British Journal of Radiology 74 (2001),657-661 © 2001 The British Institute of Radiology
Intralobar bronchopulmonary sequestration: evidence of air trapping shown by dynamic xenon-133 SPECT
K Suga, MD,
A Hara, MD,
T Matsumoto, MD and
N Matsunaga, MD
Department of Radiology, Yamaguchi University School of Medicine, 1-1-1 Minamikogushi, Ube, Yamaguchi 755-8505, Japan
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Abstract
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Dynamic single photon emission computed tomography with xenon-133 gas in a 29-year-old male patient showed xenon-133 retention within an intralobar bronchopulmonary sequestration (BPS) with a focal hyperlucent lung area on CT. Left lower lobectomy showed no fistulous connection between the anomalous and normal bronchial trees, but non-contiguous, incompletely developed visceral pleura between the sequestration and the adjacent normally ventilated lung. These features strongly support the role of intralobar collateral air drift and air trapping in producing secondary changes of a focal hyperlucent lung area in BPS.
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Introduction
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Intralobar bronchopulmonary sequestration (BPS) is defined as a segment of lung parenchyma separated from the tracheobronchial tree contained within an otherwise normal lung and with an anomalous systemic blood supply [1–5]. Emphysematous changes are frequently seen within the sequestrated lung [3, 6–8] and are considered to result from air trapping via collateral pathways from the adjacent lung [9]. Although this hypothesis has recently been supported by lung density analysis with dynamic CT [3], no direct and confident evidence of this ventilatory abnormality has been provided. We describe the findings of dynamic single photon emission computed tomography (SPECT) with xenon-133 (133Xe) gas in a patient with an intralobar BPS confirmed surgically and pathologically, which provided strong evidence of the role of intralobar collateral air drift and air trapping in producing secondary changes of regional emphysema in this anomaly.
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Case report
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A 29-year-old male non-smoker with occasional oppressive sensations in the chest exhibited multiple opacities in the retrocardiac region on a chest radiograph. A continuous cardiac murmur was audible over the left lower thorax. Routine laboratory examinations and spirography were normal, but arterial gas analysis showed slight hyperoxaemia (PaO2 105.0–109.3 mmHg) in room air. Conventional CT (5 mm collimation at 5 mm intervals) showed a 3 cm long blind pouch of the left posterior basal segmental bronchus with no direct bronchial communication to the left main bronchus, the proximal portion of which was directed peripherally to the medial basal portion of the left lower lung. A focal low attenuation area in the lung parenchyma surrounding the dilated, anomalous bronchus was visible on high resolution CT (3 mm collimation at 3 mm intervals, high spatial frequency reconstruction algorithm) (Figure 1
). There was a lack of normal branches of pulmonary bronchi and arteries to the lateral and posterior basal segment inferior lobes, although the remainder of the bronchi and pulmonary arteries of the left lower lobe were normally branched. Dynamic contrast enhanced CT showed two large, anomalous arteries arising from the descending thoracic aorta and several abnormal veins draining to the azygos vein near the dilated, anomalous bronchus. The peripheral branches of the aberrant arteries were especially abundant in the peripheral portions of the left lower lobe. Radionuclide angiography after intravenous bolus injection of 20 mCi of 99Tcm-diethylenetriaminepentaacetic acid–human serum albumin showed no activity in the posterior medial basilar portion of the left lower lobe during the pulmonary arterial phase but activity during the systemic phase.
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Figure 1. High resolution CT images showing an anomalous left posterior basal segmental bronchus (white arrow) and large, anomalous arteries arising from the descending thoracic aorta ( ). Focal low attenuation areas surround the anomalous bronchus (arrows) and there are increased vascular markings especially in the peripheral portion of the left lower lobe (arrowheads).
