The present study reports a preliminary experience on CTLB performed with a non-coaxial technique and a 16 G needle, with a particular focus on procedural outcome and operator learning curve. Although CTLB procedural outcome has been extensively studied over years, operator learning curve on CTLB is still an unexplored ground. Su et al [9] previously investigated learning curve for lung biopsies performed on a cone-beam CT system in association with a virtual navigation software, but a comparable analysis of lung biopsies performed with conventional CT systems has never been investigated before.

Learning curve analysis showed procedural streamlining over time as suggested by the reduction of mean procedural time in group B compared to group A. This effect could be explained by the progressive experience-related optimization of the procedural steps, such as a more “fluid” placement of the needle within the lesion, and a fewer number of CT scans required for lesion targeting. A positive shift was evident from group A to group B in terms of sensitivity, specificity and diagnostic accuracy; this improvement was predominantly influenced by the marked reduction of false negative results in group B (1 vs 10 of group A). It is our opinion that these results are the consequence of at least two different factors: (1) an increased amount of adequate material due to an improved use of the needle; (2) a refined analysis of the diagnostic CT / PET-CT images before the procedure, with a more accurate selection of the target portion of the lesions; a more effective needle insertion within the lesion during the procedure; both factors could be traceable back to an increased operator experience over time.

The overall complication rate of study population was 49.57% (59/120 patients), with operative management occurred in 11/120 (9.16%) patients, all treated with chest tube placement for a non-limiting pneumothorax, and with a median hospitalization of 3 days. This data are in agreement with those reported by other authors with smaller needles sizes [10,11], suggesting that the use of non-coaxial technique and 16 G needles is basically safe; however, about 50% of patients had procedural complications (predominantly minor complications), without an improvement of complication rate over time.

Our experience confirms that a smaller diameter of the lesion [12] [13] and the presence of emphysema along the parenchymal needle path [22, 23] are predisposing factors for complications during CTLB. On the contrary, the presence of pleural contact on CT images resulted as a protecting factor from the onset of complications (p = 0.012) [24] with a negative correlation between complication risk and contact surface extent (p < 0.001); a possible explanation of this result could be the presence of inflammatory adhesions or tumor infiltration of the pleura that nailed the lung against the thoracic wall during the needle passage. Comparative studies with post-biopsy surgical findings could better clarify this aspect. This study has some undeniable limitations: the sample size is relatively small with single-arm design, however, the number of procedures included was adequate for a valuable learning curve analysis and we have reason to think that a longer observation period and a greater number of procedures would have flattened the distance between groups A and B in terms of procedural time and diagnostic yield, interfering with the learning curve analysis; furthermore, the inclusion of a second arm would not have added information on the operator learning curve. Secondly, a specific analysis of the quality of pathological specimens was not possible in our population due to the retrospective nature of the study.

In the era of personalized medicine, the goal of CTLB is to provide an adequate amount of material to achieve an accurate diagnosis and, in cases of malignancy, to allow the molecular characterization of the lesion [14]. However, the use of CTLB should take into account the following critical aspects: diagnostic accuracy is extremely variable, ranging from 71% to 97% [6, 15], and procedural complications are relatively common, up to 62% [16] , with pneumothorax being the forerunner [10, 16]. Biopsy technique and needle caliper are essential elements that may affect procedural outcome: the use of a coaxial (needle in needle) technique could improve the diagnostic accuracy if compared to non-coaxial approach [4] but arises the risk of pneumothorax, perilesional bleeding and/or fatal complications [3, 4, 10]. On the other hand, non-coaxial technique is usually performed with small needles reducing chances to obtain both diagnosis and lesion molecular profile [4, 17, 18]. According to our preliminary results, non-coaxial technique in association with 16 G needles seems a feasible approach for CTLB with satisfactory outcomes, comparable with those previously reported for CTLB [19-21]. Practice over time improves procedural length and operator diagnostic performance, maintaining an adequate complication rate.

 Declaration of Interest

All the Authors declare to have no conflict of interest.