CT and myasthenia gravis: correlation between mediastinal imaging and histopathological findings.

The surgical strategy in patients with myasthenia gravis (MG) is influenced by the suspicion of thymoma based on mediastinal imaging. Aim of this retrospective study was to analyse the accuracy of CT of the mediastinum in predicting the histological findings in patients with MG referred for thymectomy. Thirty-four CT-scans of MG patients referred for thymectomy between October 1989 and October 2003 were retrospectively evaluated by three cardio-thoracic surgeons and three radiologists. Data were analysed by Kappa statistics to judge inter-observer variance and were compared to the histopathological findings to determine predictive value. Observer agreement among the radiologists was fair (Kappa=0.28) and among the cardio-thoracic surgeons slight (Kappa=0.08). The average negative predictive value of no thymoma on CT was 91% (range 78-100%). The average positive predictive of thymoma on CT value was only 39% (range 29-58%). The average sensitivity of CT imaging in the study population was 75% (range 25-100%) and the average specificity was 62% (range 42-81%). In patients with MG undergoing thymectomy, CT is helpful in detecting thymoma, but the high inter-observer variation indicates that it remains difficult to distinguish lymphoid follicular hyperplasia from thymoma. This will influence the surgical strategy in patients with myasthenia gravis.