PICTORIAL INTERLUDE Renovascular anatomy as depict- ed by multislice helical CT Jonathan P Hack FCRad(D) SA SunninghilI Hospital, Sandton Multislice helical computed tomo- graphy (MSCT) represents state-of- the-art in modern CT imaging at pre- sent. The four channel or 'quad' mul- tislice scanner uses between 8 and 32 detector rows for image acquisition instead of the single channel and detector row of older conventional and helical CT scanners. A four channel (quad) multidector row CT is eight times faster than sin- gle slice CT. Eight slices are obtained per second (four slices per rotation at two rotations per second) as opposed to single slice helical CT (one slice per rotation at one rotation per second.). This provides the following benefits: Improved temporal resolution. Faster image acquisition results in fewer motion artifacts (voluntary and involuntary). Improved spatial resolution. Thinner slices, combined with appro- priate data overlap, improves resolu- tion along the z-axis, reducing partial volume artifacts and thus increasing diagnostic accuracy. Improved vascular opacification. Because scanning is completed rapid- ly, contrast can be administered at a faster rate, improving vascular opaci- fication and conspicuity. Reduced image noise. Rapid scan- ning allows for an increase in mA thus reducing image noise and thus improving image quality. Efficient X-ray tube utilisation. As imaging is completed more rapidly,' tube heating is reduced, thus eliminat- ing the need to wait for tube cooling between scans. During the lifetime of a tube, eight times more images are produced, reducing cost. As shown in this pictorial essay, MSCT has an accuracy comparable to conventional angiography in identify- ing renal arterial anatomy and also has the added ability to simultaneously define renal venous anatomy. Scanning technique and image display All images were obtained during the imaging of prospective living renal donors, using an Mx8000 quad multi- slice CT scanner (Philips Medical Systems, Cleveland, Ohio). Post- processing was performed on an MxView workstation (Philips Medical Systems, Cleveland, Ohio). Phase 1: 6.5 mm effective slice width images are obtained from the diaphragm to the symphasis pubis in order to evaluate for urolithiasis and to provide baseline density measure- ments of renal masses. 37 SA JOURNAL OF RADIOLOGY • June 2003 Non-ionic low osmolar contrast medium is then introduced intra- venously via an antecubital vein utilis- ing an 18 gauge cannula at a rate of 5 ml per second. Phase 2: After a delay determined by a bolus tracking device, 1.3 mm effective slice width images are obtained from above the celiac axis to below the iliac arteries in order to map the renal arteries and veins. Phase 3: After a delay of 65 sec- onds, 3.2 mm effective slice width images are obtained from the diaphragm to symphasis pubis. This allows for further evaluation of the renal venous system, the renal parenchyma and remaining intra- abdominal viscera. Plain film post CT: This allows us to detect medullary sponge kidney, papillary necrosis, as well as duplica- tion anomalies of the collecting sys- tems. Images are displayed as multipla- nar reformatted images (MPR), angiographic maximum intensity projection images (MIP), 3D surface- shaded images or as 4D volume- rendered images. Renovascular anatomy Arterial anatomy The renal arteries are two large arteries which arise from the sides of the aorta immediately below the supe- rior mesenteric artery at the upper margin of L2. Their relative positions may vary according to the position of the kidneys. Although the right renal artery may travel in an oblique plane, they are often both horizontal. In 70% of cases there are single arteries bilaterally (Figs 1 and 2). PICTORIAL INTERLUDE Fig.1. Volume rendered (40) image of normal renal arieries. Fig. 2. MIP image of normal renal eneties. Anatomic variants Thirty per cent of patients have multiple renal arteries, which may be : (i) supplementary arteries (to the hilum) (Figs 3 - 5); (ii) capsular arter- ies; (iii) polar arteries, which may arise from the main renal artery or from the aorta (Figs 4 - 6); and (v) extrahi- lar branching (Figs 3 and 4). Fig. 3. MIP Image demonstrafing a supplementary ariery on the left and eariy extra hllar branching on the right. Fig. 4. 30 surface shaded image demonstrating bilateral supplementary stteties, early extra hilar branching on the left and a left sided polar ariery. Fig. 5. 40 volume rendered image demonstrating a left sided polar and supplementary ariery. Fig. 6. Curved MPR demonstrating a small left sided polar ariery. 38 SA JOURNAL OF RADIOLOGY • June 2003 Venous anatomy The right renal vein is short (± 2 - 2.5 cm) and is single in 85% of cases. It does not usually receive any signifi- cant tributaries. The left renal vein is long (± 8.5 cm). It is single and preaortic in posi- tion in 85% of cases and it receives the left spermatic, inferior phrenic and, usually, the left adrenal veins (Figs 7 and 8). It passes just below the origin of the superior mesenteric artery. Fig. 7. Curved MPR demonstrating normal renal veins. Fig. 8. Curved MPR demonstrating large left gonadal veins and the left adrenal vein. Anatomic variants Right renal vein: (t) multiple veins (Fig 9); and (il) gonadal and adrenal veins may occasionally drain into the right renal vein. Left renal vein: (i) multiple veins (Fig.lO); (it) circumaortic vein (Figs 11 and 12); and (iit) retro- aortic vein (Fig. B). Lumbar veins may drain into the renal vein (Fig. 14). PICTORIAL INTERLUDE Fig. 9. Volume rendered image demonstrating complete duplication of the right renal vein. Fig. 10. Volume rendered image demonstrating partial duplication of the left renal vein and a large left gonadal vein. Fig. 11. Curved MPR demonstrating a clrcumeor- tic left renal vein. Fig. 12. Volume rendered image demonstrating a circumaortic left renal vein. Fig. 13. Curved MPR demonstrating s retro-sortic left renal vein. Fig. 14. Curved sagittal MPR demonstrating a large lumbar vein draining into the left rensl vein. Acknowledgement Images 3, 4 and 10 courtesy of J Rydberg, et al. Further reading I. Pozniac MA, Balison DJ, Lee FT Jr, Tambeaux RH, Uehling OT, Moon TD. CT angiography of potential renal transplant donors. Radiographies 1998; 18: 556-587. 2. Rydberg J, Kopecky KK, Tann M, et al. Evaluation of prospective living renal donors for Iaparoscopic nephrectomy with multislice CT: The marriage of minimally invasive imag- ing with minimally invasive surgery. Radio- gmphics2001; 21: 5223-5226. 3. Gray G. Gray's Anatomy. The Classic Collector's Edition. New York: Bounty Books, 1977: 556- 557,619. 4. http://www.indyrad.jul?uj.edu/multjslice-ctl (Jast accessed 0 I April 2003), 39 SA JOURNAL OF RADIOLOGY • June 2003 http://www.indyrad.jul?uj.edu/multjslice-ctl