Idiopathic fibrosing mediastinitis mimicking malignancy: when imaging deceives.

Woman in her 30s presented with dry cough and shortness of breath since 8 months and swelling of the face and lower limbs since 2 months. Imaging revealed a fluorodeoxyglucose-avid mediastinal mass encasing the superior vena cava and right pulmonary artery, raising a strong suspicion for malignancy. Investigations, including extensive serological testing, bronchoscopy with endobronchial ultrasound lymph node sampling and thoracoscopic biopsy, excluded secondary causes. Histopathology demonstrated dense fibrocollagenous tissue with lymphoplasmacytic infiltrates, confirming idiopathic fibrosing mediastinitis. She showed minimal response to corticosteroids and tamoxifen but exhibited substantial clinical and radiological improvement following rituximab therapy. This highlights the diagnostic complexity of idiopathic fibrosing mediastinitis and supports the emerging role of B-cell-directed immunotherapy in refractory cases.