Introduction
Medical thoracoscopy (MT) is a widely accepted and effective tool for the diagnosis, staging, and management of pleural diseases [1]. International guidelines recommend the use of MT for patients with exudative pleural effusion that remains undiagnosed after initial imaging and fluid analysis [2,3]. In selected cases where pleural mesothelioma is strongly suspected, upfront MT may be considered to expedite both diagnosis and management [2]. Conventional MT relies on having pleural effusion to establish a buffer zone between the lung and the chest wall. Traditional teaching suggests that safe introduction of a thoracoscope into the pleural cavity necessitates a minimum depth of 2 to 4 cm of pleural fluid or air to prevent direct injury to the lung and other intrathoracic organs [4]. In patients without a pleural effusion, video-assisted thoracoscopic surgery (VATS) is often necessary, which requires general anaesthesia and is associated with higher morbidity.
‘Dry MT’ refers to the iatrogenic introduction of air into the pleural cavity to create space for the insertion of a thoracoscope, thereby eliminating the need for VATS. Data on the effectiveness and safety of dry MT are limited. Various techniques for inducing pneumothorax have been described, without head-to-head comparisons. No comprehensive review has previously addressed this topic. Published evidence lacked the specificity required for a systematic review, which prompted us to conduct a scoping review [5]. Iterative and methodological processes were used to describe and interpret the literature, without critically appraising the quality of the individual studies [6]. This scoping review aimed to map the existing literature on dry MT, focusing on its indications, procedural techniques, diagnostic yield, and safety profile. It also sought to identify gaps in current knowledge and research to inform future investigations.
Materials and Methods
1. Protocol and registration
A formal protocol for this scoping review was developed in accordance with the Joanna Briggs Institute methodology for scoping reviews and is reported in line with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) checklist.
Institutional review board approval was not required in accordance with local ethical guidelines for scoping reviews. Informed consent was not obtained, as no new patient data were collected.
2. Eligibility criteria
Publications were eligible for inclusion if they were published from any time up to 31 March 2025, written in English, and had a full-text manuscript available. Articles needed to address three specific areas of interest: (1) participants: adults (≥18 years) undergoing pleural investigation or management; (2) procedural context: dry MT, pleuroscopy, or local anaesthetic thoracoscopy; and (3) procedural concept: induction of pneumothorax as part of MT to facilitate access to the pleural cavity, pleural biopsy, and/or pleurodesis. Publications were excluded if they met at least one of the following criteria: (1) non-human studies; (2) inclusion of a paediatric population (age <18 years); (3) focus on other techniques such as surgical VATS; and (4) discussion of MT without mentioning the induction of pneumothorax.
3. Information sources and search
Potentially eligible studies were identified through a systematic search of PubMed (National Library of Medicine) and Google Scholar, with the search queries detailed in Appendix 1. Additional articles were found using citation chaining and manual screening of reference lists from relevant articles. No publication date restrictions were applied, and the final search was conducted on March 31, 2025. While there were no language restrictions during the initial search, only English articles involving human adult patients (≥18 years) with full-text availability were included in the final analysis.
4. Selection of sources of evidence
All identified records were imported into EndNote 2025 for reference management and duplicate removal. Two reviewers (Toh ESY and Tung KM) independently screened the titles and abstracts against the pre-defined eligibility criteria. Studies that appeared potentially relevant proceeded to a full-text review, which was also conducted independently by two reviewers (Shanmugam V and Vignesh S). Any disagreements at either stage were resolved through discussion or by consulting a third reviewer (Huan NC). The selection process was documented using a PRISMA-ScR flow diagram, which detailed the number of records identified, screened, assessed for eligibility, and included in the final review, as well as the reasons for exclusion at the full-text stage.
5. Data charting process and items
Data charting was performed using a standardized Excel spreadsheet for data extraction, which was developed in advance by the review team (Nyanti LE and Huan NC). To ensure clarity and consistency, the spreadsheet was pilot tested on a subset of five studies. Two independent reviewers (Nyanti LE and Woo FB) conducted the data extraction in duplicate. Any discrepancies were resolved through discussion or adjudication by a third reviewer (Huan NC).
The following data was extracted: (1) study characteristics: authors, year of publication, country, study design, and sample size; (2) patient details: characteristics of pleural effusion (if present) and indications for dry MT; (3) procedure details: type of MT used, biopsy tools, availability of thoracic ultrasound (TUS) during the procedure, TUS features, anaesthetic options, and methods of pneumothorax induction (e.g., Boutin needle, Veress needle, slow dissection, etc.); (4) procedure outcomes: definitions of procedural success, diagnostic yield, and complications (e.g., bleeding, infection, persistent air leak, injuries to underlying structures, etc.); and (5) other clinical data, such as predictors of procedural success or failure.
