Continuing Education Activity

Retroperitoneal fibrosis is a rare immune-mediated condition characterized by chronic inflammation and fibrosis in the retroperitoneum, which can lead to the compression of retroperitoneal structures such as the ureters, aorta, and vena cava. This fibrotic process often results in the encasement and compression of these structures, especially the ureters, causing symptoms such as vague abdominal pain, hypertension, renal failure, and other complications. Although 70% of cases of retroperitoneal fibrosis are idiopathic, certain medications, surgeries, smoking, and asbestos exposure are recognized risk factors.

The most common presentation includes vague abdominal pain and azotemia. Laboratory findings and clinical presentation are often nonspecific, and diagnosis is typically made incidentally through imaging studies, with obstructive ureteral uropathy being the most common finding. In selected cases, a biopsy may be required. Treatment options may include medical therapy and/or surgical management. This activity outlines the evaluation, diagnosis, and management of retroperitoneal fibrosis, emphasizing the importance of collaboration among healthcare professionals through team-based, interprofessional care for affected patients.

Objectives:

• Identify patients with possible retroperitoneal fibrosis based on their clinical history and presentation.
• Implement a comprehensive diagnostic approach that includes both clinical evaluation and imaging studies to confirm the diagnosis of retroperitoneal fibrosis.
• Select appropriate treatment modalities for retroperitoneal fibrosis based on patient-specific factors, such as disease extent, complications, and response to initial therapies.
• Collaborate with interprofessional team members to optimize treatment and care for patients with retroperitoneal fibrosis.

Introduction

Retroperitoneal fibrosis is a relatively rare immune-mediated condition characterized by a chronic, progressive periaortic inflammatory and fibrotic process in the retroperitoneum, which can lead to the compression of retroperitoneal structures such as the ureters, aorta, and vena cava.[1] This fibrotic process can often result in the encasement and extrinsic compression of the ureters and other retroperitoneal structures, including the aorta and inferior vena cava. The condition may be idiopathic, drug-related, or secondary to immune-mediated disease.[2][3][4][5][6]

Retroperitoneal fibrosis may be asymptomatic but typically presents with dull pain or discomfort in the abdomen, back, flank, or inguinal area. Additional common nonspecific signs include hypertension and some degree of azotemia. Diagnosis is often made incidentally during studies conducted for unrelated reasons, and a tissue biopsy may be necessary in some cases. Treatment primarily involves medical therapy, such as steroids, though some cases may require surgical management.

Retroperitoneal fibrosis was originally called Ormond disease, named after John Ormond, an American urologist who described two cases in 1948. However, the first reported case was documented by French urologist Joaquin Albarran in 1905.[7] Older terms for retroperitoneal fibrosis, which are no longer used, include chronic periureteritis, fibrous retroperitonitis, Ormond disease, periureteritis fibrosis, and periureteritis plastica.[7]

Etiology

More than 70% of retroperitoneal fibrosis cases are classified as idiopathic. However, many cases previously considered idiopathic are now recognized as caused by immunoglobulin G4 (IgG4)-related disease, an immune-mediated fibroinflammatory disorder first described as a distinct clinical entity in 2003. IgG4-related disease, which can affect multiple organs.[2][8][9][10][11] IgG4-related disease accounts for 35% to 60% of all cases of idiopathic retroperitoneal fibrosis.[12][13][14][15][16] This prevalence has led to the classification of idiopathic retroperitoneal fibrosis as either IgG4-related or -unrelated.[2][17] 

A total of 30% of retroperitoneal fibrosis cases have an identifiable cause. Numerous drugs have been implicated in the development of retroperitoneal fibrosis, particularly methysergide (12%), methyldopa, bromocriptine, and other ergot alkaloids.[18][19] Additional medications associated with the condition include beta blockers, hydralazine, and analgesics.[18] In addition, biological agents such as tumor necrosis factor (TNF) inhibitors etanercept and infliximab have also been identified as secondary causes of retroperitoneal fibrosis.

Retroperitoneal fibrosis and inflammatory periaortitis account for an estimated 4% to 10% of all abdominal aortic aneurysms.[16][20] Malignancies, including carcinoid tumors, Hodgkin and non-Hodgkin lymphomas, sarcomas, colorectal cancer, and cancers of the breast, prostate, and bladder, account for 8% of retroperitoneal fibrosis cases, with lymphoma being the most common among them.[21] In such cases, treatment of the underlying malignancy is recommended.[21]

Infections such as actinomycosis, histoplasmosis, and tuberculosis, radiation therapy to the abdomen for conditions such as testicular seminoma, colon, and pancreatic cancers, retroperitoneal hemorrhage, and major abdominal surgeries such as lymphadenectomies have been identified as additional causes of secondary retroperitoneal fibrosis.[21] Exposure to asbestos and tobacco smoke significantly increases the risk of retroperitoneal fibrosis, with a 3- to 4-fold increase associated with each factor.[1][22][23][24] When combined, asbestos exposure and a significant smoking history result in an alarming 8- to 12-fold increase in risk.[24]

Ceroid, a complex polymer of oxidized proteins and lipids commonly found in atherosclerotic plaques, has been hypothesized to act as an antigen that initiates the periaortic inflammatory response.[25][26]

Epidemiology

The true incidence of retroperitoneal fibrosis is unknown, but it is generally estimated to be 1.4 cases per 100,000 individuals annually.[27] Retroperitoneal fibrosis most commonly affects patients between the ages of 40 and 60, although it may also be found in children and older adults.[28][29]

Retroperitoneal fibrosis shows a male predominance, with a male-to-female ratio estimated at approximately 2:1 to 3:1.[22][26][28] The overall prevalence of IgG4-related disease is unknown. Please see StatPearls' companion resource, "IgG4-Related Disease," for more information.

