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Do Blebs Cause Primary Spontaneous Pneumothorax?

2002; Raven Press; Volume: 9; Issue: 4 Linguagem: Inglês

10.1097/00128594-200210000-00013

1536-7959

Marc Noppen,

Trauma Management and Diagnosis

The goals for treatment of symptomatic or large (>20%) primary spontaneous pneumothorax (PSP) are double:removal of air during the first episode and prevention of recurrence during the second or subsequent episodes. 1,2 There is good consensus that thoracoscopy should be the treatment of choice for prevention of recurrence, and that in patients with visible blebs or bullae (referred to hereafter as emphysemalike changes or ELCs), some form of ELC treatment (bleb-/bullectomy) should be performed, as well as some form of intraoperative pleurodesis. 2 It is indeed assumed by many that ruptured ELCs are the cause of PSP, and thus some form of ELC treatment (e.g., stapling, oversewing, laser coagulation) should be performed. 2 Assuming ruptured ELCs are the cause of PSP, this seems an intrinsically logical strategy. I will, however, demonstrate that there is no unequivocal proof for the ruptured ELC hypothesis and thus systematic ELC treatment is not indicated for the prevention of PSP recurrence, even when ELCs are present. (By the way, if one is so convinced that ruptured ELCs cause PSP, why then advocate pleurodesis as well as ELC treatment?) CIRCUMSTANTIAL EVIDENCE FOR THE ELC RUPTURE PARADIGM First, the vast majority of PSP patients have ELCs located most often at the apex of the lung. Incidence ranges from 75 to 100%, depending on the diagnostic technique and thoroughness (computed tomography, video-assisted thorascopic surgery [VATS], thoracotomy). 3–5 Even among nonsmokers with PSP, approximately 80% of PSP patients are reported to have ELCs. 6Therefore, almost every PSP patient has ELCs. Second, thoracoscopic or open limited-access surgical treatment of ELCs by means of stapling, oversewing, or coagulation is successful. Thoracoscopic (VATS) procedures have a long-term recurrence rate of 5 to 10%. 7,8 Open surgical procedures seem perhaps even more effective, 8 although not everybody agrees on this. 9,10 There is some evidence that recurrence after VATS seems to be related to the preoperative failure to detect and ablate ELCs. 11Therefore, if you treat the ELCs, the patient is cured. If you fail to treat the ELCs, PSP will recur. Third, contralateral ELCs are present in the majority of patients presenting with PSP. Incidence ranges from approximately 50%12 to almost 100%. 13,14 Sihoe et al. 12 have reported that the presence of contralateral ELCs is associated with a higher rate of subsequent occurrence of PSP in that lung, which may even allow for preventive contralateral surgery! Therefore, the presence of ELCs predicts the occurrence of PSP. All this seems, at first sight, rather convincing for ELC rupture as the cause of PSP. Every PSP patient has ELCs. If you treat them, the patient is cured; if you fail to treat them, PSP recurs; and if the patient has ELCs, he'll probably get PSP! So, why bother? Just "VATS" every recurrent PSP! Well, for one, VATS or open surgical treatment is expensive, and certainly not free of marked morbidity: between 15 to 31.7% of patients complain of chronic ipsilateral pain after VATS, 15–18 and 41.9 to 51.8% of patients experience chronic pain after open surgery, 16,18 which is far too much for a treatment advocated to be "the best buy" for preventing an almost always benign nuisance in young, otherwise healthy patients. Furthermore, mortality of VATS or open surgery is not nil (1–2%). 19 Finally, and most important from an intellectual point of view, ELC treatment is unnecessary in the vast majority of patients with recurrent PSP because, as I will show, ELC rupture is not the main cause of recurrent PSP! WHAT IS THE EVIDENCE? So, the majority of recurrent PSP patients have ELCs, I agree. But in how many patients in whom VATS or surgery is performed, are the ELCs actually ruptured or leaky? Surprisingly, this has only been addressed rarely. True, ruptured ELCs have been seen in 6 of 166 recurrent PSPs (3.6%) undergoing thoracoscopy, 20 in 7 of 28 thoracotomy-treated PSPs (25%), 21 and in 72 of 95 cases of spontaneous pneumothorax (mixed primary and secondary, first time and recurrent; 73%) patients. 