Vascular and Endovascular Surgery
Computed Tomography angiogram: Can it be used for lower extremity vein mapping
Journal: Vascular and Endovascular Surgery Manuscript ID: Draft Manuscript Type: Original Manuscripts Date Submitted by the Author: n/a Complete List of Authors: Wright, Mark; University of Arkansas for Medical Sciences, Surgery Eidt, John; Greenville Hospital systems, Surgery Wright, Lonnie; University of Arkansas for Medical Sciences, Radiology ALI, AHSAN; UNIVERSITY OF ARKANSAS FOR MEDICAL SCIENCES, Surgery Keywords: vein mapping, CTA, Duplex
High Resolution Computed Tomography Angiogram: Can it be used for vein mapping?
Mark P. Wright, MD1
Lonnie Wright, MD2
John F. Eidt, MD1
Ahsan T. Ali, MD1
1 Division of Vascular Surgery, Department of Surgery, University of Arkansas for Medical Sciences, Little Rock Arkansas
2 Department of Radiology, University of Arkansas for Medical Sciences, Little Rock, Arkansas
Presented at the 60 th Annual meeting for the Society for Vascular Surgery, Philadelphia,
Financial disclosure: None
For Correspondence and reprints:Ahsan T. Ali, MD
Associate Professor of Surgery
Department of Surgery
University of Arkansas for Medical Sciences 4301 West Markham Street
Slot # 520
Little Rock, AR 72205
Background: Computed-tomography (CTA) has replaced angiography when evaluating arterial anatomy. CTA has not been used routinely for vein mapping. Objective of this study was to evaluate the accuracy of CTA for venous anatomy and compare it to a standard venous duplex ultrasound (DUS).
Methods: Sixteen patients with 22 limbs underwent CTA followed by a DUS. The greater saphenous vein (GSV) diameter was measured at; saphenofemoral junction, mid-thigh, knee joint and mid-calf. GSV diameter was then measured using DUS a by registered vascular technician. These were compared using linear regression.
Results: There was no difference in the diameter of the GSV when measured using a CTA or DUS. All anomalies were identified with CTA while one was missed with DUS. Sclerosis of the vein was identified with DUS but not with the CTA.
Conclusion: CTA is as accurate as DUS and can be used for vein mapping the GSV.
Catheter based angiography has been the standard prerequisite for delineating arterial anatomy for assessment and treatment of peripheral vascular disease. However, in the last decade, advances in cross sectional imaging technology have made diagnostic arteriogram almost obsolete. Arterial anatomy is nowadays very accurately imaged by a computed tomography angiogram (CTA). It is safer compared to diagnostic arteriogram and accessible at all times. This has led to decrease in the number of arteriograms where they are primarily being done for therapeutic interventions1.
For lower extremity bypass, the greater saphenous vein (GSV) remains an ideal conduit2. Pre-operative imaging for GSV has been Duplex ultrasound (DUS) in a non-invasive vascular laboratory3.
We hypothesized that CTA can not only be used for arterial anatomy but also provide accurate vein mapping and is comparable to DUS. This pilot study which was undertaken to determine the role a standard CTA as an initial modality for assessing superficial venous anatomy for bypass in the lower extremities.
This study was carried out at the University of Arkansas for Medical Sciences, Little Rock Arkansas from 2005-2006. Patient selection criteria were limited to all the patients with lower extremity ischemia who underwent a CTA and then had a DUS for preoperative vein mapping before a venous bypass.
Commuted Tomography: CTAs were performed in the Department of Radiology using Phillips Brilliant® 64 model (Phillips Healthcare: Andover, MA) using standard protocol of 1mm axial cuts with a contrast bolus of 80-125 mL using Visipaque® Iodixanol (GE Healthcare, Wauwatosa, WI) Images were analyzed on a Vitrea (Vitrea-Toshiba Medical Systems) work station.
Vein was measured using cross sectional imaging (Figure-1) as well as using 3-D reconstructions (Figure-2) at four locations:
a- Sapheno-femoral junction (SFJ),
c- above knee
d- Just below knee.
The above anatomic locations are similar to corresponding measurements when DUS is used. If no contrast was used, then only the cross section images were utilized.
