|Year : 2015 | Volume
| Issue : 1 | Page : 1-5
The role of MRI in the evaluation of vascular malformations
Ahmed G Sadek, Mohamed A Borg, Hisham S El-Din, Adel G El-Badrawy, Ahmed I Tawfik
Department of Diagnostic Radiology and Vascular Surgery, Mansoura University, Mansoura, Egypt
|Date of Submission||06-May-2015|
|Date of Acceptance||12-May-2015|
|Date of Web Publication||26-Nov-2015|
Ahmed I Tawfik
Department of Diagnostic Radiology, Faculty of Medicine, Mansoura University, Mansoura
Source of Support: None, Conflict of Interest: None
The aim of this study was to evaluate the role of MRI and MR angiography in the assessment of vascular malformations as compared with the usefulness of duplex sonography and digital subtraction arteriography.
Participants and methods
A total of 40 patients (age range, 1-35 years; 21 male and 19 female) with diagnosed vascular malformations on the basis of color duplex imaging were examined on a 1.5 T whole-body MR scanner. Using parameters based on a fast localizer sequence, we acquired axial or coronal T1-, T2-, short-time inversion recovery (STIR) and contrast-enhanced T1-weighted images. Dynamic postcontrast three-dimensional (3D) gradient-echo MRIs were used for patients with high-flow arteriovenous malformation. MR data sets were evaluated for the detection of the lesion, determination of the malformation extent, involvement of surrounding structures, and vascular details with regard to the nidus, feeding arteries, and draining veins. Results were compared with findings from the digital subtraction angiography (DSA).
All MRIs revealed 14 low-flow venous vascular malformations, 12 high-flow arteriovenous malformations, and 14 hemangiomas. The STIR sequence was helpful for determining the extent of vascular malformation, whereas dynamic postcontrast 3D MR angiography helped in the classification of the type of the vascular malformation. MR angiography was inferior to DSA in revealing the vascular details and for interventional procedure planning.
MRI and MR angiography appear to play a significant role in the assessment of vascular malformations. The protocol for imaging such vascular malformations should include dynamic postcontrast 3D gradient-echo MRI with STIR sequences. However, DSA is still required for more vascular detail delineation and definitive treatment decisions.
Keywords: Digital subtraction angiography (DSA), Fast localizer sequence, Vascular malformations
|How to cite this article:|
Sadek AG, Borg MA, El-Din HS, El-Badrawy AG, Tawfik AI. The role of MRI in the evaluation of vascular malformations. Benha Med J 2015;32:1-5
|How to cite this URL:|
Sadek AG, Borg MA, El-Din HS, El-Badrawy AG, Tawfik AI. The role of MRI in the evaluation of vascular malformations. Benha Med J [serial online] 2015 [cited 2017 Jun 25];32:1-5. Available from: http://www.bmfj.eg.net/text.asp?2015/32/1/1/170550
| Introduction and aim of the work|| |
Congenital vascular malformations usually present as well-defined small circumscribed lesions or as complex vascular masses affecting both the venous and arterial systems and the lymphatic system , . Vascular malformations differ in structural appearance; many unknown genetic and environmental influences on the primitive vascular system in early embryonic life play a role in their development , . These vascular anomalies are divided into low-flow venous vascular malformations, high-flow arteriovenous malformations, or hemangiomas according to their natural history, clinical appearance, and histological nature  . The different morphologic and functional lesion characteristics of the vascular malformations have been evaluated using different diagnostic imaging tools; however, subclassifications of congenital vascular malformations remain poorly structured  .
The treatment plan for vascular malformations depends on the localization of the lesion and includes both minimally invasive interventional procedure and surgery. Although small superficial lesions with no muscular tissue invasion are easily treated, large deep-vascular malformations that extend into adjacent musculature, bones, and joints frequently require complex surgery  . Osteopathy, pain, intermittent bleeding, or bony overgrowth need palliative therapies ,, .
