Histomorphological Spectrum of Mediastinal Masses with Special Emphasis on Rare Lesions

Abstract

Introduction: Mediastinal lesions are not frequently observed in routine clinical practice. A wide variety of disease process can occur within the mediastinum. Tissue from needle biopsies forms the major diagnostic material. There is need for detailed studies to make pathologists aware of the wide histological spectrum and to know the unusual lesions that can be encountered during diagnosis. Aim: To describe the histomorphological spectrum of various mediastinal lesions and to highlight the rare lesions that posed a diagnostic challenge. Materials and Methods: This was a retrospective study done on all mediastinal masses over a period of two years from January 2016 to December 2018. The clinical data and imaging findings were collected from the test request forms and patients’ files for all the cases. Haematoxylin and eosin stained slides of all cases and immunohistochemistry markers and cytochemical stains wherever done were reviewed and analysed. Mean, median and percentage were used for statistical analysis. Results: Thirty-four cases of mediastinal lesions were included in the study. Of these, 28 cases (82.4%) presented as anterior mediastinal masses, three cases (8.8%) each in the middle and posterior mediastinum. Thymoma (n=15) followed by lymphoma (n=4) were the most frequent neoplasms reported. There were five lesions which were rare in the mediastinum with unusual presentation that posed diagnostic difficulties. These lesions included Primitive neuroectodermal tumour in an adult, Primary Mediastinal B Cell Lymphoma (PMBCL), Malignant Peripheral Nerve Sheath Tumour (MPNST) with nodal metastasis, Seminoma deposits in mediastinal node occurring as late relapse and dedifferentiation of thyroid carcinoma in mediastinal node metastasis without an obvious primary. Conclusion: Primary mediastinal tumours were more frequent than metastasis. Although thymomas and lymphomas are dealt extensively in literature, this article highlights the fact that pathologists must be aware of those lesions that don’t display the classical histological and/or clinical features as observed in this study.