Imaging the complications of renal transplantation
Imaging the complications of renal transplantation:
The first successful kidney transplant was performed in 1954, followed by the first successful kidney and pancreas transplant in 1966. However, these grafts did not last as long as one would expect if these organs were transplanted today. Reasons for this discrepancy include improvements in surgical technique over the years, and more importantly improvements in anti-rejection chemotherapy. For example, cyclosporine was first introduced in 1983, and was the first anti-rejection drug to be used.
In the UK in 2007, 2218 kidney transplants were performed, an increase of 7% compared with the previous year. However, the demand for donor kidneys vastly outweighs the supply and it has been proposed that donating organs after death should become compulsory in the United Kingdom, or that 'domino surgeries' should be allowed as in the USA (which will be discussed later).
Irreversible renal failure is the main indication for renal transplantation. The main causes of such renal failure are: diabetic nephropathy, chronic pyelonephritis and chronic glomerulonephritis. Most patients will not receive a donor organ immediately and so will have to undergo peritoneal or haemodialysis until a donor organ is found. However, the patient must be well enough to undergo major surgery at the time that a suitable organ is found, which may not be the case in a patient who has undergone haemodialysis for many years.
Availability of organs:
Donor kidneys may be harvested from a brain-dead patient (cadaveric transplantation) or from a living donor. There are many ethical issues surrounding the use of organs from a living donor, for example a patient may pay another person with a suitable organ to coax them into donating. As receiving payment for donating an organ is illegal, most living donor organs are from relatives. However, in the USA, several living non-directed donors (LND) have come forward- these people are willing to donate a kidney to a patient in need, even though they do not know the recipient. Such transplantations have given rise to 'domino surgeries' whereby a the donation of one organ from a living non-directed donor will result in 2 patients receiving an organ. This is because if the LND is donating to a patient whose partner or relative was willing to donate but is not a tissue match, the LND organ may go to the donor, and the partner or relative who was originally willing to donate may still donate, but to a recipient chosen via UNOS' criteria (UNOS is the United Network for Organ Sharing, which manages the coordination of transplants in the USA). Diagram C below demonstrates a domino scenario.
(from Montgomery et al, 2006).
The transplanted kidney is placed either in the left or right iliac fossa, depending on previous surgery and the particular surgeon's preference. The epigastric artery, round ligament and spermatic cord are structures which may interfere with the placement of the donor organ and may therefore be divided in order that the donor organ will have enough space to lie comfortably in that area of the relevant iliac fossa. In order to restore the blood supply to the graft, the external iliac artery and vein are used to connect the graft to the recipient's blood supply. An end-to -side anastomosis is usually used, whereby the end of the donor renal artery and vein are attached to the side of the external iliac artery and vein respectively. In many cases, the donor organ will have more than one renal artery. In such instances, it is important to mainly blood flow in each artery as the intrarenal anastomoses may not be adequate to perfuse the entire organ. In such cases, the renal arteries may be anastomosed separately, or together in the form of a Carrel patch or a side-to-side anastomosis (see diagram below). Multiple renal veins may be sacrificed as collaterals exist which will drain the deoxygenated blood via the main renal vein. Both the artery and vein are sutured in place using nonabsorbable microfilament sutures, which is typical in vascular surgery, as the time taken for smooth muscle cells to migrate into the suture line to strengthen the anastomosis is longer than the time taken for absorbable sutures to be absorbed, which may result in a weakness in the join and potential leakage.
(Kobayashi et al 2007)
The donor ureter must also be connected to the recipient's bladder, and this must be carried out in such a way as to prevent reflux into the donor kidney. In complex cases, the recipient's existing ureter may be used; the donor ureter is anastomosed with the recipient's ipsilateral ureter.
-anti-rejection drugs making diabetes harder to control
Hyperacute rejection occurs as soon as the graft is in place- within minutes to hours. The most common reason being major compatibility issues, either with the blood group or HLA matching. Hyperacute rejection is mediated by pre-existing antibodies; for example, a person of blood group A already has circulating anti-B antibodies, which would precipitate hyperacute rejection. In these cases, the newly transplanted kidney will abruptly cease to function, due to severe damage to the vasculature and endothelium, as well as due to thrombus formation. Although the risks of encountering a hyperacture rejection can be reduced by careful ABO and HLA matching, in countries like Japan where they do not have an established cadaveric organ donation scheme in place, ABO-incompatible renal transplants are increasingly performed. Such a procedure would need to be followed by several anti-rejection therapies, including immunoadsorption to remove the preformed circulating antibodies to the graft, anti-CD20 antibodies in order to prevent B lymphocyte mediated rejection, and iv pooled Ig for immunomodulation or anti-idiotypic antibodies. Although the results are usually acceptable, mismatched transplantation carries more risks and results in a greater number of prophylactic drugs being used post-transplantation to reduce the risks of rejection.
