The peripheral vessels

Diseases of the arterial system

 

Arterial occlusive disease

Arterial occlusive disease may be divided into acute and chronic. Peripheral arterial occlusive disease is commonly staged according to the Fontaine classification into four degrees:

I: Asymptomatic atheroslerotic lesions
Il: Intermittent claudication
a) mild (free walking distance > 100 - 200 m)
b) severe (walking distance less than 100 m)
Ill: Rest pain
IV: Trophic changes with necrosis and gangrene.

Acute arterial occlusions
These occlusions are due to arterial emboli or acute thrombosis in approximately 90%. Other etiologies are dissections of the arterial wall (traumatic or spontaneous), external compression, spasm (trauma, iatrogenic, drugs) or hemodynamic problems.

The majority of arterial emboli originate in the left heart (86 %). Other sources are aneurysms and ulcerative plaques of large arteries. Usually the emboli get trapped at arterial bifurcations and cause further thrombosis by apposition or stagnation of blood flow. The most frequent location of arterial emboli is the common femoral artery (46 %). On arteriography a fresh embolus shows a smooth cut-off of the contrast column and few or no collaterals (Fig. 9 A). A special form of peripheral embolism is cholesterol embolism caused by showers of cholesterol crystals released from atherosclerosis of the aorta and pelvic vessels which lead to microemboli in digital arteries (blue toe syndrome).

Acute and subacute arterial thrombosis is caused by atherosclerosis in over 90%. Rarely inflammatory processes, trauma, hematologic diseases or interventional procedures are the cause. The clinical signs depend on the location and extent of the thrombosis, however they are generally less severe than with acute embolic disease. On arteriography also an acute thrombotic occlusion may show a relative sharp cut-off of the contrast column and few collaterals unless there is a pre-existing stenotic lesion (Fig. 9 B).

Chronic arterial occlusive disease
Chronic arterial occlusive disease leads to progressive stenosis and/or occlusions and is due mainly to obliterative arteriosclerosis. It usually starts after the age of 40 and is dependent on certain risk factors such as smoking, diabetes, hypertension, hyperlipidemia etc. The sites of predilection are the arteries of the pelvis and lower extremities, the origins of the neck vessels and the carotid bifurcation.

Figure 9. Angiograms of acute arterial occlusion. A) Acute embolic occlusion at the typical location of the trifurcation just below the knee joint. There is a typical cut-off of the contrast column and only a few collaterals are seen. B) Acute thrombotic occlusion of the superficial femoral artery secondary to atherosclerotic stenosis. Note contrast around fresh thrombus (arrows) and tortuous collaterals as seen in pre-ex is ting stenosis.

Atherosclerosis of the thoracic aorta leads mainly to elongation and calcification of the aortic wall as well as ectasia. This may be recognised on the chest X-ray. Atheromatous plaques and ulceration may lead to peripheral and cerebral emboli. The primary imaging method for arteriosclerotic disease of the thoracic aorta is Computed tomography (Fig.10). Thoracic aortography is used to demonstrate the arteriosclerotic disease at the origin of the neck vessels or to further clarify aneurysms and search for embolic sources. Arteriosclerosis of the abdominal aorta involves mainly the infra-renal portion and often continues into the pelvic arteries. Stenosing plaques are found particularly at the aortic bifurcation, the distal common and proximal external iliac artery. The primary screening test for aorto-iliac disease is colour doppler ultrasound (Fig. 1). CT is mainly used for further work up in aneurysmal disease (Fig 2). For the exact diagnosis and extent of aorto-iliac disease, many vascular surgeons still need aortography as the prime diagnostic tool, especially if an operative or percutaneous interventional therapy is considered (Fig. 11). The role of MRI in atheroslcerotic disease of peripheral arteries has not yet been fully established apart from diagnostic use in aorto-iliac aneurysms and dissection particularly in patients with contra-indications to the administration of contrast medium. However, rapid advances in

Figure 10.Thoracic aortic aneurysm A) Chest X-ray showing aortic aneurysm with somewhat lobulated margins in the arch and the proximal descending aorta. B,C) CT at the level of the arch and aortopulmonary window showing true size of the aneurysm and marginal thrombus formation.

Figure 11. Aortogram of the same patient as in fig. 2. AP (A) and oblique (B) projection. The oblique projection shows the relation of the renal arteries to the neck of the aneurysm including the kinking of the aorta better than CT. This however can also be demonstrated in a similar fashion with 3D-reconstruction of spiral CT (fig. 24).

technology may change this pattern in the near future.

Occlusion of the distal aorta usually starts at the bifurcation and may extend proximally to the origin of the inferior mesenteric artery, or if the latter is occluded, to the oring of the renal arteries (Fig. 12). Occlusion proximal to the renal arteries is extremely rare. The etiology of the distal occlusion is a pre-existing stenosis or massive embolism. This if often called the Leriche-syndrome. Originally however, this term was used for a complex of symptoms in young men with occlusion of the aortic

Figure 12. Translumbar aortography in acute occlusion of the infrarenal aorta. The intercostal arteries (arrows) serve as major collaterals.

