ORIGINAL ARTICLE Ultrasound findings of BK polyomavirus-associated nephropathy in renal transplant patients Mauro Dugo 1 • Margherita Mangino 1 • Mario Meola 2 • Ilaria Petrucci 2 • Maria Luisa Valente 3 • Licia Laurino 4 • Mario Stella 5 • Stefania Mastrosimone 1 • Anna Brunello 1 • Bice Virgilio 1 • Monica Rizzolo 1 • Maria Cristina Maresca 1 Received: 16 March 2016 / Accepted: 8 June 2016 Ó Italian Society of Nephrology 2016 Abstract BK polyomavirus (BKV) is an emerging patho- gen in immunocompromised patients. BKV infection occurs in 1–9 % of renal transplants and causes chronic nephropathy or graft loss. Diagnosis of BKV-associated nephropathy (BKVAN) is based on detection of viruria then viremia and at least a tubule-interstitial nephritis at renal biopsy. This paper describes the ultrasound and color Doppler (US-CD) features of BKVAN. Seventeen patients affected by BKVAN were studied using a linear bandwidth 7–12 MHz probe. Ultrasound showed a widespread streak– like pattern with alternating normal echoic and hypoechoic streaks with irregular edges from the papilla to the cortex. Renal biopsy performed in hypoechoic areas highlighted the typical viral inclusions in tubular epithelial cells. Our experience suggests a possible role for US-CD in the non- invasive diagnosis of BKVAN when combined with blood and urine screening tests. US-CD must be performed with a high-frequency linear probe to highlight the streak–like pattern of the renal parenchyma. Keywords BK virus Á Ultrasonography Á Kidney transplantation Á Nephritis Introduction The BK-virus (BKV) is a polyomavirus belonging to the polyomaviridae family. Since its discovery in 1971 [1], there has been a growing recognition of the importance of BKV as a human pathogen in immunocompromised pop- ulations. Despite the large prevalence of infection (more than 80 % of the world’s population is thought to be seropositive for BKV), primary infection is usually asymptomatic or associated with upper respiratory tract symptoms. Following the primary infection, BKV persists in a latent form in the kidneys and urinary tract due in part to its tropism for genitourinary epithelium. Intermittent exacerbations of the infection associated with low-level viruria occur in up to 40 % of immunocompetent adults. BKV-associated nephropathy (BKVAN) occurs in up to 10 % of kidney allograft recipients [2], causing allograft failure in 15–60 % of affected patients [3]. Definitive diagnosis of BKVAN infection requires: (1) a kidney biopsy to reveal the interstitial nephritis and tubular cytopathic changes; and (2) an adjunctive immunohisto- chemistry test specifically directed against BKV or cross- reacting SV40 large T antigen [4]. Non-invasive tests for BKVAN are detection of viremia by plasma BKV DNA polymerase chain reaction (PCR) and of viruria by BKV- DNA PCR and reverse transcription-PCR for BKV RNA. Urinary sample cytology also reveals the typical inclusion– bearing epithelial cells termed ‘‘decoy cells’’, whereas electron microscopy shows three-dimensional cast-like polyomavirus particles (‘‘Haufen’’) [5]. The role of imaging in diagnosis of BKVAN is limited. Tourret et al. [6] first reported computed tomography (CT) scan features of BKVAN that consisted of multiple wedge- shaped areas and streaky zones of lesser enhancement that extended from the papilla to the renal cortex. The authors & Mauro Dugo maurodugo59@gmail.com 1 Nephrology and Dialysis Department, Ca’ Foncello Hospital, Treviso, Italy 2 S. Anna of Advanced Studies, Internal Medicine University of Pisa, Pisa, Italy 3 Department of Cardiac, Thoracic and Vascular Sciences, University of Padua, Padua, Italy 4 Pathology Department, Ca’ Foncello Hospital, Treviso, Italy 5 Pathology Department, Vincenzo Cervello Hospital, Palermo, Italy 123 J Nephrol DOI 10.1007/s40620-016-0327-0