6. Critical appraisal of individual sources of evidence
Critical appraisal was not performed, in line with the objectives and methodology of a scoping review. This type of review aims to map the characteristics of existing literature rather than evaluate the quality or risk of bias in individual studies.
7. Synthesis of results
Data were synthesized descriptively. Findings were organized thematically based on key variables or domains outlined in the ‘Data charting process and items’ section. Frequency counts were reported where applicable, such as the number of studies that discussed specific induction techniques. A narrative synthesis highlighted variations or innovations in pneumothorax induction during dry MT. Summary tables and figures were used to present the data and facilitate interpretation.
Results
1. Selection of sources of evidence
Seventy-four abstracts were identified, and 65 were reviewed after removing duplicates. After a full-text review, 13 articles met the inclusion criteria and were included in the final analysis (Table 1 and Figure 1). Most articles excluded in the ‘irrelevant study topic’ category were review articles that described the technical aspects and outcomes of conventional MT rather than dry MT with pneumothorax induction.
2. Characteristics of sources of evidence
Thirteen full articles were reviewed, detailing a total of 357 patients. The publications included: retrospective cohort studies (n=7) [7-13], case reports (n=4) [14-17], prospective cohort study (n=1)18, and case series (n=1) [19]. Most dry MT articles originated from Asia (n=7) [7-9,11,12,15,16], followed by Europe (n=5) [10,13,17-19], and North America (n=1) [14].
3. Results of individual sources of evidence and synthesis of results
1) Presence and characteristics of pleural fluid
Out of a total of 357 cases, 146 (40.9%) were completely ‘dry’ (complete absence of pleural fluid). The proportion of dry cases varied substantially across studies: Corcoran et al. [18] reported 22 dry cases out of 77 (28.6%) MTs; Watanabe et al. [9], 16 out of 56 (28.6%), Huan et al. [7], 10 out of 31 (32.3%), Imabayashi et al. [8], 10 out of 18 (55/6%), Yang et al. [11], 51 out of 72 (70.8%), and Faurschou [19], six out of seven cases (85.7%). Three studies reported exclusively dry cases: Marchetti et al. [13] (n=29), Lao et al. [15] (n=1), and Tamburrini et al. [17] (n=1).
The definition of minimal effusions varies across studies, with some defining it as either (1) less than 3 cm in depth on TUS [7,9,11,14,16,18] or (2) specific fluid volumes ranging from 4 to 300 mL8. Two studies described anatomical subclassification for patients with minimal pleural effusions: (1) minimal effusion at MT entry site, and (2) effusions absent at entry site but present elsewhere within pleural space, most commonly accumulating above the hemidiaphragm, referred to as ‘distal effusions.’ Corcoran et al. [18] and Huan et al. [7] reported ‘distal effusions’ in 31.2% and 61.3% of cases, respectively.
2) Indications for dry MT
The most frequently reported procedural indication was pleural abnormalities observed on imaging, particularly in computed tomography (CT) and positron-emission tomography (PET) scans.
Six studies described cases with pleural nodularity or thickening on CT [7,9,11,13,17,18]. Asymmetric pleural thickening, and fissural nodules in the absence of effusion were highlighted by Joy et al. [14] and Watanabe et al. [9], respectively. Huan et al. [7] identified pleural thickening or masses on CT as a key indication for dry MT, whereas Tamburrini et al. [17] emphasized the role of PET in visualizing metabolically active pleural thickening, even when effusion is absent. One study did not specify procedural indications [10].
Dry MT was utilized for pleural staging in five studies [7,8,15,16,18]. Imabayashi et al. [8] highlighted the effectiveness of dry MT in completing pleural staging for non-small cell lung cancer (NSCLC). Corcoran et al. [18] and Huan et al. [7] documented its application in cases of cytology-negative exudative effusions or in patients with known extra-thoracic malignancies, where diagnostic uncertainty remained despite fluid analysis.