Pathophysiology

Idiopathic retroperitoneal fibrosis is currently hypothesized to be a manifestation of a systemic autoimmune disease, potentially arising as a primary form of chronic periaortitis that triggers a periaortic fibroinflammatory response. The condition is often associated with elevated acute phase reactants, autoantibodies, and other known autoimmune diseases. Retroperitoneal fibrosis also affects other vascular segments, such as the thoracic aorta and mesenteric arteries, which supports the idea that it is a primary systemic inflammatory disease of large arteries and may be multifocal.[30]

The pathogenesis of idiopathic retroperitoneal fibrosis involves a complex interaction of chemokines, cytokines, and other provocative factors, such as transforming growth factor-β (TGF-β), CXCL11, CXCL12, interleukins (ILs) such as IL-4, IL-6, IL-10, IL-12, and IL-13, and type 2 helper T (T_H2) cells. These factors mediate the inflammatory response and promote fibrosis.[31][32][33] This mechanism is relevant to IgG4-related and non–IgG4–related forms of idiopathic retroperitoneal fibrosis.[34][35]

The exact pathophysiology of drug-induced retroperitoneal fibrosis remains unclear.[1][36][37][38] IgG4-related disease is a systemic fibroinflammatory disorder characterized by the presence of IgG4-producing plasma cells, with retroperitoneal fibrosis being one of its possible manifestations. As many as 27% of all patients with IgG4-related disease may develop retroperitoneal fibrosis.[16][39][40][41][42]

IgG4-related disease is characterized by tumor-like swelling of affected organs, which most commonly include the kidneys, orbital adnexal structures, pancreas, retroperitoneum, and salivary glands. This swelling features a lymphoplasmacytic infiltrate enriched with IgG4-positive plasma cells and varying degrees of fibrosis.[43][44] The condition may also lead to sclerosing cholangitis, Riedel thyroiditis, pancreatitis, lung disease, prostatitis, and inflammatory pseudotumor of the orbit.[44][45][46][47] Isolated IgG4-related retroperitoneal fibrosis can also occur.[48] Please see StatPearls' companion resources, "IgG4-Related Disease," "Nonspecific Orbital Inflammation," "Riedel Thyroiditis," and "Cholangitis," for more information.

Patients with IgG4-related disease often do not present with overt symptoms and are typically afebrile. However, they may exhibit lymphadenopathy (in about 40% to 80% of cases), a history of allergies or asthma (in 40% of cases), and kidney failure due to tubulointerstitial nephritis or membranous glomerulonephritis. Those with involvement of multiple organs frequently demonstrate substantial, unexplained weight loss of 20 to 30 pounds.[49][50][51][52][53][54][55][56][57] 

Patients with idiopathic retroperitoneal fibrosis who are IgG4-positive tend to be older at disease onset, are more likely to be male, and often have kidney involvement characterized by nephritis or renal masses. These patients are also more likely to exhibit eosinophilia, distant organ involvement including lymph nodes and salivary glands, and higher levels of C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), and creatinine, with lower complement levels compared to similar IgG4-positive individuals without idiopathic retroperitoneal fibrosis.[5][14][57][58][59] 

IgG4-related disease is significantly underdiagnosed due to its complex and varied presentations across different organs, as well as its recent recognition as a unique clinicopathological disorder. Many clinicians are unfamiliar with the condition and may fail to recognize it.[5][11][57][59][60] Additionally, IgG4-related disease is associated with a higher overall risk of developing malignancies, particularly pancreatic cancer and lymphoma.[61]

Recognition of IgG4-related disease is crucial because patients often respond exceptionally well to glucocorticoid therapy and rituximab, either separately or in combination, though the optimal timing of these treatments remains controversial.[62][63][64][65] Please see StatPearls' companion resources "IgG4-Related Disease" and "Rituximab," for more information.

Histopathology

Grossly, retroperitoneal fibrosis appears as a smooth, flat, tan-colored dense mass that encases the retroperitoneal structures. It is typically centered around the fourth and fifth lumbar vertebrae, often at the aortic bifurcation, and can invade the ureter or psoas muscle. Histologically, retroperitoneal fibrosis presents as a nonspecific inflammatory process characterized by an infiltrate comprised of macrophages, plasma cells, and lymphocytes. The aggregates typically have a core rich in CD20 B cells and a periphery abundant in CD3 T cells. Plasma cells may also be positive for IgG4.[12]

Fibroblastic proliferation with densely hyalinized collagen is arranged in a woven or spiral (storiform) pattern, accompanied by varying degrees of chronic lymphocytic and plasma cell infiltrates, which may be IgG4-positive.[1] The resulting fibrous tissue comprises an extracellular matrix of type-1 collagen fibers organized in thick, irregular bundles, often encircling smaller vessels. Vasculitis of small retroperitoneal vessels is observed in about 50% of cases. This is also described as a fibroproliferative process infiltrated by eosinophils and occasionally IgG4-positive plasma cells.

The plasma cells in idiopathic retroperitoneal fibrosis may be positive for IgG4, which allows for the differentiation of the disorder pathophysiologically into IgG4-related and non–IgG4-related groups.[12][13][14][15] Histologically, at least 10 IgG4⁺ plasma cells per high-power field (HPF) are typically required for diagnosis, with many cases showing more than 50 IgG4⁺ cells per HPF.[49] Fat necrosis and obliterative phlebitis may also be present. Additional features of IgG4-related retroperitoneal disease include an IgG4⁺/total IgG plasma cell ratio above 40%, elevated serum IgG4 levels, high plasma cell density (>10%), obliterative phlebitis, and significant eosinophilic infiltration.[21][27]

The histopathological findings in idiopathic and secondary retroperitoneal fibrosis are often indistinguishable. Malignant retroperitoneal fibrosis may show neoplastic cells dispersed within the fibrous matrix, and in cases of lymphoma, an inflammatory infiltrate is typically present. In contrast, Erdheim-Chester disease is characterized by the presence of foamy histiocytes.[66] Please see StatPearls' companion resource, "Lymphoma," for more information.

History and Physical

The most common presenting symptom of retroperitoneal fibrosis is relatively vague discomfort, typically described as dull pain in the abdomen, back, inguinal, or flank areas, affecting over 90% of patients.[26][28][37][67][68] Testicular pain is reported in over 50% of male patients with retroperitoneal fibrosis.[69] The pain may radiate to the inguinal area and is typically poorly localized, non-colicky, unaffected by body position or physical activities, and is often worse at night. Nonsteroidal antiinflammatory drugs (NSAIDs) are usually sufficient for pain control. Obstructive uropathy is the most common potentially serious presentation, occurring in about 80% of cases, while gastrointestinal involvement is relatively rare.[70] Fatigue and substantial weight loss are present in 60% and 54% of patients, respectively.

