A Rare Case of Granulomatosis With Polyangiitis Presenting as Retroperitoneal Fibrosis in the Peri-Iliac Region Causing Hydronephrosis.

Wegener's granulomatosis, now more commonly referred to as granulomatosis with polyangiitis (GPA), is a rare, idiopathic, systemic inflammatory disease, most commonly involving the respiratory tract, kidneys, and sinonasal region. The condition affects small and medium-sized blood vessels, such as arteries, arterioles, venules, and capillaries. Some cases of the disease presenting as retroperitoneal fibrosis and/or affecting the aorta have been reported. Although advances in the treatment of GPA have contributed to a decline in mortality, early diagnosis is still of vital importance due to the possible complications of the disease. Here, we present the case of a 69-year-old man with acute-onset abdominal pain. Ultrasound of the abdomen showed left-sided hydronephrosis. Computed tomography detected cavitating pulmonary lesions and peri-iliac alterations caused by retroperitoneal fibrosis with involvement of the crossing ureter. Laboratory results revealed high antineutrophil cytoplasmic antibody levels and high inflammatory markers. A lung biopsy performed via bronchoscopy revealed necrotizing granulomas and solidified the diagnosis of GPA both in the lung and the peri-iliac region. Treatment with immunosuppressive agents and glucocorticoids was initiated. A follow-up after two months showed regression of the pulmonary lesions and partial resolution of the hydronephrosis as well as reduced inflammatory markers in the blood tests.