Vascular lab measurements: DUS vein mapping was performed in a vascular laboratory by a registered vascular technician in the division of vascular surgery. A 5-7 mHz probe (Phillips Healthcare, Andover, MA) was used at the sapheno-femoral junction, mid-thigh, above knee, below knee and the ankle. GSV measurements at the ankle were not used for the study. Both the vascular lab results and CTA eight measurements were tabulated and measured independently. The radiologist and the sonographer were blinded to each other as the studies took place at different times and departments. In all patients, the DUS was performed after the CTA as part of pre-operative work-up. Finally, the data was verified in the operating room when the vein was harvested for a bypass in patients.
Data was reported as mean ± standard deviation. A one-way analysis of variance (ANOVA) was used to compare diameter at corresponding points between the CT and DUS measurements.
The measurements of the GSV were not significantly different when using CTA compared to a DUS at four points of measurements in all the 22 limbs (Figure-3) and Table-1 Duplications of the GSV were not recognized with DUS on two occasions; however no anomalies were missed by the CTA. In one patient, the sclerosis of the GSV was identified using DUS, which was not ascertained when using CTA. The measurements were confirmed in the operating room in 10 patients and were found to be accurate. In one subject, the CTA helped with the incision planning as an unusual posterior division of the GSV was the appropriate conduit and was not identified in the vascular laboratory.
High resolution computed tomography scans have revolutionized the diagnostic imaging for various disciplines such as cardiology or vascular surgery1. Diagnostic angiography are not as frequent and catheter based arteriogram are now generally reserved for interventions. At the University of Arkansas for Medical Sciences, a tertiary care medical center, any arterial and/or venous studies are performed at an accredited vascular lab which is supervised by the division of vascular surgery. The ideal conduit for lower extremity bypass is a single piece of the GSV2. The lesser saphenous vein (LSV) is not measured in a routine lower extremity vein mapping study. A typical vein map takes 30-40 minutes for both extremities. A standard vein mapping protocol involves; measurement of the diameter of the vein at the five points starting with the sapheno-femoral junction. We have only used 4 points in the measurement and did not include the ankle. The cost of the study is a $590-00 charge for a bilateral lower extremity vein mapping including physician charge. Although, DUS is reproducible; it does have a few minor issues. It is user dependent. It also does not provide a global anatomy. Infrequently, aberrant anatomy can be over looked as seen in the current study where duplication was missed. The lack of accessibility during after-hours or the weekend is certainly a limitation across most facilities. However, one clear advantage with DUS is the ability to assess the quality and compressibility of the vein for sclerosis.
Advantage of CTA is its reproducibility and easy access in odd hours. CTA allows the surgeon to appreciate the global anatomy of the GSV. Furthermore, CTA allows for the assessment of the lesser saphenous vein, which is not routine in most vascular lab protocol.
The CTA did not give information about the quality of the vein where the technologist can physically compress the vein. It may be difficult to identify areas of sclerosis as CTA did not identify a segment of sclerosis or thrombosis, which was identified by the DUS. However, in our experience, an asymptomatic thrombosis of the GSV is a rare finding by DUS. It can be hypothesized that asymptomatic thrombosis of the GSV would result in a small, fibrotic vein that would be deemed inadequate for bypass by CTA. In this study, all CTAs were adequate for measuring the GSV diameter and no special protocols were required. Venous phase was not used. Additionally, CTA identified four anatomic anomalies (duplications) and DUS only identified only two of the anomalies. The use of CTA as screening tool has been reported recently4 5.
The CTA can reliably provide sufficient information about the venous conduit that may preclude a formal DUS for vein mapping. This study is unique in that the results of both the DUS and CTA were confirmed in the operating room in majority of the cases (n=10 patients). Since the data was tabulated before the bypass or vein harvest took place. The CTA was part of work-up for peripheral interventions or bypass. We found CTA highly accurate. The CTA also provided global anatomy, which helped in planning incisions for vein harvest. We recommend that CTA can be a useful screening tool and can be used as an adjunct for preoperative assessment of venous anatomy. Thus the DUS can be reserved for assessing vein quality if the CTA is inconclusive.
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GSV (location) DUS (mm) CTA (mm) SF junction 4.5 ± 0.9 4.8 ± 1.1 Mid Thigh 3.3 ± 0.7 3.5 ± 0.9 Knee Joint 3.4 ± 0.9 3.4 ± 0.9 Mid Calf 2.7 ± 0.8 2.7 ± 0.8