Retroperitoneal fibrosis (RPF), is a condition that has previously been described as chronic periaortitis. It is an uncommon fibrotic reaction in the retroperitoneum that typically presents with ureteral obstruction.
The disease is part of a spectrum of entities that have a common pathogenetic process consisting of an inflammatory response to advanced atherosclerosis of the abdominal aorta, combined with auto-immunologic factors:
- idiopathic retroperitoneal fibrosis (IRF)
- perianeurysmal retroperitoneal fibrosis
- isolated periaortitis: corresponds to a non-aneurysmal form of chronic periaortitis
- inflammatory abdominal aortic aneurysm (IAAA)
Retroperitoneal fibrosis is an uncommon condition with a reported estimated incidence of 1.38 cases per 100,000 people 4. The mean age is approximately 64 years with a male-to-female ratio of 3:1 5.
- idiopathic: Ormond disease (70% benign)
- beta blockers
- methysergide (discontinued migraine medication)
- inflammation: pancreatitis, pyelonephritis
- malignant: desmoplastic reaction, lymphoma
- prolonged exposure to asbestos
- retroperitoneal bleeding, e.g. after trauma or medical procedure
Contrast enhancing fibrosis encompassing the retroperitoneal structures causing ureteric and vascular obstruction and displacement.
Displacement of the aorta and IVC anteriorly away from the vertebral bodies is suggestive of malignant aetiology. Invasion and disruption of bone and/or soft tissue structures suggests an aggressive process - infection or malignancy. Multiple subcentimeter lymph nodes are frequently seen in non-malignant RPF, probably reactive secondary to the disease process, and should not be confused for malignancy3.
Whilst largely superseded by cross-sectional imaging techniques, a classic triad is described3:
- medial deviation of the middle third of the ureters
- tapering of the lumen of one or both ureters in lower lumbar or upper sacral region
- Proximal unilateral or bilateral hydroureteronephrosis with delayed excretion of contrast material (reported in over half of cases and thought to be due to impaired peristalsis)
Retroperitoneal fibrosis is visible as a soft tissue density mass located around the aorta and iliac arteries. Classically, it develops around the aortic bifurcation and spreads upwards where it can envelop the renal hila. It encases but does not invade or stenosis the ureters or vessels. However, ureteric obstruction and venous thromboses can occur.
In early or active stages variable enhancement can be seen with intravenous contrast while no enhancement may be seen in the quiescent disease.
MR has been reported to be as sensitive as CT in its assessment of retroperitoneal fibrosis with the added advantage of high contrast resolution between closely apposed retroperitoneal structures. it can evaluate the urinary tracts using fast T2 weighted spin-echo sequences without requiring intravenous contrast in patients with impaired renal function.
The soft tissue mass is usually dark on T1 and T2WI unless there is an active inflammation whereby the T2W images can be hyperintense.
Uptake will be seen in active inflammation and absent in metabolically inactive disease 3.
Treatment and prognosis
Retroperitoneal fibrosis may lead to ureteric obstruction and consequent renal failure. In some cases, a blow-out of the ureter is described as a result of the obstruction.
Imaging differential considerations include:
- retroperitoneal lymphoma: non-lymphomatous RPF is often seen centred at L4/5 level. If disease is centred cranially to L4/5, consider lymphoma3.
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- 5. van Bommel EF, Jansen I, Hendriksz TR et-al. Idiopathic retroperitoneal fibrosis: prospective evaluation of incidence and clinicoradiologic presentation. Medicine (Baltimore). 2009;88 (4): 193-201. doi:10.1097/MD.0b013e3181afc420 - Pubmed citation
- 6. Rosenkrantz AB, Spieler B, Seuss CR et-al. Utility of MRI features for differentiation of retroperitoneal fibrosis and lymphoma. AJR Am J Roentgenol. 2012;199 (1): 118-26. doi:10.2214/AJR.11.7822 - Pubmed citation