Retroperitoneal fibrosis (Ormond's disease) is a chronic condition characterized by fibro-inflammatory tissue proliferation around the aorta and iliac vessels in the retroperitoneal space. 70% of cases are idiopathic and within the IgG4-related disease spectrum; 30% are secondary (drugs — ergotamine, methyldopa; malignancy — lymphoma, carcinoid; infection; radiotherapy; aortic aneurysm). The characteristic CT finding is a soft tissue mass extending from L4-L5 level to the bifurcation, encasing the aorta and IVC. Medial deviation of ureters is the pathognomonic finding — ureters that normally course laterally are pulled medially by retroperitoneal fibrosis. Ureteral obstruction and hydronephrosis are common complications. Fibrotic tissue shows low signal on T2 (mature collagen) but in the active inflammation phase may show T2 hyperintensity and enhancement — this distinction is critical for treatment response assessment. Corticosteroids are effective in treatment (especially in IgG4-related form); surgical ureterolysis may be needed for hydronephrosis.
Age Range
40-70
Peak Age
55
Gender
Male predominant
Prevalence
Rare
Retroperitoneal fibrosis results from a chronic immune-mediated inflammatory response against atherosclerotic plaque components (especially oxidized LDL and ceroid lipids) in the aortic adventitia. In the idiopathic form, antigens in the aortic wall trigger T-lymphocyte and B-lymphocyte infiltration → pro-inflammatory cytokines (IL-6, TNF-alpha) and profibrotic growth factors (TGF-beta, PDGF) are released → fibroblast proliferation and collagen deposition begin → periaortic fibrotic plaque forms. In the IgG4-related form, IgG4-positive plasma cells form the dominant cell population and obliterative phlebitis is the characteristic histological finding. Fibrotic tissue spreads from around the aorta toward the ureters, IVC, and iliac vessels → causing medial deviation of ureters (ureters normally course along the lateral border of the psoas muscle → fibrotic tissue pulls them medially). Ureteral compression leads to obstructive uropathy and hydronephrosis. The CT appearance of fibrotic tissue depends on stage: in the active inflammatory phase, soft tissue enhances due to edema and vascular proliferation and shows T2 hyperintensity → responsive to treatment. In the mature fibrotic phase, collagen becomes dominant → T2 hypointense signal (low free water), enhancement decreases → poorly responsive to treatment. This phase distinction on MRI is critical for treatment planning.
On delayed phase CT, ureters that normally course along the lateral border of the psoas muscle are pulled medially by retroperitoneal fibrotic mass — pathognomonic for retroperitoneal fibrosis. Malignant retroperitoneal masses displace ureters laterally, fibrosis pulls them medially.
On contrast-enhanced CT, a smooth-margined, homogeneous soft tissue mass encasing the infrarenal aorta and IVC is seen. The mass typically begins at L4-L5 level and extends to the aortic bifurcation, sometimes to iliac arteries. It does not narrow the aortic lumen (unlike malignant masses) — only wraps around externally. Enhancement depends on disease activity: homogeneous moderate enhancement in active phase; minimal enhancement in mature phase. Ureters are embedded within the mass and pulled medially. IVC compression may lead to lower extremity edema.
Report Sentence
A __ mm thick smooth-margined retroperitoneal soft tissue encasing the infrarenal aorta and IVC is seen, consistent with retroperitoneal fibrosis.
On delayed phase (excretory phase) CT, the ureters are seen deviated medially rather than their normal course along the lateral border of the psoas muscle. This medial deviation is usually bilateral at L4-S1 level and results from the retroperitoneal fibrotic mass encasing the ureters. Ureteral obstruction leads to proximal hydronephrosis and hydroureter — renal pelvic dilatation and cortical thinning may be visible. Delayed nephrogram shows delayed contrast excretion on the obstructed side. If ureteral stents are placed, their location and patency are assessed.
Report Sentence
Both ureters are medially deviated at L4-S1 level with bilateral hydronephrosis; consistent with ureteral obstruction from retroperitoneal fibrosis.
On T2-weighted MRI, the signal intensity of retroperitoneal fibrotic tissue reflects disease activity. In the active inflammatory phase, it shows T2 hyperintensity due to edema and cellular infiltration — this phase responds to treatment (corticosteroids). In the mature fibrotic phase, it shows T2 hypointensity due to dense collagen accumulation — this phase is treatment-resistant. Mixed pattern (hyperintense and hypointense areas together) represents partially active disease. This signal distinction plays a critical role in treatment planning and response monitoring — T2 signal decrease on follow-up MRI indicates treatment response (fibrosis maturation).
Report Sentence
Retroperitoneal fibrotic tissue shows __ signal on T2, consistent with __ phase disease.
On T1-weighted MRI, retroperitoneal fibrotic tissue shows signal isointense to muscle — similar T1 signal in both active and mature phases. On gadolinium-enhanced T1, active phase shows prominent enhancement, mature phase shows minimal enhancement — enhancement degree correlates with vascularity and inflammatory activity. Contrast-enhanced T1 sequences are helpful in evaluating fibrotic tissue extent, ureteral obstruction level, and IVC compression. Subtraction images (post-contrast T1 - pre-contrast T1) are useful in demonstrating true enhancement.
Report Sentence
Retroperitoneal fibrotic tissue shows __ enhancement on contrast-enhanced T1, consistent with __ disease activity.