Figure 13.Translumbar aortography for bilateral iliac occlusion demonstrating the main collaterals. The internal iliac arteries are also markedly diseased, the left is completely occluded. The distal filling of the femoral arteries is established via intercostal arteries (not visualized) to the superficial circumflex iliac (SCI) and from the 4th and 5th lumbar and the iliolumbar arteries. Further collateralization is via the middle sacral artery (MS) and the inferior mesenterica artery (IMA) feeding the hemorrhoidal arteries to the branches of the internal iliacs (I), particularly the inferior gluteal and the obturator artery (O). The latter shows collaterals to the medial femoral circumflex artery (FC). EI = external iliac artery, CF = common femoral artery.

bifurcation consisting of erectile impotence, weakness of the lower extremities and cold and pulsless feet. The symptoms of occlusion of the distal aorta or the iliac arteries depend on the extent of the occlusion and the collateral circulation as well as the associated peripheral disease. The most important collaterals are the visceral arteries particularly the inferior mesenteric artery, the intercostal and lumbar arteries as well as branches of the internal iliac, the common femoral and the deep femoral artery. For planning therapy, angiography must show the extent of the stenoses or occlusions, the collaterals and the peripheral outflow (Fig. 13).

The angiographic signs of arteriosclerosis in the aorta and pelvic arteries are irregular contour and filling defects caused by atheromatous plaques. Stenoses are often eccentric and multiple projections may be needed to show the significance of a lesion (Fig. 14). The stenosis may be relatively smooth, short or quite diffuse. Other reasons for arterial stenoses are dissecting aneurysms, aortitis/arteritis, perivascular fibrosis, tumor compression or postradiation fibrosis and congenital hypoplasia or so called abdominal coarctation. Additional atheroslerotic disease at other sites in the periphery or the visceral arteries may point to the correct diagnosis. Small aneurysms from ulcerated plaques as well as larger aneurysms are further atherosclerotic findings.

In peripheral arteriosclerosis the upper extremities are involved to a significantly lesser degree than the lower extremities. In particular, the proximal lesion of the subclavian artery is often not symptomatic because of well developed collaterals. An occlusion of the proximal subclavian artery however may lead to the subclavian steal syndrome with reversal of the flow in the vertebral artery secondary this collateral supply to the arm. This may lead to cerebral hypoperfusion with neurologic symptoms. Occlusive disease of the forearm and finger arteries is usually atheroslcerotic in nature, rarely embolic, traumatic or secondary to Buerger's disease. Arteriosclerosis is the most common cause of the secondary Raynaud phenomenon.

In the lower extremities the major site for atherosclerotic disease is the superficial femoral artery especially in the region of the adductor canal, the popliteal artery and the trifurcation. In diabetes, the small arteries of the calf and feet are particularly involved and there is often combined disease in the femoral, popliteal and calf arteries as well as changes in the deep femoral artery. The main arteriographic findings again are stenoses, occlusions and collateral vessels. According to the clinical findings, retrograde aortography to demonstrate the distal aorta and the iliac and peripheral arteries of both legs or a direct antegrade femoral arteriogram for unilateral disease is performed. If femoral pulses are absent,

Figure 14. Angiography of pelvic and peripheral arteries. A) Oblique view shows severe stenoses especially in the right external iliac artery. B) There is diffuse bilateral disease with occlusion of the left superfreial femoral artery. C) Diffuse bilateral disease of the popliteal arteries and occlusion of the posterior tibial arteries. There is slower flow on the right than on the left probably secondary to the more severe iliac disease.

a translumbar or a transaxillary approach may be needed. It is important that the angiogram demonstrates the location and the length of the stenoses and occlusions for optimal planning of the therapeutic procedure. Apart from the narrowing itself, the significance of stenosis may be better appreciated by the presence of collaterals, poststenotic dilatation or differences in contrast flow. The length of an occlusion may be angiographically overrated in the early phase because of the stasis proximal to the occlusion and flow through collaterals distal to the occlusion. Typically a thrombotic occlusion develops by beginning proximal to a stenosis and propagating regrogradely until it reaches the closest large collateral (Figs. 13, 14).

Figure 15. Retrograde aortography of pelvic (A) and femoral arteries (B) in patient with dilative atherosclerosis. There is incomplete filling distally due to extremely slow and turbulent flow.

A special form of peripheral arteriosclerosis consists of elongation and kinking of the iliac arteries and the so-called dilating form of arteriosclerosis with aneurysmal ectasia. Angiographically the latter shows a typical sequence of aneurysmal ectasia and relative stenosis (Fig. 15). Because of turbulence and slow blood flow there is an increased thromboembolic risk. Finally there may be steal syndromes, e.g. of the internal iliac artery caused by an external iliac artery occlusion with consequent erectile impotence or a reversal of flow in the inferior mesenteric artery secondary to obstruction of the proximal abdominal aorta.

M6nkeberg's medial sclerosis is primarily not a stenosing process but characterized by massive diffuse calcification of the arterial wall. It may, however, be combined with stenosing arteriosclerosis and is seen in diabetes, hyperparathyroidism (patients on hemodialysis) and in vitamin D hypovitaminosis.