The inferior vena cava can become obstructed due to extrinsic compression from the retroperitoneal mass, leading to deep venous thrombosis and lower extremity edema. Patients may also experience upper-leg claudication from arterial compromise of the lower extremities or symptoms of mesenteric ischemia due to compression of the mesenteric arteries.[1][8][26][71]

The bulk of retroperitoneal fibrosis typically centers around the distal aorta between the L4 and L5 vertebrae, encasing the ureters. This can lead to hydronephrosis due to extrinsic compression and encasement of the ureters, which interferes with ureteral peristalsis.

Other presenting symptoms may include:

• Anorexia
• Anuria
• Azotemia from bilateral ureteral obstruction (more than 50% of cases)
• General malaise
• Hydrocele or varicocele (up to 60% of men with retroperitoneal fibrosis)
• Low-grade unexplained fever
• Lower urinary tract symptoms (dysuria, frequency, or urgency)
• Nausea
• Oliguria
• Phlebitis
• Renal cortical thinning (8% to 30% of cases)
• Renovascular hypertension (30% to 60% of cases)
• Thrombophlebitis
• Vomiting [1][28][29][37][67][72][73][74][75][76][77]

Ascites, bowel obstruction, jaundice, peripheral edema, spinal cord compression, and thromboses are late symptoms indicating advanced disease. Retroperitoneal fibrosis should be suspected in patients with chronic, vague, dull abdominal or flank pain (unilateral or bilateral) associated with newly diagnosed renal failure or hypertension. However, retroperitoneal fibrosis is most often identified incidentally during imaging for secondary problems or unrelated conditions.

The physical examination may reveal tenderness at the costovertebral angle (CVA), and renovascular hypertension due to impingement on the renal artery is common. A study reported hypertension in up to 57% of patients on presentation.[78] Lower extremity edema, evidence of thrombophlebitis, or deep vein thrombosis may also be present. Testicular tenderness is common in men, and a hydrocele may be present. In children, issues with hip extension and pain or discomfort extending to the hip or gluteal areas may be observed.[76][77][79]

Evaluation

Retroperitoneal fibrosis is most often discovered incidentally during the evaluation of urinary tract obstruction, unexplained renal failure, or vascular insufficiency. The initial patient assessment typically includes laboratory studies and a renal ultrasound or computed tomography (CT).

Laboratory Findings

Laboratory findings in retroperitoneal fibrosis can vary, with no specific hematological or biochemical abnormalities highly suggestive of the condition.

• Alkaline phosphatase is often elevated and has been suggested as a useful marker of disease activity.[80]
• Creatinine concentration and blood urea nitrogen (BUN) are frequently elevated, depending on the presence and extent of ureteral obstruction.[81]
• Normocytic anemia may be observed, likely related to renal insufficiency and chronic inflammation.[37]
• Urine cytology is recommended.[21]
• Antinuclear antibody (ANA) titers are positive in up to 60% of patients with idiopathic retroperitoneal fibrosis and can be useful in predicting a relapse after treatment.[37][82][83]
• Eosinophilia may be present, and, along with higher IgG4 serum levels, suggests a higher relapse rate.[84]
• ESR and CRP levels are elevated in one-half to two-thirds of patients with retroperitoneal fibrosis.[28][85] These levels can be used as indicators of treatment effectiveness.[85] 
• Thyroid function tests are essential, as approximately one-quarter of idiopathic retroperitoneal fibrosis patients will have autoimmune thyroiditis, often demonstrating thyroid microsome and thyroglobulin antibodies.[18]

Some experts recommend additional laboratory testing, including:

• Autoantibody testing: This may include anti-thyroid microsome, anti-thyroglobulin, anti-neutrophil cytoplasmic antibodies, or anti-smooth muscle antibodies.
• Serum immunoglobulin levels: This may include IgG4.[13][21] Notably, high serum IgG4 levels are suggestive but not diagnostic of IgG4-related disease, and low levels do not rule it out.[49][86][87][88]
• Serum protein electrophoresis and free light chain assay: Polyclonal hypergammaglobulinemia would be a typical finding.

Imaging studies, including computed tomography (CT) and magnetic resonance imaging (MRI), are typically used for the initial diagnosis. However, imaging alone cannot definitively differentiate between benign and malignant retroperitoneal fibrosis.[89] Therefore, if a biopsy is not performed initially, it should be considered in patients who either fail to respond to standard steroid therapy or present with any of the specific clinical scenarios outlined below.

Diagnostic Evaluation

Imaging studies, including computed tomography (CT) and magnetic resonance imaging (MRI), are typically used for the initial diagnosis. However, imaging alone cannot definitively differentiate between benign and malignant retroperitoneal fibrosis.[89] Therefore, if a biopsy is not performed initially, it should be considered in patients who either fail to respond to standard steroid therapy or present with any of the specific clinical scenarios outlined below. Antegrade or retrograde ureteropyelography is recommended.[21] When evaluating patients with retroperitoneal fibrosis, particularly those with a history of cancer, it is crucial to assess for possible recurrence or exacerbation of malignancy, as outlined below.[21]

Renal ultrasound: This study often reveals a poorly marginated, irregularly contoured periaortic retroperitoneal mass that is typically hypoechoic or anechoic and may be associated with hydronephrosis.[1][17]

Contrast-enhanced CT scan: This study is the examination of choice for visualizing the extent of retroperitoneal fibrosis and detecting any associated lymphadenopathy or tumors.[90] On nonenhanced CT, retroperitoneal fibrosis typically exhibits attenuation values similar to those of the psoas muscle (1 to 25 Hounsfield units).[90] The fat plane between the mass and the psoas muscle may be obscured. Following intravenous contrast administration, enhancement patterns vary with disease stage—early stages often show avid enhancement, while late or inactive stages may exhibit minimal or no enhancement.[17][91]

