ª Springer Science+Business Media New York 2015
Abdominal Imaging
Abdom Imaging (2015) DOI: 10.1007/s00261-015-0358-3
The ‘‘bear paw’’ sign Colin M. Segovis, Raymond B. Dyer Department of Radiology, Wake Forest Baptist Medical Center, Wake Forest University School of Medicine, Medical Center Blvd., Winston-Salem 27157, NC, USA
The ‘‘bear paw’’ (Fig. 1A, B) metaphorically describes the CT appearance of a kidney diffusely involved with xanthogranulomatous pyelonephritis (XGP), a chronic inflammatory process arising from an incomplete immune response to chronic infection [1, 2]. The bear’s paw pattern reflects replacement of the renal paren-
chyma by hypoattentuting masses arranged in a ‘‘hydronephrotic’’ pattern (Fig. 2) [3]. The hypoattentuating ‘‘masses’’ are a cellular infiltrate of lipid laden macrophages (‘‘foam cells’’), which collect in response to subacute/chronic infection, and form thick yellow material in gross specimens [4]. A
Fig. 1. A ‘‘Bear paws’’! The grizzly bear; the narrative of a hunter naturalist, historical, scientific and adventurous (1909) by Wright, William H. (William Henry), 1856–1934, published by New York, C. Scribner’s sons (http://commons.wikimedia.
org/wiki/File:Bear_paws.jpg), accessed 30 December 2014. B Brown Bear, U.S. Fish and Wildlife Service (http://digitalmedia. fws.gov/cdm/singleitem/collection/natdiglib/id/5778/rec/1), accessed 30 December 2014.
Correspondence to: Colin M. Segovis; email: [email protected]
C. M. Segovis, R. B. Dyer: The ‘‘bear paw’’ sign
central calculus within a contracted renal pelvis, and inflammatory changes in the perinephric fat are typical. Interestingly, it is unclear if nephrolithiasis is a cause or result of XGP [4]. Clinically, XGP occurs most commonly in middle age, and affects women approximately twice as often as men [2, 5]. Symptoms of XGP—flank pain, dysuria, nocturia, and fever—are nonspecific, as are the hematuria, pyuria, and leukocytosis that can accompany the diagnosis [5].
References
Fig. 2. Unenhanced axial CT image at the level of the mid right kidney reveals a centrally obstructing stone, with replacement of the renal parenchyma by hypoattenutating collections in a ‘‘hydronephrotic’’ pattern. The appearance is characteristic of XGP, and resembles the bear paws in Fig. 1.
1. Parker MD, Clark RL (1989) Evolving concepts in the diagnosis of xanthogranulomatous pyelonephritis. Urol Radiol 11:7–15 2. Craig WD, Wagner BJ, Travis MD (2008) Pyelonephritis: radiologic-pathologic review. RadioGraphics 28:255–277 3. Dyer RB, Chen MY, Zagoria RJ (2004) Classic signs in uroradiology. RadioGraphics 24:S247–S280 4. Fan CM, Whitman GJ, Chew FS (1995) Xanthogranulomatous pyelonephritis. AJR 165:1008 5. Goldman SM, Hartman DS, Fishman EK, et al. (1984) CT of xanthogranulomatous pyelonephritis: radiologic-pathologic correlation. AJR 142:963–969
Abdominal Imaging
Abdom Imaging (2015) DOI: 10.1007/s00261-015-0358-3
The ‘‘bear paw’’ sign Colin M. Segovis, Raymond B. Dyer Department of Radiology, Wake Forest Baptist Medical Center, Wake Forest University School of Medicine, Medical Center Blvd., Winston-Salem 27157, NC, USA
The ‘‘bear paw’’ (Fig. 1A, B) metaphorically describes the CT appearance of a kidney diffusely involved with xanthogranulomatous pyelonephritis (XGP), a chronic inflammatory process arising from an incomplete immune response to chronic infection [1, 2]. The bear’s paw pattern reflects replacement of the renal paren-
chyma by hypoattentuting masses arranged in a ‘‘hydronephrotic’’ pattern (Fig. 2) [3]. The hypoattentuating ‘‘masses’’ are a cellular infiltrate of lipid laden macrophages (‘‘foam cells’’), which collect in response to subacute/chronic infection, and form thick yellow material in gross specimens [4]. A
Fig. 1. A ‘‘Bear paws’’! The grizzly bear; the narrative of a hunter naturalist, historical, scientific and adventurous (1909) by Wright, William H. (William Henry), 1856–1934, published by New York, C. Scribner’s sons (http://commons.wikimedia.
org/wiki/File:Bear_paws.jpg), accessed 30 December 2014. B Brown Bear, U.S. Fish and Wildlife Service (http://digitalmedia. fws.gov/cdm/singleitem/collection/natdiglib/id/5778/rec/1), accessed 30 December 2014.
Correspondence to: Colin M. Segovis; email: [email protected]
C. M. Segovis, R. B. Dyer: The ‘‘bear paw’’ sign
central calculus within a contracted renal pelvis, and inflammatory changes in the perinephric fat are typical. Interestingly, it is unclear if nephrolithiasis is a cause or result of XGP [4]. Clinically, XGP occurs most commonly in middle age, and affects women approximately twice as often as men [2, 5]. Symptoms of XGP—flank pain, dysuria, nocturia, and fever—are nonspecific, as are the hematuria, pyuria, and leukocytosis that can accompany the diagnosis [5].
References
Fig. 2. Unenhanced axial CT image at the level of the mid right kidney reveals a centrally obstructing stone, with replacement of the renal parenchyma by hypoattenutating collections in a ‘‘hydronephrotic’’ pattern. The appearance is characteristic of XGP, and resembles the bear paws in Fig. 1.
1. Parker MD, Clark RL (1989) Evolving concepts in the diagnosis of xanthogranulomatous pyelonephritis. Urol Radiol 11:7–15 2. Craig WD, Wagner BJ, Travis MD (2008) Pyelonephritis: radiologic-pathologic review. RadioGraphics 28:255–277 3. Dyer RB, Chen MY, Zagoria RJ (2004) Classic signs in uroradiology. RadioGraphics 24:S247–S280 4. Fan CM, Whitman GJ, Chew FS (1995) Xanthogranulomatous pyelonephritis. AJR 165:1008 5. Goldman SM, Hartman DS, Fishman EK, et al. (1984) CT of xanthogranulomatous pyelonephritis: radiologic-pathologic correlation. AJR 142:963–969
