View source for Embolus

{{about|the medical use of the term|its use in spider anatomy|Palpal bulb}}
{{short description|Unattached mass that travels through the bloodstream}}
[[File:Blausen 0089 BloodClot Motion.png|thumb|Illustration depicting an embolism within the bloodstream, and lodging at a site of vascular narrowing due to plaque]]
An '''embolus''' ({{IPAc-en|ˈ|ɛ|m|b|ə|l|ə|s}};<ref>{{Cite OED|embolus}}</ref> {{plural form}}: '''emboli'''; from the Greek ἔμβολος "wedge", "plug") is an unattached mass that travels through the [[circulatory system|bloodstream]] and is capable of creating blockages. When an embolus [[Vascular occlusion|occludes]] a blood vessel, it is called an [[embolism]] or embolic event.<ref name="Robbins&Cotran">{{cite book |author=Kumar V. |author2=Abbas A.K. |author3=Fausto N.|title=Pathologic Basis of Disease}}</ref> There are a number of different types of emboli, including [[blood clots]], [[cholesterol]] plaque or crystals, [[Fat embolism syndrome|fat globules]], [[Air embolism|gas bubbles]], and [[foreign body|foreign bodies]], which can result in different types of embolisms.

The term is distinct from [[embolism]] and [[thromboembolism]], which may be consequences of an embolus, as discussed below.<ref name=":0">{{Cite web|url=http://www.medterms.com/script/main/art.asp?articlekey=3224|title=Medical Definition of Embolus|access-date=2010-10-10|archive-date=2014-07-14|archive-url=https://web.archive.org/web/20140714191327/http://www.medterms.com/script/main/art.asp?articlekey=3224|url-status=dead}}</ref>

The term was coined in 1848 by [[Rudolf Virchow]] as part of his foundational research into [[Thrombus|blood clots]].<ref>{{cite book| title=The Timetables of Science| first=Alexander| last=Hellemans| author2=Bryan Bunch| publisher=Simon and Schuster| location=New York, New York| year=1988| isbn=0-671-62130-0| pages=[https://archive.org/details/timetablesofscie00hell_0/page/317 317]| url-access=registration| url=https://archive.org/details/timetablesofscie00hell_0/page/317}}</ref><ref name=":1">{{Cite book|last=Virchow, Rudolf, 1821-1902.|url=https://www.worldcat.org/oclc/37534011|title=Thrombosis and emboli (1846-1856)|date=1998|publisher=Science History Publications|isbn=0-88135-113-X|location=Canton, Mass|oclc=37534011}}</ref>

== Nomenclature ==
The term embolus refers generally to any free-floating mass in the bloodstream, or such a mass once lodged at a site of blockage. A related term is embolism, which describes the phenomenon of an embolus lodging in a vessel and creating a blockage.<ref name="Robbins&Cotran" /> An embolism is technically a consequence of an embolus, but the terms are sometimes used interchangeably.<ref>{{Cite web|title=Arterial embolism: MedlinePlus Medical Encyclopedia|url=https://medlineplus.gov/ency/article/001102.htm|access-date=2020-12-09|website=medlineplus.gov|language=en}}</ref> Emboli and embolisms can be named according to their composition (such as [[air embolism]]) or the site where they lodge ([[pulmonary embolism]]).

In contrast to emboli, which can cause occlusion at sites distant from their points of origin, there are also non-traveling blockages that develop locally from vascular trauma and inflammation or other epithelial pathology, such as [[atheroma]]ta and [[Thrombus|thrombi]]. If these local blockages dislodge into circulation, they become emboli and if not broken down during circulation, may cause embolism(s).<ref name=":0" /> For example, a [[thromboembolism]] is the result of a thrombus that has broken off the interior of a blood vessel and caused a vessel blockage elsewhere in the circulation.

Details of embolism classification are discussed below.

==Classification by substance==
The physical composition of the embolic material is the defining feature for classification, and this composition reflects the underlying pathophysiologic mechanism of the embolus' formation. Furthermore, different types of emboli result in different types of embolisms, each with distinct clinical characteristics.