Arterial disease of inflammatory nature (arteritis)
In contrast to atherosclerosis only about 5 % of all arterial diseases are of a non-degenerative, inflammatory origin.

Thromboangitis obliterans (Buerger's disease) is an inflammatory process involving primarily peripheral arteries of medium and small calibre in young men. Accordingly the symptoms involve mainly the calf and feet or hands with claudication, rest pain and coldness, as well as dysaesthesia and motor-disturbance. The etiology most likely is an immune-mediated

Figure 16. Arteriography of the femoro-popliteal arteries in Buerger's disease. There is a chronic occlusion of the right popliteal artery with numerous corkscrew collaterals (A). Note the "string of pearls" changes in the small muscular branches on the left (B) with absence of atherosclerotic changes in the popliteal artery.

inflammatory reaction to various noxious substances particularly nicotine. On angiography stretched vessels and segmental peripheral occlusions in the region of the calf and feet or of the smaller branches of the deep femoral artery are seen. Corkscrew collaterals representing vasa vasorum along the occluded vessel are fairly typical (Fig. 16). The diagnosis is made more likely in the presence of additional disease in the upper extremity in young, usually male patients under the age of 40 with a history of smoking and lacking arterioslerotic disease in other larger vessels.

Takayasu's arteritis is a non specific aortitis and arteritis of elastic arteries which is most likely to be auto-immune related. There is a predilection for young women who have fever, myalgia, dizziness and an increased blood sedimentation rate. Most commonly the brachiocephalic arteries are involved frequently with long fusiform stenoses particularly involving the carotids (so-called aortic arch syndrome or pulsless disease type l). A second type involves mainly the abdominal aorta and its major branches particularly the renal arteries. A third type is a combination of type one and two and in a fourth type finally also the pulmonary arteries are involved.

Figure 17. Abdominal aortography showing bilateral fibromuscular dysplasia with typical "string of pearls"- like changes of the renal arteries.

Other arteritides may be caused by a number of diseases causing stenosis and occlusion such as periarteritis nodosa, giant cell arteritis, as well as specific arteritis in tuberculosis, lues and other infectious diseases. In these cases, not only stenotic areas, but frequently micro- or macroaneurysms are seen.

Fibromuscular dysplasia
This disease is seen mainly in younger women between 20 and 40 years of age. Fibromuscular dysplasia involves mainly medium sized arteries such as the renal and internal carotid artery and there is an increased incidence of cerebral aneurysms. Rarely the vertebral artery, the iliac and subclavian arteries or visceral arteries are involved. According to histopathologic and angiographic findings various types are differentiated. The most frequent form is the medial fibromuscular dysplasia which exhibits the "string of pearls" arteriographic sign (Fig. 17). Short focal lesions are seen in medial hyperplasia or intimal fibroplasia.

Vascular compression syndromes
Thoracic outlet syndrome: These compression syndromes may involve the sublcavian artery as well the subclavian vein (inlet obstruction). The cause of vascular compression may be a cervical rib or fibrous band, a costo-clavicular compression between the clavicle and the first rib and finally a compression between muscular structures such as the scalene

Figure 18. Digital subtraction angiography of left arm in thoracic outlet syndrome. A) Normal subclavian arteriogram. B) Severe stenoses of the sublcavian artery at the level of the clavicle (e) crossing the first rib (r) with elevation of the arm. C) Note thromboembolic changes in the arm with occlusion of the radial artery (arrows).

Figure 19.Cystic adventitial degeneration of popliteal artery. A) Femoral arteriogram shows eccentric smooth stenosis above the knee joint. B) CT at same level shows crescent like stenosis due to low attenuation cystic degeneration of the arterial wall (Cy). V = femoral vein.

or the pectoralis minor muscle. The diagnosis is made by subclavian arteriography (arm phlebography) with provocation by special manoeuvres with an elevated or extended arm. Various degrees of stenosis or complete occlusion may be seen during these manoeuvres (Fig. 18). Furthermore poststenotic dilation or thrombotic layers within the lumen may

Figure 20. Secondary Raynaud's syndrome in 36-year old smoker with Buerger's disease. Arteriogram of lower arm and hand shows diffuse distal disease with occlusion of both palmar arches, multiple digital arteries and distal occlusion of the ulnar artery.

be seen. Complications such as arterial emboli with secondary Raynaud syndrome may be the first clinical signs.

In the lower extremity the entrapment syndrome of the popliteal artery is mainly seen in young men and is caused either by an abnormal course of the popliteal artery or an abnormal origin of the medial head of the gastrognemius muscle. Finally a cystic degeneration of the adventitia may cause filiform smooth stenosis of the popliteal artery (Fig 19), more rarely in the external iliac and common femoral artery. In this disease young men are mainly affected. Both diseases can be reliably diagnosed by computed tomography or MRI. Further arterial compression syndromes may be caused by external compression from tumors, bony structures or hematomas.

Raynaud's syndrome
The primary Raynaud syndrome or Raynaud's disease due to central disturbance of peripheral vasomotor regulation causing vasospasm has to be differentiated from the secondary Raynaud phenomenon caused by various underlying vaso-occlusive diseases.

