USMLE Step 1 Review - Vascular system, heart, pericardium - 2

Dr.AhmadDr.Ahmad مدير عام
Abnormal lipid metabolism
[FONT=&quot]Fredrickson's hyperlipidemias[/FONT]
Type I (familial hyperchylomicronemia; increased chylomicrons [deficient lipoprotein lipase]; supranate), type IIa (familial hypercholesterolemia; increased LDL [deficient LDL receptors, defective apo B-100], CH; atherosclerosis, tendon xanthomas, xanthelasmas), type IIb (familial combined hyperlipidemia; increased LDL, VLDL, CH, and TG; atherosclerosis); type III (familial dysbetalipoproteinemia; increased chylomicron, IDL remnants [mutations of apo E]; atherosclerosis), type IV (familial hypertriglyceridemia; increased VLDL due to decreased catabolism; most common genetic hyperlipidemia; infranate), type V (mixed hypertriglyceridemia; type I and type IV; defects in apo CII gene; diabetic ketoacidosis and alcoholism are common factors; turbid supranate and infranate; eruptive xanthomas)
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Absence of apo B --> malabsorption (very low triglyceride and cholesterol levels), CNS disease (ataxia, retinitis pigmentosa, nystagmus, sensory abnormalities), and acanthocytosis

Diseases of the arterial system
Hardening of the arteries; subclassified as atherosclerosis (formation of atheromas), Monckeberg's medial calcification, and arteriolosclerosis (hyaline and hyperplastic types)
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Most common disease afflicting the aorta; more common in males, age related; primarily involves intima of elastic and muscular arteries; fatty streak (early lesion) and fibrous plaque (advanced lesion); proposed mechanisms: thrombogenic (mural thrombus incorporated into an atheroma), monoclonal (proliferation of smooth muscle cells), reaction to injury theory (most popular; endothelial cell injury [smoking, LDL] --> monocytes and lymphocytes adhere to injury --> emigrate into vessel wall --> release of cytokines --> smooth muscle proliferation, chemotaxis [macrophages, lymphocytes, smooth muscle cells imbibe oxidized LDL produced by free radicals from injured epithelial cells and macrophages --> become foam cells] --> fatty streaks enlarge and disrupt endothelial surface --> platelets adhere to damaged endothelium and release PDGF [contributes to smooth muscle proliferation] --> smooth muscle cells synthesize collagen, elastin, proteoglycans --> fibrous plaques) (cont.)
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atherosclerosis involves abdominal aorta > coronary arteries > popliteal artery > descending thoracic > internal carotid > circle of Willis
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[FONT=&quot]Complications of atherosclerosis[/FONT]
Plaque ulcerates --> ruptures --> thrombus formation (lines of Zahn --> alternating layers of platelets and fibrin [pale], and layers of blood [dark]); thromboembolism of plaque material to distant sites may result in infarction; may weaken vessel wall resulting in aneurysm; primary pathogenesis of ischemic heart disease; associated with peripheral vascular disease (may lead to claudication and amputation of extremity); may result in CNS disease; primary cause of renovascular hypertension; may produce gastrointestinal disease (mesenteric angina, bowel infarction, ischemic strictures [colon])
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[FONT=&quot]Monckeberg's medial calcification[/FONT]
Age-related, clinically insignificant degenerative disease that commonly involves muscular arteries (e.g., femoral arteries, uterine arteries)
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Either hyperplastic (proliferative) or hyalinized; hyperplastic type characterized by smooth muscle proliferation in an "onion-skin" pattern with narrowing of the lumen (e.g., renal vessels in malignant hypertension and progressive systemic sclerosis); hyaline type associated with arterioles that have a glassy, pink appearance on H and E staining ("small-vessel disease" of diabetes mellitus [nonenzymatic glycosylation of basement membrane of vessels renders them permeable to proteins] and hypertension [increased pressure imposed on arteriolar walls drives protein into vessels])
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Localized dilatation of an artery that results from weakening by atherosclerosis (most common), inflammation, a congenital abnormality (e.g., Ehlers-Danlos syndrome), trauma, or hypertension; natural history is to enlarge and rupture; may be fusiform (spindle shaped), saccular (round), or dissecting
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[FONT=&quot]Aortic aneurysms[/FONT]
Different etiologies depending on location; in ascending aorta, most commonly secondary to dissecting aortic aneurysm that has extended proximally (tertiary syphilis is no longer the most common cause); in distal aorta (thoracic and abdominal) and in the extremities, most commonly secondary to atherosclerosis
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[FONT=&quot]Abdominal aortic aneurysm[/FONT]
Most common aneurysm; most often in men over age 55; due to weakening of wall by atherosclerosis owing to lack of vasa vasorum below renal artery orifices; majority asymptomatic; if symptomatic, pulsatile mass with mid-abdominal to lower back pain, abdominal bruit; rupture is most common complication (most rupture into left retroperitoneum) --> severe back pain, pulsatile mass, hypotension; abdominal ultrasound is gold standard
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[FONT=&quot]Berry aneurysm[/FONT]
Most commonly located at bifurcations of cerebral vessels (anterior communicating artery with anterior cerebral artery); most are congenital and are associated with vessels that lack an internal elastic membrane and muscle wall; association with adult polycystic kidney disease (10-15%) and coarctation of the aorta
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[FONT=&quot]Mycotic aneurysms[/FONT]
Secondary to weakening of vessel wall by an infectious process (e.g., septic embolism, infective endocarditis, fungal vasculitis [Aspergillus, Mucor, Candida])
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[FONT=&quot]Syphilitic aneurysm[/FONT]
Syphilitic aneurysm involving arch of aorta is second most common manifestation of tertiary syphilis; Treponema pallidum produces endarteritis obliterans (vasculitis; numerous plasma cells) of vasa vasorum in ascending and transverse portions of aortic arch --> ischemia in outer adventitial and outer medial tissue of aorta --> weakening of wall --> aneurysm formation and aortic regurgitation from stretching of aortic valve ring; linear calcifications often seen in ascending aorta by CXR; can be associated with respiratory distress, cough; death usually occurs from rupture or heart failure
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[FONT=&quot]Dissecting aortic aneurysm[/FONT]
Most common catastrophic disorder of the aorta; elastic tissue fragmentation (95%) with or without mucoid degeneration (cystic medial necrosis) in middle and outer part of media --> weakens vessel wall; predisposing causes: Marfan's syndrome (fibrillin defect), Ehlers-Danlos syndrome (defect in collagen), pregnancy (increased plasma volume), copper deficiency (cofactor in lysyl oxidase), coarctation of aorta (wall stress), trauma; hypertension is single most important factor for initiating dissection (shearing force to intimal surface --> intimal tear --> entry of column of blood); entry of blood into pericardial sac is most common cause of death; type A (most common; worst type; involves ascending aorta), type B (begin below subclavian artery); acute onset of severe chest pain (tearing), radiates to back; increased aortic diameter on CXR; retrograde arteriography is gold standard
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[FONT=&quot]AV fistulas[/FONT]
Abnormal communications between arteries and veins; either congenital or acquired (most commonly due to penetrating knife injury); large AV fistulas reduce systemic resistance and bypass microcirculation --> increase venous return to heart --> high-output cardiac failure

