Ultrasonographic features of kidney transplants and their complications: an imaging review

Abstract

Renal transplantation is the treatment of choice for managing patients with end-stage kidney disease. Being submitted to a very serious surgical procedure, renal transplant recipients can only benefit from follow-up imaging and monitoring strategies. Ultrasound is considered as the principal imaging test in the evaluation of renal transplants. It is an easily applied bedside examination that can detect possible complications and guide further imaging or intervention. In this imaging review, we present essential information regarding the sonographic features of healthy renal transplants, detailing the surgical technique and how it affects the sonoanatomy. We focus on various complications that occur following renal transplantation and their sonographic features by reviewing pertinent literature sources and our own extensive imaging archives.

Figure 1

(a) Normal transplant kidney on gray scale ultrasound, demonstrating good contrast resolution between cortex and medulla. Slight dilatation of the collecting system and pig-tail catheter (arrow) is noted. (b) Normal renal artery and vein of the transplant kidney on color Doppler ultrasound. (c) Normal homogeneous blood flow throughout the transplant kidney on color Doppler ultrasound. Interlobar, arcuate, and the peripheral cortical branches are illustrated. (d) Normal renal vein waveform on spectral Doppler ultrasound. (e) Normal intrarenal artery waveform on spectral Doppler ultrasound shows a brisk systolic upstroke and high diastolic flow. Resistive index is normal (RI = 0.71). (f) Normal waveform of the renal artery on spectral Doppler ultrasound.

Figure 2

(a,b) Acute tubular necrosis (ATN) of 2 cadaveric renal transplants a few days after transplantation. Gray scale ultrasound demonstrates edematous appearance and loss of normal cortical medullary differentiation in both transplanted kidneys.

Figure 3

Acute rejection. On gray scale ultrasonography, the kidney is mildly swollen with compression of its sinus fat. Spectral Doppler waveforms of intrarenal arteries are monophasic with loss of diastolic flow and increased resistivity index (RI = 1).

Figure 4

Emphysematous pyelonephritis. Ultrasound image demonstrates mildly increased cortical echogenicity and gas in the parenchyma of the renal graft, which produces echogenic lines with distal reverberation artifacts.

Figure 5

Spectral Doppler ultrasound image shows a tardus parvus waveform in an intrarenal arterial branch, distal to renal artery stenosis.

Figure 6

Transplant kidney infarct. It is not evident on B-mode ultrasound (a). Power Doppler imaging reveals a large blood flow defect in the largest part of the kidney (b). Perfusion absence is confirmed by contrast enhanced ultrasound with contrast agent (arrow) (c).

Figure 7

Intrarenal arteriovenous fistula following biopsy. Color Doppler ultrasound demonstrates a highly vascular lesion (arrow) with aliasing. Spectral Doppler image shows the characteristic mixed arterial venous waveform, with high velocities and low impedence.

Figure 8

Arteriovenous fistula. Color Doppler ultrasound shows an abnormal focus of increased turbulent flow in the midpole.

Figure 9

Gray scale sonogram shows two anechoic areas, without septations, next to a renal transplant. Ultrasonographically guided aspiration revealed increased levels of creatinine, compatible with urinomas.

Figure 10

Gray scale ultrasound shows mild hydronephrosis of a renal allograft secondary to ureteral stricture.

Figure 11

Gray scale ultrasound of a well-functioning renal transplant demonstrating slight dilatation of its collecting system. The increased volume of urine produced and the loss of ureter's tonicity, due to denervation, contribute to mild benign pelvicalyceal dilatation.

Figure 12

Renal transplant calculus. Ultrasonographic image of a renal graft demonstrating a shadowing echogenic focus located in the middle calyceal group (arrow). There are no obstructive effects of the collecting system of the kidney.

Figure 13

Hematoma. Longitudinal ultrasound image demonstrating a complex echogenic mass in contact with the upper pole of the transplanted kidney. There were no clinical signs of renal dysfunction, in the previous days, except from pain in the area due to an incidental injury of the recipient.

Figure 14

(a to c) Ultrasonographic images of a large peritransplant fluid collection 1 month after surgery, which begins from the lower part of the kidney and continues inferiorly to the scrotum. In contrast to the major part of the collection in the abdomen, which is completely anechoic, its extension in the scrotum has multiple thick septations. After ultrasonographically guided drainage the collection proved to be a lymphocele.

Figure 15

Presence of an anechoic area next to the renal transplant's hilum with no compressive effects on the graft, representing a small lymphocele on gray scale ultrasound.