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Methods
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Dynamic 133Xe SPECT was performed using a continuous repetitive rotating acquisition mode with a triple detector SPECT system (GCA 9300 A/HG; Toshiba Medical, Tokyo, Japan) [10, 11]. After 5–6 min inhalation of 133Xe gas (concentration 60–72 MBq l-1), an equilibrium image and 10–12 subsequent washout images were acquired with an acquisition time of 30 s, with 64 x 64 pixels and an energy window of 80 keV±20%. Each detector was continuously and repeatedly rotated in clockwise (for 15 s) and counterclockwise (for 15 s) directions across the same projection arc. With the use of three detectors, a gantry rotation of 120° around the chest provided projections over a full 360° arc. Averaged projection data at the same angle (per 6°) in both directional rotations were used for reconstructing a single SPECT image. The change of 133Xe activity in the lungs during the 30 s acquisition time was therefore averaged. The SPECT data were reconstructed into equilibrium and washout images in transaxial planes using a Butterworth pre-filter (order No. 8, cut-off frequency 0.13 cycles cm-1) and ramp backprojection filter, with a slice thickness of 1 pixel (3.2 mm), gapless. On the selected transaxial SPECT slice matched with CT slices, 133Xe clearance curves (corrected for the background) were obtained by the mean counts of 1 pixel for each region of interest placed over each lung region, and the real half-time (T1/2), defined as the 133Xe clearance time required to reach the 50% level of the equilibrium count rate during washout, was calculated [10, 11].
133Xe gas was normally distributed throughout the left lower lobe, except for a lack of activity corresponding to the dilated anomalous bronchus and vessels in the equilibrium phase (Figure 2), but significant 133Xe retention was seen in the posterior basal segment inferior lobe with T1/2 ranging from 82–87 s (normal 48.4±4.3 s in seven healthy non-smokers [10]), and also in the peripheral regions of the left lower lobe with increased vascular marking for the peripheral aberrant arteries, with T1/2 ranging from 71–74 s (Figure 3). 133Xe clearance was normal, with T1/2 ranging from 43–51 s in the symmetrical portions of the contralateral lung. Perfusion SPECT with 99Tcm-macroaggregated albumin (MAA), which was performed after the 133Xe study in the same position, showed perfusion defect in the lateral and posterior basal segment inferior lobes (Figure 4). Angiography showed that the lateral and posterior basal segment inferior lobes were supplied by two aberrant arteries bifurcating from the descending thoracic aorta, while the apical segment and anterior basal segment inferior lobes were supplied by the pulmonary artery (Figure 5). Perfusion of the left lower lobe partly drained from the pulmonary vein into the left atrium and partly from the azygos vein. Consequently, a diagnosis of intralobar BPS was obtained, and left lower lobectomy was carried out. At surgery, the two aberrant arteries arising from the descending thoracic aorta were seen, and the pleural surface of the left lower lobe showed enlargement of the capillary network. The resected specimen did not show any fistulous communication or evidence of infection within the sequestrated lung, nor emphysematous changes in the sequestrated lung and the remaining lung parenchyma. There was non-contiguous, incompletely developed visceral pleura between the intralobally sequestrated lung of the posterior basal segment inferior lobe and the adjacent lung parenchyma.
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Figure 2. The equilibrium phase of xenon-133 at the same lower lung level as in Figure 1 shows that xenon-133 gas is normally distributed throughout the left lower lobe, except for the lack of activity corresponding to the large, anomalous vessels.
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Figure 3. The series of xenon-133 washout phase SPECT images shows significant xenon-133 retention in the lung surrounding the anomalous bronchus and in the peripheral lung of the remaining left lobe, with increased vascular marking (arrows). EQ, equilibrium; WO, washout.
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Figure 4. The perfusion SPECT image shows normal pulmonary arterial perfusion only in the left anterior basal segment inferior lobe at this lung level. S5=inferior lingular segment; S8=anterior basal segment inferior lobe.
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Figure 5. Angiography of the anomalous arteries and pulmonary artery. (a) The arterial phase of selective angiography of the anomalous arteries (arrow) shows that the lateral and posterior basal segment inferior lobes are supplied by the aberrant arteries bifurcating from the descending thoracic aorta. (b) The venous phase shows that the perfusion of the left lower lobe is partly drained from the pulmonary vein into the left atrium and partly from the azygos vein (arrows). (c) Pulmonary angiogram shows that the apical and anterior basal segment inferior lobes are supplied by the pulmonary artery (arrows). A6, apical inferior lobe artery, A8, anterior basal segmental artery.
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Discussion
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In this case of intralobar BPS, dynamic 133Xe SPECT clearly showed an influx of 133Xe gas into the sequestrated lung despite the absence of direct bronchial communication with the normal bronchial tree, as well as significant 133Xe retention in the sequestrated lung with focal hyperlucency on CT. Although the sequestrated lung had its own visceral pleura, it did not completely separate the sequestrated lung from the adjacent lung. These features strongly indicate the role of intralobar collateral air drift and air trapping in producing secondary hyperlucent change in intralobar BPS.
