Computed Tomography Findings of Human Polyomavirus BK (BKV)-Associated Cystitis in Allogeneic Hematopoietic Stem Cell Transplant Recipients

Background: Over 70% of the general population worldwide is positive for antibodies against polyomavirus hominis type 1 (BKV). Polyomavirus can be reactivated in immunocompromised patients and thereby induce urogenital tract infection, including cystitis. Purpose: To describe the computed tomography (CT) findings of human polyomavirus-induced cystitis in adult patients after allogeneic hematopoietic stem cell transplantation (allogeneic HCT). Material and Methods: The study population was a retrospective cohort of 11 consecutive adult patients (eight men, three women; age range 22-59 years, mean 42.9 years) who received allogeneic HCT between December 2003 and December 2007 and were tested positive for urinary BKV infection. All CT scans were evaluated with regard to bladder wall thickness, mucosal enhancement, distinct layering of thickened bladder wall, and presence of intravesical clots, perivesical stranding as well as attenuation values of intravesical urine. Clinical data concerning transplant and conditioning regimen variables and laboratory parameters were correlated with degree and extent of imaging findings. Results: All patients had clinical signs of cystitis with different degrees of thickening of the urinary bladder wall. Well-delineated urinary bladder layers were present in six patients. Thickening of the urinary bladder wall was continuous in nine of 11 patients. Increased attenuation of intravesical urine was found in seven patients with hemorrhagic cystitis. Four patients had intraluminal clots. Perivesical stranding was not a major CT finding, occurring in a mild fashion in three of 11 patients. The clinical classification of hemorrhagic cystitis did not correlate with the analyzed imaging parameters. Patient outcome was not influenced by this infectious complication. Conclusion: CT findings in patients with polyomavirus BK cystitis consist of different degrees of bladder wall thickening usually with good delineation of all mural layers and increased mucosal enhancement. These findings are not specific for BKV cystitis, but awareness of this differential diagnosis should help in the early diagnosis and correct management of this infectious complication.