| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
1 All authors: The Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins Hospital, 601 N Caroline St., Rm. 3254, Baltimore, MD 21287.
Received January 21, 2004;
accepted after revision July 14, 2004.
Address correspondence to E. K. Fishman
(efishman{at}jhmi.edu).
Abstract
 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
MATERIALS AND METHODS. One hundred consecutive potential living renal donors who underwent 4-MDCT were evaluated. CT was performed with 120 mL of IV contrast material at an injection rate of 3 mL/sec. Both late arterial and venous phase acquisitions were obtained at 25 and 55 sec from the start of IV contrast injection, respectively. The number of the right and left renal veins and its anatomic variations were assessed by two reviewers. Late arterial phase images were evaluated initially, and then venous phase images were analyzed to assess opacification of the renal vein and to see whether venous phase data sets changed or added information about the venous anatomy as seen on late arterial phase images.
RESULTS. The retroaortic left renal vein was found in two subjects, and the circumaortic left renal vein was detected in three subjects. The renal veins were adequately opacified on late arterial phase images in all subjects. There were six subjects who had a normal left renal vein with a small posterior branch coursing posterior to the aorta and draining into the inferior vena cava, which were difficult to differentiate from the lumbar vein or ascending lumbar vein; in three of these six subjects, the small posterior branch was opacified only on venous phase images.
CONCLUSION. Late arterial phase images obtained at 25 sec after the start of contrast injection can reveal the renal vein anatomy except for a small posterior branch of the left renal vein difficult to differentiate from the lumbar or ascending lumbar vein, as seen in three subjects. The data suggest that venous phase imaging is not necessary for the evaluation of renal vein anatomy.
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
To evaluate potential renal donors, radiologists traditionally use renal angiography and excretory urography to select the patient and the kidney for nephrectomy. Recently, several studies have shown that helical CT angiography can replace excretory urography and renal angiography in the evaluation of potential renal donors [4–11]. Rubin et al. [4] and Platt et al. [6] have reported excellent agreement between CT angiography and both catheter angiography and surgery in predicting the number of renal arteries and the presence of early branching. More recently, MDCT, which offers shorter image acquisition time, improved spatial resolution, and more detailed data sets compared with single-detector helical CT, has been used to provide accurate anatomic information [12–16].
Because of limited operative visibility and surgical exposure, laparoscopic donor nephrectomy requires precise preoperative vascular mapping. In addition to evaluating the renal artery, the status of the donor kidney and collecting system and anatomic definition of the renal venous system are important for living laparoscopic donor nephrectomy. The renal veins are often visualized on arterial phase images, and most investigators have reported CT angiography with the use of initial arterial phase images to be superior to conventional angiography in visualization of the venous anatomy [4–6]. A second acquisition should improve the accuracy of venous identification because of increased venous enhancement. However, a second acquisition will substantially increase the radiation dose [17]. Knowing the degree of opacification of the renal venous structure is essential to develop an optimal protocol for the evaluation of potential donor nephrectomy patients. However, to our knowledge, no formal assessment of venous opacification with arterial and venous phase scanning has been reported.
The renal vein is the most important venous structure to evaluate before laparoscopic surgery. Particularly, a major anomaly of the left renal vein that includes the retroaortic and circumaortic renal veins is important to detect because of the potential for inadvertent venous injury. In this study, we evaluated opacification of the renal veins with the use of late arterial and venous phase images using MDCT. The purpose of this study was to assess whether both renal arteries and renal veins can be evaluated using single-phase MDCT data sets alone to eliminate the need for data sets from both the arterial and venous phases. In this study, we also evaluated the left adrenal and gonadal veins, even though they are not as critical as the renal vein, because depiction of these veins on preoperative imaging may facilitate the dissection of these veins and help avoid vascular injury; to our knowledge, the degree of opacification of these veins on arterial and venous phase images has not been evaluated previously.
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
CT Technique
The MDCT examinations were performed on a Somatom Volume Zoom scanner
(Siemens Medical Solutions) using a detector collimation of 4 x 1 mm to
obtain a 1.25-mm slice thickness. The data were reconstructed at 1-mm
intervals (0.25-mm overlap). The other parameters were 120 kVp, 125 mAs, and
0.5-sec rotation speed. The gantry speed was 0.5 sec per rotation, and the
table speed was 6 mm per rotation. After fasting for at least 2–3 hr,
each subject ingested 750–1,000 mL of water over a 15- to 20-min period
before scanning began. We injected 120 mL of iohexol (Omnipaque 350, Amersham
Health) through the peripheral venous line at a rate of 3 mL/sec. Late
arterial and venous phase volumetric data sets were acquired at 25 and 55 sec,
respectively, from the start of an IV injection of contrast material. All
image data were reconstructed with the body soft-tissue algorithm. A timing
bolus or computer-assisted software was not used in this study. The area
scanned extended from above the kidneys to just below the common iliac
arteries on the late arterial phase images and from above the kidneys to the
top of the iliac crests on the venous phase images.
