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