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Original Research |
1 Section of Interventional Ultrasound, Department of Internal Medicine, St.
Anna Hospital, corso Giovecca 203, 44100 Ferrara, Italy.
2 Department of Internal Medicine, St. Anna Hospital, 44100 Ferrara,
Italy.
3 Division of Oncology, City Hospital, 47900 Rimini, Italy.
Received September 27, 2005;
accepted after revision December 7, 2005.
Address correspondence to S. Sartori
(srs{at}unife.it).
Abstract
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SUBJECTS AND METHODS. Transthoracic sonography was performed on 285 patients after transthoracic sonographically guided lung biopsy. Disappearance of the sliding lung and comettail artifacts and appearance of reverberation artifacts were considered evidence of pneumothorax. Upright chest radiography was performed within 30 minutes of transthoracic sonography. If a discrepancy between transthoracic sonographic and chest radiographic findings occurred, CT was performed. When it was diagnosed, pneumothorax was sonographically monitored. After visualization of resolution of pneumothorax, chest radiography was performed to confirm the resolution.
RESULTS. Pneumothorax occurred in eight (2.8%) of the patients. Transthoracic sonography depicted all cases of pneumothorax and excluded pneumothorax in the other cases. Chest radiography did not depict one case of pneumothorax, which was confirmed on CT. Sensitivity, specificity, positive predictive value, negative predictive value, and overall accuracy were all 100% for transthoracic sonography and 87.5%, 100%, 100%, 99.6%, and 99.6%, respectively, for chest radiography. The 95% confidence intervals (CI) of the differences in sensitivity, negative predictive value, and overall accuracy were -10% to 35%, -0.1 to 0.9%, and -0.1 to 0.9%. Transthoracic sonographic visualization of resolution of pneumothorax was always confirmed with chest radiography.
CONCLUSION. These preliminary results suggest that transthoracic sonography is as effective as chest radiography in the detection of pneumothorax after transthoracic sonographically guided lung biopsy and may become the method of choice for excluding, diagnosing, and monitoring pneumothorax after transthoracic sonographically guided biopsy. Chest radiography may be needed only for assessment of the extent of pulmonary collapse after transthoracic sonographic diagnosis of pneumothorax or in the presence of discrepancy between transthoracic sonographic findings and clinical presentation.
Keywords: biopsy • interventional radiology • lung • sonography
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Study Design
Transthoracic sonographically guided biopsy was performed with an 18-gauge
Menghini-modified (SureCut, Hospital Service) or semiautomated Tru-Cut needle
(Precisa, Hospital Service). If the lung lesion disappeared during the
procedure, systematic sonographic examination of the entire lung was performed
immediately after biopsy to assess the presence of pneumothorax, and upright
expiratory posteroanterior chest radiographs were obtained within 30 minutes.
When necessary, an additional lateral chest radiograph was obtained. If the
lesion did not disappear after biopsy, transthoracic sonography and chest
radiography were repeated in 3 hours. All sonographic examinations were
performed by the same experienced physician well trained in chest sonography.
A real-time sonographic system with a 5-MHz convex transducer (SSA-370A,
Toshiba Medical Systems) was used. If necessary, a 7.5-MHz linear probe also
was used. When pneumothorax was suspected, M-mode images were obtained to
document the presence of frozen echoes. All patients were examined in the
supine and prone positions. When considered appropriate, the seated position
also was used. Transthoracic sonography was performed as a systematic
examination of the ventral and dorsal intercostal spaces, starting from the
biopsy site. The following parameters were assessed to diagnose or exclude
postbiopsy pneumothorax.
The boundary between visceral pleura and lung surface is visualized with transthoracic sonography as an echoic line, the so-called pleural line. Respiration-dependent up-and-down movement of the pleural line with respect to the parietal pleura and chest wall is called lung sliding or the gliding sign and can only be seen under real-time conditions (Fig. 1). Presence of lung sliding excludes pneumothorax.