Disorders involving the venous system
Thrombosis of a vein without inflammation (90% in legs); predisposing factors: damage to vessel endothelium (e.g., inflammation, varicose veins), stasis of blood flow (e.g., bed rest), and hypercoagulability (e.g., oral contraceptive use); swelling, pain, edema distal to thrombosis, varicosities, ulceration
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[FONT=&quot]Deep venous thrombosis[/FONT]
Deep venous insufficiency: thrombosis --> obstruction of deep saphenous vein --> increased venous pressure --> increased blood flow to veins around ankles that communicate with superficial system --> veins in ankle rupture --> stasis dermatitis (swelling, hemorrhage --> hemosiderin deposition, ulcers) and secondary varicosities in superficial saphenous system; swelling of the calf and positive Homan sign (dorsiflexion of foot) and Mose sign (compression of calf) strongly suggests deep saphenous vein thrombophlebitis; complications: thromboembolism, thrombophlebitis, varicose veins; doppler ultrasonography (best test); x-ray venography is gold standard
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Pain and tenderness along the course of a superficial vein; usually occurs postoperatively in patients over 40; most commonly secondary to varicose veins but may be associated with phlebothrombosis (common), intravenous catheters, polycythemia, IV drug abuse, or a neighboring infection; involved vein is palpable cord with pain, induration, heat, and erythema along skin surface
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[FONT=&quot]Migratory thrombophlebitis[/FONT]
Venous thrombi disappear at one site and reappear at another; may be a paraneoplastic sign of underlying pancreatic cancer (Trousseau's sign)
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[FONT=&quot]Thoracic outlet syndrome[/FONT]
Abnormal compression of neurovascular compartment in the neck due to a cervical rib, spastic scalenus anterior muscle, or positional change in the neck and arms; diagnosis confirmed by arteriogram
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[FONT=&quot]Superior vena cava syndrome[/FONT]
Secondary to extrinsic compression of the SVC from a primary lung cancer (smoking) and less commonly a malignant lymphoma --> puffiness and blue to purple discoloration of the face, arms, and shoulders and CNS findings of dizziness, convulsions, and visual disturbances (congested retinal veins), JVD; diagnosis confirmed by venography

Disorders involving the lymphatic system
[FONT=&quot]Acute lymphangitis[/FONT]
Inflammation of the lymphatics ("red streak") most commonly secondary to Streptococcus pyogenes
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[FONT=&quot]Chylous effusions[/FONT]
Collections of lymphatic fluid in a body cavity secondary to a malignant lymphoma or trauma
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Abnormal interstitial collection of lymphatic fluid caused by congenital disease or blockage of lymphatics; primary type presents at birth (congenital lymphedema) or is delayed and first presents in adolescence (lymphedema precox); Milroy disease (hereditary lymphedema caused by faulty development of lymphatics); Turner's syndrome (lymphedema of hands and feet); secondary causes: lymphatic obstruction by tumor (e.g., peau d'orange appearance in inflammatory carcinoma of the breast), radiation (postradical mastectomy with axillary dissection; most common cause in US), infestation by filarial organisms (Wuchereria bancrofti), lymphogranuloma venereum (chlamydial disease --> localized lymphedema in vulva or scrotum); nonpitting edema, does not resolve with overnight elevation; complication of long-standing lymphedema is lymphangiosarcoma