8 These are strange and highly disparate figures. In general, however, it is unusual to find clearly leaking ELCs during thoracoscopy, 22,23 and in a substantial percentage of patients (as much as 25%), 22 no ELCs whatsoever are seen! Furthermore, 20% of smokers who have never had PSP have ELCs on their lungs, 3,24 and there is no predictive relationship between the number and size of ELCs and the occurrence of first 25,26 or recurrent 27 PSP, just as there are no differences in thoracoscopic findings related to ELCs between first-time and recurrent PSP. 28 The latter is not so trivial an observation as some may think: If an ELC rupture really is the cause of PSP, then the number of ELCs present logically should parallel the likelihood of occurrence of PSP—be it the first, second, or more episode. All of this, an objective reader shall admit, is rather unexpected: If one would hold ELC rupture as the cause of (recurrent) PSP, one should indeed expect 1.) ELCs to be present in every case (which is not true), 2.) ELCs to be ruptured in every case (which is not true), 3.) ELCs to be absent in matched subjects without PSP (which is not true), and 4.) ELCs to have some predictive value regarding the occurrence of first or recurrent PSP (which is not true). Clearly, there is something rotten in the state of Blebmark. "If you treat the ELCs, the patients are cured." Is this really so? And if this is so, why on earth would surgeons advocate to add some form of pleurodesis to their highly recommended ELC treatment? Well, there are only four studies in the English literature in which patients have been treated by ELC treatment only, without any form of pleurodesis. (In every other VATS or surgical ELC treatment published, some form of pleurodesis [abrasion, pleurectomy, talc poudrage] has been associated with the procedure.) In the first study, 19 excision of bullae via thoracotomy was performed in 45 patients. There were no recurrences. However, 15 of these 45 patients were selected out of 294 patients with 398 episodes of pneumothorax, 383 of which (96.2%!) were treated initially and successfully conservatively with observation and simple chest drainage. Thirty other patients were operated later—after successful conservative treatment—for unclear reasons. Thus, we are talking about a highly select, small subgroup of patients (15 patients) with persisting pneumothorax despite conservative treatment—that is, the "worst cases." Results therefore cannot be extrapolated to "bullectomy as treatment of every case of recurrent pneumothorax," but instead refer only to "bullectomy in rare cases of persistent pneumothorax," which is a completely different issue. Furthermore, in this group of 45 operated patients, there was one (2.2%) evolution to pneumonectomy for persistent bleeding and one (2.2%) immediate postoperative death. And lastly, Ferguson et al. 19 note that "the involved area of the lung was excised," which suggests more than just "bleb- or bullectomy," as is performed today by stapling (I'll come back to this issue later). In a second paper, wedge resection of ELCs by thoracotomy unaccompanied by pleurodesis/pleurectomy was evaluated in 120 patients. 15 In that study, 5% early and 5% late (total, 10%) failures were observed. Hatz et al., 8 in a third study, compared VATS staple excision of ELCs without pleurodesis in 72 patients with visible ELCs with VATS pleurodesis in only 37 patients without visible ELCs. There was a 4.6% failure rate in the ELC treatment group versus 0% in the pleurodesis group! Lastly, Loubani and Lynch 29 compared bullectomy alone with bullectomy plus chemical pleurodesis, and observed a 20% recurrence rate after bullectomy alone (versus 4% after bullectomy plus pleurodesis)! Although none of these studies fulfill the standards of "prospective, randomized, large-scale comparative" studies, they all point in the same direction: There is no proof—not even a trend—that bullectomy adds a substantial advantage to simple pleurodesis. What can we conclude from all this? First, that bleb-/bullectomy alone has slightly lower to equal success rates as medical thoracoscopic recurrence prevention by talc poudrage (which is the gold standard in the European pulmonological world; approximately 90–95% success). Second, that associated pleurodesis is more efficient in recurrence prevention than bleb-/bullectomy alone. And third, that surgical or VATS bleb-/bullectomy has a higher morbidity and mortality rate of equal efficacy than medical thoracoscopic treatment (and is a lot more expensive). My conclusion is as follows: Bleb-/bullectomy should not be performed systematically for recurrence prevention of PSP in every patient (even if ELCs are present) because it adds nothing to pleurodesis in recurrence prevention success (and this is because ELC rupture is not the main cause of recurrent PSP), because it is expensive, and because it has a higher morbidity and even mortality compared with medical thoracoscopic pleurodesis. And what about Sihoe et al., 12 who reported that the presence of contralateral ELCs increases the likelihood of sustaining a contralateral pneumothorax? Well, they were wrong. As pointed out in a letter to the editor, 25 their statistics were erroneous. The presence of contralateral ELCs thus is not associated with increased risk for developing a pneumothorax on that side, because it is not a predisposition of developing a first pneumothorax 25,26 or of developing a recurrence 27 on the