Comet-tail artifacts become visible when a marked difference in acoustic impedance exists between an object and its surroundings. These artifacts are evoked only at the boundary between the visceral pleura and the aerated lung [9, 10]. It follows that the presence of comet-tail artifacts excludes the diagnosis of pneumothorax. Comet-tail artifacts are best visualized under real-time conditions, but they can be seen on frozen sonograms. These artifacts are sporadic in healthy lung (Fig. 1) and more numerous in diffuse parenchymal disease (Fig. 2).
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When pneumothorax is diagnosed on the basis of the absence of the gliding sign and comet-tail artifacts and the presence of reverberation artifacts, the lung point, defined as the border between aerated lung and pneumothorax, is assessed (Fig. 4).
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If pneumothorax was detected, whether or not it necessitated chest tube drainage, the lung was examined daily with transthoracic sonography. After sonographic visualization of resolution of pneumothorax, upright posteroanterior and lateral chest radiographs were obtained to confirm the resolution.
Statistical Analysis
Estimates of sensitivity, specificity, positive predictive value, negative
predictive value, and overall accuracy of transthoracic sonography and chest
radiography were calculated. A statistical software program (SPSS 10, SPSS)
was used to calculate 95% confidence intervals (CI) based on binomial
distribution for sensitivity and specificity of transthoracic sonography and
chest radiography and, if present, for the differences observed between
transthoracic sonography and chest radiography.
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In all patients with pneumothorax, transthoracic sonography showed absence of lung sliding and comet-tail artifacts and presence of horizontal reverberation artifacts. The lung point was identified in seven patients, whereas it was not identified in the patient who needed chest tube insertion.
The sensitivity, specificity, positive predictive value, negative predictive value, and overall accuracy of transthoracic sonography were 100%. Chest radiography had a sensitivity of 87.5%, specificity of 100%, positive predictive value of 100%, negative predictive value of 99.6%, and overall accuracy of 99.6%. The 95% CIs for sensitivity and specificity of transthoracic sonography were 63-100% and 89.5-100%, respectively; those of chest radiography were 47.3-99.6% and 89.5-100%. The 95% CIs of the differences in sensitivity, negative predictive value, and overall accuracy between transthoracic sonography and chest radiography were -10 to 35%, -0.1 to 0.9%, and -0.1 to 0.9%.
Transthoracic sonographic monitoring of postbiopsy pneumothorax correctly showed resolution of pneumothorax in all cases, depicting reappearance of lung sliding and comet-tail artifacts and disappearance of horizontal reverberation artifacts and frozen echoes. There was 100% concordance with chest radiographic findings
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Sonograms of the lung are exclusively composed of artifacts, but the artifacts generated by healthy lung can differ from those of several pulmonary pathologic conditions [2-5, 9]. Results of some studies [6, 8] have suggested that transthoracic sonography may be useful in the detection of pneumothorax. In particular, disappearance of lung sliding and comet-tail artifacts and detection of horizontal reverberation artifacts have been shown to be reliable signs of pneumothorax. More recent prospective studies [10, 14] confirmed these findings, and we have documented them in 100% of cases of pneumothorax in our study group.
Transthoracic sonography has been reported to have a high negative predictive value in detection of pneumothorax. The positive predictive value may be slightly lower, because a number of coexisting situations can hamper sonographic examination and cause false-positive findings [14]. In particular, bullous emphysema, pachypleuritis with pleural adhesions, and phrenic paralysis may impair lung excursion and prevent visualization of lung sliding, simulating the presence of pneumothorax [10, 14, 23, 24]. In our study, patients were enrolled after prebiopsy sonographic assessment of lung sliding and comettail artifacts, and no false-positive findings were observed after transthoracic sonographically guided pulmonary biopsy. Consequently, to exclude the presence of coexisting conditions that could hamper the diagnostic accuracy of transthoracic sonography, we recommend that preliminary assessment of these signs be performed immediately before patients undergo transthoracic sonographically guided interventional procedures. In this limited number of cases (in our experience, 1%), chest radiography should be preferred to transthoracic sonography.