The data were then transferred to a free-standing workstation (O2, Silicon Graphics) that runs 3D software (Virtuoso, Siemens Medical Solutions) for subsequent review.
Image Analysis
Two radiologists initially assessed the late arterial phase images to
determine the opacification of the relevant venous anatomy. The renal vein was
defined as opacified when it was seen as a high-density linear structure along
its entire course. The adrenal vein was defined as opacified when an enhancing
linear or branching structure draining the left adrenal area inserted into the
superior surface of the left renal vein. The gonadal vein was defined as
opacified when an enhancing linear or branching structure draining from the
pelvis or lower abdomen inserted into the inferior surface of the left renal
vein. The evaluation of renal vein anatomy included the number of the right
and left renal veins and the presence or absence of anatomic variations
including the retroaortic left renal vein and circumaortic left renal vein.
When a branch of the left renal vein coursing posterior to the aorta and
draining into the inferior vena cava was encountered, it was defined either as
(1) the circumaortic renal vein when it was larger than the caliber of the
lumbar vein and had a classic appearance of the circumaortic renal vein or as
(2) a small posterior branch when it was similar to or smaller than the lumbar
vein in caliber and difficult to differentiate from the lumbar vein or
ascending lumbar vein connected to the left renal vein. The number of left
adrenal veins and left gonadal veins was also assessed.
The reviewers assessed the venous phase images to evaluate opacification of the venous anatomy and to see whether the venous phase data sets changed or added information to the venous anatomy seen on late arterial phase images. We were unable to correlate CT findings with surgical results in this study design. The venous phase images were used as a reference. The renal arteries were assessed during the clinical evaluation but not further evaluated in this retrospective study because we previously assessed the renal arteries using late arterial phase images in living renal donors who underwent preoperative MDCT performed with the same protocol as this study [14].
The images were evaluated on the workstation. The reviewers used source images, reformatted images, and 3D display images. The workstation allowed the reviewers to edit CT volume data to create optimal 3D CT angiographic images in real-time at frame rates of 10–30 frames per second. Reviewers relied primarily on these techniques, and each reviewer subjectively chose the display parameters including width, level, opacity, and brightness.
Analysis of the adrenal vein and gonadal vein was limited to the left side because the left kidney is preferred for laparoscopic living donor nephrectomy given that the left kidney has a longer renal vein and is technically easier to remove [18, 19] and the right adrenal and right gonadal veins normally drain directly into the inferior vena cava and not into the right renal vein.
When discrepancies were found between the two reviewers, the CT examinations were evaluated by the two reviewers and consensus was obtained by discussion. The age and sex of the subjects whose left adrenal vein or left gonadal vein was not opacified on late arterial phase images were statistically evaluated with the chi-square test and an unpaired Student's t test; a p value of less than 0.05 was considered significant. The sensitivity of the late arterial phase in the detection of the renal vein, left adrenal vein, and left gonadal vein was also obtained.
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
|
|
|
|
|
|
Multiple renal veins with separate renal hilar origins and separate insertions into the inferior vena cava were found in 22 subjects on the right (21 subjects had two right renal veins [Fig. 4A, 4B] and one had three right renal veins [Fig. 5A, 5B]), but none was found on the left side. Among the 22 subjects who had multiple right renal veins, 14 were women and eight were men. The sensitivity of late arterial phase images in the detection of the right renal vein, left renal vein anterior to the aorta in classic anatomy, retroaortic renal vein, and circumaortic renal vein was 100%.
|
|
|
|
Left Adrenal Vein
The left adrenal vein was opacified on late arterial phase images in 92
subjects (32 men and 60 women; average age, 41.0 years). In seven subjects,
the left adrenal vein was not opacified on late arterial phase images and was
opacified on venous phase images (all seven were women; average age, 44.0
years) (Fig. 6A,
6B). There was no significant
difference in the age (p = 0.48) or sex (p = 0.06) of the
subjects in these two groups.
|
|
Overall, the left adrenal vein was opacified in 99 subjects on venous phase images. In one subject, the left adrenal vein was not identified on either late arterial or venous phase images. In this subject, the left adrenal gland was located immediately above the left renal vein. Two left adrenal veins were detected in two subjects (Figs. 1A, 1B, 1C and 5A, 5B). One of these two had a retroaortic renal vein (Fig. 1A, 1B, 1C). The sensitivity of late arterial phase imaging in the detection of the left adrenal vein was 93%.
