RENAL TRANSPLANTATION ULTRASOUND

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, a better understanding of tissue rejection and the introduction of azathioprine and steroid in 1963, and more specifically ciclosporin A by Calne in the 1970s, 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
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 appearances
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. The transplant kidney should be assessed in the same way as the native organ, that is in two planes.

Features to be observed include:
● 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 maybe 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 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.