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Diagnosis Please |
1 From the Russell H. Morgan Department of Radiology and Radiological Sciences, Johns Hopkins University School of Medicine, 600 N Wolfe St, Baltimore, MD 21287. Received January 10, 2003; revision requested March 20; revision received August 27; accepted October 14. Address correspondence to D.A.B. (e-mail: dbluemke@jhmi.edu).
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History |
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Prior to admission, the patient had undergone coronary artery bypass graft placement for triple-vessel coronary artery disease (5 years previously) and right carotid endarterectomy (1 year previously). Pathologic specimens of the carotid artery showed dense fibrous tissue and chronic inflammation surrounding the vessel wall.
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Imaging Findings |
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Discussion |
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Depending on the involved organ systems, different clinical and radiologic manifestations are observed in patients with multifocal fibrosclerosis. In the case presented, there is extensive soft-tissue proliferation, most extensively surrounding the kidneys, but there is also involvement of the abdominal aorta, renal arteries, and thoracic aorta. This patient additionally had soft-tissue fibrosis around the carotid arteries (not shown, but stated in the history). While the abdominal findings alone are typical of perirenal fibrosis and RPF, their combination with the same pattern of disease in the mediastinal and cervical areas denotes generalized systemic involvement; this is termed multifocal fibrosclerosis. These findings were confirmed by means of core biopsy of the tissue surrounding the kidneys and examination of the endarterectomy specimen. In this patient, symptoms of congestive heart failure and coronary artery disease were caused by atherosclerotic disease; atherosclerotic narrowing of the renal ostia also likely contributed to the patient’s renal failure and hypertension.
Mediastinal fibrosis in multifocal fibrosclerosis is characterized by hypointense tissue on T1- and T2-weighted MR images in the mediastinum, especially around the aorta, as in this case. Mediastinal fibrosis can also be associated with superior vena cava obstruction, stenosis of the pulmonary veins, tracheal obstruction (eg, symptoms similar to asthma), esophageal stricture, pulmonary artery obstruction with cor pulmonale, and coronary artery occlusion (1,4). Histologically, it has a similar appearance to that observed in patients with RPF (1,13). Cross-sectional imaging findings are those of an infiltrative soft-tissue process, with variable degrees of deformation of the mediastinal anatomy (2,4).
RPF was a prominent component of multi-focal fibrosclerosis in the case presented, and RPF is the most common manifestation of multifocal fibrosclerosis. RPF is characterized by fibrous tissue proliferation surrounding the aorta and extending into periaortic tissue as a plaque-like infiltrative soft-tissue process (14). In most cases, it is localized around the lower aorta and common iliac arteries in the retroperitoneal space (12), but the pelvic cavity can also be involved (5). About two-thirds of the cases are considered idiopathic; in the remaining one-third, an inciting factor (eg, methysergide, malignancies, radiation therapy, surgery, hemorrhage, retroperitoneal infection, autoimmune diseases) can be identified (15). It has also been suggested that RPF could be secondary to a local autoallergic reaction to components of atherosclerotic plaques, occurring in areas in which the aorta has severe atherosclerotic plaque (13). There is a male-to-female ratio of approximately 3:1. In 70% of patients, the age at diagnosis is between 30 and 60 years, but the disease has been described in children (16).
Two histologic patterns of RPF have been described. One pattern consists of chronic fibrosis that is relatively avascular, acellular, and often calcified. The second pattern demonstrates collagen bundles interspersed with an equal or greater volume of inflammatory cells and mucopolysaccharide. In the later group, small blood vessels are numerous, and the infiltrative process is pleomorphic, consisting of lymphocytes, plasma cells, eosinophils, Russell bodies, fibroblasts, and mast cells. Neutrophils are absent (12). It is hypothesized that the more active type of inflammation matures into the more chronic histologic pattern.
The diagnosis of retroperitoneal fibrosis is often suggested by imaging studies performed to enable the evaluation of nonspecific clinical signs and symptoms. Medial deviation and narrowing of the ureters near the lower lumbar spine (17) demonstrated by excretory urography represents a classic radiologic presentation of RPF. Renal failure may be profound, despite low-grade obstructive uropathy. One proposed mechanism of obstruction is interference with ureteral peristaltic activity rather than mechanical obstruction (18).
Sonographic findings of RPF consist of hydronephrosis and visualization of fibrotic tissue as a hypoechoic mass in the para-aortic region (19). Computed tomography (CT) shows retroperitoneal plaque-like, infiltrative soft-tissue surrounding vessels and ureter. The soft-tissue attenuation seen on CT scans is similar to that of muscle (20). Enhancement is variable after intravenous administration of iodinated contrast material. MR images show an infiltrative soft-tissue process with homogeneous low signal intensity compared with that of the adjacent psoas muscle seen on T1-weighted images (21). However, RPF can show moderate to high signal intensity on T2-weighted images, depending on the degree of associated inflammatory response. Extensive inflammation early in the disease process results in increased T2 signal intensity (21,22). In a series of 17 patients, malignant RPF was characterized by ill-defined margins, increased signal intensity on T2-weighted images, and heterogeneous MR signal intensity (23). MR imaging characteristics, however, are not specific for distinguishing benign from malignant cause. Therefore, biopsy is essential to confirm the diagnosis. Fluorodeoxyglucose positron emission tomography can play a role in establishing the diagnosis and sites of involvement in patients with multifocal fibrosclerosis, and it could be helpful in evaluating disease activity and patient response to corticoid therapy by showing high fluorodeoxyglucose uptake in involved areas (likely caused by active inflammation) (24).
Localized extensions of RPF (19,22,25–32) may be associated with more typical presentations (eg, periaortic disease) that may lead to the correct imaging diagnosis. In the case presented, subtle periaortic abnormalities were present and suggest the diagnosis of RPF.
The primary diagnostic consideration in this case would be treated lymphoma. The other differential diagnoses usually considered for RPF, including sarcoma, metastatic lymphadenopathy, amyloidosis, and extramedullary hematopoiesis (22,33,34), would not appear as hypointense soft tissue on T1- and T2-weighted images around the kidneys and thoracic and abdominal aorta. A particular characteristic of RPF is the tendency to infiltrate and envelop surrounding structures without displacing them. Malignancies, such as lymphomas and sarcomas, typically cause displacement of surrounding structures, especially the aorta (21,35). In addition, the anterior margin of RPF is clearly delineated, respecting peritoneal boundaries, while the posterior margin is poorly defined and not easily separated from subjacent structures (20).
Therapy for multifocal fibrosclerosis includes removal of any identifiable inciting agents, including a search for occult tumors, and suppression of inflammatory process. Steroid therapy is of value in most cases when there is no associated malignancy. In steroid-resistant cases, other forms of immunosuppression may be useful. Medroxyprogesterone acetate, progesterone, and tamoxifen have been described as alternative forms of treatment. Surgical intervention is considered for steroid-resistant cases and for patients who do not tolerate steroids. Long-term follow-up is indicated, as recurrences are unpredictable and may occur from 3 months to more than 10 years after the initial diagnosis and treatment (15).
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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