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RENAL PSEUDOTUMORS
0022-5347/05/1732-0600/0 THE JOURNAL OF UROLOGY® Copyright © 2005 by AMERICAN UROLOGICAL ASSOCIATION
Vol. 173, 600, February 2005 Printed in U.S.A.
DOI: 10.1097/01.ju.0000151493.72850.5c
Pathology Page RENAL PSEUDOTUMORS A number of entities are capable of mimicking renal neoplasia. Some entities, such as renal cysts and some renal abscesses, may be confidently diagnosed radiologically and managed conservatively. Unfortunately, many uncommon renal lesions mimic neoplasia closely, regardless of attempts to characterize them accurately, and inevitably are resected because of diagnostic uncertainty and concern for the possibility of malignancy. Renal pseudomasses may be categorized as developmental, infectious, granulomatous or vascular in nature. Splenorenal fusion denotes the congenital presence of splenic tissue within the renal capsule. It is rare and typically discovered incidentally. Rarely, it may cause hypersplenism (anemia). Radiologically, it mimics organizing capsular hematoma, angiomyolipoma and renal cell carcinoma. It consists of hemorrhagic appearing tissue that is sharply demarcated from the adjacent renal parenchyma (fig. 1). Acute or chronic infections that result in renal abscess may create diagnostic difficulties, mimicking malignancy radiologically and intraoperatively, since the inflammatory process may extensively invade perirenal soft tissues. Pathologically, the lesions are characterized by the presence of abscess formation with varying degrees of surrounding reactive and reparative changes. The causative organisms may be gram-negative or gram-positive bacilli, including Actinomyces species. Actinomycosis abscesses contain sulfur granules that may facilitate diagnosis on fine needle aspiration and may allow conservative management. The granulomatous category includes sarcoidosis, xanthogranulomatous pyelonephritis and malakoplakia. Renal granulomatous inflammation associated with sarcoidosis is in most instances a microscopic finding only but there have been occasional reports of renal sarcoidosis presenting as a mass lesion indistinguishable from malignancy. Xanthogranulomatous pyelonephritis is commonly the end result of obstructive uropathy secondary to nephrolithiasis. Typically, the affected kidney is enlarged and often nonfunctioning. Although imaging studies provide an accurate diagnosis in up to 90% of cases, some cannot be distinguished from malignancy, particularly when the process is segmental or focal rather than diffuse. Microscopically, it is composed of a
FIG. 2. Reprinted with permission from MacLennan, G. T., Resnick, M. I. and Bostwick, D. G.: Pathology for Urologists. Philadelphia: W. B. Saunders Co., 2003.
polymorphous assortment of acute and chronic inflammatory cells, including abundant lipid-laden foamy macrophages, a feature that imparts a yellow color to the mass (fig. 2). There have been more than 50 reported cases of renal malakoplakia, a condition related to defective macrophage function and most commonly encountered in the lower urinary tract. The kidney typically shows a diffuse multinodular cortical enlargement or a single yellow cortical mass that may infiltrate perirenal soft tissues, gross findings that would readily simulate malignancy on radiological imaging studies. Abscesses and areas of cystic degeneration may also be present. Vascular lesions that may mimic malignancy include arteriovenous malformation (AVM), anticoagulant induced subcapsular hemorrhage and subepithelial renal pelvic hematoma. Renal AVM may be located within renal parenchyma or in the renal sinus. It may be difficult to distinguish AVM from an enhancing solid renal mass after gadolinium administration and it may also simulate a parapelvic cyst on ultrasound. Hemorrhage related to anticoagulant therapy may form hematomas within renal parenchyma or in perirenal soft tissues, or may result in the formation of clots in the collecting system. In all instances it may be difficult to distinguish these lesions from neoplasia. Subepithelial renal pelvic hematoma is a rare lesion that usually presents with hematuria. Imaging studies demonstrate a pelvic filling defect that closely simulates malignancy, resulting in nephrectomy in most instances. It has been associated with pregnancy and long standing ureteropelvic junction obstruction. In summary, there are many entities that mimic renal malignancy. Unfortunately, in the majority of such cases the correct diagnosis is only apparent after pathological evaluation of the nephrectomy specimen. Zofia Tynski and Gregory T. MacLennan Institute of Pathology University Hospitals of Cleveland Case Western Reserve University Cleveland, Ohio
FIG. 1 600
Vol. 173, 600, February 2005 Printed in U.S.A.
