The retroperitoneal fibrosis mass centers around the distal aorta between L4 and L5 and encases the ureters. This can lead to hydronephrosis via extrinsic compression on the ureters leading to interference with ureteral peristalsis. Presenting symptoms usually include lower back and/or flank pain. This pain is often described as dull, non-colicky, unchanged with position, and with radiation into the groin or lower abdomen. The pain is relieved with aspirin rather than narcotics. In 2 of the largest retrospective series looking at RPF, the pain was present upon presentation in over 90 percent of patients[2]. Testicular pain was noted in more than 50% of male patients in one randomized trial of 40 patients[7]. Other possible associated symptoms include nausea, generalized malaise, anorexia, weight loss, oliguria, anuria. In retrospective studies, fatigue and substantial weight loss were present in 60% and 54% of presenting patients respectively. The inferior vena cava can also be obstructed due to extrinsic compression from the mass leading to deep venous thrombosis and lower extremity edema. Patient’s may also describe upper-leg claudication related to arterial compromise of the lower extremities, or symptoms of mesenteric ischemia due to compression of mesenteric arteries[3][8][2][9].

On physical exam, CVA tenderness to percussion is often present. Patient’s may have hypertension due to renal artery impingement. One study found hypertension present in 57% of patients on presentation. Lower extremity edema or evidence of thrombophlebitis or DVT may be present. A hydrocele may be evident on GU exam, as well as testicular tenderness.

Retroperitoneal fibrosis is often discovered incidentally in the workup of urinary tract obstruction or venous/arterial insufficiency. The diagnosis is often made by imaging studies, including CT imaging studies and MRIs. A definitive diagnosis requires a tissue biopsy, though it is controversial whether a biopsy is necessary for patients with imaging studies demonstrating findings characteristic of RPF.

Typically, initial evaluation of the patient a laboratory workup is obtained, as well as an initial renal ultrasound, if the patient is presenting with complaints of flank pain. Laboratory findings can be varied, and no hematologic or biochemical abnormality is specific to RPF. Often an elevation in creatinine concentration and blood urea nitrogen is found, depending on the presence and extent of ureteral obstruction. Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) are elevated in one half to two-thirds of RPF patients. Anemia can also be observed, likely related to renal insufficiency and chronic inflammation. Renal ultrasound often reveals a poorly marginated, periaortic mass that is typically hypoechoic and may be associated with hydronephrosis[3].

A contrast-enhanced CT scan is the exam of choice to visualize the extent of RPF and the presence of lymphadenopathy and tumor. On non-enhanced CT, RPF exhibits the same attenuation numbers to that of the psoas muscle (1 to 25 Hounsfield units). After administration of intravenous contrast, enhancement depends on the stage of the disease. Avid enhancement is often seen in early stages of the disease, whereas in late and inactive stages of the disease, there may be little or no enhancement. The mass is typically confluent and encasing the anterior and lateral sides of the aorta, often encircling and compressing the IVC. Typical findings also include hydronephrosis and medial deviation of the proximal ureter and mid-ureter and a smoothly tapered ureter at the level of the obstruction. One benefit of CT is it enables CT-guided biopsy to obtain tissue for pathologic diagnosis[9][10][11].

MRI is considered equivalent to CT in diagnosing and monitoring RPF, but it has a higher contrast resolution. It is helpful as the mass itself has characteristic T1 and T2-weighted images. RPF is characterized by diffusely low signal intensity on T1-weighted imaging, although the T2 signal may vary considerably, with high signal intensity consistent with the active disease. With treatment, T2 signal often diminishes and provides a measure of therapeutic efficacy. Gadolinium enhancement may also be valuable in assessing response to treatment. Associated decreases in gadolinium contrast enhancement should be expected after appropriate therapy[10][2].