The primary vasospastic Raynaud's disease occurs mainly in young patients who frequently suffer from migraine and who may have a positive family history. There is typically a generalized symmetric hypocirculation which may be triggered by coldness or agitation. The prognosis is usually relatively good.

In contrast, secondary Raynaud's phenomenon is usually asymmetric or unilateral and of longer duration and trophic disturbance may be found. The main etiologies are atherosclerosis, Buerger's disease and arterial emboli as well as changes secondary to arteritis, trauma etc. On arteriography stenoses and occlusions of palmar and digital arteries are seen (Fig. 20).

Traumatic arterial perfusion disorders
Closed arterial injuries after trauma, operations or interventional procedures may cause acute ischemia by infection, laceration or dissection of the arterial wall leading to thrombotic occlusion. Early angiography is indicated especially in acute aortic rupture secondary to deceleration trauma which causes a typical lesion (intimal tear or false aneurysm) in the area of the ductus ligament. Open arterial trauma may lead to complete transection or a false aneurysm. The brachial, femoral and popliteal arteries are the most frequently involved. Chronic repeated trauma may also cause occlusion as in for instance, the Hypothenar-Hammer-syndrome with its typical occlusion of the ulnar artery in workmen using carving knives or pneumatic drills.

Aneurysms

Classification

Aneurysms may be divided into 3 different types true, false and dissecting aneurysms.
a) True aneurysms are localised outpouchings, saccular or spindle shaped which involve all three layers of the arterial wall. The pathogenesis is mainly a degeneration of the media and in 70% to 80% the etiology is atherosclerosis. Other causes are congenital weakness of connective tissue (Marfan-, Ehler-Danlos-syndrome); cystic medial necrosis or post-stenotic. Rarely, it may be due to an infection such as lues.
b) False aneurysms represent aneurysms caused by an interruption of the intima and media leading to a localised and usually asymmetric outpouching in the arterial lumen which is bounded only by adventitia or surrounding connective tissue. The etiology is usually trauma, iatrogenic or infectious and is rarely atherosclerotic.
c) Dissecting aneurysms are caused by a dissection of the arterial wall, usually the intima and/or media, with formation of a false lumen between the arterial wall layers. This false lumen may thrombose or may continue to be perfused, especially if there is a distal re-entry into the true lumen. Frequently the true lumen is compressed by the false lumen. The etiology and pathogenesis is usually a degenerative process due to a primary or secondary weakness of the vessel wall as in Marfans, cystic medial necrosis, hypertension or atherosclerosis. Less frequently it is seen after iatrogenic manipulations (puncture, catheter interventions etc.), in coarctation and trauma.

Aortic aneurysms
The majority of thoracic aortic aneurysms are due to atherosclerosis and trauma. The atherosclerotic aneurysm usually involves the descending aorta frequently extending into the abdominal aorta. Often parts of the aneurysms contain thrombus. Diameters above 5 - 6 cm have a high incidence of rupture and are an indication for operation. Traumatic aneurysms are typically located in the region of the ligamentum arteriosum (above 80%) (Fig. 21). Only about 7 to 10% survive the first 24 hours if not treated. In less than 20% the rupture is immediately above the aortic valve which leads to pericardial tamponade from which patients rarely recover. Rupture in the area of the descending aorta at the diaphragmatic hiatus is extremely rare (1 %). Chronic traumatic aneurysms in the region of the isthmus show a typical ring or crescent like calcification.

Figure 21. Acute traumatic rupture of the aorta. Thoracic aortography shows false aneurysm (arrows) in typical location of the arch in the region of the ductus ligament.

Figure 22. Schematic drawing of dissecting aneurysms. A) Type A with dissection beginning just cranial to the right coronary artery and re-entry in the descending aorta. B) Type B dissection originating distally to left subclavian artery. C) Type A dissection with thoracoabdominal extension to the aortic bifurcation.

About 25 % of aneurysms in the thoracic aorta are dissecting aneurysms in older patients with hypertension and atherosclerosis. According to the Stanford classification two types are distinguished (Fig. 22): Type A: Originating in the ascending aorta, usually cranial to the right coronary artery and type B originating distal to the left subclavian artery. Type A may be limited to the ascending part of the aorta or may involve the aortic arch with or without the braehiocephalic vessels or may continue to the descending aorta and even to the abdominal aorta. Occasionally the dissection may extend retrogradely into the coronary artery and the sinus of valsalva which may lead to myocardial infarction and/or aortic insufficiency. The type B dissection may similarly continue to dissect more distally. Type A dissection must be operated on immediately. Type B dissections are usually managed conservatively unless there is involvement of the renal or visceral arteries or danger of aortic rupture.

