Simultaneous idiopathic mediastinal and retroperitoneal fibrosis presenting with acute respiratory failure: A case report and literature review.

Simultaneous idiopathic mediastinal and retroperitoneal fibrosis is an exceptionally rare fibro-inflammatory disorder with nonspecific clinical manifestations and challenging imaging findings. A 33-year-old man presented with acute respiratory distress and bilateral obstructive uropathy. Contrast-enhanced CT demonstrated infiltrative soft-tissue masses involving the mediastinum and retroperitoneum, encasing major vessels and the left ureter. CT-guided biopsy confirmed dense collagenous fibrosis without evidence of malignancy. Following exclusion of secondary causes, idiopathic mediastinal and retroperitoneal fibrosis was diagnosed. Corticosteroid therapy led to marked clinical improvement. This case highlights the essential contribution of multidetector computed tomography in identifying the characteristic distribution of fibro-inflammatory lesions, defining their relationship with adjacent vascular and urinary structures, guiding tissue sampling, and narrowing the differential diagnosis. Careful integration of imaging findings with histopathological and laboratory investigations is mandatory to distinguish idiopathic fibrosis from IgG4-related disease, lymphoma, metastatic malignancy, Erdheim-Chester disease, infectious fibrosing mediastinitis, and other fibro-inflammatory disorders. Contrast-enhanced CT was essential for lesion characterization, biopsy guidance, and diagnostic assessment. This rare entity should be considered in patients with simultaneous mediastinal and retroperitoneal infiltrative masses.