A periaortic soft-tissue mantle at L4–L5 that encases the aorta and draws the ureters medially — separate idiopathic or IgG4-related fibrosis from lymphoma and malignant fibrosis, and report the ureteric obstruction.
Orient first
- Most are idiopathic or IgG4-related; secondary causes include drugs, radiotherapy and malignancy.
- Fibrosis does not displace the aorta anteriorly from the spine, whereas lymphoma and metastatic nodes often lift it.
- Medial deviation of the middle third of the ureters with hydronephrosis is typical.
Acquire the study
- Portal venous phase CT abdomen-pelvis with coronal reformats.
The manoeuvre
- Periaortic soft-tissue mantle below the renal arteries; its thickness in mm and craniocaudal extent.
- Is the aorta lifted off the spine? (favours lymphoma/metastasis).
- Ureters: medial deviation, hydronephrosis, level of obstruction.
- IVC compression; other IgG4 organs (pancreas, kidneys, bile ducts).
What confirms it
- A periaortic mantle with medial ureteric deviation and no nodal mass; biopsy when atypical.
What licenses you to exclude it
- A normal periaortic fat plane excludes retroperitoneal fibrosis.
The classic misread
- Calling an inflammatory abdominal aortic aneurysm fibrosis — measure the aortic diameter.