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Original Research |
1 Institute for Diagnostic and Interventional Radiology, Johann Wolfgang Goethe
University Hospital, Theodor-Stern-Kai 7, Frankfurt am Main, Hessen 60590,
Germany.
2 Department of Diagnostic and Interventional Radiology, Cairo University
Hospital, Cairo, Egypt.
Received June 28, 2008;
accepted after revision December 31, 2008.
N.-E. A. Nour-Eldin and N. N. N. Naguib contributed equally to the research
work.
Abstract
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MATERIALS AND METHODS. This retrospective study covered 124 ablation sessions for lung tumors (10 primary lesions, 114 metastatic lesions) in 82 patients (46 men, 36 women; mean age, 64.0 years) treated between December 2005 and January 2008. The exclusion criteria for ablation therapy were lesions with a maximal diameter greater than 5 cm and the presence of more than five lesions. A bipolar electrode needle was used under CT guidance. Four patients were treated with two ablation electrodes simultaneously.
RESULTS. The incidence of pneumothorax (detected with CT) was 11.3%
(14 of 124 sessions). Pneumothorax was graded mild (lung surface retraction,
2 cm), moderate (lung surface retraction, 2-4 cm), or severe (lung
surface retraction, 
4 cm). Significant risk factors encountered in the
development of pneumothorax were age greater than 60 years (p =
0.046), emphysema (p = 0.02), tumor diameter 1.5 cm (p
= 0.0008), lesions in lower part of lung, (p = 0.027), aerated lung
parenchyma traversed by the needle track for a distance 2.6 cm
(p = 0.0017), and traversal of a major pulmonary fissure (p
= 0.0004). Pneumothorax developed in one of the four patients in whom multiple
electrodes were used. The mean depth of lung lesions complicated by
pneumothorax was 2.9 ± 1.55 cm (range, 0-5.5 cm). Conservative
treatment was performed in four of the 14 pneumothorax sessions (28.6%). In
six of the 14 sessions (42.9%), immediate complete evacuation was achieved
with an intercostal catheter and manual evacuation; chest tube placement was
indicated in four sessions (28.6%). Two patients were treated with manual
evacuation because evidence of a progressive increase in pneumothorax on the
24-hour follow-up CT scan indicated failure of conservative treatment.
CONCLUSION. The development of pneumothorax complicating radiofrequency ablation can be unpredictable, but the many risk factors involved can make the incidence higher among some patients than others. Some of these risk factors are technically avoidable and have to be ruled out.
Keywords: lung neoplasms • pneumothorax • radiofrequency ablation • risk factors
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The patients were advised to stop taking anticoagulant and antiplatelet medications 2 days-1 week before the procedure. Prophylactic antibiotics were not routinely administered. Patients under went CT in the supine position immediately before treatment to confirm the number and size of tumors. The ablation parameters, including type, number and length of applicators, the position of the patient, and the site of puncture, were based on tumor size and anatomic location. The anatomic description of the location of lesions in the lung was divided into three zones: upper third, middle third, and basal third.
Radiofrequency Ablation
All lung radiofrequency ablation procedures were performed with CT
fluoroscopic guidance and 5mm collimation (Somatom 4, Siemens Healthcare).
Radiofrequency ablation was per formed under complete aseptic conditions by
two interventional radiologists with 8 and 15 years of experience in
radiofrequency ablation technique. Combination sedation and analgesia with
fentanyl citrate (1 µg/kg body weight) and midazolam hydrochloride
(0.010-0.035 mg/kg) were administered in a stepwise manner until the patient
was drowsy. Sedation was administered by the same interventional radiologist
for all procedures. Continuous ECG, pulse oximetry, and blood pressure
monitoring was performed throughout the procedure.
Radiofrequency ablation was performed with a bipolar internally cooled applicator (ProSurge, Celon Medical Instruments) (electrode length, 20-40 mm; shaft diameter, 15 gauge [1.8 mm]; shaft length, 100-250 mm) and a system (Power System, Celon Medical Instruments) comprising a power control unit (Laboratory Power, Celon Medical Instruments) and triple peristaltic pump (Aquaflow, Celon Medical Instruments). The length of the needle electrode chosen was based on the distance between the skin surface and the lesion. Each lesion was ablated with one needle applicator, except in four cases in which two applicators were applied simultaneously to ablate the lesion. CT monitoring was used during ablation to observe the procedure, visualize potential complications, and administer prompt treatment when needed. Radiofrequency electrode track coagulation was routinely performed at the end of the procedure to prevent seeding of malignant cells in the needle track during removal of the needle electrode.