DOI: 10.1097/01.ju.0000151493.72850.5c
Pathology Page RENAL PSEUDOTUMORS A number of entities are capable of mimicking renal neoplasia. Some entities, such as renal cysts and some renal abscesses, may be confidently diagnosed radiologically and managed conservatively. Unfortunately, many uncommon renal lesions mimic neoplasia closely, regardless of attempts to characterize them accurately, and inevitably are resected because of diagnostic uncertainty and concern for the possibility of malignancy. Renal pseudomasses may be categorized as developmental, infectious, granulomatous or vascular in nature. Splenorenal fusion denotes the congenital presence of splenic tissue within the renal capsule. It is rare and typically discovered incidentally. Rarely, it may cause hypersplenism (anemia). Radiologically, it mimics organizing capsular hematoma, angiomyolipoma and renal cell carcinoma. It consists of hemorrhagic appearing tissue that is sharply demarcated from the adjacent renal parenchyma (fig. 1). Acute or chronic infections that result in renal abscess may create diagnostic difficulties, mimicking malignancy radiologically and intraoperatively, since the inflammatory process may extensively invade perirenal soft tissues. Pathologically, the lesions are characterized by the presence of abscess formation with varying degrees of surrounding reactive and reparative changes. The causative organisms may be gram-negative or gram-positive bacilli, including Actinomyces species. Actinomycosis abscesses contain sulfur granules that may facilitate diagnosis on fine needle aspiration and may allow conservative management. The granulomatous category includes sarcoidosis, xanthogranulomatous pyelonephritis and malakoplakia. Renal granulomatous inflammation associated with sarcoidosis is in most instances a microscopic finding only but there have been occasional reports of renal sarcoidosis presenting as a mass lesion indistinguishable from malignancy. Xanthogranulomatous pyelonephritis is commonly the end result of obstructive uropathy secondary to nephrolithiasis. Typically, the affected kidney is enlarged and often nonfunctioning. Although imaging studies provide an accurate diagnosis in up to 90% of cases, some cannot be distinguished from malignancy, particularly when the process is segmental or focal rather than diffuse. Microscopically, it is composed of a
FIG. 2. Reprinted with permission from MacLennan, G. T., Resnick, M. I. and Bostwick, D. G.: Pathology for Urologists. Philadelphia: W. B. Saunders Co., 2003.
polymorphous assortment of acute and chronic inflammatory cells, including abundant lipid-laden foamy macrophages, a feature that imparts a yellow color to the mass (fig. 2). There have been more than 50 reported cases of renal malakoplakia, a condition related to defective macrophage function and most commonly encountered in the lower urinary tract. The kidney typically shows a diffuse multinodular cortical enlargement or a single yellow cortical mass that may infiltrate perirenal soft tissues, gross findings that would readily simulate malignancy on radiological imaging studies. Abscesses and areas of cystic degeneration may also be present. Vascular lesions that may mimic malignancy include arteriovenous malformation (AVM), anticoagulant induced subcapsular hemorrhage and subepithelial renal pelvic hematoma. Renal AVM may be located within renal parenchyma or in the renal sinus. It may be difficult to distinguish AVM from an enhancing solid renal mass after gadolinium administration and it may also simulate a parapelvic cyst on ultrasound. Hemorrhage related to anticoagulant therapy may form hematomas within renal parenchyma or in perirenal soft tissues, or may result in the formation of clots in the collecting system. In all instances it may be difficult to distinguish these lesions from neoplasia. Subepithelial renal pelvic hematoma is a rare lesion that usually presents with hematuria. Imaging studies demonstrate a pelvic filling defect that closely simulates malignancy, resulting in nephrectomy in most instances. It has been associated with pregnancy and long standing ureteropelvic junction obstruction. In summary, there are many entities that mimic renal malignancy. Unfortunately, in the majority of such cases the correct diagnosis is only apparent after pathological evaluation of the nephrectomy specimen. Zofia Tynski and Gregory T. MacLennan Institute of Pathology University Hospitals of Cleveland Case Western Reserve University Cleveland, Ohio
FIG. 1 600