Retroperitoneal fibrosis (RPF) is a rare disease characterized by proliferation of an abnormal fibroinflammatory tissue, which usually surrounds the infrarenal portion of the abdominal aorta, inferior vena cava and iliac vessels. This process may extend to neighbouring structures, often entrapping the ureters or other abdominal organs . Its pathogenesis is not well established, there are two main theories: the first one propose that RF is an exaggerated inflammatory reaction to atherosclerosis aortic disease induced by LDL lipoproteins. The second one says that RPF is a manifestation of an autoimmune systemic disease .
Double inferior vena cava and unilateral kidney agenesis are congenital anomalies that usually do not have clinical implications [3, 4].
RPF is generally idiopathic, but can also be secondary to the use of certain drugs, malignant diseases, infections, and surgery.
It has an insidious presentation which makes diagnosis difficult, often with non-specific systemic and local symptoms. The triad of ill-defined abdominal pain, pulsating mass and high ESR is characteristic. The local affectation is caused by the entrapment of the retroperitoneal structures, mainly the ureters (60-100%) causing obstructive uropathy and renal failure with abdominal/lumbar pain, oedema, varicocele, dysuria, oligoanuria, deep venous thrombosis, etc. General symptoms include asthenia, anorexia, fever, myalgias and arthralgias.
Radiology is indispensable, both for the initial diagnosis and follow-up. Biopsy is considered necessary only in atypical localization or suspicion of an underlying infectious or tumour process. When secondary to malignant disease, retroperitoneal fibrosis is usually more irregularly shaped and atypically localized. Image findings:
- US: RPF is usually identified as a hypoechoic or anechoic, well-demarcated although irregularly contoured retroperitoneal mass. It is important to look for associated hydronephrosis [1, 5].
- CT: RPF is typically seen as a well-delimited but irregular soft-tissue periaortic mass, which extends from the level of the renal arteries to the iliac vessels. The mass usually lies anterior and lateral to the aorta, without causing aortic displacement [1, 5].
- MRI: RPF typically has low signal intensity on T1-weighted images. On T2-weighted images the signal intensity is variable reflecting the degree of associated active inflammation.
Both computed tomography and magnetic resonance imaging mirrors the active disease showing soft-tissue enhancement after administration of intravenous contrast materials [1, 5].
In most patients corticosteroids achieve prompt improvement of symptoms and often lead to a reduction in size of the retroperitoneal mass and resolution of obstructive complications [1, 2, 5].
Recognizing imaging features of retroperitoneal fibrosis is vital to assure correct diagnosis and optimal treatment, the most important challenge is differentiation of benign RPF from malignant forms.