Peripheral vascular malformations

This disease group has still been erroneously referred to as hemangiomas. It can be divided in two types: high flow anomalies and low flow malformations.

High flow arteriovenous malformations are typically represented with shunt circulation, the speed of flow increases, afferent arteries and efferent veins expand due to the increased volume of blood flow. With Duplex US examination, as a direct sign of shunt circulation, a very high flow velocity with a low resistance index can be registered or pulsatile flow in the veins can be noted at the nidus. The traditional diagnostic tool is catheter angiography, which still provides the most detailed picture about the feeding arterial branches of the shunt, and about its draining veins. Moreover, it informs about the extent of the nidus and about the velocity of the flow. A major advantage of the catheter method is the possibility for intervention. The feeding arteries can be selectively or super-selectively localized and occluded through embolo-therapeutic procedures. The contrast enhanced MRA produces images similar to DSA revealing the architecture of the abnormal vessels.

Low flow malformations can be made up of veins, capillaries and lymphatic vessels in a variable, mixed form resembling tumor-like structures. They can also be made up as a network of vessels traveling in different directions, with various calibers. Ultrasonography examination can identify the expanded venous plexus, while a lymphatic vessel malformation system is often seen containing cystic components. Radiography is usually used to assess the accompanying bone structure alterations and deformities. Traditional angiography can be completely negative or it may only indicate filling defects (opification decrease) in the venous stage. The most precise localization can be made with MRI: on T2 weighted images the slow flowing malformations typically appear as high signal intensity abnormalities, and they differentiate clearly from the nearby healthy tissues.

8.2.2.3. Atherosclerosis

Imaging methods have two purposes a) to prove the atherosclerotic process and to identify the plaques of the region in question and b) to quantify the degree of the consequent stenosis and to assess its hemodynamic significance. The diagnostic strategy has to be indicated in a way that the chosen procedure is able to provide information for therapeutic decision making for the given vascular territory, it has to be the least invasive for the patient and it should be as cost effective as possible. (One cannot forget the fact that atherosclerosis is an endemic disease and therefore the diagnostic protocol can put from a few thousand, up to ten thousand examinations worth of excess on the burden of the healthcare system.)

8.2.2.3.1. Stroke – cerebrovascular diseases

In the majority of the cases, the cause of stroke is related to the atherosclerotic lesion of the supplying arterial system of the brain. Ultrasound examination can reliably depict a long segment of the four main extracranial large vessels supplying the brain. It is diagnostically advantageous that the majority of atherosclerotic lesions that cause cerebrovascular symptoms are to be found in the carotid bifurcation and therefore they can be well represented on carotid US examinations.

71 US can depict plaques and it can measure their size and characterize their composition. Lipid-rich plaques that are covered with a thin, easily rupturing fibrotic cap, that are mostly soft in composition are considered unstable. Also, inhomogeneous structure and irregular surface are both likely to indicate a poor prognostic factor. Exulceration, a consequently appearing excavation on the surface of the plaque carries the highest risk for embolisation. Color Doppler examination can help to precisely define the contours of the plaque. It can clearly depict the residual lumen of the narrowed arterial segment and it is able to confidently differentiate cases of complete obstruction from lesions causing a high grade stenosis.

Contrast enhanced ultrasound examination is able to show angiogenesis at the basal part of the plaque and it is as sensitive as MRI examination. One of the main diagnostic goals of cerebrovascular imaging is to determine the grade of stenosis of the internal carotid artery, since the risk of stroke grows parallel with the grade of the stenosis. Possible cerebrovascular events can be avoided with reconstructive surgery or with stent implantation. A 50% diameter reduction is usually considered the limit at which a stenosis is thought to be hemodynamically significant. Under this level the grade of stenosis can be well estimated with 2D planimetric measurements. In order to quantify stenotic lesions that reduce the diameter by more than 50% it is better to consider the hemodynamic effect caused by the narrowed lumen, based on the measurements of flow velocity increase. If a significant stenosis is found, the patient has to be closely followed. A stenosis of about 70% is suggestive for surgical or interventional procedure. In these cases and in equivocal cases it is important that the duplex sonography is followed by an imaging method that can visualize the cerebrovascular system completely.

Arteria carotis interna stenosis

Fig. 13.v Duplex ultrasonography with targeted Doppler measurement

Fig. 14. Contrast enhanced MR-angiography

The traditional catheter angiography is still considered the gold standard imaging method due to its high detail anatomic imaging and due to its ability to determine the hemodynamics of the circulation. The complete assessment of the arterial cerebrovascular system can be achieved with CTA and MRA techniques that give a map-like visualization of the cerebrovascular arterial tree.

The aim in both methods is to depict the arterial system from the aortic arch to the Circle of Willis with a good image quality. The main advantage of MRI is that it combines intracranial assessment with angiography, therefore certain therapy modifying lesions (e.g.: acute

ischemic lesion) can be diagnosed in the most precise manner.