The mass is generally confluent, encasing the anterior and lateral aspects of the aorta and often compressing the inferior vena cava.[17] The mass typically develops initially around the aortic bifurcation and extends superiorly where it may envelop the renal hila.[17] Although the mass encases the ureters and blood vessels, it usually does not directly invade them.[17] 

Typical findings of retroperitoneal fibrosis include hydronephrosis (bilateral in 68% of cases and unilateral in 20%) and medial deviation of the mid-ureters (maiden waist sign), which presents as a smoothly tapering ureteral appearance at the obstruction site, usually at the L4-L5 vertebral level.[68][91][92][93] These features, along with a lack of ureteral distensibility, are most evident with retrograde or antegrade pyelography. Localized lymphadenopathy is observed in about 25% of cases.[28] A significant advantage of CT imaging is its ability to guide a biopsy for pathological diagnosis.[17][71][91]

• Medial deviation of the ureters is the characteristic sign of retroperitoneal fibrosis and is defined as a separation of 5 cm or less between the 2 ureters or their appearance directly overlying and anterior to the lumbar vertebral bodies.[94] While retroperitoneal fibrosis is a common cause, this type and degree of medial deviation of the ureters can also be observed in cervical and prostate cancers. This may also be simulated by psoas muscle hypertrophy.[94]

• While there are no specific imaging characteristics for renal IgG4-related disease, the most common finding is multiple small, nodular lesions in the renal cortex.[6] Renal parenchymal changes may include a range of nodular lesions or diffuse patchy infiltrates, along with generalized nonspecific renal enlargement.[6]

Magnetic resonance imaging: MRI is considered equivalent to CT for diagnosing retroperitoneal fibrosis and superior for monitoring due to its higher contrast resolution. MRI provides detailed information on tissue activity and disease progression, with the retroperitoneal mass exhibiting characteristic T1- and T2-weighted imaging features.[95][96] Retroperitoneal fibrosis typically presents with diffusely low signal intensity on T1-weighted imaging, while T2-weighted imaging may show variable signal intensity, with high signal intensity indicating more active disease.[96][97][98] 

The apparent diffusion coefficient is generally higher, and diffusion-weighted imaging is lower in chronic or late-stage retroperitoneal fibrosis compared to active disease or malignancy.[96][97][98][99][100] Active retroperitoneal fibrosis will be enhanced by gadolinium contrast.[97][98][100]

With treatment, the T2 signal intensity often diminishes, serving as a measure of therapeutic efficacy. Gadolinium enhancement can be valuable in assessing treatment response, but MRI can still be performed without contrast if necessary. Decreases in gadolinium contrast enhancement should be anticipated following appropriate therapy.[17][26]

Imaging findings suggestive of a retroperitoneal malignancy include anterior elevation of the aorta (indicative of lymphoma), localized bone destruction, infiltration of surrounding structures, lateral displacement of the ureters, or an unusually large or bulky retroperitoneal mass.[101]

Positron emission tomography: Positron emission tomography (PET) with 18F-fluorodeoxyglucose (18F-FDG) is used to identify areas of increased metabolic activity that require higher utilization of tagged glucose.[102] In patients with retroperitoneal fibrosis, PET is not as dependable or diagnostic as CT or MRI for the initial evaluation. However, it is reliable for assessing the active inflammatory (metabolic) activity of the lesion after diagnosis.[103] PET appears to be more effective than laboratory tests (ESR and CRP) or other imaging methods in determining disease progression and activity. PET may also identify unexpected disease sites and help pinpoint the most active site for biopsy.[104][105][106] Some clinicians may obtain a baseline PET scan because high 18F-FDG activity is associated with a good response to glucocorticoid therapy, aiding disease tracking.[105][107]

Lymphangiography: Lymphangiography is not typically included in the standard workup for retroperitoneal fibrosis but may be useful in selected cases, especially when retroperitoneal fibrosis is suspected but initial CT or MRI imaging is inconclusive or negative. Due to the delicate structure of the lymphatics, their obstruction often occurs before ureteral blockage in retroperitoneal fibrosis. This can be demonstrated in lymphangiography, such as with dynamic contrast-enhanced MR lymphangiography, which may show lymphatic blockage at the L3/L4 level, contrast enhancement of collateral vessels, failure to visualize lymphatics above L3/L4, and delayed drainage in the iliac and para-aortic lymphatic chains.[108][109]

Tissue biopsy: Tissue biopsy is a controversial step, as the benefits of obtaining a histological diagnosis must be weighed against the risks, including patient discomfort and potential complications, such as bleeding. In straightforward cases, biopsies are often omitted unless the results are expected to alter the treatment approach. When a biopsy is performed, it should target the thickest and most metabolically active site identified on a PET scan.

The general expert consensus opinion is that a biopsy is indicated and should be considered in certain clinical scenarios, which include:

• An open surgical intervention for ureteral or vena cava compression is planned, where an open tissue biopsy of the retroperitoneal mass during surgery is suggested.
• Apparent infiltration of surrounding structures by the mass.
• Atypical location of the mass.
• Clinical, imaging, or laboratory findings suggest a possible underlying malignancy.
• Confluent or unusually extensive lymphadenopathy.
• CT-guided biopsy was insufficient for a diagnosis, such as in lymphoma cases.[110]
• Diagnostic uncertainty.
• Displacement of the aorta.
• Suspected Erdheim-Chester disease.
• Extension of the mass superiorly beyond the renal hilum.
• Failure to respond to initial steroid therapy.
• History of a prior malignancy that could potentially involve the retroperitoneum.
• Limited local expertise or experience with the radiological diagnosis of retroperitoneal fibrosis.
• Involvement of other organ sites, such as the pancreas or mesentery.
• Presence of perirenal fibrosis.
• A pressing need for a definitive histological diagnosis.
• Unusual or bulky appearance on imaging.[1][67][101][111][110]

Treatment / Management

Initial Acute Management

The initial management of retroperitoneal fibrosis is determined by the patient's clinical status. Patients presenting with signs of ureteral compression, hydronephrosis, and uremia require emergent decompression, typically achieved via percutaneous nephrostomy tubes or indwelling ureteral double J stents.[112] Ureteral stent placement is generally preferred due to its association with improved quality-of-life scores and ease of placement in cases of ureteral obstruction caused by retroperitoneal fibrosis.[27] Another advantage of ureteral stent placement is the ability to perform retrograde pyelograms during the procedure to assess the anatomy.In most cases (95%), ureteral stents can be successfully removed after appropriate steroid therapy, usually within 30 days.[113] However, in critically ill patients with electrolyte abnormalities and oliguria or anuria, nephrostomy tube placement is often preferred as an initial intervention. Please see StatPearls' companion resource, "Percutaneous Nephrostomy," for more information.