ipsilateral side. This was to be expected, because contralateral pneumothoraces occur much less frequently (2–25%) 12,13,14,30 as expected from the incidence (as much as 96%) of the contralateral presence of ELCs. 13,14 This evidence clearly points to ELC rupture as the cause of (recurrent) PSP in only a minority of patients, and hence makes systematic bleb/bulla ablation in every patient to prevent recurrence obsolete. ELC treatment thus should be limited to those patients with true, complicated pneumothorax (persistent and clearly the result of a visible, ruptured ELC), which represents only a small minority of patients. Simple, medical thoracoscopic pleurodesis is as effective, less expensive, has a lower morbidity, and has no mortality. This should be the true treatment of choice to prevent recurrence of PSP! Now, because ruptured ELCs are proved to be the cause of recurrent PSP in only a minority of patients, how, then, does the air get into the pleural space? Let's talk about pathophysiology. Distal airway inflammation, which is invariably present in PSP, probably is the key factor in the pathogenesis of PSP. 31–34 Intrinsic (hereditary predisposition, bronchial anatomic abnormalities) 35 and extrinsic (smoking) 36 factors may be involved in this process. Together with intrinsic (long and tall physiognomy leading to a higher pressure gradient at the apex, in turn leading to a greater distending pressure of the alveoli at the apex) 37 and extrinsic (barometric pressure swings) 38 pressure phenomena, these inflammatory and mechanical factors may lead to anatomic changes, primarily at the apices. These abnormalities include ELCs, but also encompass more diffuse changes at the lung apices as a whole: Light and electron microscopic studies have shown that only approximately 25% of ELCs in PSP are truly ruptured, whereas in roughly 75% of cases "structural pleural changes at the top of the lung" were found. This was called pleural porosity.21,39 It appears that the mesothelial layer at the lung apices (in and around ELCs) can show "elastofibrosis" and porosity 40 without true rupture of ELCs. Therefore, instead of ELC as the cause of recurrent PSP, the term pleural porosity, which can be present in and around ELCs, or be present without ELCs, may better describe the pathophysiology underlying the occurrence or recurrence of PSP. Increased intra-alveolar pressure (resulting from the previously mentioned phenomena) may then lead to 1.) true rupture of ELCs when present, 2.) air leakage by porosity through the ELCs, or 3.) air leakage through a porous lung surface with or without ELCs, with the latter mechanism probably being the most frequent. Yet another route of air leakage from the alveoli to the pleural space may be the air movement from the alveoli to the peribronchovascular interstitium, which then follows the same route as interstitial fluid or asbestos fibers: to the (diseased) subpleural space and across the mesothelium into the pleural space 41,42 or, finally, via the interstitium, bronchovascular bundles and hilum, to the mediastinum. As pressures rise, rupture of the mediastinal pleura may then occur. 43 Whatever the exact route (and one route does not exclude another), this means that ELCs should be considered an epiphenomenon—that is, as not necessarily pres-ent or related causally to the complex interplay of inflammatory and mechanical changes occurring in the (apices of the) lung. Treatment limited to ELCs is therefore less logical than a more "general" treatment of the diseased lung (apex), which is achieved indirectly by means of pleurodesis. SUMMARY Bottom-line, this is where we stand: We have no idea how PSP occurs in an individual patient, even when ELCs are present. There is some circumstantial evidence for, and more circumstantial evidence against, the role of ELC rupture in the pathogenesis of PSP in general. VATS bleb-/bullectomy plus pleurodesis probably is more effective than VATS bleb-/bullectomy alone. Medical thoracoscopic pleurodesis by means of talc poudrage, regardless of the true cause of recurrent PSP, 44 is about as effective as VATS bleb/bullectomy plus pleurodesis, but has substantially less morbidity. VATS bleb-/bullectomy with our without pleurodesis may be indicated in some patients with complicated PSP (e.g., persistent air leak) in whom ELC rupture most likely is the cause of the problem, but it cannot be considered the "best recurrence treatment" for all PSP patients with recurrent PSP. A French railroad sign (and dictum) says:un train peut en cacher un autre, or "a train may hide another; watch out when crossing!" ELCs may hide another cause. It is typically human to be masked by the apparently obvious, which is well known by illusionists and, in the medical world, by radiologists for instance (but seemingly less known by surgeons). So, my surgeon friends, please look beyond the obvious, and act accordingly.