Mycotic aneurysms are usually located in the ascending aorta and are caused by bacterial endocarditis or after a composite graft. Other infectious mycotic aneurysms have a predilection for the descending aorta. The radiologic work-up in thoracic aneurysms in non-acute situations usually starts with CT or MRl especially if contrast injection is contraindicated (Figs. 10, 25). These modalities may show the amount of thrombus and the extent of the perfused lumen as well as the relationship of the aneurysm to the neighbouring organs. CT and MRl are also used for follow-up examinations. Echocardiography may be used for screening aneurysms in the region of the sinus of valsalva and the ascending aorta or for aortic dissection. In acute situations angiography is still the method of choice for evaluation of traumatic aneurysms and type A dissecting aneurysms, or in type B if possible involvement of visceral arteries is not excluded by CT. Aortography usually shows aortic insufficiency and the involvement of brachiocephalic or coronary vessels in a better degree in type A dissection. Also in an acute traumatic aneurysm the lesion may be better shown on angiography than CT especially if there is only a localised intimal tear. This situation may change with the use of rapid spiral CT scanning, however.

Aneurysms of the abdominal aorta are caused mainly by atherosclerosis and may be seen in the plain film in up to 80% because of calcification of the aortic wall. 95% of the aneurysms are located below the renal arteries and in 18 % the bifurcation and iliac arteries are also involved. The danger of rupture ranges from 10% with a diameter of5.5 cm up to 40 to 80% with a diameter of 8 cm. Penetrating ulcerated plaques also increase the rate of rupture.

Atherosclerotic abdominal aneurysms also represent a frequent source of peripheral macro-emboli (10%) as well as cholesterol showers leading to the blue toe syndrome.

The inflammatory aneurysm is a special form of atherosclerotic aneurysm possibly caused by an auto-immune process. It typically occurs in men after the fifth decade and may lead to obstruction of the ureters.

Localised dissecting aneurysms of the aorta are extremely rare in the abdominal aorta and are usually extensions of a type B dissection. Mycotic aneurysms have no pathognomonic signs but usually occur rapidly as a complication of an infection, i.e. spondylodiscitis. They have a high rate of rupture and no other signs of atherosclerosis are usually seen if they occur in the younger patients.

For the radiologic work-up in abdominal aortic aneurysms ultrasound is the prime screening method in the acute as well as chronic stage for all types of aneurysm. It shows the perfused lumen and its clot content as well as identifying a dissecting membrane (Fig. 1). CT is used for preoperative evaluation especially with regard to the dimensions of the aneurysm, its relationship to visceral arteries and the differentiation of perfused from thrombosed lumen in atherosclerotic and dissecting aneurysms (Figs. 2 and 23). It may also demonstrate the signs of an imminent rupture or "leaking" external to the calcified media. Angiography

	Figure 23. CT of dissecting aortic aneurysm type A. A) Sean at level of pulmonary artery bifurcation shows dissection in ascending and descending aorta with partially thrombosed lumen in the ascending aorta. B) Scan at level of origin of superior mesenteric artery again shows dissection flap (arrows) and both the true and false lumen patent.
	Figure 24.3D-reconstruetion of spiral CT in patient with atherosclerotic abdominal aneurysm (A) and a patient with common iliac artery aneurysm (B, C). A) 3D shows the kinked infrarenal neck of the aneurysm with the aneurysm itself involving mainly the distal aorta and the bifurcation. Arrows mark the renal arteries. B) 2D-reconstruction shows the perfused lumen of the aneurysms and the calcifications in the arterial wall. No major thrombus is seen. C) 3D-reconstruetion shows the relation of the internal and external iliac arteries to a better degree and the tortuous external iliac arteries are depicted in their entire length.
a	Figure 25. MRl of type E dissection in transerve (A) and sagittal plane (E). The transverse scan at the level of the superior rnesenteric artery (SMA) as well as the sagittal plane show the different signal intensity of the true and false lumen. The true lumen (TL) shows signal void due to rapid bloodflow, whereas the false lumen (FL) with slow flow shows increased signal intensity. Note the narrowed origin of the SMA which is supplied from the true lumen. VC = vena cava.
b

is used mainly to show the origin of the renal arteries and the "neck" of the aneurysm for possible cross clamping (Fig. 11). In the future the use of spiral CT with 3D-reconstruction may obviate the need for preoperative angiography (Fig. 24). MR may be used to demonstrate differences in flow between the true and false lumens in dissecting aneurysms (Fig. 25).

In inflammatory aneurysms, CT shows a horse-shoe shaped 2 to 3 cm thick highly enhancing fibrotic cuff which typically spares the dorsal aortic wall (Fig. 26).

Aneurysms in peripheral arteries
Aneurysms of peripheral arteries are of atherosclerotic origin in the majority of cases. Less frequently they are post-traumatic, post-operative (grafts) or occur after an arterial puncture for angiography or percutaneous intervention. Very rarely they are mycotic. Characteristically atheroscIerotic aneurysms are found in the popliteal artery (26 %) or the inguinal region (17 %). They are often symmetric and rarely are they found in the upper extremities particularly the brachiocephalic and subclavian

Figure 26.lnflammatory aneurysm of abdominal aorta. A) CT shows typical densely-enhancing horseshoe-like cuff of tissue around the aortic aneurysm (arrows). T = thrombus, Ao = perfused aortic lumen. B) Abdominal aortogram in same patient shows aneurysm which angiographically cannot be distinguished from common atherosclerotic aneurysm.

artery. They may thrombose especially in the popliteal artery and present with acute or chronic ischemia. They also represent a source of arterio-arterial emboli.
If a palpable pulsating mass is found ultrasound and colour-doppler are the best methods for screening to show the dimensions of the aneurysm and the extent of thrombosis. Angiography is indicated only in the context of pre-therapeutic diagnosis of other aneurysms and demonstration of the general status of the peripheral vasculature.