Optimal treatment planning and hence optimal outcome require a comprehensive evaluation of the feeding artery, the nidus, and the draining vessels in cases of high-flow arteriovenous malformation as well as of the adjacent structures. In addition catheter digital subtraction angiography (DSA) of the arterial and venous systems and duplex sonography, which are well established as techniques to assess these conditions, are necessary ,, . Recently, MR angiography, which allows the noninvasive evaluation of the vasculature has become an alternative method of evaluation ,,,,, . MRI has been shown to be the most accurate in the evaluation and the characterization of the type of vascular malformation; however, it usually fails to provide the functional analysis required for proper lesion classification. Using the time-resolved contrast-enhanced three-dimensional (3D) MR angiography, this limitation can largely be overcome. On the basis of ultrafast 3D gradient-echo MRI, the technique permits the 3D display of the underlying vascular morphology with high spatial and temporal resolution. Analysis of the different vascular arterial and venous phases permits the evaluation of the speed and intensities of blood flow over time  .
The purpose of our study was to determine the accuracy of MRI and MR angiography in the classification of morphologic and functional vascular malformations.
| Participants and methods|| |
Between February 2013 and February 2015, we prospectively enrolled 40 consecutive patients (age range, 1-35 years; 21 male and 19 female) with vascular malformations already diagnosed by color Doppler examination. Informed consent was obtained from each patient before enrollment. Depending on the location and the extent of the vascular malformation in each patient, different anatomic regions were examined: head (n = 18), thigh (n = 4), leg (n = 6), trunk (n = 2), forearm (n = 3), and fingers (n = 5).
All MRI examinations were performed on a 1.5 T scanner using dedicated surface coils (phased array body coil, head coil, knee coil, and extremity coil). In all patients, the MR protocol was completed in a single session. The comprehensive routine imaging protocol was based on a localizer sequence and included axial unenhanced and contrast-enhanced T1-weighted, axial T2-weighted 2D fast spin-echo acquisition, a 2D axial and coronal short-time inversion recovery (STIR) acquisition, and finally, coronal contrast-enhanced time-resolved high-spatial-resolution 3D MR angiography.
We placed a standard 19 G plastic intravenous line in the antecubital vein for contrast administration. To determine the time of contrast bolus arrival in an artery proximal to the vascular malformation, we administered a 2 ml timing bolus followed by a 20 ml saline flush at an injection rate of 2.0 ml/s. We timed the arrival of the contrast material with a sequential 2D gradient-recalled echo sequence. To permit subsequent image subtractions, we collected 3D data sets both before and after rapid infusion of 0.3 mmol of gadobenate dimeglumine, flushed with 20 ml of saline. The contrast material was administered at a rate of 2.0 ml/s. After acquiring the early arterial phase data set, we obtained late arterial and early and late venous phase MRIs approximately every 30 s. Images were reconstructed in the coronal plane  .
Digital subtraction angiography
Patients with lesions identified as high-flow arteriovenous malformations (n = 8) underwent catheter DSA of the arterial system on a standard angiography unit using a Phillips machine after MRI (GE, Florida, USA). Four patients with vascular malformations refused to undergo angiography of the lesion.
DSA was generally performed with a 0.035-inch guidewire (Radifocus SP; Terumo, Tokyo, Japan) and a 4 or 5 Fr catheter (Bern; Boston Scientific, Natick, Massachusetts, USA) inserted into the right common femoral artery. The catheter tip was positioned just proximal to the vascular malformation. After injection of 40-60 ml of nonionic contrast material [Xenetix (iobitridol); Guerbet, Aulnay-sous-Bois, France] diluted with an identical amount of saline, multiple images including early and late arterial and venous phases of contrast enhancement were obtained using a digital subtraction technique in different positions (anteroposterior, lateral, and oblique views).
All 40 patients underwent duplex color sonography of the vascular malformations. After identifying the relevant vasculature, we assessed the feeding artery, the nidus, and the draining vessels in cases of arteriovenous malformations and measured the flow using color-flow Doppler sonography. All examinations were performed by experienced radiologists on an advanced sonography scanner (GE logic P5) with probes ranging from 4.5 to 7.5 MHz.