3) Use of TUS and pneumothorax induction techniques
TUS was utilized in all but one study [19], primarily to assess the presence or absence of pleural effusion, identify pleural adhesions, visualize needle placement during pneumothorax induction, and guide the site of MT port entry. Various techniques for inducing pneumothorax were described. Blunt dissection was the most common method, reported in six studies [8,9,13,15,16]. Additional adjunctive techniques guided by TUS included the use of Boutin needles by Corcoran et al. [18] and Watson et al. [10] while Huan et al. [7] used a Veress needle. Tamburrini et al. [17] employed a bladeless trocar under direct camera vision, and Faurschou [19] utilized a Saugman cannula. Ozawa et al. [12] described a TUS-guided liver-surface puncture technique with guidewire-assisted catheter insertion for pneumothorax induction. All studies performed pneumothorax induction under sedation; general anaesthesia was not used.
4) Instruments used for MT and biopsy
A range of thoracoscopic instruments was utilized. Most procedures employed semi-rigid thoracoscopes, including the Olympus LTF-160 [7], LFT-240 [11], and LFT-260 [9] models. Karl Storz rigid thoracoscopes and endoscopes were used by Faurschou [19] and Marchetti et al. [13]. Tamburrini et al. [17] utilized a bladeless thoracoport with an optic biopsy clamp. Two publications did not specify the type of thoracoscope used [16,18].
Flexible forceps were the most utilized biopsy tool. Some authors supplemented cryoprobes [7,8,15] or rigid forceps [7,14,19] for fibrotic or thickened pleura. Watanabe et al. [9] used a combination of flexible forceps, coagulation forceps, and a diathermy knife for thickened pleura. Faurschou [19] and Tamburrini et al. [17] performed pleural biopsies with spoon forceps and an optic biopsy clamp, respectively. The number of samples taken ranged from eight to 10 where reported [7]. Several studies did not specify the biopsy technique used [11,12,16].
5) Definition of procedural success
Yang et al. [11] defined success as the effective entry of the MT into the pleural cavity, which allows for fluid aspiration or tissue biopsy. Success rates varied according to TUS findings: 0% (n=0/3) without pleural sliding, 98% (n=47/48) in areas with pleural sliding, and 100% (n=21/21) in cases with fluid sonolucent areas at the MT entry site. Huan et al. [7] defined technical success as meeting all of the following criteria: (1) successful induction of pneumothorax allowing for thoracoscope insertion; (2) no immediate complications such as lung injury, bleeding, or severe pain; and (3) no delayed complications such as prolonged air leak. The overall success rate reported was 80.6% (n=25/31). Corcoran et al. [18] defined success as sufficient pneumothorax induction, achieving a success rate of 87.0% (n=67/77), while Joy et al. [14] reported success based on the ability to biopsy nodules in a single case report.
The remaining nine studies did not clearly define procedural success but reported variable success rates: Watson et al. [10] reported 71.0% (n=27/38); Ozawa et al. [12] reported 92% (n=23/25); Watanabe et al. [9] reported 93.8% (n=15/16); Imabayashi et al. [8] reported 94% (n=17/18); and Faurschou [19], Lao et al. [15], and Tamburrini et al. [17] each reported 100% success (n=7, n=1, and n=1, respectively). Two studies did not report success rates [13,15,16]. Additionally, four studies [7,10,11,18] indicated that reduced or absent pleural sliding on TUS—a surrogate marker for the apposition of lung and parietal pleura—was consistently associated with lower procedural success in dry MT.
6) Histopathological outcomes
All but one study reported histopathological diagnoses from pleural biopsy samples [12]. Malignancy was the most frequently reported diagnosis, with rates of 44.8% in Marchetti et al. [13], 32.8% in Corcoran et al. [18], and 29.0% in Huan et al. [7] Lung cancer was the most common malignancy, followed by mesothelioma and other metastatic cancers. Chronic pleurisy was the second most common diagnosis, reported in 58.2% of cases in Corcoran et al. [18], 25.8% in Huan et al. [7], 24.1% in Marchetti et al. [13], 19.0% in Watanabe et al. [9] and 8.8% in Yang et al. [11] Other histopathological diagnoses included tuberculous pleurisy [7,11], pleural infection [11], sarcoidosis [18], lipoma [19], pleural plaques [19], chondroma [19], and plasmacytoma [19], though these were infrequently reported and often limited to single cases.
7) Complications
Dry MT appeared to be a safe procedure with a low overall complication rate. Complications—or their absence—were reported in all but three [16,17,19] studies and occurred in only 5.9% of cases (n=21/357). Chest pain was the most frequently reported adverse event, observed in 2.5% of cases (n=9/357). Other complications, in descending order of frequency, included lung injury (1.1%, n=4/357 cases), bleeding or hemothorax (0.8%, n=3/357 cases), delirium (0.6%, n=2/357 cases), and hypoxia, dyspnea, and pleural reaction, each occurring in 0.3% of cases (n=1/357).