Intralobar BPS accounts for approximately 75% of all sequestrations, the majority of cases occurring in the left lower lobe [12–14]. The arterial supply (73%) is usually from the descending thoracic aorta. Although venous drainage is to the left atrium via the pulmonary veins in 95% of cases [14], it is rarely to either the left atrium or systemic circulation with a left-to-left shunt, resulting in slight hyperoxaemia, as in this patient.
Cases with a peripheral type anomalous bronchus, as in this patient, are considered true BPS, which can be explained by the accessory lung bud theory [5, 15, 16]. This case also unusually had a partial pleural envelope in the sequestrated lung, which, to our knowledge, has not been previously described in intralobar BPS.
Although intralobar BPS might develop a fistulous connection to the normal bronchial tree [2], no such communication or any infection within the sequestration was found in our case. The influx of 133Xe gas into the sequestrated lung is therefore explained by collateral ventilation from contiguous normally ventilated segments through the pores of Kohn [3, 9]. Hyperlucent parenchyma, or emphysematous and bullous changes within intralobar BPS without connection to normal bronchial trees, have occasionally been seen on chest radiographs or CT [3, 6]. Air may not easily leave the sequestrated lung and may be trapped there, contributing to 133Xe retention. Air trapping in intralobar BPS has been observed during mechanical ventilation of a patient undergoing resection of a sequestration [17]. Prolonged collateral ventilation and air trapping, together with associated poor local defence mechanisms and secondary inflammation, may result in tissue breakdown and emphysema [3]. Air trapping via collateral pathways from the adjacent lung, however, is not specific for BPS and occurs in lung distal to bronchial obstruction by bronchial atresia or bronchial tumours and in the lung surrounding intralobar bronchial cysts or mucoceles [9, 10, 15–20].
In cases of intralobar BPS with 133Xe influx into the sequestrated lung via collateral airways, a 133Xe ventilation study may not easily diagnose the presence or absence of the fistulous connection between the anomalous and normal bronchial trees. However, this technique is effective for diagnosing the absence of bronchial communication in cases of extralobar BPS, which is completely separated and enclosed in its own pleural investment. The absence of collateral ventilation may be related to the lower incidence of pulmonary infection in extralobar BPS [2, 4, 8].
In our case, 133Xe retention was also seen in the lung adjacent to the sequestration despite the normal bronchial connection. Since the retention was predominantly seen along the dilated peripheral branches of the aberrant arteries, it might be partly due to compression of small airways by these vessels. Air trapping may induce emphysematous change in the adjacent lung as well as in the sequestrated lung. Hyperlucency in the lung adjacent to intralobar BPS has been occasionally noted on CT [3].
Ventilatory abnormalities in the sequestration and adjacent lung area in intralobar BPS have recently been suggested by CT density analysis on ultrafast electron beam CT in a patient with pathologically proven emphysematous change [3]. However, regional lung density measured by CT reflects not only aeration change but also coincident haemodynamic change [11]. Dynamic 133Xe SPECT is more accurate and sensitive for detecting regional ventilatory abnormalities associated with airway obstruction/air trapping and permits estimation of regional 133Xe clearance [10, 11]. This cross-sectional imaging is also easily comparable with CT. Therefore, this technique is still indispensable to establish ventilatory abnormality in BPS.
The combined use of radionuclide angiography and 99Tcm-MAA perfusion scan is therefore useful for non-invasively investigating anomalous vascularization in BPS [21–25]. Perfusion SPECT is also useful for accurately demarcating the lung area with a systemic arterial supply from that with a pulmonary arterial supply in BPS. These radionuclide procedures together with 133Xe SPECT provide valuable information regarding vascular supply and airway communication in BPS.
Received for publication September 28, 2000.
Revision received February 13, 2001.
Accepted for publication April 4, 2001.
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References
|
|---|
-
Pryce DM. Lower accessory pulmonary artery with intralobar sequestration of lung. J Pathol Bact 1946;58:457–67.
-
Felker RE, Tonkin ILD. Imaging of pulmonary sequestration. AJR 1990;154:241–9.[Free Full Text]
-
Stern E, Webb WR, Warnock ML, Salmon CJ. Bronchopulmonary sequestration: dynamic, ultrafast, high-resolution CT evidence of air trapping. AJR 1991;157:947–9.[Free Full Text]
-
O'Mara CS, Baker RP, Jeyasingham K. Pulmonary sequestration. Surg Gynecol Obstet 1978;147:609–16.[Medline]
-
Felson B. Pulmonary sequestration revisited. Med Radiogr Photogr 1988;64:1–28.
