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.