CLINICOPATHOLOGICAL SPECTRUM OF MEDIASTINAL LESIONS WITH IMMUNOHISTOCHEMICAL CHARACTERIZATION OF MEDIASTINAL NEOPLASMS

Abstract

Background: Mediastinal lesions comprise a heterogeneous group of congenital, inflammatory, benign, and malignant disorders accounting for approximately 3% of all thoracic tumors and often present significant diagnostic challenges because of their varied histopathological features and anatomical complexity. Histopathological examination remains the diagnostic gold standard, while immunohistochemistry (IHC) serves as an indispensable adjunct in accurately classifying morphologically overlapping lesions and determining their tissue of origin. Materials and Methods: Prospective observational study conducted over a two-year period at the Institute of Pathology, Madras Medical College, Chennai. Eighty-one patients with mediastinal lesions who underwent CT-guided biopsy, core needle biopsy, or surgical excision were included. Clinical findings, radiological features, histopathological diagnosis, and immunohistochemical profiles were analyzed. Immunohistochemistry was performed selectively in diagnostically challenging cases using lineage-specific antibody panels to establish definitive diagnoses. Results: The mean age of the study population was 43.8 years, with a male predominance (69.1%). Breathlessness (44.4%) was the most frequent presenting symptom, while the anterior mediastinum was the predominant anatomical compartment (91.4%). Thymic lesions constituted the largest diagnostic category (37.0%), with type B thymoma representing the commonest thymic neoplasm. Metastatic tumors accounted for 18.5% of cases, followed by granulomatous lesions (11.1%), lymphomas (6.2%), cystic lesions (6.2%), germ cell tumors (6.2%), and neurogenic tumors (3.7%). Immunohistochemistry proved particularly useful in differentiating thymic epithelial tumors, lymphomas, germ cell tumors, metastatic carcinomas, mesenchymal tumors, and other poorly differentiated neoplasms through the application of appropriate lineage-specific markers. Conclusions: Mediastinal lesions demonstrate a wide clinicopathological spectrum with overlapping clinical and radiological manifestations. Histopathological examination remains the cornerstone of diagnosis, while immunohistochemistry significantly enhances diagnostic accuracy in morphologically challenging cases. The integration of clinical, radiological, histopathological, and immunophenotypic findings is essential for precise diagnosis and optimal therapeutic management.