Ureteral obstruction in retroperitoneal fibrosis often appears relatively minimal despite significant renal failure. Given the degree of outflow resistance, ureteral catheters are usually relatively easy to pass. These 2 findings suggest that the mechanism of ureteral outflow obstruction is more functional, caused by impaired ureteral peristalsis due to the surrounding fibrotic mass, rather than actual mechanical blockage.

After renal decompression, the patient must be closely monitored for postobstructive diuresis, renal function status, and appropriate fluid and electrolyte replacement. Postobstructive diuresis is characterized by prominent polyuria following the relief of complete urinary obstruction, with urine output exceeding 200 mL/h. Patients are at risk for severe dehydration, electrolyte imbalances, and hypovolemic shock. The condition usually lasts less than 48 hours. Please see StatPearls' companion resource, "Postobstructive Diuresis," for more information.

Treatment of postobstructive diuresis involves close monitoring of serum BUN, creatinine, electrolytes, and appropriate fluid replacement. Oral fluid replacement is preferred, but if the patient cannot tolerate oral intake or keep up with fluid loss, one-half normal saline can be administered intravenously, replacing half of the fluid lost (eg, 500 mL for every 1 L lost).

Some patients may require urgent intervention for vascular obstruction or compromise, such as acute mesenteric arterial compromise or iliocaval occlusion, through percutaneous transluminal angioplasty, stent placement, or other surgical procedures.[114][115] After the initial acute management, it is essential to identify any underlying causes of retroperitoneal fibrosis, such as drug reactions or malignancies, and assess comorbidities, involved organs, and any complicating factors. Any potential inciting drugs should be discontinued immediately. 

Medical Treatment

Once a diagnosis of retroperitoneal fibrosis is established, either through clinical and radiologic findings or a biopsy, the primary medical management typically involves glucocorticoid therapy for a minimum of 4 weeks. This approach has an overall favorable clinical response rate of approximately 80%.[73][116] The primary goals of therapy are to preserve renal function and alleviate any acute symptoms.[21] The expected response to treatment includes relief from pain, reduction in constitutional symptoms, improved diuresis, better renal function, and a decline in ESR, often starting within days of initiating steroid therapy. Most patients will experience improved renal function within 2 weeks of starting steroid treatment. Additionally, some patients who initially respond to therapy but later relapse may respond well to restarting steroid therapy.[67]

Various dosages and protocols have been recommended for treating retroperitoneal fibrosis. Many regimens start with an initial dosage of 60 mg of prednisolone daily, gradually tapered down to 5 mg/d. A consensus protocol suggests oral prednisone at 1 mg/kg daily (with a maximum dose of 80 mg) for 4 weeks, followed by a reassessment of the patient.[1][73] If the patient shows clinical improvement, the dose is gradually reduced over the next several months to 10 mg/d, which is maintained for 6 to 18 or even 24 months. Other reported initial regimens include 60 mg of oral prednisone daily for 6 weeks or 60 mg every other day for 8 weeks.[116][117]

Before initiating long-term steroid therapy, it is recommended to assess bone mineral density with a dual-energy X-ray absorptiometry (DEXA) scan.[21] Appropriate osteoporosis prophylaxis should include calcium and vitamin D supplementation, along with a bisphosphonate or denosumab (RANK ligand inhibitor), particularly for patients with preexisting osteopenia or low bone mineral density.[21][118][119][120] Please see StatPearls' companion resources, "Dual-Energy X-Ray Absorptiometry" and "Osteoporosis," for more information.

Common adverse effects of chronic glucocorticoid therapy include:

• Cataracts
• Cushing syndrome
• Decreased resistance to infections
• Diabetes mellitus
• Fluid retention
• Glaucoma
• Hypertension
• Obesity
• Osteoporosis
• Peptic ulcer disease
• Weight gain [121]

Please see StatPearls' companion resource, "Prednisone," for more information.

Failure to detect clinical or radiological improvement within 4 to 6 weeks of initiating steroid therapy should prompt reevaluation with a CT scan and a biopsy (if not previously performed) to confirm the diagnosis of retroperitoneal fibrosis. If retroperitoneal fibrosis is confirmed, other agents can be used concurrently with steroids, typically one of the agents listed below. The use of immunosuppressive agents is reserved for cases where steroid therapy fails, as relapse rates have been documented as high as 50% during steroid tapering.[73][122][123][124] 

Pharmacological Treatments for Retroperitoneal Fibrosis

Accepted empirical therapies generally include corticosteroids, tamoxifen, and azathioprine. Many of the other agents mentioned below are considered somewhat investigational, and a universally accepted protocol does not extend beyond initial steroid management.

Azathioprine: This is an immunosuppressive drug used in transplants, rheumatoid arthritis, and systemic lupus erythematosus. Azathioprine has traditionally been used in retroperitoneal fibrosis when steroid therapy has failed.[125] Some positive responses have been reported in limited studies.[126][125][127][128] However, up to 10% of patients may develop an idiosyncratic reaction that necessitates discontinuation of the drug. Patients require careful monitoring to avoid leukopenia. A dose of 150 mg/d of azathioprine has been suggested.[125] Please see the StatPearls' companion resource, "Azathioprine," for more information.

