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    An embolus is adetached intravascular

    solid, liquid, or gaseousmass that is carried bythe blood to a sitedistant from its pointof

    origin

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    In more than 95% of cases, PEs originate from legdeep vein thromboses (DVTs)

    Most pulmonary emboli (60% to 80%) areclinically silent because they are small

    Sudden death, right heart failure (cor pulmonale),

    or cardiovascular collapse occurs when emboliobstruct 60% or more of the pulmonarycirculation

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    Embolic obstruction of medium-sized arterieswith subsequent vascular rupture can result inpulmonary hemorrhage but usually does notcause pulmonary infarction

    Embolic obstruction of small end-arteriolarpulmonary branches usually does result in

    hemorrhage or infarction

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    Emboli in the arterial circulation.

    Most (80%) arise from intracardiac mural thrombi

    2/3 of which are associated with left ventricular

    wall infarcts 1/4 with left atrial dilation and fibrillation

    The remainder originate from aortic aneurysms,thrombi on ulcerated atherosclerotic plaques, or

    fragmentation of a valvular vegetation

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    Arterial emboli can travel to a wide variety of sites

    Major sites : lower extremities (75%)

    brain (10%) intestines, kidneys, spleen, and upper extremities

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    The consequences of embolization in a tissuedepend on: its vulnerability to ischemia,

    the caliber of the occluded vessel,

    collateral blood supply

    In general, arterial emboli cause infarction of the

    affected tissues

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    after fractures of longbones (which havefatty marrow)

    rarely in the setting of

    soft tissue trauma andburns

    characterized bypulmonary

    insufficiency,neurologic symptoms,anemia, andthrombocytopenia

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    Gas bubbles within the circulation can coalesce toform frothy masses that obstruct vascular flow(and cause distal ischemic injury).

    Decompression sickness, occurs when individualsexperience sudden decreases in atmosphericpressure

    Chronic form of decompression sickness is calledcaisson disease

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    An infarct is anarea of ischemic

    necrosis caused byocclusion of eitherthe arterial supplyor the venousdrainage

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    Myocardial infarction

    Cerebral infarction

    Pulmonary infarction

    Diabetic (gangrenous infarction)

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    Thrombotic or embolic arterial occlusion

    Other mechanism:

    Local vasospasm

    Extrinsic vessel compression (eg.tumor) Torsion of vessel (infark testis)

    Vascular trauma

    Edema (compartment syndrome)

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    Red infarcts (1) with venous occlusions (e.g., ovary),

    (2) in loose tissues (e.g., lung)

    (3) in tissues with dual circulations

    (4) in tissues previously congested by sluggishvenous outflow,

    (5) when flow is re-established to a site of previousarterial occlusion and necrosis (e.g., following

    angioplasty of an arterial obstruction).

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    White infarcts arterial occlusions in solid organs with end-arterial

    circulation (e.g., heart, spleen, and kidney)

    where tissue density limits the seepage of blood

    from adjoining capillary beds into the necroticarea.

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    1) the nature of the vascular supply,

    2) the rate at which an occlusiondevelops,

    3) vulnerability to hypoxia

    4) the oxygen content of the blood.

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