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ULTRASOUND IMAGES OF RENAL TRANSPLANTS

Although there are a number of treatment choices for patients with renal failure including peritoneal and haemodialysis, undoubtedly the treatment of
choice is renal transplantation.
From the very early days of Carrel’s experimental attempts at transplantation in the 1900s (resulting in the Nobel Prize of 191226), to the un-immunosuppressed allografting of the 1950s, the more successful and encouraging outcome of twin to twin transplants,27 a better understanding
of tissue rejection and the introduction of azathioprine and steroid in 1963,28 and more specifically ciclosporin A by Calne in the 1970s,29 have all

contributed immensely to slow but positive progress in this field. Improvements in surgical technique, newer, more effective and less toxic
anti-rejection therapy, the routine use of ultrasound in the 1970s and then Doppler a decade later, and the development of interventional radiology
have all combined to make this the successful operation and clinical outcome we now take so much for granted.
Although many different imaging modalities are available, ultrasound is the single most useful investigation in the postoperative monitoring of
the transplant. Amongst its many roles, it is sensitive to early PCS dilatation, can be used to guide biopsy procedures and to guide the drainage of
fluid collections and placement of nephrostomy tubes.
An early, baseline scan is an essential part of the postoperative management, and serial scans are to be recommended.

Normal anatomy renal transplants.

Most renal transplants are heterotopic, that is they are placed in addition to the diseased, native kidneys, which remain in situ.
The transplanted organ is usually positioned in the iliac fossa anterior to the psoas and iliacus muscles. It lies outside the peritoneal cavity.
Within the UK the majority of transplanted kidneys are cadaveric, and are harvested with their main vessels intact, which are then anastomosed to
the recipient iliac artery and vein.

Normal ultrasound images

The transplanted kidney is particularly amenable to ultrasonic investigation; its position relatively near to the skin surface allows a high frequency transducer
(5 MHz) to be used for better detail. For visualization of the vasculature or origins of the transplant vessels a 3.5–4.0MHz probe is normally required.
The ultrasonic appearances of the transplant kidney are the same as expected for a native kidney, allowing for the higher resolution [Fig. ultrasound images below]. The transplant kidney should be assessed in the same way as the native organ, that is in two planes. Features to be observed include:

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Ultrasound images of Perfusion within the transplanted kidney is easily displayed. A higher frequency may be used, as the
kidney is usually superficially situated in the iliac fossa.

image

ultrasound images Same kidney as (A). The Doppler sensitivity has been increased to demonstrate tiny arcuate vessels at the periphery of the kidney

image

ultrasound images of The increased sensitivity of power Doppler is valuable in demonstrating perfusion in the transplanted kidney.

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Ultrasound images Normal spectrum from the interlobar renal artery, demonstrating good end-diastolic flow (EDF) (low resistance) with a vertical systolic upstroke.

● Morphological appearances This should include an assessment of the relative echogenicity of the cortex, medulla and renal sinus and corticomedullary differentiation. Focal or diffuse changes in echogenicity may be observed, but are non-specific findings associated with inflammation, infection or infarction.
● Size Changes in renal size may be significant in transplanted organs; it is useful to calculate the renal volume, circumference or area, rather than just relying on the length.
● PCS dilatation Even mild PCS dilatation may be significant, as it may represent an early obstructive process. The bladder should be empty before assessing the PCS, to eliminate physiological dilatation. Any degree of hydronephrosis should be correlated with the clinical findings and biochemistry.

hydronephrosis in isolation is not a reason for nephrostomy.
● Vascular anatomy The main transplant artery and vein are anastomosed to the recipient’s external iliac artery and vein respectively and can normally be visualized throughout their length. Overall global perfusion can be assessed with colour Doppler and the smaller vessels at the periphery of the kidney (Fig.ultrasound images above) should be discernible. The normal spectral Doppler waveform is a low-resistance waveform with continuous forward end diastolic flow.

● Perirenal fluid A small amount of free fluid is not unusual postoperatively. This usually resolves spontaneously. Fluid collections around the kidney are a common complication. They may resolve on further scanning; drainage is only peformed for good clinical reasons (see below).

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