After the termination of the examination, we assessed MRI data sets for the type of lesion visualized (i.e. low-flow venous malformation, high-flow arteriovenous malformation, and hemangioma): any abnormalities in the feeding arterial or the draining venous systems and the involvement (if any) of muscle, bone, and joints by the lesion. We also decided whether the vascular detail shown was sufficient for treatment planning.
The results of the MRI analysis of the vascular lesion type and the feeding arterial and draining venous systems were correlated with the reference standard findings of the arterial DSA performed in four patients. DSA as the reference standard had been interpreted previously in an identical manner. The value of MRI and MR angiography for the assessment of vascular malformation extension and interventional planning was compared with the values of the DSA technique.
| Results|| |
All MRIs in the study cohort were technically adequate. The techniques were well tolerated by the patients and were completed within an in-room time of about 30 min. The mean MR in-room time requirements (28 : 34 ± 4 : 12 min : s) compared favorably with the arterial DSA (52 : 26 ± 5 : 32 min : s).
On the basis of all the imaging data set analyses, we classified the 40 vascular malformations in patients as follows: 14 low-flow venous malformations combined with multiple microshunts, 12 high-flow arteriovenous malformations, and 14 hemangiomas.
Muscular, bony, and joint involvement was assessed using MRI data sets. Involvement of the musculature was evident in only 10 lesions (six venous vascular malformations, two hemangiomas, and two arteriovenous malformations). None of the vascular malformations extended to the joints or the bones.
The extent of all lesions was identified by STIR and contrast-enhanced T1-weighted images. The lesion extent was best evaluated on STIR images, a finding that reflects the high signal of congenital vascular malformation and the dark signal in muscle and bone. To a lesser degree, the lesion extent could also be assessed using contrast-enhanced T1-weighted images, whereas unenhanced T1-weighted images were of very limited value.
Dynamic time-resolved contrast-enhanced 3D MR angiography played an important role in the accurate classification of the lesions in arteries and veins.
On 3D MR angiography, arteriovenous malformations were characterized by the presence of a large dilated feeding artery, nidus, and a large dilated draining vein that displayed substantial contrast enhancement during the first pass. In our study, enlarged supplying arteries were clearly depicted on the early phases of time-resolved contrast-enhanced 3D MR angiography, whereas draining veins were depicted in the late phases ([Figure 1]).
|Figure 1 A 35-year-old man with AVM in the left lumbar region. (a– c) Axial T2, T1, and sagittal STIR images with signal void vessels denoting the arterialized flow. (d) A phase-contrast MRA showing the feeding right lumbar arteries and an abnormal tortuous draining vein into the right femoral vein. (e) Six sequential images of time-resolved MRA showing the feeding arteries in the early arterial phase and the draining vein in the late venous phase, giving the dynamic images of the different arterial and venous components of the lesion and its nidus. AVM, arteriovenous malformation; MRA, magnetic resonance angiography; STIR, short-time inversion recovery.|
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We found contrast-enhanced 3D MR angiography to be inferior to DSA in the delineation of the vascular details depicted and in providing the data needed for planning interventional procedures.
| Discussion|| |
Using both STIR sequences with time-resolved contrast-enhanced 3D MR angiography proved to be able to provide the exact delineation and accurate characterization of the extent and the morphological classification of vascular malformations. The vascular detail provided by this noninvasive technique was sufficient for treatment planning. Hence, STIR and time-resolved contrast-enhanced 3D MR angiography complement each other in the evaluation of patients with vascular malformations. Using invasive arterial DSA can be limited to only a few patients for whom more vascular information details are required for optimal therapeutic planning.