Complications, particularly pneumothorax, were assessed with CT during the ablation procedure and immediately after ablation. Regular clinical assessment of vital signs was performed for at least 8 hours before the patient was discharged and continued until the patient could be clinically discharged. Patients with pneumo thorax or pulmonary hemorrhage underwent clinical and CT follow-up 1 or 2 days before discharge.
Study Protocol for Pneumothorax Management
Pneumothorax that developed while the patient was on the CT scan table was
graded mild (lung surface retraction of 2 cm), moderate (measured lung
surface retraction, 2-4 cm), or severe (lung surface retraction, 4 cm)
(Fig. 1).
Mild pneumothorax was a small accumulation of air accumulated in the pleural sac that did not increase with time and was not associated with mediastinal shift, respiratory distress, or circulatory disturbance. It was managed conservatively by close clinical observation of vital signs and monitoring for any manifestations of respiratory distress. CT of the chest was performed 1-6 hours after the development of pneumothorax. Discharge of the patient was permitted if serial chest radio graphs showed no progressive increase of pneumothorax.
Moderate pneumothorax necessitated immediate manual evacuation of air by application of an 8-gauge intercostal chest catheter connected to a triple-way valve system. With successful complete evacuation of air, treatment was the same as that of patients with mild stable pneumothorax. Failure of manual air evacuation or progressive respiratory distress necessitated insertion of an intercostal chest tube and water-seal drainage.
The manifestations of marked pneumothorax were respiratory or circulatory distress and a mediastinal shift or progressive pneumothorax that did not respond to manual evacuation. It was managed by insertion of an intercostal chest tube and water-seal drainage with overnight hospitalization and close monitoring of vital signs. Patient discharge was permitted after complete recovery.
Study Design and Statistical Analysis
Radiologic evaluation of preprocedural, intraprocedural, and postprocedural
images was performed in consensus by two senior radiologists (8 and 15 years'
experience). Clinical symptoms, side effects and complications, and imaging
findings of pneumothorax were recorded. The sampling unit for analysis was
number of sessions (n = 124 sessions). Each factor was compared
between groups by use of univariate analysis. Groups were defined as patients
with or without pneumothorax. The variables evaluated included patient factors
such as age, sex, presence of pulmonary emphysema; tumor factors such as size,
distance between the lesion and the pleural surface, and location (upper,
middle, or lower zone); and ablation and technical factors such as length of
aerated lung traversed by the electrode, use of multiple electrodes, and
crossing a major pulmonary fissure in the ablation track. Depth of the lesion
was defined as the shortest distance between the lesion and the parietal
pleura measured on axial CT scans. This distance was not necessarily the same
as the distance traversed by the needle track because the latter is affected
by the accessibility of the lesion, the angulation needed for application of
the electrode, and the subcostal or subscapular position of the lesion.
Univariate analyses were performed with the Mann-Whitney U test for numeric values and the Fisher's exact test for categoric values. A value of p < 0.05 was considered to indicate a statistically significant difference in all analyses. Risk related to needle gauge was alleviated by use of the same needle gauge in all cases. SPSS statistical software was used (version 8.0, SPSS).
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The mean size of the lesions associated with pneumothorax was 1.91 ± 1.3 cm. The risk of pneumothorax correlated significantly with the size of the lesion; lesions smaller than 1.5 cm in diameter (mean, 1.02 ± 0.4 cm; range, 0.4-1.5 cm; p = 0.0008) were more likely to be associated with pneumothorax than were lesions larger than 1.5 cm (mean, 3.01 ± 0.4 cm; range, 1.6-5 cm; p = 0.055). Ablation of basal and middle lung zone lesions was associated with a 71.4% incidence of pneumothorax (10 sessions), in comparison with upper zonal lesion ablation, which was associated with a 28.6% incidence of pneumothorax (p = 0.027). Lesions complicated by pneumothorax were located a mean distance of 2.9 ± 1.55 cm (range, 0-5.5 cm) from the pleural surface, and this depth had a significant correlation with the incidence of pneumothorax (p = 0.03). The mean distance of lung traversed in the ablation track in sessions complicated by pneumothorax was 2.9 ± 1.55 cm (range, 0-5.5 cm). The occurrence of pneumothorax correlated with an increase in the distance of lung traversed in the ablation track from less than 2.5 cm (mean, 1.7 ± 0.8 cm; p = 0.37) to a more significant greater than 2.5 cm (mean, 4.1 ± 1.07 cm; range, 2.8-5.5 cm; p = 0.0017). Crossing a major pulmonary fissure in the ablation track was associated with pneumothorax, occurring in four sessions (28.6%) (p = 0.0004). One of four cases in which two electrodes were applied was complicated by pneumothorax.
