The present study evaluates the awareness of and conformance to the Fleischner recommendations for SSN management among radiologists and pulmonologists in clinical practice. Our survey shows that over two years after publication, awareness is widespread. Nevertheless, conformance to the FR varies considerably and overmanagement with more follow-up or additional diagnostic procedures not indicated is common.
To our knowledge, this is the first study to evaluate the awareness of and conformance to the Fleischner recommendations for SSN management. Previously, a number of survey studies have been performed to evaluate management of small, solid pulmonary nodules [11–15]. A shared conclusion of these studies was that there is high heterogeneity among specialists with respect to guideline conformance. Contrarily, a high percentage of respondents reported awareness of the guidelines . In our study, which included both radiologists and pulmonologists, the results are comparable. Despite high awareness and straightforward clinical scenarios, between 31 and 69 % of the radiologists chose management recommendations not corresponding to the FR. Among pulmonologists, awareness was significantly lower and management of SSNs even more variable, which may well be due to the radiological origin of the recommendations. Most interestingly, we also observed a variable conformance to the FR within individual readers for the four lesions types.
There may be several explanations for management deviations: (1) respondents may be aware of the FR but apply them erroneously, use a deviating, locally developed protocol or no clearly described method at all. It remains unclear to which extent one or more of these factors contributed to the variability we observed. Besides the Fleischner recommendations for SSN management, other management standards are publicly available, with LUNG-RADS or ACCP guidelines being the most important [16, 17]. Interestingly however, among our respondents only a few individuals (N = 7) reported to apply these guidelines in daily practice. (2) Respondents may not agree with the FR and therefore deliberately chose a deviating strategy. After all, the FR are mainly based on expert opinion due to limited availability of data, especially in a non-lung cancer screening setting. In our study, non-conformance was surprisingly mostly categorized as overmanagement. Therefore, disagreement due to the conservativeness of the FR does not seem to be a major explanatory factor for the heterogeneity. (3) Some deviation in management might be erroneously due to respondents who overread or ignored the presented clinical scenarios (e.g., new versus persistent SSN). This may at least partly explain why overmanagement was highest for the persistent, pure ground-glass nodule, with the description ‘persistent’ as the clue for yearly serial follow-up and not a 3-month follow-up scan.
Awareness and conformance
Awareness of the Fleischner recommendations for SSN management was significantly higher in clinicians with higher exposure to SSNs, and in more experienced radiologists. However, it has to be noted that awareness among radiologists was generally very high (ie. only eight individuals reported unawareness), limiting statistical power. Guideline awareness among pulmonologists—which was significantly lower and only showed association to SSN exposure—has not been assessed previously. Previously reported factors associated with guideline conformance in solid nodule management included awareness of the guidelines, presence of a written management policy, working in a teaching practice, fellowship training in cardiothoracic radiology (either personally or a direct colleague), and years of experience [11, 13, 14]. Our results are largely comparable, with the exception that we did not find an influence of experience or fellowship-training in radiologists. This might be due to the fact that SSNs and their management are a relatively new entity, in which the more experienced clinicians have not yet developed their own long-standing practice patterns in solid nodule management . Adding to what was previously discussed in the literature, we showed that higher exposure is associated with conformance.
Over- and undermanagement
The surprisingly strong tendency towards overmanagement is an important finding because unnecessary scans and invasive procedures lead to extra costs, radiation exposure, and potentially, to procedure-related risks. On the other hand, undermanagement is also a very important issue. It may lead to unnecessary morbidity and mortality caused by advanced tumour stages. The latter, however, is still under discussion and more results from long-term outcome studies are needed, given the mainly indolent and slowly progressing nature of SSNs.
We found that overmanagement according to the FR was common among both radiologists and pulmonologists (18–58 % and 25–83 %, respectively), which is in line with results from the previous studies in solid nodule management, which reported overmanagement in 39–62 %  and 17–93 % . Pulmonologists showed a stronger tendency towards overmanagement compared to radiologists, including invasive procedures as biopsy and resection. The reason for this remains unclear based on our results, but might be related to their reported lack of confidence in SSN management, with tissue diagnosis and a definite answer as the safest option.
On the other hand, we found undermanagement for the persistent part-solid subsolid lesion by both groups of respondents. This type of lesion, if persistent and demonstrating a solid component exceeding 5 mm, is considered highly suggestive for invasive adenocarcinoma. Nevertheless, 33 % of radiologists and 54 % of pulmonologists would have not recommended an immediate (invasive) work-up. This indicates either insufficient knowledge about the meaning of this type of lesion or the desire to avoid overdiagnosis by at least a subgroup of colleagues.
As mentioned above, some deviation in management may be erroneously due to respondents overlooking or ignoring clinical information on nodule persistence. This seems most relevant in case 1, in which 33 and 42 % of the radiologists and pulmonologists, respectively, called for a 3-month follow-up interval (which is indicated in the case of a new nodule) instead of the indicated serial annual follow-up (in the case of a persistent SSN). To a lesser extent, this might also account for some of the undermanagement in case 3, in which 19 and 16 % of the respondents chose a 3-month follow-up interval instead of further work-up. Determining the true impact of respondents noting persistence in the presented cases is impossible, but over- and undermanagement may thus be somewhat lower than presented. Nevertheless, this argument cannot fully explain the large heterogeneity throughout and between the cases and respondents. Moreover, previous guideline conformance studies showed comparable percentages of non-conformance. We believe that the heterogeneity in SSN management found in this study is mainly caused by personal interpretation and an inherent tendency to adjust guidelines by individual clinicians.
Measurements of nodule dimensions
We further found that only a small minority of respondents obtain transverse measurements in two dimensions, as proposed in the Fleischner document. Most indicated that they measure the single maximum nodule diameter in either the axial or any other plane. In our study the influence of our finding was likely limited given the small number of nodules and a solid component size clearly under or over the threshold of 5 mm (case 2 and 3). Also, the influence of our finding in general is probably limited, given that one should only determine whether the SSN or its solid component is ≤5 mm or >5 mm. On the contrary, for the evaluation of solid pulmonary nodules where a similar measurement technique should be used and classification into four different size categories is required (<4 mm, 4–6 mm, 6–8 mm and <8 mm; ), this may well be of far more importance.
The strength of the current study is that we succeeded in including a sufficient number of both radiologists and pulmonologists. Given that in clinical practice detection and follow-up of subsolid pulmonary nodules is not a monodisciplinary affair, it is important to obtain information on SSN management in both groups involved. Also, we were able to include both single-slice and animated multi-slice images of the nodules in the online questionnaire. We therefore also tested knowledge on nodule interpretation, which more closely resembles clinical practice than a written clinical scenario, as previously used in other survey studies on solid nodule management.
Our study also has some limitations. First, as with any survey there might be a response bias, which can neither be excluded nor quantified. However, in case a response bias was introduced, we believe it is far more likely that there has been weighting towards respondents with an affinity for subsolid nodules than for those without. If so, our results on awareness and conformance are probably higher than in reality. Second, due to technical reasons we only included solitary SSNs in the survey, while the FR also includes management of multiple subsolid nodules. Since management recommendations between solitary and multiple SSNs do not differ significantly and are both part of the same Fleischner document, we believe our study design is nevertheless valid to assess the presented study purpose.
In conclusion, although awareness of the Fleischner recommendations for SSN management is widespread among both radiologists and pulmonologists, management choices differ substantially from these recommendations, and over- and undermanagement are common.