Evaluation of living Renal donors by CT What radiologists should know

Dr Ahmed Refaey, FRCR Consultant Radiologist Prince Sultan Military Medical City- Riyadh

• Radiologists are responsible for providing accurate anatomic information about the donor’s renal parenchyma, arteries, veins and collecting system .

• Laparoscopic nephrectomy is the preferred surgical procedure for harvesting kidneys from living donors

• There is also a lack of visualization of the posterior and medial superior aspects of the kidney and renal veins with laparoscopic nephrectomy, that is why, comprehensive preoperative evaluation of potential donors is crucial .

• Multidetector CT protocol : • Unenhanced kidney phase :to detect

nephrolithiasis and serves as a baseline for the enhancement of lesions.

• The arterial phase ( 20-30 s.): not only for depicting the arterial anatomy, but venous anatomy as well.

• Nephrographic phase ( 70 s.) • Delayed or excretory phase ( 5 min.).• Delayed scout view

CT protocol

• The arterial phase ( 20-30 s.)• Nephrographic phase ( 70 s.) • Delayed scout view

Points must be included in the Radiologist report

• Evaluation of kidneys • Evaluation of renal arteries• Evaluation of renal veins• Evaluation of upper urinary tract• Evaluation of amount of peri-renal fat

Evaluation of kidneys

• Location and length of kidneys• Detection of any renal abnormality

Priorities for removal of kidneys

• The donor must retain one normal kidney• If both kidneys are normal, the kidney with

less complicated vascular anatomy is removed.

• The left kidney is preferred for laparoscopic living donor nephrectomy because it has a longer renal vein and it is technically easier to remove.

Normal kidney

• Nephrolithiasis

• Nephrolithiasis may be a contraindication for living donor nephrectomy because of the risk that recurrent stones, obstruction and infection may injure the remaining kidney.

• In some centers, a kidney with a small stone ( < 4 mm ) may be safely harvested, particularly if calculi are located in lower pole and the donor has no history of lithiasis or metabolic disease.

• Renal masses• Simple, even large cyst may be easily excised ,

and is not contraindication for donor nephrectomy.

• Kidneys with small angiomyolipoma ( < 5mm ) may be safely transplanted.

• Renal anomalies that exclude donation, are:

-unilateral agenesis -horseshoe kidney -polycystic disease -medullary sponge kidney

disease -renal papillary necrosis

Evaluation of renal arteries

• Number• Length• Other anomalies

• Renal arterial anatomy and variants

• There are 3 types of renal arteries which enter the kidney : hilar, polar and capsular.

• The inferior polar arteries are important because they provide vessels to the upper urinary tract. An unnoticed section of an inferior polar artery may lead to graft pyelouretral necrosis with secondary stenosis or urinary tract leakage.

Number of renal arteries

• The presence of more than two arteries within a kidney is a contraindication for donation.

• Donation is only possible if one of the three arteries is a small suprior polar artery less than 2 mm in diameter . such an artery may be sacrificed because the resultant volume of renal infarct does not substantially affect graft function.

• When a kidney has two or more arteries with a separate aortic ostium, the vessel with the greatest diameter is considered to be the main renal artery and the others are considered accessories.

• A- the distance between the right arterial origin and the first segmentary bifurcation

• B- the distance between the right IVC margin and the 1st segmentary bifurcation.

• C- the distance between the left arterial origin and the 1st segmentary bifurcation.

•There are three renal artery measurements that must be taken:

• Short renal artery :

- Short left renal artery : segmental branching less than 1 cm from the origin of the left renal artery.

- Short right renal artery :segmental branching behind the IVC

Evaluation of renal veins

• number • course • length of main renal veins • tributaries

• Three main renal venous measurements must be taken:

• * A) the distance between the segmentary confluence of the right renal vein and the IVC

• * B) the distance between the segmentary confluence of the left renal vein and the IVC

• * C) the distance between the confluence of the left renal vein and the left margin of aorta

• Late segmental confluence

• Right renal vein late segmental confluence occurs less than 1 cm from the IVC

• Left renal vein late segmental confluence occurs less than 1 cm from the left aortic margin.

• Renal vein anomalies• circumoartic and

retroaortic veins , present in 6 % and 3 % respectively

• Renal vein tributaries• Reliable visualization and knowledge of the location

and diameter of renal vein tributaries are important because of the limited visual field of laparoscopic nephrectomy and for prevention of hemorrhagic complications during surgery.

• In most cases, the right renal vein has no venous tributaries

• The left renal vein typically has several major venous tributaries.

• The left adrenal vein joins the left renal vein superiorly.

• The left gonadal vein joins the left renal vein inferiorly

• A gonadal vein with a diameter larger than 5 mm should be reported because the surgeon may need to use an alternate sectioning technique ( eg, staples or plastic clips rather than cautery).

• Sagittal thin-section MIP image shows the left gonadal vein, which is large , with diameter of 9 mm ( arrow), draining into the inferior margin of the left renal vein ( *) . the hemiazygos vein (arrowheads) also drains into the superior margin of the left renal vein.

Prominent Left gonadal vein

• Retroperitoneal ( lumbar, ascending lumbar and hemiazygos) veins enter the left renal vein just lateral to the aorta along its posterior aspect.

• A prominent lumbar vein with a diameter larger than 5 mm should be reported to ensure an appropriate surgical approach.

• Sagittal thin-section MIP image shows the lumbar vein ( arrow) which is large with a diameter of 7 mm, draining into the posterior aspect of the left renal vein(*). The hemiazygos vein ( arrowhead) also drains into the superior aspect of the lumbar vein before anastmosing with the posterior margin of the left renal vein.

Evaluation of perirenal fat

• Kidneys that are to be transplanted must have all perirenal fat removed.

• Large amounts of preirenal fat make surgery difficult and obscure anatomic landmarks.

Amount of perirenal fat

Evaluation of Upper urinary tract

• Delayed topograms acquired in the excretory phase adequately depict the pelvicalyceal system and uretrs and require less radiation than delayed phase CT images. If excretory topogram result is unclear, conventional abdominal radiography is more useful than excretory phase CT.

Evaluation of upper urinary tract

Conclusion

• Because of Laparoscopic nephrectomy is the preferred surgical procedure for harvesting kidneys from living donors, and lack of visualization of the posterior and medial superior aspects of the kidney and renal veins with laparoscopic nephrectomy, Radiologists are responsible for providing accurate anatomic information about the donor’s renal parenchyma, arteries, veins and collecting system .

Points must be included in the Radiologist report

• Evaluation of kidneys • Evaluation of renal arteries• Evaluation of renal veins• Evaluation of upper urinary tract• Evaluation of amount of peri-renal fat

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