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Reversed blood flow in the vertebral artery is indicative of a steal syndrome. It indicates a high grade stenosis or an occlusion at the proximal segment (before the origin of the vertebral artery) of the ipsilateral subcalvian artery.

8.2.2.3.2. Renovascular hypertension

The stenosis of the renal artery causes therapy resistant hypertension. If clinical suspicion is raised a radiological examination or scintigraphy is indicative for the diagnosis. If the stenosis is detected on time, then surgical reconstruction or catheter dilatation of the vessel can be used to cease hypertension and avoid a possible renal failure that the stenosis related hypoperfusion could have eventually caused.

With Doppler examination, if the renal arteries can be directly visualized, a high velocity flow and a post-stenotic turbulence is notable. From a dorso-lateral angle the flow of intrarenal segmental arteries can be analyzed: if proximal arterial segments have any stenosis, then the registered Doppler curves show a post-stenotic appearance. However, this technique requires a great deal of experience and is very operator-dependant, thus it is not performed on a regular basis.

Perfusion scintigraphy is able to identify significant arterial stenosis by comparing the

different perfusion rates between the two kidneys. The method can be made more sensitive by giving the patient an ACE inhibitor, which in turn, further decreases the activity of the

involved kidney. Upon ending ACE inhibition, on the repeated renal scan an improving perfusion is indicative of arterial stenosis. The identification of bilateral lesions with this method is rather difficult, since the use of ACE inhibitors is contraindicated.

CTA and MRA are both capable of diagnosing renal artery stenosis. Both methods are able to identify anatomic variations, atherosclerotic lesions at the origin of the vessels or at distal segments on the artery. These techniques, not only identify the contour irregularities and the narrowed lumen, but they are also able to reveal the secondary parcenhymal lesion of the kidney. However, in patients with decreased renal function, both types of contrast materials should be avoided or only applied with care.

Renal artery stenosis

Fig. 15. Contrast enhanced MR angiography

Fig. 16. Control CT angiography after stent implantation to correct a bilateral arterial stenosis

73 8.2.2.3.3. Mesenteric ischemia

Stenotic lesions or occlusion of the unpaired splanchnic branches of the aorta cause chronic mesenteric ischemia, which in turn presents as abdominal angina. Acute occlusion is usually caused by mesenteric embolism, and it presents as acute abdominal catastrophe; as a grave condition with high lethality. In all circumstances CTA provides the best diagnostics and it is also able to demonstrate actual state of the abdominal organs.

8.2.2.3.4. Peripheral arterial disease (PAD)

Obliterative diseases of the lower extremity arteries can occur from the subrenal aorta to the distal, end-arteries of the limbs. It can affect any segment, in any combination; depending on its severity and the dynamics of its development it causes variable arterial pressure changes and consequent complaints. The gradually developing atherosclerotic stenosis/occlusions appear as intermittent claudication. The acutely presenting critical limb ischemia is usually related to arterial embolism and requires urgent surgery. Imaging examination is not even necessary if the actual clinical state does not suggest a revascularization.

According to the traditional approach the adequate method for imaging is catheter

angiography, possibly DSA technique. It requires the repeated injections of smaller volumes of dye, and with a few steps it is able to demonstrate the whole arterial system in a way, that on the appropriately adjusted late phase images, the depiction of arterial outflow is possible even at the slower flowing territories.

The advantage of DSA is that smaller branches and collaterals can also be visualized; it provides hemodynamic information and even makes an ad hoc balloon catheter dilatation or stent implantation possible. In case there is no femoral artery appropriate for catheterization, an alternative approach from the brachial artery can also be used. Stenotic lesions can be semi-quantitatively categorized: below 50% is considered mild, between 50-75% moderate and above 75% pronounced stenosis is differentiated.

DSA examination in lower extremity obliterative arterial disease

Fig. 17. Proximal aortic occlusion – Leriche’s syndrome

Fig. 18. Bilateral multiplex femoral artery stenosis

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Left sided segmental occlusion at the iliofemoral segment

Fig. 19. Contrast enhanced MR angiography Fig. 20.CT angiography

Multi-slice CT is able to perform CT angiography scans that can cover a field from the diaphragm to the ankles to depict the complete arterial tree with a good intensity and with appropriate spatial resolution. In most cases this provides an adequate diagnostic value and it is especially advantageous for the rapid assessment of patients in a debilitated state. Contrast enhanced MRA, with a large field of view, for the depiction of abdominal and peripheral arteries requires a special table toggling technique. This method applies the prolonged injection of intravenous bolus of contrast medium, and in three table-toggling steps it can visualize the arterial system of the abdominal aorta and the peripheral arteries up to the ankle with an acceptable spatial resolution.

Altogether both CTA and MRA examinations give the best diagnostic value for lesions

presenting at the aortoiliac and femoropopliteal regions with a relatively limited extension and a reasonable severity.