Vascular anomalies (malformations)

 

Classification
There is no simple classification. Because of the various clinical and angiographic manifestations a vast number of descriptive terms has been arbitrarily used. A rational classification of hemangioma and vascular malformations has been proposed by Mulliken and co-workers based on endothelial characteristics. Two main groups of vascular anomalies may be distinguished according to these authors, the pediatric cutaneous vascular lesion (hemangioma) and vascular malformations.
a) Pediatric cutaneous vascular lesions or pediatric hemangioma usually
appear within the first months of life. They are not present at birth and more than 90% of the pediatric hemangiomas regress spontaneously by the age of 5 to 7 years. The majority should not be treated to allow for the natural history of involution. Only if they produce symptoms such as eyelid hemangioma or subglottic hemangioma etc. do they need to be treated. Steroid therapy usually proves successful within a couple of weeks in the treatment of pediatric hemangiomas in contrast to arteriovenous malformations which do not respond to steroids.
b) Vascular malformations are present at birth whether or not clinically evident and grow with the child. Vascular malformations can be categorised into arterio-venous malformations (AVMs), capillary malformations (formerly cavernous or capillary hemangioma), venous malformations, congenital arteriovenous fistula (AVF) and lymphatic malformations. Mixed malformations are also grouped under the common term vascular malformations.
Post-traumatic AVF or large AVF-like shunts in renal cell carcinoma or other tumors are different because they are acquired. Most AVF are of the acquired type. Vascular malformations include also those entities which occur in syndromes like the Klippel-Trénaunay or Parkes-Weber syndrome as well as cutaneous capillary malformations such as naevus flammeus.

Work-up for vascular malformations
Colour doppler imaging is the first step in the investigation of a suspected vascular malformation. Both, high flow lesions (A VM, A VF) and low flow lesions (capillary and venous malformations) are easily diagnosed. Though CT can be useful, MR is the preferred non-invasive tool for distinguishing between high and low flow lesions and for determining relationship to adjacent structures (Fig. 27). Angiography or direct puncture in venous or lymphatic malformations is then performed to define the angio-architecture, particularly the degree and site of AV-shunting, the presence of aneurysms, venous outflow and the potential route of access for endovascular therapy.

On angiography capillary malformations usually show slow flow with delayed filling of a sponge like vascular mass with minimal or absent AV -shunting.
Arterio-venous malformations (A VM) show meandering and dilated feeding arteries and early venous filling (Fig 27). Depending on the degree of
AV-shunting there may be very rapid flow.

50 % of AVMs occur in the region of the head and neck and other preferred locations are the extremities and branches of the internal iliac

Figure 27. 28-year old male with AVM above the right knee. A, B) T1 weighted MR image in transverse (A) and coronal plane (B) showing the low-signal vascular spaces of the A VM (arrows) in the vastus medialis muscle. C, D) Early (C) and late (D) arterial phase of femoral angiogram showing the dilated feeding artery (arrows) and early filling of the accompanying veins (arrowheads) joining the superficial femoral vein (FV).

artery. In Rendu-Weber-Osler disease they may be seen also in the gastrointestinal tract and in the lungs.

In venous malformations the supplying arteries are of normal size and AV -shunting usually is minimal or absent. There is contrast pooling in the late phase in the dilated abnormal venous structures. Often venous malformations are incompletely filled on arteriography when closed system venography or direct puncture of the pathologic venous structure is thus needed. Venous malformations may be very large and may occur in connection with syndromes such as Klippel-Trénaunay or Parkes-Weber syndrome. Venous malformations often show calcifications within them (phleboliths).

Arteriovenous fistulas are pathologic connections between artery and vein with direct AV-shunting. The shunts have a tendency to increase

Figure 28. Iatrogenic fistula of the deep femoral artery after thrombectomy with Fogarty balloon. Selective DSA of deep femoral artery (A) shows arteriovenous fistula (F) with immediatefilling of the deep femoral vein (V).

ver time and large fistulas may lead to left heart failure.

Angiographically these lesions are best evaluated with digital subtraction angiography because of the very fast blood flow. The most frequent causes are iatrogenic i.e. punctures for biopsy (liver, kidney) and other frequent causes are trauma or rupture of an aneurysm into a neighbouring vein (Fig. 28).

