Advanced Ankylosing Spondylitis With Posterior Mediastinal Mass: A Rare Radiological Confluence.

Ankylosing spondylitis (AS) is a chronic inflammatory spondyloarthropathy that predominantly affects the axial skeleton. While hallmark features such as sacroiliitis and syndesmophytes are well recognized, the presence of mediastinal masses may pose a diagnostic dilemma and raise concerns for malignancy or atypical infection. We report a middle-aged man in the fifth decade of life with longstanding untreated AS presenting with progressive quadriparesis. Imaging revealed classical findings of bamboo spine, Romanus lesions, and sacroiliitis, alongside a mediastinal mass on chest radiograph and magnetic resonance imaging. The differential included primary malignancy, granulomatous disease, and lymphoma. Evaluation is planned further with positron emission tomography-computed tomography. This case illustrates the importance of considering extramusculoskeletal manifestations in AS, particularly mediastinal lesions that may mimic malignancy. Radiological evaluation and early intervention are essential for timely diagnosis and management.