-
Ikezoe J, Murayama S, Goodwin JD, Done SL, Verschakelen JA. Bronchopulmonary sequestration: CT assessment. Radiology 1990;176:375–9.[Abstract/Free Full Text]
-
Paul D, Mueller C. Case report: Pulmonary sequestration. J Comput Assist Tomogr 1982;6:163–5.[Medline]
-
Hang JD, Guo QY, Chen CX, Chen LY. Imaging approach to the diagnosis of pulmonary sequestration. Acta Radiol 1996;37:883–8.[Medline]
-
Culiner M, Wall C. Collateral ventilation in intralobar pulmonary sequestration. Dis Chest 1965;47:118–22.
-
Suga K, Nishigauchi K, Kume N, Koike S, Takano K, Tokuda O, et al. Dynamic pulmonary SPECT of xenon-133 gas washout. J Nucl Med 1996;37:807–14.[Abstract/Free Full Text]
-
Suga K, Nishigauchi K, Kume N, Takano K, Koike S, Shimizu K, et al. Pulmonary dynamic densitometry acquired by spiral CT to detect ventilation abnormalities in obstructive airway disorders: comparison with dynamic Xe-133 SPECT. Radiology 1997;202:855–62.[Abstract/Free Full Text]
-
Savic B, Birtel FJ, Tholen W, Funke HD, Knoche R. Lung sequestration: report of seven cases and review of 540 published cases. Thorax 1979;34:96–101.[Abstract/Free Full Text]
-
Sade RM, Clouse M, Ellis FH Jr. The spectrum of pulmonary sequestration. Ann Thorac Surg 1974;18:644–58.[Medline]
-
Frick HP, Harnack GA, Martini GA, editors. Pulmonary sequestration. Advances in internal medicine and pediatrics (1st edn). Berlin: Springer-Verlag, 1979:58–92.
-
Gerle RD, Jaretskt AJ, Ashley CA, Berne AS. Congenital bronchopulmonary foregut malformation; pulmonary sequestration communicating with the gastrointestinal tract. N Engl J Med 1968;278:1413–5.
-
Nuchtern JG, Harberg FJ. Congenital lung cyst. Semin Pediatr Surg 1994;3:233–43.[Medline]
-
Takahashi M, Ohno M, Mihara K, Matsuura K, Sumiyoshi A. Intralobar pulmonary sequestration. Radiology 1975;114:543–9.[Abstract]
-
Haller JA, Tepas JJ, White JJ, Rickard LR, Robotham JL. The natural history of a case bronchial atresia. J Thorac Cardiovasc Surg 1980;79:868–72.[Abstract]
-
Robotham JL, Menkes HA, Chipps BE, Inners CR, Alderson P, Hutchins GM, et al. A physiologic assessment of segmental bronchial atresia. Am Rev Respir Dis 1980;121:533–40.[Medline]
-
Culiner MM, Grimes OF. Localized emphysema in association with bronchial cysts or mucoceles. J Thor Cardiovasc Surg 1961;41:307–13.
-
Gooneratne N, Conway JJ. Radionuclide angiographic diagnosis of bronchopulmonary sequestration. J Nucl Med 1976;17:1035–7.[Abstract/Free Full Text]
-
Kawakami K, Tada S, Katsuyama N, Mochizuki S. Radionuclide study in pulmonary sequestration. J Nucl Med 1978;19:287–9.[Abstract/Free Full Text]
-
Hilfiker ML, Telepak RJ, Jewell PF, Hartshorne MF. Fourier phase analysis of first-pass data: noninvasive detection of pulmonary sequestration. J Nucl Med 1995;36:244–6.[Abstract/Free Full Text]
-
Prosin MA, Mishkin FS, King Jr ML. Radionuclide diagnosis of pulmonary sequestration. J Nucl Med 1976;15:636–8.[Abstract/Free Full Text]
-
Suga K, Matsunaga N, Nishigauchi K, Yoneshiro S, Shimizu A, Takano K, et al. Radionuclide angiography and ventilation/perfusion studies in two patients with systemic arterial supply to the basal segment of the left lung. Clin Nucl Med 1997;22:526–31.[Medline]
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Abstract
Introduction