Left Gonadal Vein
The left gonadal vein was opacified on late arterial phase images in 83
subjects (29 men and 54 women; average age, 41.7 years). In 16 subjects, the
left gonadal vein was not opacified on late arterial phase images and was
opacified on venous phase images (three men and 13 women; average age, 38.8
years) (Figs. 4A,
4B and
6A,
6B). No significant difference
between these two groups in terms of the age (p = 0.34) or sex
(p = 0.20) of the subjects was detected.
Overall, the left gonadal vein was opacified in 99 subjects on venous phase images. In one subject, the left gonadal vein was not identified on either late arterial or venous phase images; the circumaortic renal vein was seen in that subject (Fig. 2). There were two left gonadal veins in seven subjects (Fig. 7). The sensitivity of late arterial phase in detection of the left gonadal vein was 84%.
|
Data about the number of subjects with each venous anatomy and opacification on late arterial and venous phases are summarized in Table 1.
|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
The acquisition protocols to evaluate potential living renal donors vary in the literature. The delay time for early phase postcontrast scanning after a bolus injection of IV contrast material ranged from 10 to 31 sec with an injection rate that ranged from 2.5 to 5 mL/sec [4–15]. Some investigators use test injection [4, 6, 15] or an automated bolus-triggering technique [10, 13]. Del Pizzo et al. [9] reported that using a short scanning delay (arterial phase images obtained 14–20 sec after the start of IV contrast injection), there were seven cases of discordance about the renal vein anatomy between CT angiography and surgery including four missed supernumerary tributary veins and early venous bifurcations mainly because of poor opacification of the venous system. Kim et al. [13] reported that vascular phase images obtained with a bolus-tracking technique from 24 to 31 sec (mean, 27 sec) after the start of IV contrast injection using 4-MDCT achieved a 98% detection rate for the renal arteries and 98% for the renal veins. Arterial evaluation was not hindered by early venous contamination on late arterial phase images obtained at 25 sec after the start of IV contrast injection when the arteries were evaluated with a combination of the real-time axial scrolling, reformatted images, and 3D images on a workstation in a previous study [14]. In this study, the renal arteries were assessed using late arterial phase images in 74 consecutive living kidney donors, and CT and surgical findings agreed in 93% of subjects by the average of three reviewers [14].
For second-phase postcontrast images, we scan at 55 sec after the start of IV contrast injection to increase the accuracy of the assessment of the venous anatomy. Some investigators use a longer delay time—from 75 to 150 sec after the start of contrast injection—to improve renal parenchymal assessment [6, 11, 15]. Delayed imaging of the urinary collecting system can be obtained with a topogram using a low-kilo-volt peak or conventional film-screen radiography. Kim et al. [13] obtained excretory phase CT images for the evaluation of the urinary collecting system and ureters. Some investigators also acquire unenhanced scans to localize the kidneys, assess renal calcifications and vascular calcifications, and characterize a potential renal mass [8, 11].
We encountered multiple right renal veins with a separate renal origin and separate caval entry in 22%, multiple left adrenal veins in 2%, and multiple left gonadal veins in 7% of the subjects in this study. Previous studies showed that the incidence of multiple right renal veins ranged from 11% to 28% and that of multiple left renal veins was 1–2% [22, 23]. Multiple left gonadal veins are reported to occur in approximately 15% of people [22]. The retroaortic renal vein was found in 2% of the subjects in this study. The single left retroaortic renal vein was reported to be found in 2–3% [8, 22].
The incidence of circumaortic left renal vein varies in the surgical and imaging literature from 1% to 11%, but cadaveric studies report a higher incidence from 2% to 17% [24]. As Trigaux et al. [24] suggested, this discrepancy between the surgical, radiology, and anatomy literature may be attributable to the limitations in the field of surgery and to the imaging techniques used. The small retroaortic component of the left renal vein branch may be obscured because of the small field of view of the surgeon or because of the limited resolution of some imaging techniques.
The left renal vein often communicates with the retroperitoneal veins including the lumbar, ascending lumbar, and hemiazygos veins [22]. In this study, it was occasionally difficult to determine whether a small vein connected to the left renal vein coursing posterior to the aorta and draining into the inferior vena cava should be defined as circumaortic renal vein or as communication of a retroperitoneal vein, such as the lumbar vein or ascending lumbar vein, to the left renal vein on CT. In this study, when a branch of the left renal vein coursing posterior to the aorta and draining into the inferior vena cava was encountered, it was defined either as (1) a circumaortic renal vein when it was larger than the lumbar vein in caliber and had the classic appearance of the circumaortic renal vein or as (2) a small posterior branch when it was similar to or smaller than the lumbar vein in caliber and difficult to differentiate from the lumbar vein or ascending lumbar vein connected to the left renal vein. In the usual clinical setting, such a small posterior branch is not called the "circumaortic renal vein," and from our recent experience, these small posterior branches may not be differentiated from the lumbar vein during laparoscopic surgery and are unlikely change the surgical approach.
