Imaging of Hemodialysis Access Fistulas

In general early and late complications in hemodialysis shunts have to be distinguished. Typically, early complications relate to surgical problems or atypical draining veins (Fig. 11). Late complications in hemodialysis shunts may occur in the feeding artery, the arterial anastomosis (Fig. 12), the fistula itself, the venous anastomosis and the draining vein (Fig. 13). Arterial complications are relatively infrequent; most common problems are due to stenoses at the venous anastomosis, most often due to intimal hyperplasia. Stenosis in he-modialysis arteriovenous fistulas is usually associated with thrombosis of the access. It is also important to visualize the draining veins, since stenoses of outflow veins remote from the fistula may occur. These are probably related to the unusual arterial pressure to which these veins are subjected (Fig. 14).

Recognition of the cause of impaired access function is important to prevent complete thrombosis of the dialysis fistula. The role of MRA in imaging of these fistulas has been evaluated in various studies [18-21]. Although CE MRA is less sensitive to disturbed flow compared to conventional nonenhanced techniques (PC and TOF MRA), flow

Fistula Arm Dialysis

Fig. 11a. b. Postsurgical CE MRA study in a patient with dialysis access fistula of the lower arm in which insufficient flow was present for adequate dialysis. MIP reconstruction of two consecutive CE 3D MRA datasets (Gd-BOPTA, 0.1 mmol/kg; acquisition time per dataset 4 sec) demonstrates first (a) early enhancement of the fistula vein (arrowin a) and (b) increasing drainage into collateral veins (arrowheads in b). After surgical occlusion of the collateral veins sufficient flow was achieved [Images courtesy of Dr. G. Schneider]

Dialysis Fistula Radiology

Fig. 12a-c. MIP reconstruction of a CE 3D MRA dataset (Gd-BOPTA, 0.1 mmol/kg) demonstrating artherosclerotic occlusion of the arterial anastomosis in a hemodialysis shunt (arrowsin a, b). Note the irregular surface of the shunt (arrowsin c) after 3-year access for he-modialysis [Images courtesy of Dr. G. Schneider]

Fig. 12a-c. MIP reconstruction of a CE 3D MRA dataset (Gd-BOPTA, 0.1 mmol/kg) demonstrating artherosclerotic occlusion of the arterial anastomosis in a hemodialysis shunt (arrowsin a, b). Note the irregular surface of the shunt (arrowsin c) after 3-year access for he-modialysis [Images courtesy of Dr. G. Schneider]

Stenose Shunt

Fig. 13. High grade stenosis of the draining vein in a hemodialysis shunt (arrow as demonstrated on CE MRA [Image courtesy of Dr. G. Schneider]

Hemodialysis Shunt

Fig. 14. Normal appearance of a hemodialysis shunt with two draining veins (arrows which were both used for puncture [Image courtesy of Dr. G. Schneider]

Fig. 13. High grade stenosis of the draining vein in a hemodialysis shunt (arrow as demonstrated on CE MRA [Image courtesy of Dr. G. Schneider]

Fig. 14. Normal appearance of a hemodialysis shunt with two draining veins (arrows which were both used for puncture [Image courtesy of Dr. G. Schneider]

related artifacts may still be present under the extreme flow conditions that can occur in dialysis fistulas (flow rates may range 100-3, 000 ml/min). Bos et al [22] eliminated these flow artifacts by temporal interruption of the flow by means of an inflated cuff placed around the upper arm. They injected gadolinium contrast agent diluted 20:1 with saline directly into the fistula. On image evaluation, they found a slightly (3.7%) higher degree of stenosis on CE MRA compared to DSA which they concluded was due either to a real overesti-mation of stenosis on MRA because of limited res-

Pictures Mra Hand
Fig. 15. CE MRA of the hand in a 28 year old volunteer. Both superficial (A) and deep (B) arches are visible and complete. (C = ulnar artery, D = radial artery)

olution, or to an underestimation of luminal diameter on DSA. They found low interobserver variation both with MRA (3.2%) and DSA (3.6%).

One advantage of CE MRA is that images are acquired in 3D, and can be reformatted to visualize the fistula in any desired plane. Also functional information on the hemodialysis access can be obtained by performing flow measurements [23]. However, an important disadvantage of MRA is that no interventions can be performed, at least using current commercial products.

Essentials of Human Physiology

Essentials of Human Physiology

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