Transthoracic sonography is considered a promising technique for detection and exclusion of pneumothorax in critically ill and trauma patients [11-14, 25]. Conversely, there are only limited and conflicting data available on the use of transthoracic sonography in the diagnosis of postinterventional pneumothorax. In an early case study, transthoracic sonography depicted two cases of pneumothorax after transthoracic sonographically guided biopsy of peripheral lung lesions [15]. In a subsequent study, however, transthoracic sonography did not depict five of 13 cases of postinterventional pneumothorax [16]. In that study, however, sonographic examination was restricted to the area around the needle entry site, and that methodologic limitation is likely to have hampered the diagnostic accuracy of transthoracic sonography. When transthoracic sonographic examination was extended to the entire anterior chest wall, the sensitivity and specificity of transthoracic sonography were 80% and 94% in an evaluation of pneumothorax after fluoroscopically guided lung biopsy [23]. Reissig and Kroegel [10] studied the accuracy of transthoracic sonography in detection of pneumothorax in 53 patients undergoing transbronchial biopsy or chest tube placement. Conducting systematic sonographic examination of the anterior and posterior intercostal spaces on the side of biopsy or tube thoracostomy, those authors found 100% sensitivity and 100% specificity of transthoracic sonography in the diagnosis or exclusion of postinterventional pneumothorax. Our study design was similar to that of Reissig and Kroegel, and our findings confirm their results but with a substantially larger number of patients. Moreover, our results suggest that transthoracic sonography can be helpful in documenting resolution of pneumothorax, replacing chest radiographic monitoring and avoiding patient exposure to ionizing radiation.
Despite its sensitivity in detection of pneumothorax, transthoracic sonography is not considered a reliable tool for estimating the volume of pneumothorax [14, 26]. Although the size of pneumothorax can be roughly approximated by assessment of the lung point, the depth of pulmonary collapse cannot be evaluated. Chest radiography is necessary to determine the extent of pneumothorax when the lung point is identified far from the biopsy site [10]. For this reason, we did not attempt sonographic estimation of the size of postbiopsy pneumothorax. An interesting finding, however, was that we identified the lung point in all cases of pneumothorax except the one necessitating chest tube drainage. Although anecdotal, this observation also has been reported by other authors [23] and suggests that unsuccessful detection of the lung point may be a sign of deep pulmonary collapse and be an indication for mandatory prompt performance of chest radiography. Further confirmation with a larger number of patients is needed to substantiate such a hypothesis.
Our study had two limitations. First, CT was performed only when discrepancies were found between transthoracic sonographic and chest radiographic findings. Consequently, it is possible, although unlikely, that small, asymptomatic cases of pneumothorax were not detected with both transthoracic sonography and chest radiography and that the diagnostic accuracy of transthoracic sonography was overestimated but without consequence for the patients' clinical conditions. The second limitation was caused by the low prevalence of pneumothorax after transthoracic sonographically guided pulmonary biopsy [18, 20-22]. In our series the prevalence was 2.8%. It follows that despite the large number of patients enrolled, the low number of cases of pneumothorax detected may make the estimate of sensitivity questionable and decrease the ability to generalize the data. This limitation makes evaluation of sensitivity in larger series of cases of pneumothorax mandatory before any definitive conclusion can be drawn.
Despite the limitations, according to several reports [10-14, 23, 25], our results suggest that transthoracic sonography, performed by trained physicians, is an accurate tool for exclusion of the presence of pneumothorax. It is a safe and noninvasive bedside method, is at least as accurate as chest radiography, and does not expose patients to ionizing radiation. Moreover, the technique has been reported to have good interobserver reproducibility when the operators are skilled [23].
If further prospective studies confirm our findings, transthoracic sonography should be considered the method of choice in clinical practice for excluding, diagnosing, and monitoring pneumothorax after transthoracic sonographically guided interventional procedures. Chest radiography may be needed only for assessment of the extent of pulmonary collapse after pneumothorax has been diagnosed with transthoracic sonography and the lung point has been identified far from the biopsy site or in the presence of a discrepancy between transthoracic sonographic findings and the patient's clinical condition.
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