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Communications to the Editor |

CT Scanning and Bilateral Surgery for Unilateral Primary Pneumothorax?CT Scanning and Bilateral Surgery for Unilateral Primary Pneumothorax? FREE TO VIEW

Marc Noppen, MD, PhD, FCCP
Author and Funding Information

Affiliations: Academic Hospital Brussels, Belgium,  Hong Kong SAR, China

Correspondence to: Marc Noppen, MD, PhD, FCCP, Pneumology Service, Academic Hospital AZ-VUB, Laarbeeklan 101, B-1090 Brussels, Belgium; e-mail: marc.noppen@az.vub.ac.be



Chest. 2001;119(4):1293-1294. doi:10.1378/chest.119.4.1293
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To the Editor:

I read with great interest the article (August 2000) by Sihoe and coworkers1on the predictive role of CT scanning on the risk of occurrence of primary spontaneous pneumothorax (PSP). I was particularly amazed in the finding that the detection of lung blebs or bullae by CT scan in the contralateral lung of patients with PSP was significantly correlated with the risk of occurrence of PSP in that lung. Indeed, there is—to my knowledge—no unequivocal evidence that rupture of blebs or bullae is actually the cause of PSP; blebs and bullae may in fact be considered also as “innocent bystanders” of the disease process that will eventually lead to PSP.2 Therefore, I recalculated the statistics given by Sihoe et al1: they found that 4 of 15 patients with contralateral blebs developed PSP in that lung (26.7%), whereas none of the 13 patients who did not have contralateral blebs developed PSP, a difference that was considered statistically significant (p = 0.04,χ 2 analysis). However, when recalculating the data on the basis of the proposed contingency table, I found theχ 2 statistic to be nonsignificant:χ 2 = 2.160 with one degree of freedom (p = 0.142; Table 1)!

Furthermore, in this situation, one should use a correction for the fact that the frequency in at least one cell of the table is < 5, eg, Fisher’s Exact Test. Even then, the p value is still much above significance (p = 0.1002)! This absence of significance may also explain why the authors could not find any correlation between the size/number of blebs score and the subsequent occurrence of PSP. Hence, on the basis of their own data, I cannot support the far-fetched conclusions of the authors, that “CT scanning can be used to predict the risk of occurrence of this condition, allowing preemptive surgical intervention in selected patients.” This is not only in accordance with our personal experience, but also with that of others.3

Table Graphic Jump Location
Table 1. Contingency Table Based on the Data by Sihoe et al1

Table Graphic Jump Location
Table 2. Updated Contingency Table
Sihoe, ADL, Yim, APC, Lee, TW, et al (2000) Can CT scanning be used to select patients with unilateral primary spontaneous pneumothorax for bilateral surgery.Chest118,380-383. [CrossRef] [PubMed]
 
Noppen M, Schramel F. Spontaneous pneumothorax Eur Respir Rev 2001 (in press).
 
Janssen, JP, Schramel, FMNH, Sutedja, TG, et al Videothoracoscopic appearance of first and recurrent pneumothorax.Chest1995;108,330-334. [CrossRef] [PubMed]
 

CT Scanning and Bilateral Surgery for Unilateral Primary Pneumothorax?

To the Editor:

There are three kinds of lies; lies, damned lies and statistics. Benjamin Disraeli (1804–81)

There was indeed a mistake made in the statistical analysis of our data, as pointed out by Dr. Noppen. The computer software we used for the χ2 comparison did not automatically apply Yates’ correction for a small sample size, and this generated a two-sided p value of 0.0443. This mistake, however, prompted us to update our clinical data, since the article was submitted over a year ago. We recently called up each of the 28 patients and had a 100% response. Two additional patients with contralateral bullae were found to have developed pneumothoraces, but still none of the patients without contralateral bullae developed pneumothorax on that side. The contingency table with the updated figures is shown in Table 1.

Using Fisher’s Exact Test on the updated figures, a p value of 0.017 was obtained. We therefore firmly stand by our conclusion that CT scan can be used to predict the occurrence of primary spontaneous pneumothorax (PSP).

Dr. Noppen brought up another point in his letter. He suggested that blebs and bullae may be “innocent bystanders” and are not the cause of pneumothorax. His view therefore challenged the role of bullectomy, the mainstay of surgical treatment for this condition. Our experience using video-assisted thoracoscopic surgery to treat PSP shows that in about 10% of patients, the cause of PSP could be clearly attributed to ruptured bullae.

There are few medical conditions like PSP that are managed by so many medical specialists (accident and emergency physicians, general internists, pulmonologists, pediatricians, general surgeons, and thoracic surgeons) utilizing a whole range of management strategies, ranging from simple observation, needle aspiration, tube drainage, and chemical pleurodesis, to surgery, which includes bullectomy, commonly combined with pleurodesis or partial pleurectomy. Despite the wide range of options, the common therapeutic goals are to reexpand the lung and prevent recurrence. In that respect, surgery has offered by far the most successful therapy for this condition, as measured by the low recurrence rate (≤ 4%), compared to a much higher recurrence rate with chemical pleurodesis, which does not address the bullae (8 to 25%) or tube drainage alone (≥ 40%). Therefore, although the exact pathogenetic mechanism behind this common condition remains largely unknown, the outcomes of various treatment modalities are well documented, and these data should guide the physicians’ choice of therapy for their patients, until new knowledge on its pathogenesis is available.


Figures

Tables

Table Graphic Jump Location
Table 1. Contingency Table Based on the Data by Sihoe et al1
Table Graphic Jump Location
Table 2. Updated Contingency Table

References

Sihoe, ADL, Yim, APC, Lee, TW, et al (2000) Can CT scanning be used to select patients with unilateral primary spontaneous pneumothorax for bilateral surgery.Chest118,380-383. [CrossRef] [PubMed]
 
Noppen M, Schramel F. Spontaneous pneumothorax Eur Respir Rev 2001 (in press).
 
Janssen, JP, Schramel, FMNH, Sutedja, TG, et al Videothoracoscopic appearance of first and recurrent pneumothorax.Chest1995;108,330-334. [CrossRef] [PubMed]
 
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