Colchicine: This medication is typically used when treating gout and is known for its antiinflammatory and immunosuppressive effects. In very limited studies and case series, it has shown reasonable efficacy (67%) in treating idiopathic retroperitoneal fibrosis together with steroids.[129][130][131][132][133] Although insufficient evidence exists to recommend the routine use of the drug, its low adverse effect profile and safety make it a reasonable option for a clinical trial in patients who are refractory to other therapies.[130] The usual dose of colchicine is 0.6 mg once or twice daily. Please see StatPearls' companion resource, "Colchicine," for more information.

Methotrexate: Methotrexate is a folic acid antagonist commonly used in cancer chemotherapy and as an immunosuppressant in autoimmune disorders such as inflammatory bowel disease, psoriasis, systemic lupus erythematosus, and rheumatoid arthritis. Please see StatPearls' companion resource, "Methotrexate," for more information.[134][135][136] Although data on its use in idiopathic retroperitoneal fibrosis are limited, a weekly methotrexate regimen combined with daily prednisone has shown remissions in 79% of patients at a median follow-up of 2 years.[137] In addition, it has also been shown to be effective in patients who are refractory or intolerant of steroids and in cases of retroperitoneal fibrosis recurrences.[137][138]

For retroperitoneal fibrosis, methotrexate is initiated at a dosage of 7.5 to 10 mg weekly, in combination with 25 mg of daily prednisone. The methotrexate dosage is then gradually increased by 2.5 mg/week, up to a maximum of 20 mg if tolerated. Methotrexate should be avoided in patients taking incompatible drugs, those with renal failure (estimated glomerular filtration rate <30 mL/min/1.73 m²), blood dyscrasias, pregnancy, or advanced liver disease. Please see StatPearls' companion resource, "Methotrexate," for more information.

Mycophenolate mofetil: This is a newer immunosuppressive agent and inosine monophosphate dehydrogenase inhibitor), which is commonly used in organ transplants and for various rheumatic immune-mediated diseases such as rheumatoid arthritis.[139] This medication has shown reasonable efficacy in treating idiopathic retroperitoneal fibrosis.[140][141][142][143][144]

The best evidence for mycophenolate mofetil's efficacy comes from a small study involving 28 previously untreated patients with retroperitoneal fibrosis who were treated with mycophenolate mofetil and prednisone. At a mean follow-up of over 2 years, about 89% showed clinical improvement and a low relapse rate of approximately 7%.[144] Additional studies have also demonstrated its effectiveness.[122][145][146][147] The recommended dose for treating retroperitoneal fibrosis is 1000 mg twice daily, combined with prednisone 25 mg daily. Mycophenolate mofetil should be avoided in patients with low white blood cell counts or significant gastrointestinal disorders.

Rituximab: This monoclonal antibody, designed as an anticancer drug, targets the CD20 cell surface protein on B lymphocytes, leading to their inactivation or destruction. Several small case studies support its use in treating idiopathic retroperitoneal fibrosis, especially in cases of refractory or recurrent disease.[62][64][148][149][150] The overall remission rate is approximately 75%, including in cases resistant to steroid treatment, with median follow-up extending up to 3 years and relatively few adverse effects reported.[62] Rituximab is particularly effective in IgG4-related disease and is recommended for IgG4-related retroperitoneal fibrosis patients who are intolerant to or refractory to steroids.[63][64][65][151][152] Please see StatPearls' companion resource, "Rituximab," for more information.

A typical dosage regimen of rituximab involves 375 mg/m² weekly for 4 consecutive weeks or 2 infusions of 1000 mg each, administered 2 weeks apart. This treatment may be repeated after 6 months in patients who respond well. Patients with a history of recurrent or severe infections should probably be treated with alternative agents. Please see StatPearls' companion resource, "Rituximab," for more information.

Sirolimus: As a mammalian target of rapamycin (mTOR) inhibitor, sirolimus has shown preliminary success in a small study involving 12 patients with idiopathic retroperitoneal fibrosis.[153] Notably, mTOR has been found to be highly active in retroperitoneal fibrosis, suggesting that targeting it could be an effective therapy.[153] The study aimed to determine the efficacy of sirolimus and its potential to reduce or replace chronic prednisone therapy, which can have significant adverse effects when used chronically.[153] Initial results indicated that combining sirolimus with a tapering dose of prednisone was effective and allowed most patients to avoid long-term prednisone use.[153] However, this is based on a single, limited study, and further research is needed to confirm these findings.[153]

Tamoxifen: Tamoxifen, an antiestrogen, has shown reasonable efficacy in treating retroperitoneal fibrosis, according to several small, limited studies.[154][155][156][157][158][159] Although its exact mechanism of action is not fully understood, tamoxifen is thought to increase the production of TGF-β, which inhibits fibrous tissue proliferation.[160] Other proposed mechanisms include blocking growth-promoting histamine-like receptors, inhibiting calmodulin (a calcium-binding messenger protein), reducing epidermal growth factor production, and inhibiting protein kinase C. Please see StatPearls' companion resource, "Tamoxifen," for more information.[161][162]

Regardless, tamoxifen's overall effect is anti-inflammatory, reducing fibroblastic activity. Although it is not as effective as steroids for treating retroperitoneal fibrosis, it has a good success rate and fewer relapses.[163] Therapeutic dosages have varied from 10 to 40 mg daily, typically for durations ranging from 6 months to 3 years.[159] Please see StatPearls' companion resource, "Tamoxifen," for more information.

Tofacitinib: Tofacitinib is a selective, oral, second-generation Janus kinase (JAK) inhibitor used for various inflammatory and immune-related disorders, such as psoriatic and rheumatoid arthritis. Preliminary reports suggest that tofacitinib may be effective as monotherapy for idiopathic retroperitoneal fibrosis and IgG4-related disease in a very limited number of patients.[164] However, further studies and clinical trials are needed to confirm its efficacy and potential therapeutic usefulness. Please see StatPearls' companion resource, "Tofacitinib," for more information.

