The diagnostic value of Doppler ultrasonography after pediatric kidney transplantation

Abstract

Ultrasonography (US) plays a major diagnostic role in the pre- and post-transplant evaluation of recipient and donor. In most cases, US remains the only necessary imaging modality. After pediatric kidney transplantation, US can ensure immediate bedside diagnosis of vessel patency and possible postoperative non-vascular complications. Criteria for US diagnosis of kidney vessel thrombosis and stenosis in the transplant will be presented. Non-vascular complications after kidney transplantation include hydronephrosis, hematoma, lymphocele, and abscess. US can detect suggestive, but nevertheless non-specific, acute signs (sudden increase in volume and elevated resistive index), and chronic rejection, which therefore remains a histological diagnosis. US is of little or no help in detection of tubular necrosis or drug toxicity, but it can exclude other differential diagnoses. This educational review provides a practical and systematic approach to a multimodal US investigation of the kidney transplant. It includes a short overview on possible indications for contrast-enhanced ultrasonography (CEUS) in children after kidney transplantation.

Keywords: CEUS; Doppler; Pediatric kidney transplantation; Ultrasonography; Vascular complications.

Fig. 1

Doppler sonography of an interlobular kidney artery using a bidirectional power Doppler. Signals above the Zero-Line in the pulse-wave (PW)-Doppler indicate a flow toward the probe (interlobular artery), and signals below the Zero-Line indicate a flow away from the probe (kidney vein)

Fig. 2

a, b Kidney vein stenosis due to a lymphocele with kinking of the transplant vessels. a Aliasing and highly increased venous velocity of > 100 cm/s in the transplant vein. b Lymphocele: echofree fluid collection laterally to the kidney transplant with fibrous septae

Fig. 3

a, b Kidney artery stenosis of a kidney graft. a The maximum systolic velocity is increased to 333 cm/s, aliasing in the kidney artery. b Tardus-parvus-pulse in the post-stenotic course indicated by a high diastolic flow and a resulting low resistive index (RI)

Fig. 4

Arteriovenous fistula after kidney biopsy. In the pulse-wave (PW)-Doppler, a turbulent flow pattern with a high flow velocity of > 300 cm/s is depicted

Fig. 5

a Kidney abscess after transplant urosepsis. b Urosepsis, positive urothelial sign

Fig. 6

Hematoma after kidney biopsy. Longitudinal section through the kidney transplant with a mixed echorich-echopoor oval mass on top. Linear probe

Fig. 7

a Severe acute rejection with macrohematuria because of inner bleeding/rupture into the pelvis in a 10-year-old girl with chronic graft nephropathy. The girl had already returned to hemodialysis after recurrent antibody-mediated rejection episodes. On palpation “hard” kidney. Nephrectomy and histologically acute and chronic antibody mediated rejection with macroscopic blood clots. Power Doppler with overall reduced vascularity, inhomogeneous material (blood/hematoma) in the renal pelvis and proximal ureter (arrows), longitudinal section. b Same 10-year-old patient, longitudinal section. Massive organ swelling, echopoor line in the upper kidney transplant pole indicating inner rupture and bleeding (arrows), proven pathologically after transplant nephrectomy

Fig. 8

Chronic allograft nephropathy: echogenic kidney with reduced corticomedullary differentiation and scarce vascularity. In the pulse-wave (PW)-Doppler broad systolic peaks, low flow velocities (< 15 cm/s) and reduced-absent end diastolic flow