The role of biopsy is controversial. If surgical intervention is planned for treatment of compression of ureters and/or IVC, an open biopsy of the mass is recommended. A CT-guided biopsy can be obtained during initial workup prior to any treatment as well. Expert consensus suggests a biopsy of the mass in certain scenarios. These cases include:

• When the location of the mass is atypical 
• When clinical and laboratory findings suggest the presence of an underlying infection or malignancy 
• Bulky appearance on imaging studies; extension above the origin of the renal arteries or anterior displacement of the aorta 
• Local experience with RPF is limited
• Lack of response to initial therapy

The pathological findings in idiopathic and secondary RPF are often indistinguishable. Microscopically, the fibrous tissue is comprised of an extracellular matrix composed of type-1 collagen fibers organized in thick irregular bundles, often encircling small vessels. The infiltrate consists of macrophages, plasma cells, B and T lymphocytes. The aggregates usually have a core rich in CD20+ B cells and periphery rich in CD3+ T cells. Most plasma cells are positive for immunoglobulin G4 (IgG4)[12].

Initial Management

Initial management of RPF depends on the patient’s clinical status. Patient’s with signs of ureteral compression with hydronephrosis and uremia require emergent decompression by either percutaneous nephrostomy tube or indwelling ureteral stents. Ureteral stent placement is usually not difficult in the setting of ureteral obstruction caused by RPF. The advantage of ureteral stent placement is the opportunity for retrograde pyelograms at time of the procedure to evaluate the anatomy. In critically ill patients with electrolyte abnormalities and little or no urine output, nephrostomy tube placement is favored.

After renal decompression, the patient must be monitored closely for post-obstructive diuresis, renal function status and appropriate replacement of fluids and electrolytes. Post-obstructive diuresis is a prominent polyuria that occurs after relieving complete obstruction of the urinary system (exceeding more than 200 mL per hour). Patients are at risk for severe dehydration, electrolyte imbalances, and hypovolemic shock. The condition usually lasts less than 48 hours. Treatment includes close monitoring of serum BUN, creatinine and electrolytes, and replacement of fluid. Oral replacement is preferred, but if the patient cannot tolerate oral liquids or is unable to keep up with the loss, one-half normal saline is used to replace half of the fluid loss (500 mL for every 1 L lost).  After initial management, it is necessary to identify the potential cause of RPF. Any potential inciting drug should be discontinued immediately.

Medical Treatment

Once a diagnosis of RPF is made, whether by radiologic findings or biopsy proven, the common primary medical management has been steroid therapy. The medical literature describes an 80% response rate when treating RPF with steroids alone. This includes resolution of pain and constitutional symptoms within days after initiation of treatment, rapid decline in ESR and diuresis. Dosages and duration of steroid therapy vary considerably, but most regimens start with an initial dose of 60 mg daily tapered to 5 mg daily. One expert consensus recommends treating with prednisone 1 mg/kg per day for approximately 4 weeks. If improvement is observed, the dose is tapered over months to 10 mg/day and maintained for an additional 6 to 18 months. Chronic steroid therapy up to 2 years has been shown to provide a significant improvement in clinical symptoms and regression of retroperitoneal mass. Failure to detect clinical or radiologic improvement within 4 to 6 weeks of initiation of therapy should prompt reevaluation with CT scan and a biopsy to determine if the diagnosis of RPF is correct. If it is confirmed that the disease is RPF, other agents can be used concurrently with steroids. These agents include azathioprine, methotrexate, mycophenolate mofetil, cyclophosphamide, and cyclosporine. Medroxyprogesterone acetate, progesterone, and tamoxifen have also been found to be beneficial in the treatment of RPF. [13][14][15] Use of immunosuppressive agents is reserved for when steroid therapy fails, as relapse rates have been documented as high as 50% during steroid tapering [16][17][18][19].