Additional agents: Other agents that have been used include cyclophosphamide, cyclosporine, infliximab, medroxyprogesterone acetate, progesterone, tacrolimus, and tocilizumab. However, very limited data exist on their usefulness, duration, or efficacy in treating retroperitoneal fibrosis.[15][116][126][165][166][167][168][169][170][171][172][173]

Monitoring and close follow-up of a patient's response to therapy is essential. The patient should be evaluated clinically within 1 month of initiating treatment to assess the resolution of pain and improvement of any ureteral obstruction. Subsequently, clinical evaluations should be performed every 2 to 3 months. Laboratory tests, including ESR, CRP, serum creatinine, and BUN, should be conducted by clinicians every 30 days for the first 3 months and then every 2 to 3 months thereafter. A CT scan should be obtained 1 month after the start of therapy and approximately every 3 months to monitor changes in the size of the fibrotic mass.

The use of maintenance prednisone is somewhat controversial. While it is effective in reducing recurrences, chronic oral steroid use is associated with numerous complications, including Cushingoid effects, weight gain, hypercholesterolemia, and increased infection risk.[73][121] Please see StatPearls' companion resource, "Prednisone," for more information. Patients with IgG4-related disease are likely to require ongoing oral steroids or rituximab.[21][151][174][175] The optimal duration of oral prednisone therapy for retroperitoneal fibrosis has not yet been established.[21]

Following the discontinuation of medical therapy, it is recommended to monitor for disease relapse by obtaining a renal ultrasound, ESR, CRP, and serum creatinine concentration every 3 to 6 months; CT scans every 6 months for the first year, then every 1 to 2 years; and laboratory testing every 6 to 12 months thereafter. Surveillance should be continued indefinitely. The overall cumulative relapse rates have been estimated at approximately 20%, 40%, and 50% at 5, 10, and 15 years, respectively.[83] Positive predictors of relapse include male gender, a positive smoking history, high ANAs, eosinophilia, and elevated serum IgG4 levels.[83][84][176]

Surgical Treatment (Ureterolysis)

Surgical treatment for retroperitoneal fibrosis involves ureterolysis—a procedure where the ureters are separated from the surrounding fibrotic retroperitoneal mass and repositioned.[177] First described in 1934, ureterolysis has been highly effective in treating patients with ureteral obstruction due to retroperitoneal fibrosis, especially those who have not responded to medical therapy and present with ureteral obstruction and hydronephrosis.[177]

Surgical ureterolysis can protect the ureters from future obstruction by retroperitoneal fibrosis and enable appropriate biopsies. However, it does not prevent the progression or recurrence of the disease, nor does it address unassociated organs or systemic symptoms.[1][17][178][179] Surgical management (ureterolysis) is reserved for the following scenarios: 

• Technical difficulties, discomfort, intolerance, or complications with double J stenting and nephrostomy management.
• Lack of regression of the mass after medical (steroid) therapy, with persistent encasement of the ureters and other structures.[180]
• Findings suggest an underlying malignancy, where an open procedure is needed to obtain a definitive diagnosis.

Surgical management can be approached with an open, laparoscopic, or robotic exploration and entails ureterolysis and manipulation of the ureters to prevent recurrent obstruction.[181][182] The traditional or classic approach has been to carefully dissect the ureters from the retroperitoneal mass and transpose them laterally, possibly with the interposition of retroperitoneal fat between them and the remaining fibrous tissue mass.[183][184][185] 

The newer approach involves wrapping the ureters in omental fat (preferred) or Gore-Tex™. This technique serves as an additional barrier to prevent future encasement by fibrous tissue, promotes revascularization, and repositions the ureters to a more protected intraperitoneal position.[183][184][185][186][187][188][189] However, the actual efficacy of the omental or Gore-Tex™ wrap as a barrier in preventing future fibrosis or promoting revascularization is still unclear.[178] Additionally, the middle 10 to 20 cm portion of the mid-ureter that is skeletonized and repositioned during ureterolysis is at risk of postoperative ischemia, which has been reported in 12% to 30% of surgical cases, regardless of the surgical procedure used.[178][190][191][192][193][194]

A robotic surgical approach is recommended when feasible due to the relative invasiveness of the open surgery.[181] When performed, robotic procedures offer magnified 3-dimensional anatomical visualization, facilitate easier ureteral dissection, and result in faster patient recovery times.[178][181][178][190][192][195] Patients with compromised ureteral vascular supply from previous surgeries or other medical conditions are at a higher risk of treatment failure and complications, regardless of the surgical technique used.[185] Bilateral ureterolysis is recommended, even if only 1 ureter is significantly involved and obstructed, to reduce the risk of future issues with the contralateral ureter.[196]

Ureterolysis surgeries are best performed at high-volume centers where surgeons are experienced in complementary procedures such as Boari flap, ureteral reimplantation, renal autotransplantation, hysterectomy, nephrectomy, and bowel resection. Immediate access to a skilled vascular surgeon is also crucial if needed.[89][178][180][190][191][192][197] Success rates for ureterolysis at these centers are approximately 95%, although about 20% of patients may require a secondary procedure.[180] 

In rare cases where medical therapy has failed and ureterolysis is not technically feasible, treatment options include extensive ureteral reconstructive techniques (excluding intestinal segments), such as Boari flaps and renal autotransplantation, or long-term minimally invasive options, such as long-duration double J stents. Regular renal ultrasonography is recommended at least monthly for the first 4 months, then bimonthly for a year, and biannually thereafter.

Differential Diagnosis

The differential diagnoses for retroperitoneal fibrosis include:

• Retroperitoneal lymphoma: Retroperitoneal fibrosis typically centers at the L4 to L5 level. If imaging studies reveal a mass located higher than L4 to L5, lymphoma (either Hodgkin or non-Hodgkin) should be considered as a potential diagnosis.
• Retroperitoneal Erdheim-Chester disease: This is a rare, non-Langerhans cell, nonfamilial multisystemic granulomatosis with widespread manifestations and variable severity. This condition can sometimes involve the retroperitoneum and cause hydronephrosis, although it most commonly affects the bones and presents with bone pain.
• Retroperitoneal lymphangioma: Lymphangiomas are congenital benign tumors characterized by the localized proliferation of well-differentiated lymphatic tissue. Diagnosis is confirmed histologically, and treatment typically involves surgical excision.[198][199][200][201][202]

Various other retroperitoneal tumors, lesions, and masses include:

• Benign neurogenic tumors (schwannomas and neurofibromas)
• Castleman disease
• Eosinophilic angiomatosis with polyangiitis (formerly Churg-Strauss syndrome)
• Granulomatosis with polyangiitis (formerly Wegener granulomatosis)
• Lipomas
• Neurofibromatosis
• Paragangliomas
• Primary sclerosing cholangitis
• Sarcoidosis
• Sarcomas, such as liposarcomas (70%) and leiomyosarcomas (15%)
• Sjögren syndrome [202][203]

Prognosis

Patient symptoms often begin to improve within a few days of initiating treatment. After several weeks, CT may reveal significant resolution of the mass. Complete resolution of all associated manifestations depends on the disease's severity and the degree of entrapment of retroperitoneal structures.

