EMBOLISMEMBOLISMDr.CSBR.Prasad, M.D.

Def: An embolus is a detached intravascular solid, liquid, or

gaseous mass that is carried by the blood to a site distant from its point

of origin.

Almost all emboli represent some part of a dislodged thrombus Unless specified embolism means Thromboembolism

Rare forms of emboli

droplets of fat bubbles of air or nitrogen Cholesterol emboli from AS debri tumor fragments bits of bone marrow, or even foreign bodies such as bullets

Effect of embolus

Occlusion

Emboli lodge in vessels too small to permit further passage, resulting in partial or

complete vascular occlusion

Consequences

Infarction

The potential consequence of such thromboembolic events is the ischemic

necrosis of distal tissue, known as infarction

Clinical outcome

Depends on: the site of origin & the site of lodgment

The clinical outcomes are best understood from the standpoint of

whether emboli lodge in the pulmonary or systemic circulations.

Saddle embolusLerisch syndrome

Paradoxical embolism

PULMONARY THROMBOEMBOLISM

•Incidence of 20 to 25 per 100,000 hospitalized patients

•In more than 95% of instances, venous emboli originate from deep leg vein thrombi

•Depending on the size of the embolus, it may occlude the main pulmonary artery, impact across the bifurcation (saddle embolus), or pass out into the smaller, branching arterioles

•in general, the patient who has had one pulmonary embolus is at high risk of having more.

•Rarely, an embolus may pass through an interatrial or interventricular defect to gain access to the systemic circulation (paradoxical embolism)

• Most pulmonary emboli (60% to 80%) are clinically silent because they are small. With time, they undergo organization and are incorporated into the vascular wall in some cases, organization of the thromboembolus leaves behind a delicate, bridging fibrous web.

  •    Sudden death, right heart failure (cor pulmonale). or cardiovascular collapse occurs when 60% or more of the pulmonary circulation is obstructed with emboli.

  •    Embolic obstruction of medium-sized arteries may result in pulmonary hemorrhage but usually does not cause pulmonary infarction because of the dual blood flow into the area from the bronchial circulation. A similar embolus in the setting of left-sided cardiac failure (i.e., with sluggish bronchial artery flow), however, may result in a large infarct.

  •    Embolic obstruction of small end-arteriolar pulmonary branches usually does result in associated infarction.

• Multiple emboli over time may cause pulmonary hypertension with right heart failure.

PULMONARY THROMBOEMBOLISM

Consequences of Pul.embolism• The morphologic consequences depend on the

size of the embolic mass and the general state of the circulation

• Large emboli - Sudden death often ensues - acute cor pulmonale (ECG-elecromechanical dissociation)

• Smaller emboli – with good CVS – hemorrhages resorption & reconstitution of

the preexisting architecture – with CVS compromise - 10% infarction

Here is large pulmonary thromboembolus seen in cross section of this lung. The typical source for such thromboemboli is from large veins in the legs and pelvis.

Figure 4-17  Large embolus derived from a lower extremity deep venous thrombosis and now impacted in a pulmonary artery branch

Pulmonary thromboembolus

Recent, small, roughly wedge-shaped hemorrhagic

pulmonary infarct

Non thrombotic forms of pul.emboli

• uncommon but potentially lethal• air (may be iatrogenic) • bone marrow (after trauma and bone

marrow necrosis in sickle cell patients) • fat (trauma and surgery)• amniotic fluid (during parturition) and • foreign bodies (in I/V drug abusers)

SYSTEMIC THROMBOEMBOLISM

• refers to emboli travelling within the arterial circulation

• Common source: Mural thrombi in heart (80%)

• Less common source: Aorta (AS, Aneurysm)

Mural thrombi

SYSTEMIC THROMBOEMBOLISM

The major sites for arteriolar embolization• Lower extremities (75%) and • Brain (10%)• the intestines, kidneys, spleen, and upper

extremities involved to a lesser extent

SYSTEMIC THROMBOEMBOLISM

The consequences of systemic emboli depend on:

the extent of collateral vascular supply in the affected tissue

the tissue's vulnerability to ischemia and the caliber of the vessel occludedin general, arterial emboli cause infarction of

tissues downstream of the obstructed vessel

Tissues supplied by end-arteries without significant collateral supplies will be the most susceptible.

Obstruction of blood supply leads to ischemia which when prolonged leads to necrosis and atrophy.

Where there is reperfusion after ischemic necrosis the tissues will show a hemorrhagic necrosis.

Where there is infection by Clostridia (gram positive bacilli), gangrene sets in.

FAT EMBOLISM

• Presence of microscopic fat globules in the circulation

• Causes: # of long bones Soft tissue trauma Burns

FAT EMBOLISM Fat embolism syndrome is characterized by

pulmonary insufficiency, neurologic symptoms, anemia, and Thrombocytopenia

Symptoms:typically begin 1 to 3 days after injury, sudden onset of tachypnea, dyspnea, and

tachycardia

FAT EMBOLISM

Fat embolism syndrome: Pathogenesis mechanical obstruction and biochemical injury

Fat globule platelet complexesFat globule RBC complexesRelease of FFA > toxic injury to endothelium >

inflammation > further damage to the vessels

FAT EMBOLISM

Demonstration of fat embolism in specimens:

By means of frozen sectionsRoutine processing dissolves fat

Figure 4-18  Bone marrow embolus in the pulmonary circulation. The cleared vacuoles represent marrow fat that is now impacted in a distal

vessel along with the cellular hematopoietic precursors.

AIR EMBOLISM

• Gas bubbles within the circulation can obstruct vascular flow

• Entry of gas into circulation occurs duringObstetric proceduresChest wall injury

AIR EMBOLISM

Dose: should be > 100ml to produce any clinical effect

Bubbles act like physical obstructions and may coalesce to form frothy masses sufficiently large to occlude major vessels

AIR EMBOLISM Decompression sickness:Scuba and deep sea divers, underwater construction workers, and individuals in unpressurized aircraft Gas: NitrogenClinically: bends, chokes, ischemia, infarctionTreatment: slow decompressionCaisson disease: chronic form of decompression

sickness

AMNIOTIC FLUID EMBOLISM Uncommon complication of laborUncommon complication of labor Has a mortality rate of 20% to 40%Clinically: sudden severe dyspnea, cyanosis, and

hypotensive shock, followed by seizures and comaPathogenesis: DICThe underlying cause: infusion of amniotic fluid or fetal

tissue into the maternal circulation via a tear in the placental membranes or rupture of uterine veins

The classic findings: the presence in the pulmonary microcirculation of squamous cells shed from fetal skin, lanugo hair, fat from vernix caseosa, and mucin derived from the fetal respiratory or gastrointestinal tract

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