T2 helps in differentiating high-flow arterialized vascularity that appears signal void from slow-flow venous vascularity, giving a high signal intensity on T2-weighted image ([Figure 2]). The high accuracy of STIR images in defining the extent of vascular malformations has been described before and is already used widely in clinical practice ,,,, .
|Figure 2 A 15-year-old female patient with subcutaneous low-flow venous malformation in the left lower thigh. (a) A STIR image with good anatomical delination of the extent of the vascular lesion confined to the subcutenous tissue. (b) Axial T1-weighted image showing the intermediate signal intensity of the vascular clusters. (c) Axial T2-weighted image showing high signal intensity of the vascular clusters denoting its slow flow. STIR, short-time inversion recovery.|
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In our study, we found STIR images to be valuable for delineating the extent of vascular malformations. Because of the inherent signal characteristics of this sequence, the fluid-filled vascular structures of the malformations are extremely bright and appear as high signal intensity, whereas the surrounding structures such as muscle, fat, or bones are totally dark and appear as low signal intensity. The vast contrast between abnormal and normal structures made it easy to detect muscular and bony involvement. Contrast-enhanced T1-weighted images with fat saturation were also effective for defining the extent of the lesions. Similar results have been reported by Goyal et al.  .
In addition to the delineation of the lesion morphology, a comprehensive assessment of vascular malformations requires the functional analysis of the involved vessels. Conventional T2-weighted STIR or contrast-enhanced T1-weighted images are not sufficient for this purpose. Thus, feeding arteries, nidus, and draining veins of high-flow arteriovenous malformations are poorly visualized, shown only as areas of reduced signal ,,,, . This diagnostic void that required the use of invasive arterial DSA has now been partially filled by time-resolved contrast-enhanced 3D MR angiography. Although the spatial and temporal resolution of 3D MR angiography is inherently inferior to that of DSA, our study results show that for most vascular malformations, dynamic contrast-enhanced 3D MR angiography is already a reasonable supplement and is most likely to replace invasive DSA. The benefits of an MRI-based all-in-one examination became particularly evident on comparing MR examination times with those required for duplex sonography and arterial DSA. MRI and MR angiography were completed in 30 min or less in all patients, whereas the DSA requires more time. Our study does not provide a direct cost comparison, but our data suggest a considerable cost advantage of MRI over the standard imaging protocol.
Standard MR hardware and software that permit data collection with surface coils in both the axial and the coronal planes are sufficient for the detection and the delineation of vascular malformations, whereas time-resolved contrast-enhanced 3D MR angiography requires scanners equipped with high-performance gradients capable of reducing the minimum time repetition to less than 3 ms. Despite the comparatively long acquisition time (22 s) required for a single MR angiography data set, all arteriovenous malformations in our patients were assessed correctly. Faster acquisition times might prove important when assessing high-flow arteriovenous malformations or in developing treatment plans for these patients.
Although time-resolved contrast-enhanced 3D MR angiography is insufficient for determining the extent of vascular malformations with the required accuracy, the dynamic enhancement profile depicted with this technique permits the most accurate classification of vascular malformations. Furthermore, the technique yields clinically important data regarding the feeding artery, the nidus, and the draining vein in cases of high-flow arteriovenous malformation that is crucial for therapy planning. In the patients evaluated in this series, the findings of time-resolved contrast-enhanced 3D MR angiography and DSA were in complete agreement regarding the underlying morphology of feeding arteries and draining veins. The three-dimensionality inherent to the technique permitted reformations in any desired plane, and therefore we could depict even the most tortuous vessels.
We performed dynamic contrast-enhanced 3D MR angiography using gadobenate dimeglumine, a paramagnetic contrast agent with high intravascular relaxivity due to mild albumin binding, which ensures maximal vascular enhancement  . It has been approved in both Europe and the USA merely for imaging the liver and the central nervous system. Thus, we used gadobenate dimeglumine in an off-label manner. The contrast medium proved most useful in the assessment of vascular malformations, providing diagnostic image quality and prolonged enhancement of the arterial and venous vessels in our patients. Venous overlap caused by the early presence of the contrast agent in the venous system in arteriovenous malformations did not hamper the analysis of the arterial system if the analysis was performed with multiplanar reformations.
Given our definitive results regarding lesion classification and delineation, we believe that STIR sequences and time-resolved contrast-enhanced 3D MR angiography permit the accurate assessment of vascular malformations, including lesion classification, the extent of the lesion, and analysis of feeding arteries, nidus, and draining veins in cases of high-flow arteriovenous malformations. The use of invasive arterial DSA could be limited to those patients in whom the vascular detail provided by MR angiography is not sufficient for optimal therapeutic planning.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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