Objective thoracoscopic criteria in differentiation between benign and malignant pleural effusions by Ellayeh, M, Bedawi, E, Banka, R, Sundaralingam, A, George, V, Kanellakis, N, Hallifax, R, Abdelwahab, H, Rezk, N, Hewidy, A, Ali, R, Wrightson, J, Rahman, N