On PET-CT, active retroperitoneal fibrosis shows increased FDG uptake in the periaortic area (SUVmax typically 3-8). FDG uptake reflects inflammatory cell activity (especially activated lymphocytes and macrophages). FDG uptake decreases parallel to treatment response — SUVmax decrease on follow-up PET-CT confirms treatment response. In the mature fibrotic phase, FDG uptake is minimal or absent. PET-CT also helps distinguish the idiopathic form from malignant retroperitoneal processes (lymphoma — very high FDG uptake, multiple involvement sites). It is also used to screen for other organ involvement in IgG4-related disease (pancreas, salivary glands, bile ducts).
Report Sentence
Increased FDG uptake is seen in periaortic fibrotic tissue on PET-CT (SUVmax: __); consistent with active inflammatory phase.
On B-mode US, bilateral hydronephrosis (pelvic and calyceal dilatation) is seen — the most common first-detected finding of ureteral obstruction from retroperitoneal fibrosis. A hypoechoic-isoechoic soft tissue mass around the aorta may be visible but US evaluation is limited due to retroperitoneal location (bowel gas artifact). Ureteral dilatation may be traced but the obstruction level cannot be reliably determined by US — CT or MRI required. US is valuable for hydronephrosis screening and follow-up; used for percutaneous nephrostomy guidance.
Report Sentence
Bilateral hydronephrosis is seen, suggesting ureteral obstruction; CT or MRI is recommended for etiology.
Criteria
70% of cases. Elevated serum IgG4 (>135 mg/dL). Histology shows IgG4+ plasma cells, storiform fibrosis, obliterative phlebitis. Other IgG4 organ involvement may coexist (autoimmune pancreatitis, sclerosing cholangitis, Mikulicz disease).
Distinct Features
Good response to corticosteroids. T2 hyperintensity and enhancement prominent in active phase. Rituximab is second-line therapy.
Criteria
Form developing from drugs (ergotamine, methyldopa, beta-blocker), malignancy (lymphoma, carcinoid, retroperitoneal sarcoma), radiotherapy, infection, or post-surgery. The underlying cause must be treated.
Distinct Features
In malignancy-related forms, mass may be more irregular and heterogeneous. Aortic lumen invasion suggests malignant form (idiopathic form preserves lumen). In drug-related form, discontinuation may lead to regression.
Criteria
Thick perianeurysmal fibrotic tissue surrounding infrarenal aortic aneurysm. Aneurysm wall is thick and enhancing. Evaluated within retroperitoneal fibrosis spectrum.
Distinct Features
Aneurysm is present (>3 cm aortic diameter). Fibrotic tissue is integrated with aneurysm wall. Ureteral obstruction may accompany. Treatment may combine surgical (EVAR or open repair) and medical (corticosteroid).
Distinguishing Feature
Retroperitoneal lymphoma usually appears as multiple enlarged lymph nodes around the aorta and IVC — discrete nodular structures are visible. In RP fibrosis, a smooth, homogeneous plaque-like mass is seen. Lymphoma may narrow the aortic lumen or invade the vessel wall; fibrosis preserves the lumen. Very high FDG uptake (SUV >10) on PET-CT in lymphoma.
Distinguishing Feature
Retroperitoneal sarcoma is usually a large, heterogeneous, irregularly marginated mass — containing necrosis and hemorrhage. RP fibrosis is smooth and homogeneous. Sarcoma can invade aorta/IVC creating luminal deformity; fibrosis preserves the lumen. Sarcoma displaces ureters laterally, fibrosis pulls medially.
Distinguishing Feature
Erdheim-Chester disease may show similar periaortic fibrotic tissue but bone involvement (bilateral symmetric femur/tibia metaphyseal osteosclerosis), perirenal fat infiltration ('hairy kidney'), and orbital/cerebral involvement accompany. In RP fibrosis, bone and other organ involvement is absent (pancreas/salivary gland involvement may occur in IgG4 form).
Distinguishing Feature
Inflammatory aortic aneurysm has an aneurysm present (>3 cm) with perianeurysmal fibrotic tissue integrated with the aneurysm wall. In idiopathic RP fibrosis, aortic diameter is normal or minimally dilated without true aneurysm. Treatment approaches differ.
Urgency
urgentManagement
medicalBiopsy
NeededFollow-up
3-monthTreatment of retroperitoneal fibrosis depends on disease activity and complications. In the active inflammatory phase, corticosteroid therapy is first-line (prednisolone 30-60 mg/day, gradual taper) — dramatic response especially in IgG4-related form. Tamoxifen, mycophenolate mofetil, and rituximab are used as steroid-sparing agents. Biopsy is recommended for malignancy exclusion — especially with atypical presentation or treatment non-response. Ureteral obstruction requires emergent DJ stent or percutaneous nephrostomy → followed by medical therapy. Surgical ureterolysis is performed for refractory obstruction. Treatment response is followed by MRI: T2 signal decrease and enhancement reduction indicate response. Serum IgG4 and CRP/ESR levels are biochemical response markers. MRI follow-up at 3-6 month intervals is recommended — relapse rate reaches 50% upon treatment discontinuation.
Early recognition of ureteral obstruction in RPF and stent placement preserves renal function. Steroid therapy is effective in active phase. IgG4 levels should be checked. Biopsy may be needed to exclude malignant RPF.