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The '''colon''' smells like [[poo]]... 'cause that's where poo comes from.  This article also covers the '''rectum''' and '''cecum''' as both have a similar mucosa.   
[[Image:Blausen_0603_LargeIntestine_Anatomy.png|thumb|right|Anatomy of the colon and rectum. (WC)]]
The '''colon''' is section of the large bowel.  This article also covers the '''rectum''' and '''cecum''' as both have a similar mucosa.   


It commonly comes to pathologists because there is a suspicion of [[colorectal cancer]] or a known history of [[inflammatory bowel disease]] (IBD).  
It commonly comes to pathologists because there is a suspicion of [[colorectal cancer]] or a known history of [[inflammatory bowel disease]] (IBD).


An introduction to gastrointestinal pathology is found in the ''[[gastrointestinal pathology]]'' article.  The ''[[anus]]'' and ''[[ileocecal valve]]'' are dealt with in separate articles.
An introduction to gastrointestinal pathology is found in the ''[[gastrointestinal pathology]]'' article.  The ''[[anus]]'' and ''[[ileocecal valve]]'' are dealt with in separate articles.


Technically, the rectum and cecum are ''not'' part of the colon.  Thus, inflammation of the rectum should be ''proctitis'' and inflammation of the cecum should be ''cecitis''.
Technically, the rectum and cecum are ''not'' part of the colon.  Thus, inflammation of the rectum should be ''proctitis'' and inflammation of the cecum should be ''cecitis''.
=Anatomy=
*The [[rectum]] has several definition. These are discussed in the ''[[rectum]]'' article.
*The large bowel may be submitted with segment names or with the distance to the anal verge.
A conversion between named segments and distance - as per NCI of the United States:<ref>URL: [https://training.seer.cancer.gov/colorectal/anatomy/figure/figure1.html]https://training.seer.cancer.gov/colorectal/anatomy/figure/figure1.html]. Accessed on: 8 February 2018.</ref>
{| class="wikitable sortable"
!Named segment
!Distance to anal verge (cm)
|-
|Anus
|0-4
|-
|[[Rectum]]
|4-16
|-
|Rectosigmoid
|15-17
|-
|Sigmoid
|17-57
|-
|Descending
|57-82
|-
|Transverse
|82-132
|-
|Ascending
|132-147
|-
|Cecum
|150
|}


=Common clinical problems=
=Common clinical problems=
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# Subtotal colectomy - part of colon removed --or-- some of the rectum remains.
# Subtotal colectomy - part of colon removed --or-- some of the rectum remains.
# Right hemicolectomy - right colon + distal ileum.
# Right hemicolectomy - right colon + distal ileum.
# Lower anterior resection (LAR) - proximal rectum +/- sigmoid (for proximal rectal malignancies).
# [[Lower anterior resection]] (LAR) - proximal rectum +/- sigmoid (for proximal rectal malignancies).
#* Specimens have should have intact mesorectum - ''total mesorectal excision'' (TME) - reduces local recurrence.<ref name=pmid8665198>{{Cite journal  | last1 = Arbman | first1 = G. | last2 = Nilsson | first2 = E. | last3 = Hallböök | first3 = O. | last4 = Sjödahl | first4 = R. | title = Local recurrence following total mesorectal excision for rectal cancer. | journal = Br J Surg | volume = 83 | issue = 3 | pages = 375-9 | month = Mar | year = 1996 | doi =  | PMID = 8665198 }}</ref>  
#* Specimens have should have intact mesorectum - ''[[total mesorectal excision]]'' (TME) - reduces local recurrence.<ref name=pmid8665198>{{Cite journal  | last1 = Arbman | first1 = G. | last2 = Nilsson | first2 = E. | last3 = Hallböök | first3 = O. | last4 = Sjödahl | first4 = R. | title = Local recurrence following total mesorectal excision for rectal cancer. | journal = Br J Surg | volume = 83 | issue = 3 | pages = 375-9 | month = Mar | year = 1996 | doi =  | PMID = 8665198 }}</ref>  
# Abdominoperineal resection (APR) - anus + rectum - results in a permanent [[stoma]] (for distal rectal malignancies).
# [[Abdominoperineal resection]] (APR) - anus + rectum - results in a permanent [[stoma]] (for distal rectal malignancies).
# [[Stoma]] - these are often done emergently and then get cut-out after the patient's condition has settled.
# [[Stoma]] - these are often done emergently and then get cut-out after the patient's condition has settled.
#[[Doughnuts]] (also ''donuts'') from an end-to-end anastomosis stapler.
#*Often accompany lower anterior resections.