Acute rejection may occur within weeks to months post-operatively, and the onset is sudden. As with hyperacute rejection, the graft becomes tender and swollen, and there is a reduction in the functionality of the graft. Cellular and antibody mediated mechanisms lead to acute rejection; a graft undergoing acute rejection will demonstrate infiltrates of lymphocytes, plasma cells and macrophages, as well as vascular endothelial damage due to antibodies, when viewed under a microscope.
Chronic rejection only begins months to years after the transplant has occurred. There is a progressive deterioration of the transplanted organ and microscopically a mononuclear cellular infiltrate will be seen.
The cost, invasiveness and potential damage that radiological intervention may cause are all aspects that must be taken into account when investigating renal transplant problems. Ultrasound is a relatively quick and simple procedure, and as it is a non-invasive procedure, there is no risk of damaging the transplanted kidney. Ultrasound is excellent when visualising fluids and tissues surrounded by fluid, and therefore investigating perinephric fluid collections such as uroceles may initially be carried out using ultrasound to guide diagnosis. In addition, ultrasound may be used for guidance when draining such a collection, as the images are real time. Doppler ultrasound is also useful in detected vascular abnormalities after transplantation, such as renal artery stenosis, or reduced arterial flow to the organ for other reasons.
(Brown et al 2000)
Uroceles are formed by extravasation of urine into regions around the kidneys, ureters or bladder. Leaks at the uretovesicle anastomsis are due to surgical technique or necrosis of the distal ureter. Leaks elsewhere in the collecting system usually occur secondary to ischaemia, which itself may be caused by poor anastomotic technique, variation in the vascular supply, rejection, medication or problems caused during harvesting of the graft.
Renal Artery Stenosis:
Stenosis of the renal artery occurs in up to 10% of newly transplanted kidneys, and is the most common vascular complication of renal transplantation. The most common sites for renal artery stenosis are the proximal donor artery, or the region of the anastomosis. Stenosis may occur in the distal donor artery, but is usually attributed to injury to the intima caused by the perfusion cannula, although some sources claim that stenoses both proximally and distally in the donor artery are caused by rejection. Stenosis of the recipient's renal artery is rare and may result from existing atherosclerotic disease or injury caused by the vascular clamp used during surgery. Doppler ultrasound is ideal for investigating the vascularity of the transplanted kidney; however, in cases where the presentation is typical of renal artery stenosis but no evidence for this is shown on ultrasound, angiography may be performed. Angiography may also be performed in patients with clinical symptoms of hypertension due to renal artery stenosis, and a positive finding on ultrasound, in order to gain a greater insight into the nature of the obstructive cause.
Renal Artery Thrombosis:
Renal artery thrombosis is rare and usually leads to graft loss. Occurring early in the postoperative period, associated findings include severe rejection, severe tubular necrosis, and faulty surgical anastomosis. Failure to visualise intrarenal arterial and venous flow on Doppler ultrasound are indicative of potential renal artery thrombosis, although as the symptoms mimic those of rejection, angiography may be required to confirm the diagnosis.
Renal Vein Thrombosis:
A rare cause of renal transplant dysfunction, renal vein thrombosis is apparent in the first week after tranaplantation and clinical symptoms include swelling and tenderness of the graft, and sudden oliguria. Renal vein thrombosis may be caused by external fluid collections compressing the renal vein, poor surgical technique, and hypovolaemia. Silent iliac compression syndrome has been attributed to the greater number of cases of renal vein thrombosis seen in grafts located in the left iliac fossa, due to compression of the left common iliac vein between the sacrum and the right common iliac artery. Renal vein thrombosis is a serious condition, as the subsequent infarction; a transplant nephrectomy is often required to prevent infection.
Renal Vein Stenosis:
This usually results from perivascular fibrosis and compression from large perinephric fluid collections adjacent to the area of vein in question.
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