Malacoplakia of the Urinary System

Malacoplakia, Greek for "soft plaque," is a rare chronic granulomatous process that most commonly affects the urinary tract (mainly bladder), but can be seen in almost any organ.

Malacoplakia of the urinary system is predominantly found in middle aged women. Patients may present with gross hematuria and signs of urinary tract infection.

There is a high association with Escherichia coli infection and suppressed immune function (e.g., diabetes, post-transplant, etc.). The impaired immune function results in phagocytosis of bacteria with incomplete digestion. The mineralized bacterial products in phagolysosomes result in calcified intracellular inclusions called Michaelis-Gutmann bodies, which are pathognomonic.

Bladder

40% of cases of urinary system malacoplakia involve the bladder. The appearance on cross-sectional imaging is nonspecific and varied. There may be circumferential bladder wall thickening or multiple, polypoid, vascular, solid masses with or without invasion of the perivesical space. Less commonly, there may be a predominantly extravesical mass. There may also be vesicoureteric reflux and dilatation of the upper urinary tract. Calcification is not generally seen, although bladder wall adherent calculi have been described after treatment.

Biopsy is needed for definitive diagnosis, given the nonspecific appearance.

Kidney

About 15% of cases of urinary system malacoplakia involve the kidney as the primary site. Malacoplakia of the kidney, unlike that of the bladder, is progressive, nephrotoxic, and potentially lethal. The appearance is that of an infiltrative multifocal process.

On cross sectional imaging, the kidney is enlarged and contains multiple (in 75% of cases) or a solitary hypovascular mass(es). Approximately 50% of cases are bilateral. The lesions range from a few millimeters up to 4 cm and may coalesce into large masses that distort the contour of the kidney.

On ultrasound, the lesions are poorly defined and hypoehoic. On MRI, the lesions are hypointense on T1- and T2-weighted images and there is delayed enhancement of intervening fibrous stroma.

Ureters

About 10% of cases malacoplakia have ureteral involvement. Isolated involvement of ureter without renal involvement is very rare and is thought to reflect a less aggressive variant of the disease.

References

• Craig WD, Wagner BJ, Travis MD. Pyelonephritis: radiologic-pathologic review. Radiographics. 2008 Jan-Feb;28(1):255-77;
• Inoue T, Nishiyama H, Yoshimura K, Ito N, Kamoto T, Habuchi T, Ogawa O. Solitary upper ureteral malakoplakia successfully diagnosed by ureteroscopic biopsy and treated conservatively. Int J Urol. 2007 Sep;14(9):859-61.
• Long JP Jr, Althausen AF. Malacoplakia: a 25-year experience with a review of the literature. J Urol. 1989 Jun;141(6):1328-31.
• Wong-You-Cheong JJ, Woodward PJ, Manning MA, Davis CJ. From the archives of the AFIP: Inflammatory and nonneoplastic bladder masses: radiologic-pathologic correlation. Radiographics. 2006 Nov-Dec;26(6):1847-68.