If medical management is ineffective in reducing the mass, surgical therapy may be necessary to remove the fibrotic tissue while protecting the ureters and other retroperitoneal structures. Ureteral catheters are generally easy to place and can relieve obstructive uropathy while awaiting the effects of medical treatment. Percutaneous nephrostomies can be utilized if ureteral catheters are unacceptable or cannot be placed. 

The prognosis for retroperitoneal fibrosis is generally excellent with appropriate treatment, particularly as IgG4-related disease often responds well to glucocorticoid therapy. Without medical or surgical intervention, progressive ureteral obstruction is likely, leading to renal failure.[1] Most cases respond to steroid therapy, and surgery is overwhelmingly successful in refractory cases. However, malignant retroperitoneal fibrosis carries a much poorer prognosis, with an average survival of only about 3 to 6 months.[95][204]

Complications

Potential complications of retroperitoneal fibrosis include:

• Anemia
• Anuria
• Hypertension
• Intestinal necrosis
• Jaundice
• Nausea and vomiting
• Scrotal edema
• Neuropathy
• Persistent hydronephrosis
• Weight loss
• Thrombosis of the inferior vena cava
• Ureteral stenosis, strictures, fistulas, devascularization, or ischemic injury
• Adverse effects from steroids and other medical therapies
• Progressive kidney failure and death (if untreated)
• Postoperative complications from ureterolysis (reported at 8% to 16% of cases)
• Need for a secondary surgery in about 20% of ureterolysis cases.

Deterrence and Patient Education

Patients and their families should be thoroughly informed about the nature of the disease, the potential consequences of non-compliance with treatment, and the possible need for surgery if medical therapy is unsuccessful. They should also be educated about the importance of long-term follow-up, as the disorder may recur.

Pearls and Other Issues

Retroperitoneal fibrosis is a rare disorder often discovered serendipitously during the evaluation of a patient with renal insufficiency caused by ureteral compression or encasement by a retroperitoneal mass. Retroperitoneal fibrosis should be included in the differential diagnosis for patients presenting with unexplained renal failure or ureteral obstruction.[205]

During the initial management, it is vital to determine the severity of the patient's renal impairment and perform a procedure to allow decompression of the collecting system to protect the kidneys. The approach should be tailored to the patient's overall condition during diagnosis. After decompression, careful monitoring for postobstructive diuresis is crucial, with fluid and electrolyte replacement as needed.

After ensuring the kidneys are protected, the next step in the workup for retroperitoneal fibrosis is to obtain a definitive diagnosis. Some experts argue that if CT imaging studies are highly characteristic of retroperitoneal fibrosis, a biopsy may not be necessary, and medical therapy with steroids can be initiated directly.

Failure to respond to steroid therapy should raise suspicion about the underlying diagnosis and prompt a biopsy. When initiating steroid therapy, it is important to consider a DEXA scan and osteoporosis prophylaxis. Additionally, the patient's infection status should be assessed serologically for hepatitis, herpes zoster, and tuberculosis, and appropriate pre-treatment vaccinations should be considered.[21][206][207] Constant monitoring is essential as opportunistic infections, such as Pneumocystis pneumonia, become more likely.[21][208]

If surgical intervention is deemed necessary, an open biopsy should be obtained at that time. A PET scan can help identify the optimal location for the biopsy. A biopsy is essential in specific scenarios to aid in diagnosis and guide medical therapy. While a CT-guided biopsy is typically sufficient, an open biopsy may be required in particular situations, such as when lymphoma is suspected or when the diagnosis remains uncertain. 

Surgical management is indicated in cases of ureteral obstruction (hydronephrosis) where double J stents or percutaneous nephrostomy tubes cannot be placed, if medical therapy fails to address the disorder, or if an underlying malignancy is suspected. Such procedures can be performed robotically, laparoscopically, or open, with numerous maneuvers available to increase the effectiveness of the procedure.

Enhancing Healthcare Team Outcomes

Retroperitoneal fibrosis is a complex disorder best managed by an interprofessional healthcare team, including a urologist, general and vascular surgeon, internist, radiologist, interventional radiologist, rheumatologist, pharmacist, primary care physician, and pathologist. Medical therapy typically involves steroids and other immunosuppressive agents. Notably, it is crucial for the pharmacist to educate the patient about the potential adverse effects of these treatments.

Once treatment begins, outcomes often depend on the chronicity of the condition and patient compliance. While most patients experience a reversal of fibrosis, some may continue to have residual renal and ureteral impairment, remain unresponsive to treatment, or suffer recurrences. An interprofessional healthcare team is essential in managing adverse reactions and complications from treatment. Physicians, advanced practitioners, nurses, pharmacists, and other allied healthcare professionals must collaborate seamlessly to ensure a well-coordinated treatment plan and effective response to adverse events or effects.

Effective communication and collaboration within the healthcare team are fundamental, as they enable a swift and comprehensive response to minimize patient harm from recurrences and adverse effects of long-term steroid use. This coordinated effort ensures that patient safety remains a priority in retroperitoneal fibrosis treatment and optimizes overall outcomes.

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Disclosure: Joshua Engelsgjerd declares no relevant financial relationships with ineligible companies.

Disclosure: Stephen Leslie declares no relevant financial relationships with ineligible companies.

Disclosure: Chad LaGrange declares no relevant financial relationships with ineligible companies.