc99m radionuclide 'milk' scanning in the detection of gastro-oesophageal reflux

The analytical sensitivity of radionuclide 'milk' scans for detecting gastro-oesophageal reflux (GOR) has been assessed using an in vitro simulation test. Five factors were found to affect the ability to detect simulated reflux: isotope concentration, absolute gamma camera sensitivity, absorber thickness overlying the 'oesophagus' and volume and duration of reflux. We found that a critical volume-duration product must be exceeded for reflux to be detected. Radionuclide milk scanning appears to be much less sensitive in detecting transient events like GOR than might be expected from previously reported static simulation studies.

Quantitative ventilation-perfusion lung scans in infants and children: utility of a submicronic radiolabeled aerosol to assess ventilation

The quantitative assessment of regional pulmonary ventilation and perfusion provides useful information regarding lung function. Its use in infants and young children, however, has been minimal because of practical and technical limitations when the distribution of ventilation is assessed by radioactive gases. In 16 infants and children we used an inexpensive commercially available nebulizer to produce a submicronic aerosol labeled with 99mtechnetium-diethylenetriamine pentacetic acid to assess ventilation quantitatively, and intravenous injections of 99mtechnetium-labeled macroaggregates of albumin to assess pulmonary perfusion quantitatively. Studies were safely completed in both ambulatory and critically ill patients, including two premature infants who had endotracheal tubes in place for ventilatory support. No sedation or patient cooperation is required. This technique enables any department of nuclear medicine to measure regional pulmonary ventilation and perfusion in infants and children.

Bronchiectasis in childhood

Although bronchiectasis is relatively uncommon, it should be considered in a child with any of the following findings that persist: infiltrate on x-ray cough, purulent sputum, crackles or harsh breath sounds on auscultation of the chest, or hemoptysis. It is very likely that a pediatrician will encounter one or more children with this condition. This article deals with the pathogenesis, diagnosis, and treatment of bronchiectasis in childhood.

Postural effects on gas exchange in infants

In adults with unilateral lung disease, pulmonary gas exchange is better when the patients is positioned with the good lung dependent. We studied the effects of body position on gas exchange in 10 infants with unilateral lung disease by measuring transcutaneous oxygen and carbon dioxide pressures in the supine and right and left lateral positions. We also performed krypton lung scans and measured changes in thoracic gas volumes in four of the infants. Transcutaneous oxygen pressure (mean +/- S.E.) was greater with the good lung uppermost (82 +/- 7.6 mm Hg) than with the good lung dependent (73 +/- 7 mm Hg) (P less than 0.02) or in the supine position (78 +/- 7 mm Hg). There were no changes in transcutaneous carbon dioxide pressure. The proportion of ventilation to the good lung was greater with the good lung uppermost than with the good lung dependent (P less than 0.01) or in the supine position (P less than 0.02) (64 +/- 3, 46 +/- 6, and 59 +/- 7 per cent, respectively). There were no significant changes with position in functional residual capacity, tidal volume, or dynamic lung compliance. We conclude that oxygenation in infants with unilateral lung disease is best with the good lung uppermost--the reverse of what has been observed in adults.

Investigating the small lung: which imaging procedure?

Ventilation and perfusion radionuclide lung scans, using krypton 81m and technetium-99m macroaggregates, were performed together with a variety of other imaging procedures in 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 by other means, and 4 main categories of disturbed function could be seen in the radiological small lung--namely, absence of ventilation and perfusion, absent perfusion with preserved ventilation, generalised or segmental decreases in ventilation, and perfusion and segmental perfusion defects in areas of decreased ventilation. The clinical history and other imaging procedures, including fluoroscopy and penetrated mediastinal views, enabled a firm diagnosis to be made in each of these 18 patients. In 3 main pulmonary arteries were absent, 2 had lung aplasia, 2 had lobar aplasia, 9 had varying degrees of pulmonary hypoplasia (two with additional sequestrated segments), 1 had lobar emphysema, and 1 had post-infective lung mal-development (MacLeod's syndrome).