Discussion
In this scoping review, we summarize the current evidence regarding the indications, techniques, success rates, and safety of dry MT. A total of 357 cases were reported across 13 published manuscripts. We noted a significant lack of high-quality studies, as the existing literature mainly consists of retrospective series and case reports, with no randomized controlled trials or direct comparisons of different pneumothorax induction techniques. The techniques described varied widely, including blunt dissection, Boutin and Veress needles, Saugman cannulas, and optic trocars. Overall, the findings from the identified studies were generally positive, indicating that dry MT is both technically feasible and safe. However, the heterogeneity of the outcomes assessed limits our ability to synthesize definitive evidence or provide clear recommendations.
Published success rates for dry MT vary between 80.6% and 100%, depending on the centre and the specific criteria used to define success. In most studies, procedural success was defined as the successful induction of pneumothorax, which allows for safe entry of the thoracoscope. However, only four studies clearly reported their definitions of success, making it difficult to draw definitive conclusions about the overall success rates. Chronic pleurisy or non-specific pleuritis were common histopathological findings, observed in more than half of cases in one study [18] and about a quarter in two others [7,13]. These findings should be interpreted cautiously, as none of the included studies offered long-term follow-up, which raises the concern that the diagnostic yield of dry MT may be overestimated. Additionally, existing studies inadequately addressed technical difficulties such as incomplete lung deflation due to adhesions, rapid lung re-expansion that hampers visualization without the ‘pressure effect’ from pleural effusion, and insufficient time for deep biopsies. These challenges may all lead to non-diagnostic or non-specific histological outcomes.
Most studies emphasized the crucial role of TUS, particularly in selecting the appropriate site for pneumothorax induction and guiding needle insertion prior to MT. Active lung sliding observed on TUS indicates the absence of significant pleural adhesions that could impede lung collapse or trocar insertion. Research in pre-VATS settings suggests that TUS has high specificity and may effectively serve as a rule-in test for detecting pleural adhesions before thoracic surgeries [20]. While Lichtenstein [21] proposed a system to quantify lung sliding amplitude, it has not been applied in the context of dry MT. The impact of reduced (or partial) lung sliding, as noted in some of the included studies [7,11], along with pleural thickening or minor adhesions, on the likelihood of successful lung collapse remains unclear. In the Italian cohort by Marchetti et al. [13], intra-procedural adhesions were recorded as either single or multiple but did not obstruct endoscopic visualization or biopsy. Importantly, only patients exhibiting clear lung sliding at the designated MT entry site were included in the study.
Pleural biopsy is a practical next step when initial investigations, such as cytology results from thoracentesis, yield inconclusive findings. This procedure can be performed through image-guided pleural biopsy or dry MT. Currently there are no studies comparing dry MT to image-guided percutaneous pleural biopsy. In centres lacking advanced cytology or interventional radiology services, patients with pleural lesions but no effusion may need to undergo VATS under general anaesthesia and single-lung ventilation. However, these patients often have limited cardiorespiratory reserves and comorbidities, making VATS highly risky. Additionally, VATS entails higher costs, and longer hospital stays compared to MT. In contrast, dry MT only requires moderate sedation and local anaesthesia, making it a viable alternative. Notably, no studies on dry MT have reported the necessity for general anaesthesia, highlighting its suitability for frail or comorbid patients.
This scoping review has several limitations. First, it only included publications in English, which may introduce a language bias. Second, there is a potential for selection bias due to the absence of a uniform definition for a successful dry MT procedure across the studies. Third, we limited our search to only two electronic databases; however, we believe this approach was reasonable given the niche nature of the topic. To address this limitation, we manually screened the reference lists of the included studies to identify additional relevant research. Finally, most studies were likely conducted in expert centres by experienced operators, which may have resulted in positive publication bias and an overestimation of procedural success and safety compared to general practice.
In conclusion, inducing pneumothorax during dry MT seems technically feasible and generally safe for assessing pleural diseases when effusion is absent. However, current evidence is limited by significant variability in study designs, techniques, outcome definitions, and reporting methods. Future research should focus on standardizing definitions of procedural success and complications, identifying predictors of outcomes—including the use of ultrasound—and comparing different techniques for pneumothorax induction. Prospective studies with long-term follow-up are essential to clarify the diagnostic accuracy, safety, and clinical utility of dry MT in contemporary pleural practice.
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