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In 10 patients (71.4%), mild to moderate pneumothorax developed during ablation without interfering with electrode positioning or compromising the patient's clinical condition. Pneumothorax was managed conservatively for four patients and by manual evacuation for six patients without termination of the ablation session. In the cases of two of the four patients who had planned to undergo conservative treatment, evidence of progressive pneumothorax was found on the 24-hour CT scan. These patients were treated by manual evacuation.
For four patients (28.6%), the session was immediately terminated before completion of ablation therapy because marked and progressive pneumothorax compromised the clinical condition of the patient, did not respond to manual evacuation, and interfered with electrode positioning.
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Emphysema is characterized pathologically by permanent enlargement of airspaces distal to the terminal bronchiole with destruction of alveolar walls [20]. Emphysema is usually classified in terms of the part of the acinus predominantly affected: proximal (centriacinar, more commonly termed centrilobular, emphysema), distal (paraseptal emphysema), or whole acinus (panacinar or, less commonly, panlobular emphysema). The CT appearance of emphysema consists of focal areas or regions of low attenuation, usually without visible walls [21]. In the case of panacinar emphysema, decreased attenuation is more diffuse. The effect of emphysema (Fig. 3) as one of the major individual risk factors for pneumothorax during ablation was described by Yamagami et al. [12]. The anatomic distribution of emphysema is the most important effect of the disease process on the risk of development of pneumothorax, especially when emphysematous bullae are traversed in the electrode track.
Small lesion size carries the risk of pneumothorax owing to excessive manipulation of the needle tip during targeting of the lesion. Central positioning of the electrode within the lesion is needed to overcome the high resistance to current flow if the electrode is not centrally located within the lesion. This manipulation results in tearing of lung parenchyma when the lesion is relatively small, and the patient is required to perform a breath-hold for a longer time to allow correct positioning of the needle inside the lesion. This finding has been made by many other authors [12, 17, 22-27]. Basal lesions (Fig. 4A, 4B, and 4C) are subject to the effect of the diaphragm, being more prominent on the basal lung zone than the upper lung zone and leading to a shearing effect of both the pleura and lung parenchyma.
Previous reports [15, 16, 18, 22-24] have shown that the greater is the depth of needle penetration from the pleural surface to the edge of the lesion, the higher is the rate of pneumothorax. Crossing a major pulmonary fissure in the ablation track is another risk factor that can be attributed to the crossing of many pleural surfaces in the track of the electrode (Fig. 4A, 4B, and 4C). One study [25] showed that the number of needle passes and the needle angulation were important to the occurrence of pneumothorax. Another study [26] showed no relation between the number of pleural passes and the rate of pneumothorax. Technical skill of the radiologist is extremely important because manipulations and the duration of the procedure are optimally reduced and, hence, can efficiently reduce the incidence of pneumothorax [27].
The results reported by Hiraki et al. [22], which included 224 ablation sessions in 142 patients, support our results regarding the significant effect of increased length of aerated lung traversed by the electrode and lesion location in the basal position of the lung. Their results and ours differed, however, in that they found sex a significant variable. They also found that a history of pulmonary surgery and ablation of an increased number of lesions per session had an effect on the increased incidence of pneumothorax. We eliminated the latter risk effect from our study because our protocol calls for ablation of one lesion per session.
Patients should be observed carefully after ablation for the development of delayed pneumothorax. After two sessions in this study, pneumothorax increased progressively within 24 hours after ablation, necessitating manual evacuation.
That our analysis did not include all sessions and that repeated sessions were considered independent sessions may be liable to criticism. Repeated sessions cannot be considered independent because multiple measurements in each patient are at least somewhat correlated. However, in only two cases did pneumothorax develop repeatedly at successive ablations. Another limitation of this study was that the analysis of risk factors included a relatively low incidence of pneumothorax (14 of 124 ablation sessions).
We conclude that pneumothorax complicating radiofrequency ablation of lung neoplasms is rather unpredictable but that many risk factors involved can lead to a higher incidence among some patients. We can classify these factors into technically avoidable risk factors and inevitable risk factors. Risk can be avoided by planning needle access for the shortest distance between the pleural surface and the lesion to minimize the distance of lung parenchyma traversed, by avoiding crossing a major pulmonary fissure in the track of the needle, and by avoiding multiple pleural punctures by multiple electrodes. Inevitable risk factors include age; the presence of chronic obstructive pulmonary disease; and the presence of deep, basal, and small lesions. Patients with inevitable risk factors are at high risk of pneumothorax.
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