Pitfalls in intraoperative frozen section histology of mediastinal neoplasms.

We evaluated the reliability of intraoperative frozen section histology in 149 mediastinal tumours of which 106 lesions were localized in the anterior, 18 in the central and 25 in the posterior mediastinum. Gross non-resectability was ruled out by preoperative imaging. No preoperative cytological or histological diagnosis was obtained in any case. At thoracotomy, 3 biopsies from 3 different sites of the tumour were processed for frozen section as well as for paraffin histology and immunohistochemistry. In 67 of 73 benign lesions (91%), the intraoperative diagnosis was correct, 5 cases could not be classified by frozen section and 1 case had to be revised. Only 28 of 76 malignant lesions (36.8%) were diagnosed correctly by intraoperative frozen section. In 27 cases (35.5%), no intraoperative classification was possible and in 21 patients (27.6%), the diagnosis was wrong with the consequence of surgical overtreatment for lymphoma misinterpreted as thymic cancer in 3 cases. In patients in whom preoperative investigations suggest borderline resectability, a staged procedure to obtain histology prior to definitive surgery could prevent overtreatment.