Anatomical relationships of the anterior blood vessels to the lower lumbar intervertebral discs: analysis based on magnetic resonance imaging of patients in the prone position.
BACKGROUND
Intra-abdominal vascular injuries are rare during posterior lumbar spinal surgery, but they can result in major morbidity or mortality when they do occur. We are aware of no prior studies that have used prone patient positioning during magnetic resonance imaging for the purpose of characterizing the retroperitoneal iliac vasculature with respect to the intervertebral disc. The purpose of this study was to define the vascular anatomy adjacent to the lower lumbar spine with use of supine and prone magnetic resonance imaging.


METHODS
A prospective observational study included thirty patients without spinal abnormality who underwent supine and prone magnetic resonance imaging without abdominal compression. The spinal levels of the aortic bifurcation and confluence of the common iliac veins were identified. The proximity of the anterior iliac vessels to the anterior and posterior aspects of the anulus fibrosus in sagittal and coronal planes was measured by two observers, and interobserver reliability was calculated.


RESULTS
The aortic bifurcation and confluence of the common iliac veins were most commonly at the level of the L4 vertebral body and migrated cranially with prone positioning. The common iliac vessels were closer to the anterior aspect of the intervertebral disc and to the midline at L4-L5 as compared with L5-S1, consistent with the bifurcation at the L4 vertebral body. Prone positioning resulted in greater distances between the disc and iliac vessels at L4-L5 and L5-S1 by an average of 3 mm. The position of the anterior aspect of the anulus with respect to each iliac vessel demonstrated substantial variation between subjects. The intraclass correlation coefficient for measurement of vessel position exceeded 0.9, demonstrating excellent interobserver reliability.


CONCLUSIONS
This study confirmed the L4 level of the aortic bifurcation and iliac vein coalescence but also demonstrated substantial mobility of the great vessels with positioning. Supine magnetic resonance imaging will underestimate the proximity of the vessels to the intervertebral disc. Large interindividual variation in the location of vasculature was noted, emphasizing the importance of careful study of the location of the retroperitoneal vessels on a case-by-case basis.
Rothman Institute/Department of Orthopaedic Surgery, Thomas Jefferson University, 1015 Walnut Street, Room 801, Philadelphia, PA 19107,USA.
Alexander R
AR
Vaccaro
Christopher K
CK
Kepler
Jeffrey A
JA
Rihn
Hidekazu
H
Suzuki
John K
JK
Ratliff
James S
JS
Harrop
William B
WB
Morrison
Worawat
W
Limthongkul
Todd J
TJ
Albert
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001012:Aorta, Abdominal / Q000473:pathology; D005260:Female; D006801:Humans; D007083:Iliac Artery / Q000473:pathology; D007084:Iliac Vein / Q000473:pathology; D007403:Intervertebral Disc / Q000098:blood supply*; D008159:Lumbar Vertebrae / Q000098:blood supply*; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D016684:Prone Position; D011446:Prospective Studies; D012187:Retroperitoneal Space / Q000098:blood supply; D013122:Spinal Diseases / Q000473:pathology*; D055815:Young Adult