Monitoring a patient’s response to therapy requires close follow up. The patient should be evaluated clinically within 1 month of initiating treatment for resolution of pain and resolution of urinary obstruction. After that, the patient should be monitored clinically every 2 to 3 months. Clinicians should obtain ESR, CRP, serum creatinine and BUN monthly for the first three months, then every 2 to 3 months. A CT scan should be obtained one month after initiating therapy, then approximately every 3 months to follow the size of the fibrotic mass. Following discontinuation of medical therapy, it is recommended to monitor for disease relapse by obtaining a renal ultrasound, ESR, CRP, serum creatinine concentration every 3 to 6 months and CT every 6 months for the first year, then laboratory testing every 6 to 12 months and CT every 1 to 2 years. Surveillance should be continued indefinitely.

Surgical Treatment

Surgical management is reserved for the following scenarios: 

• Technical difficulties or complications with other cystoscopic or endoscopic obstruction-relieving maneuvers
• Lack of regression of mass after medical therapy, with persistent encasement of ureters and other structures
• Findings to suggest underlying malignancy 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. Methods employed to prevent recurrent ureteral obstruction include wrapping the ureters with omental fat to serve as a barrier to prevent encasement by fibrous tissue and promote revascularization, transplantation of ureters to an intraperitoneal position, or transposition of the ureters laterally, with interposition of retroperitoneal fat between ureters and fibrous tissue[20][21][22][23].

Retroperitoneal Lymphoma: Retroperitoneal fibrosis is centered at the L4 to L5 level. If imaging studies show mass centered more cephalad to L4 to L5, consider possible lymphoma diagnosis.

Retroperitoneal Erdheim-Chester disease: This is a rare non-Langerhans cell, non-familial multisystemic granulomatosis, widespread manifestations and variable severity that can sometimes present with involvement of retroperitoneum and hydronephrosis. Most commonly affects the bones and presents with bone pain.

Often within a few days of initiating treatment the patient's symptoms begin to improve. After several weeks CT imaging may demonstrate resolution of the mass. Full resolution of all associated manifestations is dependent on the degree of severity of the disease and the degree of entrapment of retroperitoneal structures. If medical management is not effective in treating the mass, surgical therapy can effectively remove the fibrotic tissue and protect the ureters.

Retroperitoneal fibrosis is a disorder that is rare and most commonly encountered during the workup of a patient with renal insufficiency being caused by ureteral compression by a retroperitoneal mass. During the initial management, it is vital to determine the severity of the patient's renal impairment and to perform a procedure to allow decompression of the collecting system to protect the kidneys. This will be dependent on the patient's overall status at the time of diagnosis. After decompression of the collecting system, it is critical to monitor for post-obstructive diuresis and replace fluids/electrolytes as necessary.

After the kidneys are protected, the next step in the workup of retroperitoneal fibrosis is to obtain a diagnosis. It is argued that if CT imaging studies are characteristic of RPF, no biopsy is necessary. In this case, the clinician can begin medical therapy with steroids and follow the regimen as outlined in the treatment section. If surgical intervention is deemed necessary, an open biopsy can be obtained at that time. There are certain scenarios when a CT-guided biopsy may be performed to aid in diagnosis and guide medical therapy. These reasons are listed above. 

Surgical management is necessary if ureteral stents and/or percutaneous nephrostomy tubes are unable to be placed, medical therapy is ineffective in the treatment of RPF. or if it is felt that there could be an underlying malignancy. This can be approached robotically, laparoscopically or open and numerous maneuvers are discussed to increase the likelihood of a surgical procedure being effective.

RF is a complex disorder that is best managed by an interprofessional team that includes a urologist, general and vascular surgeon, internist, radiologist, and pathologist. Medical therapy with steroids and other immunosuppressive is widely used and it is important that the pharmacist educate the patient on the potential adverse effects. Once treatment starts, the outcomes depend on the chronicity of the condition. While some patients do have a reversal of the fibrosis, others continue to have residual renal and ureteral impairment. Some patients may benefit from surgical decompression but unfortunately, most patients are debilitated and frail for complex surgery.