Diseases of the venous system

Deep venous thrombosis (DVT)
Deep venous thrombosis is considered to have an incidence of about one per 800-1000 inhabitants per year in Westem Europe, but the incidence varies considerably in different parts of the world. As many as one-third may develop pulmonary embolism. The clinical diagnosis ofDVT is very unreliable, and is said to be as accurate as tossing a coin in terms of sensitivity and specificity. An accurate diagnosis is required to start therapy without delay. AIso, anticoagulant and thrombolytic therapy carry potential risks which demand clear indications before commencing treatment. The standard therapy is bed-rest and heparin treatment ifthe DVT is above the level of the knee. In extensive cases or in young patients with iliofemoral thrombosis, fibrinolytic therapy may often be chosen. Surgical thrombectomy or local fibrinolysis is not often employed. Surgical thrombectomy may be combined with a temporary a/v fistula

Figure 29. The occurrence of thrombi in per cent from 338 patients with DVT (after HE. Schmitt 1977).

to protect thrombogenic surfaces from rethrombosing. Local fibrinolysis may be combined with a caval filter or balloon obstruction to prevent pulmonary emboli. Recurrent pulmonary emboli may require the insertion of a caval filter.

Predisposing conditions for DVT are malignant disease, surgery or other trauma, immobility, age and coagulation disorders. The well known Virchows triad of stasis of blood, intimal injury and hypercoagulability is still valid.

Consequences of DVT
Deep venous thrombosis carries the short term risks of pulmonary embolism, pain and swelling of the limb, venous gangrene or limb loss, or proximal extension of the thrombus into the inferior vena cava. It is considered that 80 % of thrombi will resolve by lysis if left untreated. About three weeks after an acute episode of DVT, the amount of remaining thrombus is likely to change much.

The long term risks of DVT are post-thrombotic syndrome with valve destruction or incompetence, eventually leading to venous obliterations and collateral vessel formation. The result may be secondary varicosis, cutaneous ulcerations, and claudication. Rethrombosis with the danger of recurrent pulmonary embolism and pulmonary hypertension may also occur.

Location and frequency of DVT (Fig. 29)
In a large study of more than 3000 lower extremities suspected of DVT, 60% actually had the disease. In 4/5 cases, the calf veins were thrombosed, in 3/5 the popliteal and femoral veins. The external iliac was thrombosed in 1/3 and common iliac in 1/5 of the cases. The most frequent thrombosis is considered to be in the soleal venous plexus. However, due to their narrow mouths into the deep veins, embolization of thrombi may 

Figure 30. Pelvic vein spur (arrow) in a patient with acute DVT of the leg veins.

not be frequent from this site. In autopsy material, the second most frequent site of thrombi is the foot veins. The significance of foot vein thrombi is unclear, however their presence reveals that the patient suffers thromboembolic disease. This may be of importance if there is suspicion of pulmonary embolism. Thrombosis of the left limb is 1.5 times more frequent than in the right. The reason for this is considered to be the slight obstruction of the common iliac vein by indentation from the crossing iliac artery. At this point, there is in approximately 20% of the population a web formed by local endothelial proliferation (Fig. 30). This web may
be like a ring, or even a bridge over the venous lumen which creates a double-lumen.

Diagnosis
The diagnosis of DVT is accomplished by ascending phlebography or ultrasound examination.
Direct phlebographic signs of deep venous thrombosis are accomplished by visualization of an intraluminal filling defect in two projections of a contrast filled vein. A thin lining of contrast around the fresh thrombotic mass is called the "railroad track sign" (Fig. 31 A, B). The protruding top of a thrombus may "float" on the top of an occluded segment, or propagate from a venous lumen into a non-occluded vein. Care should be taken not to mistake an in-flow phenomenon caused by the jet from a non-opacified vein, for a thrombus.

Figure 31. A, B) Direct signs of afresh deep venous thrombosis, intraluminal contrast defects, in the popliteal vein and leg vein (arrows). C) lndirect sign of extensive thrombosis of leg veins; no filling of posterior tibial or peroneal veins, massive collateral circulation via superficial veins.

 

Figure 32. Grey-scale ultrasound examination of the popliteal fossa with the vein (V) and artery (A). Uncompressibility of the popliteal vein indicates thrombosis of the popliteal vein.

Indirect signs of acute deep venous thrombosis are segmental interruptions of the veins and collateral circulation. In total occlusion, only superficial veins may be seen (Fig. 31 C). Often indirect and direct signs of DVT will be present at the same time.

On ultrasound, non-compressibility of thrombosed venous segments is a most important indirect diagnostic sign (Fig. 32). The direct visualization of a thrombus within the venous lumen is the most obvious means of diagnosing deep venous thrombosis. The usual appearance of an acute thrombus is hypoechoic, although very fresh thrombi also may be hyper-echoic. With organization or during lysis, the thrombus again becomes more echogenic. The importance of concomitant examination of local venous flow by duplex-scanning is stressed. Determination of vascular flow direction velocity and waveform is useful in distinguishing arteries from veins.

Lack of spontaneous flow in the major veins is a sign of obstruction (with the exception of the tibial and peroneal veins). Absence of phasic flow with respiration also suggests abnormality of the venous outflow.
When a large vein is occluded, no flow is detected. It is worth remembering that collateral veins in a similar orientation may mimic a patent vein. Collateral veins, however, usually have continuous flow, not influenced by respiration. Continuous venous flow in one limb and not in the other may be a sign of thrombotic obstruction.