The left adrenal vein and left gonadal vein were not opacified on late arterial phase images in 7% and 16% of the cases, respectively, in this study. In some subjects who had an average or more than average amount of retroperitoneal fat, the nonopacified left adrenal or gonadal vein could be identified as a linear soft-tissue density structure connected to the left renal vein on late arterial phase images. However, in subjects with minimal retroperitoneal fat, it could be detected only retrospectively by comparing the late arterial phase images and the venous phase images.
The inferior mesenteric veins enter the splenic vein and run parallel and close to the left gonadal vein. Without opacification, they were occasionally difficult to differentiate from each other, particularly in subjects with a small amount of intraabdominal and retroperitoneal fat. On venous phase images, the left adrenal vein and gonadal vein were consistently identified except in one subject in whom the left adrenal vein was not identified and in one subject in whom the left gonadal vein was not identified. In a previous study, the adrenal vein was reported to be identified in 94% of the subjects using 4-MDCT angiography [20].
Some surgeons think that depiction of the left adrenal and gonadal veins on preoperative vascular mapping procedures would facilitate this dissection and assist them in averting vascular injury. However, most of our surgeons think that these veins are less important than the renal vein and that preoperative mapping of these veins is not as critical as depiction of the renal vein. The clinical significance of preoperative mapping of the left adrenal and gonadal veins could not be determined in this study.
Our study has several limitations. First, surgical confirmation of the venous anatomy was not available. We used venous phase images as a reference. Second, the sample size of variant renal venous anatomy is small, reflecting the expected incidence of anomalous renal vein. Third, we were unable to assess venous opacification on longer delay times. Some authorities recommend a longer delay after the evaluation of renal arterial anatomy, considering the possibility of encountering a renal parenchymal abnormality, particularly the incidental renal mass, because corticomedullary phase images are not as sensitive as nephrographic phase images are for a solid renal mass [25].
A single vascular phase for the assessment of the renal artery and vein and excretory phase for the evaluation of the pelvocaliceal system and potential renal mass would be adequate for the evaluation of potential living laparoscopic renal donors without significant increase of radiation dose, as Kim et al. [13] have reported. A recent study shows that there is no significant difference between nephrographic and excretory images in the detection of renal masses of 30 mm or less in diameter [26], and the use of excretory phase images has been suggested to be an acceptable alternative to the use of nephrographic phase images when assessing the kidneys for masses [27]. With 16-MDCT, a 30- to 35-sec delay time may be better for the evaluation of arterial and venous anatomy in a single study because of its faster scanning time. Further evaluation is necessary to assess the degree of opacification and accuracy of the vascular anatomy with 16-MDCT. With the increased resolution of 16-MDCT, we could expect more detail in vascular anatomy.
In conclusion, late arterial phase images obtained at 25 sec adequately opacified the right and left renal veins in all subjects. A small posterior branch of the left renal vein that was similar to or smaller than the lumbar vein in caliber and difficult to differentiate from the lumbar vein or ascending lumbar vein was not opacified on late arterial phase images and was opacified on venous phase images in only three subjects. In 7% and 16% of the cases, the left adrenal vein and left gonadal vein, respectively, were not opacified on late arterial phase images, and venous phase images were needed to assess the anatomy of these veins. However, the clinical significance of the results of depiction of the left adrenal and gonadal veins could not be determined in this study.
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
This article has been cited by other articles:
|
|
 |
|
  S. S. Raman, S. Pojchamarnwiputh, K. Muangsomboon, P. G. Schulam, H. A. Gritsch, and D. S. K. Lu Surgically Relevant Normal and Variant Renal Parenchymal and Vascular Anatomy in Preoperative 16-MDCT Evaluation of Potential Laparoscopic Renal Donors Am. J. Roentgenol., January 1, 2007; 188(1): 105 - 114. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. S. Raman, S. Pojchamarnwiputh, K. Muangsomboon, P. G. Schulam, H. A. Gritsch, and D. S. K. Lu Utility of 16-MDCT angiography for comprehensive preoperative vascular evaluation of laparoscopic renal donors. Am. J. Roentgenol., June 1, 2006; 186(6): 1630 - 1638. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
