The Transplanted Kidney
Ultrasound evaluation of the transplanted kidney is fairly simple because the graft is commonly placed in the retroperitoneal space of the right iliac fossa in a superficial position.
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The Transplanted Kidney Giulio Argalia, Nicola Carboni, Daniela Dabbene, Giuliano Peta, Paola Piccinni, Anna Clara Renzi, and Gian Marco Giuseppetti
Ultrasound evaluation of the transplanted kidney is fairly simple because the graft is commonly placed in the retroperitoneal space of the right iliac fossa in a superficial position. The vessels are in the medial side of the organ and are connected with the recipient’s common or external iliac vessels. After identifying the transplanted kidney, images are acquired in the transverse and sagittal planes, and the renal size is recorded. The adjacent soft tissues are scanned to identify any perirenal fluid collections. After that, color or power Doppler is applied to evaluate the parenchymal flow and to identify the renal hilum and the anastomoses. Flow quantification can be measured by the resistivity index (RI), pulsatility index (PI), and systolic/diastolic ratio. The study is normally performed with a convex transducer with variable frequency between 3.5 and 5 MHz (Fig. 8.1). The healthy graft has comparable ultrasound features to the healthy native kidney; however, a more detailed two-dimensional image is obtained as the transplant is usually located more superficially. Graft sizes are similar to native kidneys; however, gradual increase of its dimensions can be seen over the first few weeks by up to 32 % of the initial length by the first month. The size of the vessels can depend on whether the donor is living or not which, in the first case, are smaller.
The Doppler ultrasound is performed by p ositioning the color box in the area of study (Fig. 8.2). The pulse repetition frequency (PRF) is set to 1–1.5 KHz and wall filter to 100 Hz, and the gain is set in order to optimize the image without having aliasing or color bleed. The spectral analysis is executed with the sample volume positioned in the vessel lumen of the interlobar artery. The RI is used as a measure of the resistances to the blood flow of the arteries of the transplanted kidney. An RI between 0.70 and 0.80 is considered normal. A value higher than 0.80 is an expression of graft dysfunction (Fig. 8.3). The US Doppler plays an important role in the differential diagnosis of vascular, urological, and surgical complications. It has less important impact in the parenchymal complications because of the lack of specific signs. Various elements can affect the RI such as age, heart rate, arterial pressure, and pharmacological therapy, so it has low diagnostic value in the parenchymal complications, especially if not repeated. The diagnostic impact increases if the measurements are repeated over time and correlated with laboratory parameters like creatinine and azotemia [1–3].
G. Argalia (*) • N. Carboni • D. Dabbene • G. Peta P. Piccinni • A.C. Renzi • G.M. Giuseppetti University Politecnica delle Marche, Az. Ospedali Riuniti, Ancona, Italy e-mail: [email protected] © Springer International Publishing Switzerland 2017 P. Martino, A.B. Galosi (eds.), Atlas of Ultrasonography in Urology, Andrology, a
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