By contrast, [[embolism]] is typically classified by the location where the emboli lands, such as in [[pulmonary embolism]].

'''[[thromboembolism]]''', the thrombus (blood clot) from a blood vessel is completely or partially detached from the site of thrombosis (clot). The blood flow will then carry the embolus (via blood vessels) to various parts of the body where it can block the lumen (vessel cavity) and cause vessel obstruction or occlusion. The free-moving thrombus is called an embolus.<ref>{{Cite book
 | last1 = Howland
 | first1 = Richard D.
 | last2 = Mycek
 | first2 = Mary J.
 | publication-date =
 | title = Pharmacology
 | edition = 3rd
 | series = Lippincott's illustrated reviews
 | year = 2006
 | publisher = Philadelphia : Lippincott Williams & Wilkins, c2006.
 | page = 227
 | isbn = 0-7817-4118-1
}}</ref> A thrombus is always attached to the vessel wall and is never freely moving in the blood circulation. This is also the key difference for pathologists to determine the cause of a blood clot, either by thrombosis or by post-mortem blood clot. Vessel obstruction will then lead to different pathological issues such as blood [[Stasis (medicine)|stasis]] and [[ischemia]]. However, not only thromboembolism will cause the obstruction of blood flow in vessels, but also any kind of embolism is capable of causing the same problem.

'''[[Fat embolism]]''' usually occurs when endogenous (from sources within the organism) fat tissue escapes into the blood circulation. The usual cause of fat embolism is therefore the [[fracture]] of tubular bones (such as the [[femur]]), which will lead to the leakage of fat tissue within the bone marrow into ruptured vessels. There are also exogenous (from sources of external origin) causes such as intravenous injection of [[emulsions]].

An '''[[air embolism]]''', on the other hand, is usually always caused by exogenic factors. This can be the rupture of [[Pulmonary alveolus|alveoli]], and inhaled air can be leaked into the blood vessels. Other more-common causes include the puncture of the [[subclavian vein]] by accident or during operation where there is negative pressure. Air is then sucked into the veins by the negative pressure caused by thoracic expansion during the inhalation phase of respiration. Air embolism can also happen during intravenous therapy, when air is leaked into the system (however this [[iatrogenic]] error in modern medicine is extremely rare).

'''[[Gas embolism]]''' is a common concern for deep-sea divers because the gases in human blood (usually nitrogen and helium) can be easily dissolved at higher amounts during the descent into deep sea. However, when the diver ascends to the normal atmospheric pressure, the gases become insoluble, causing the formation of small bubbles in the blood. This is also known as [[decompression sickness]] or the bends. This phenomenon is explained by [[Henry's Law]] in physical chemistry.

Embolism by '''other materials''' is rare. [[Septic embolism]] happens when a purulent tissue ([[pus]]-containing tissue) is dislodged from its original focus. [[Tissue embolism]] is analogous to macro-scale [[cancer]] [[metastasis]], which happens when cancer tissue infiltrates blood vessels, and small fragments of tumor are released into the blood stream. [[Foreign-body embolism]] happens when exogenous—and only exogenous—materials such as [[talc]] enter the blood stream and cause occlusion or obstruction of blood circulation.  [[Bullet]] embolism occurs in approximately 0.3% cases of [[gunshot wound]]s.<ref>{{Cite journal|url=http://www.jvascsurg.org/article/S0741-5214%2810%2902639-X/abstract|doi = 10.1016/j.jvs.2010.11.046|title = Retrograde migration and endovascular retrieval of a venous bullet embolus|year = 2011|last1 = Schroeder|first1 = Mary Elizabeth|last2 = Pryor|first2 = Howard I.|last3 = Chun|first3 = Albert K.|last4 = Rahbar|first4 = Rodeen|last5 = Arora|first5 = Subodh|last6 = Vaziri|first6 = Khashayar|journal = Journal of Vascular Surgery|volume = 53|issue = 4|pages = 1113–1115|pmid = 21215588|doi-access = free}}</ref> [[Amniotic-fluid embolism]] is a rare complication of childbirth.

