Inter‐observer variation in image interpretation and the prognostic importance of non‐expansile lung in malignant pleural effusion

Abstract

Background and objective Non‐expansile lung (NEL) frequently complicates management of malignant pleural effusion (MPE) and is an important factor in clinical practice and trials. NEL is frequently diagnosed on a single radiographic observation, but neither the inter‐observer agreement of this approach nor the prognostic importance of NEL in MPE has been reported. Methods A multicentre retrospective cohort study was performed in two UK pleural centres. NEL was defined as <50% pleural re‐apposition on post‐drainage radiographs by primary and secondary assessors at each site. Inter‐observer agreement was assessed by Cohen's kappa (κ). Kaplan–Meier methodology and multivariate Cox models were used to assess the prognostic impact of NEL versus no NEL and ‘complete NEL’ versus ‘complete expansion’, based on a single assessor's results from each site. Results NEL was identified by the primary assessor in 33 of 97 (34%) in Cohort 1 and 15 of 86 (17%) in Cohort 2. Inter‐observer agreement between assessors was only fair‐to‐moderate (Cohort 1 κ: 0.38 (95% CI: 0.21–0.55), Cohort 2 κ: 0.51 (95% CI: 0.30–0.72)). In both cohorts, NEL was associated with shorter median overall survival (Cohort 1: 188 vs 371 days, Cohort 2: 192 vs 412 days). This prognostic association was independent in Cohort 1 (hazard ratio (HR): 2.19, 95% CI: 1.31–3.66) but not in Cohort 2 (HR: 1.42, 95% CI: 0.71–2.87). Survival was inferior in both cohorts in cases of complete NEL versus complete expansion. Conclusion Radiographic NEL is common but inter‐observer agreement is only fair‐to‐moderate. NEL is associated with adverse survival. These data do not support the use of single radiographic assessments to classify NEL.

Expanding knowledge on non‐expandable lungs

“…How and where the patients are recruited may also influence the rates reported. Martin et al 2 found a two-fold difference in the incidence of NEL-34% (33/97) and 17% (15/86)between the two tertiary units. The study included only post-pleuroscopy patients, and the differences may, among other reasons, reflect differences in patient selection for the procedure.…”

“…How and where the patients are recruited may also influence the rates reported. Martin et al . found a two‐fold difference in the incidence of NEL— 34% (33/97) and 17% (15/86) — between the two tertiary units.…”

“…Its incidence, best diagnostic method and relation to clinical outcomes, especially pleurodesis success and survival, are poorly understood. The work by Martin et al ., recently published in Respirology , represents an important early step in providing data on NEL. This study included 214 patients with MPE (larger than most previous series on NEL) at two separate UK centres which add strength to the findings.…”

“…Inter‐observer variation compounds the difficulty in defining the true incidence of NEL. Martin et al . is the first to illustrate this point and found only a fair‐to‐moderate level of concordance between a primary and secondary reader (all experienced specialists) in determining if CXR shows >50% of NEL.…”

“…The incidence of NEL also critically depends on how it is defined, including cut-off values and mode of detection. Martin et al 2 defined NEL as apposition of the lung to <50% of the lateral chest wall on chest radiographs (CXR), although other studies used more stringent cut-off values (<25%). 7 NEL from malignant causes are often not uniformly trapped.…”