Venous thrombosis of the upper extremity
The clinical signs of obstructed venous retum include oedema of the upper extremity, pain, cyanosis and distended superficial veins. The etiology may be obstructing tumours in the mediastinum, a cervical rib, exostosis or trauma causing thrombosis, or effort thrombosis. Iatrogenic thrombosis of the axillary or subclavian vein is frequently seen following the insertion of central venous or pacemaker catheters.

Phlegmasia cerulea dolens
In about one per cent of patients with lower limb DVT, the extensive ischemic thrombotic state of phlegmasia cerulea dolens appears, in which the arterial flow is compromised by profound venous out-flow obstruction and resulting venous hypertension. Venous gangrene may then occur and in this situation there is a high mortality rate. Limb sal vage is more likely achieved by performing immediate venous thrombectomy than by heparin treatment. This condition is distinguished from the more common phlegmasia alba dolens ("painful white inflammation") with severe thrombotic masses throughout the extremity veins.

Figure 33. Incompetent perforating veins on the dorsal/lateral side of the leg (arrows).

Venous insufficiencyIn western communities, chronic venous
insufficiency affects about 2.5 per cent of the population, and has significant socioeconomic consequences. The pathophysiology of chronic venous insufficiency involves incompetence of valve segments with associated reflux, obstruction of the vein lumen, or a combination of these resulting in peripheral venous hypertension (Fig. 33). Ablative surgical management is effective for disease in the superficial and communicating systems, while deep venous reconstructive surgery must be considered experimental.

Primary varicose venous disease
This is a primary non-thrombotic venous defect involving the valve cusp or valve ring which prevents apposition of the valve cusps. Normally, ascending phlebography is of limited value except in some rare cases for exact localization of incompetent perforating veins prior to ligation. The preoperative diagnosis is made by clinical examination supplemented by various methods for measuring venous pressures and ultrasound (Doppler or colour-Doppler duplex scanning). The latter will accurately detect the presence or absence of valvular reflux at anatomically identified sites, with quantitative measurements of reflux severity.

Secondary varicose venous disease, postthrombotic syndrome
Secondary varicose vein disease may result from valve destruction due to scarring and organization of thrombus, or obstruction of vein segments. A number of valveless collateral veins will form after obstruction has occurred. If they appear as cork-screw bundles in the path of the

Figure 34. Post-thrombotic occlusion of the left common iliac vein. Note recanalisation by developed collateral veins.

obstructed vein, this is claimed to indicate that the recanalization originates from the vasa vasorum of the venous wall. A decrease in the number of venous valves will be visible. Destroyed valves are recognizable as stiff, scarred webs. On phlebography recanalized veins look like tubes with irregular wall patterns resembling the loosening bark of a tree, due to organized thrombotic material adherent to the walls. Obstructed veins are seen as segmental interruptions or irregular deviations from the venous path (Fig. 34). Increased collateral/superficial venous flow and varicose superficial veins often dominate the picture.

Retroperitoneal fibrosis
Retroperitoneal fibrosis is an idiopathic process which can obstruct the retroperitoneal urinary tract. It may also cause obstruction of the inferior vena cava. Ascending lumbar veins will often act as the main collateral pathways (Fig. 35).

Tumours, hematomas and Baker cysts
Neoplastic masses along the major veins may obstruct the flow and cause peripheral venous hypertension or thrombosis.

Figure 35. Collateral circulation in the ascending lumbar veins following occlusion of inferior vena cava by retroperitoneal fibrosis. Pelvic venography and cavography by contrast injections into both femoral veins.

 

Figure 36. A) Valve apiasia. Huge tubular veins in a young man with extensive variosities. B, C) Klippel-Trenaunay syndrome in the left lower limb with a large lateral venous trunk arising from the level of the popliteal vein.

Primary tumours of the venous walls (rhabdomyosareoma) are rare. In growing tumour masses into the vein lumen are called tumour thrombi.

Hematomas may clinically mimick a DVT, and may cause venous obstruction by external compression. The lumen will appear dislodged or stretched, thinner, or even occluded with a tapered end of the venous segment passing into the hematoma. A similar stretched, or tapered and occluded appearance may be presented by Baker's cysts of the knee, in the poplietal fossa. A ruptured Baker's cyst is often mistaken for acute DVT, however a carefully obtained clinical history and ultrasound verification of the diagnosis, should prevent unnecessary ascending phlebography.

Anomalies
Pelvic vein webs are described above. The popliteal and superficial femoral veins may often be duplicated. Venous hemangiomas occur, as described earlier in this chapter.

Venous dysplasia, valvular apiasia, is a rare anomaly consisting of tubular veins lacking valves and inherited. It presents mainly in young men as multiple bilateral varicose veins in the lower limbs (Fig. 36 A).

In Klippel-Trenaunay syndrome, flat haemangiomas of the skin are present together with a very large lateral venous trunk in the thigh (Fig. 36 B, C). This trunk may empty at different proximal levels. Trophic alterations of the limb may result.

 

Christoph L. Zollikofer and Frode Laerum