== Clinical significance ==
Emboli are clinically significant for their capacity to cause embolisms, which are a major cause of morbidity and mortality.<ref>{{Cite journal|last1=Khan|first1=Faizan|last2=Rahman|first2=Alvi|last3=Carrier|first3=Marc|last4=Kearon|first4=Clive|last5=Weitz|first5=Jeffrey I.|last6=Schulman|first6=Sam|last7=Couturaud|first7=Francis|last8=Eichinger|first8=Sabine|last9=Kyrle|first9=Paul A.|last10=Becattini|first10=Cecilia|last11=Agnelli|first11=Giancarlo|date=2019-07-24|title=Long term risk of symptomatic recurrent venous thromboembolism after discontinuation of anticoagulant treatment for first unprovoked venous thromboembolism event: systematic review and meta-analysis|journal=BMJ|language=en|volume=366|pages=l4363|doi=10.1136/bmj.l4363|issn=0959-8138|pmid=31340984|pmc=6651066|doi-access=free}}</ref><ref>{{Cite journal |last= |date=2019-10-31 |title=Significant risk of another thrombosis remains if anticoagulation is stopped |url=https://evidence.nihr.ac.uk/alert/significant-risk-of-another-thrombosis-remains-if-anticoagulation-is-stopped- |journal=NIHR Evidence |type=Plain English summary |doi=10.3310/signal-000830|s2cid=242392407 |url-access=subscription }}</ref> By themselves, emboli are pathologic and therefore indicate some underlying dysfunction.

It may be difficult in the clinical setting to differentiate a thrombotic event (i.e., a local clot at the site of symptoms) from an embolic event (i.e., local obstruction due to a free-floating mass that traveled through circulation from elsewhere in the body).
[[File:Pulmonary thromboembolus, recent (7307510958).jpg|thumb|This pulmonary [[thromboembolism]] was the result of a [[thrombus]] (blood clot) detaching from the wall of a distant blood vessel. It then traveled through circulation until lodging in this pulmonary vessel, becoming a thromboembolism. ]]
Septic emboli may also be a contributor to spreading infection through the bloodstream to other tissues.<ref>{{Citation |last=Elsaghir |first=Hend |title=Septic Emboli |date=2022 |url=http://www.ncbi.nlm.nih.gov/books/NBK549827/ |work=StatPearls |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=31751017 |access-date=2022-11-08 |last2=Al Khalili |first2=Yasir}}</ref>

== History ==
[[Rudolf Virchow]], the German physician and "father of pathology", is generally credited with the first explanation of the relationship between thrombi, emboli, and embolisms. He coined the terms embolism (initially called "Embolia") and thrombosis while proposing a hypothesis for the pathophysiology of pulmonary thromboembolism.<ref name=":1" /><ref>{{Cite journal|last1=Kumar|first1=David R.|last2=Hanlin|first2=Erin|last3=Glurich|first3=Ingrid|last4=Mazza|first4=Joseph J.|last5=Yale|first5=Steven H.|date=December 2010|title=Virchow's Contribution to the Understanding of Thrombosis and Cellular Biology|journal=Clinical Medicine & Research|volume=8|issue=3–4|pages=168–172|doi=10.3121/cmr.2009.866|issn=1539-4182|pmc=3006583|pmid=20739582}}</ref>

In his work, he described the consequences of thrombosis and the factors leading thereto, a concept which today is known as [[Virchow's triad|Virchow's Triad]]. However, there is some dispute regarding certain aspects of this attribution.<ref>{{Cite journal|last=Dickson|first=Brendan C.|date=September 2004|title=Virchowʼs Triad?|url=http://dx.doi.org/10.1097/01.smj.0000136235.11281.eb|journal=Southern Medical Journal|volume=97|issue=9|pages=915–916|doi=10.1097/01.smj.0000136235.11281.eb|pmid=15455989|issn=0038-4348|url-access=subscription}}</ref>

== See also ==
* [[Paradoxical embolism]]
* [[Pulmonary embolism]]
* [[Virchow's triad|Virchow's Triad]]

==References==
{{Reflist}}

[[Category:Hematology]]