Retroperitoneal fibrosis

Last revised by Arlene Campos on 11 Jan 2024

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 ureteric obstruction.

The disease is part of a spectrum of entities that have a common pathogenic process consisting of an inflammatory response to advanced atherosclerosis of the abdominal aorta, combined with autoimmunologic factors:

Historically, there have been a large number of different names for retroperitoneal fibrosis, due to its spectrum of appearances and poorly-understood pathology. These include periureteritis fibrosa, periureteritis plastica, chronic periureteritis, sclerosing retroperitoneal granuloma and fibrous retroperitonitis 8.

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.

Patients may present with systemic symptoms such as mild fever and malaise due to an ongoing inflammatory process. Sometimes patients present with flank or back pain which is not position-dependent and has a transient relief with oral non-steroidal anti-inflammatory drugs 7. If there is the involvement of the ureters, colicky ureteric pain may be present. 

Contrast-enhancing fibrosis encases the retroperitoneal structures causing ureteric and vascular obstruction and displacement. 

Displacement of the aorta and IVC anteriorly away from the vertebral bodies are suggestive of malignant etiology. 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 malignancy 3.

While largely superseded by cross-sectional imaging techniques, a classic triad is described 3:

  1. medial deviation of the middle third of the ureters (maiden waist sign 12)

  2. tapering of the lumen of one or both ureters in the lower lumbar or upper sacral region

  3. 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 stenose 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.

MRI 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 T1W and T2W 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.

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.

The disorder was first described in 1905 by the French urologist Joaquin Albarran (1860-1912) and later first described in the English literature in 1948 by the American urologist John Kelso Ormond (1886-1978) 8,10,11. Hence its sometimes-seen monicker Albarran-Ormond syndrome (for the idiopathic form) 9.

Imaging differential considerations include:

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