===Images===
===Images===
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**Rectum starts/sigmoid ends @ place where serosa ends on the posterior aspect of the bowel.
**Rectum starts/sigmoid ends @ place where serosa ends on the posterior aspect of the bowel.
***The proximal, anterior aspect of the rectum has serosa, i.e. it is not painted.
***The proximal, anterior aspect of the rectum has serosa, i.e. it is not painted.
Note:
*There are several definitions for the rectum.<ref name=pmid24130630>{{Cite journal  | last1 = Kenig | first1 = J. | last2 = Richter | first2 = P. | title = Definition of the rectum and level of the peritoneal reflection - still a matter of debate? | journal = Wideochir Inne Tech Maloinwazyjne | volume = 8 | issue = 3 | pages = 183-6 | month = Sep | year = 2013 | doi = 10.5114/wiitm.2011.34205 | PMID = 24130630 }}</ref>
**In a survey of surgeons:
**67% defined it by an anatomical landmark
***35% of all respondants considered the peritoneal reflection the proximal boundary of the rectum.
**30% defined the proximal boundary as a distance from the anal verge.


=Common non-neoplastic disease=
=Common non-neoplastic disease=
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==Volvulus==
==Volvulus==
===General===
{{Main|Volvulus}}
*Uncommonly comes to pathology.
*It is essentially a radiologic diagnosis.
*In the context of [[autopsy]], it is a gross diagnosis.
 
===Gross===
*Intestine folded over itself - typically leads to ischemia.
 
Images:
*[http://library.med.utah.edu/WebPath/GIHTML/GI032.html Cecal volvulus (utah.edu)].
*[http://pathsrvr.rockford.uic.edu/inet/GI/Photo%202%20-%20Volvulus%20of%20small%20intestine_%20gross.gif Volvulus (uic.edu)].<ref>URL: [http://pathsrvr.rockford.uic.edu/inet/GI/GI%20Station%201.htm http://pathsrvr.rockford.uic.edu/inet/GI/GI%20Station%201.htm]. Accessed on: 9 April 2012.</ref>
 
===Microscopic===
Features:
*+/-Ischemic changes and/or [[necrosis]].
 
DDx - essentially anything that causes ischemia:
*Embolus.
*Thrombosis.
*[[Vasculitis]].
 
===Sign out===
<pre>
RECTOSIGMOID, RESECTION:
- MURAL ISCHEMIA WITH PERFORATION, SEROSITIS, MICROABSCESS FORMATION AND POORLY FORMED PSEUDOMEMBRANES.
- SUBMUCOSAL FIBROSIS.
- NEGATIVE FOR MALIGNANCY.
 
COMMENT:
The findings are consistent with volvulus and the submucosal fibrosis suggests this may have been recurrent.
</pre>


=Inflammatory diseases=
=Inflammatory diseases=
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{{Main|CMV}}
{{Main|CMV}}
*Abbreviated ''CMV colitis''.
*Abbreviated ''CMV colitis''.
===General===
{{Main|Cytomegalovirus colitis}}
*Uncommon.
*Immunosuppressed population at risk, e.g. transplant recipients, individuals with [[HIV]].
 
===Microscopic===
Features:
*Enlarged nucleus - classically in endothelial cells.
 
DDx:
*[[Infectious colitis]] without a distinctive morphology.
*CMV colitis superimposed on [[inflammatory bowel disease]].
 
====Images====
<gallery>
Image:CMV_colitis_-_intermed_mag.jpg | CMV colitis - intermed. mag. (WC/Nephron)
Image:CMV_colitis_-_high_mag_-_cropped.jpg | CMV colitis - high mag. (WC/Nephron)
</gallery>
www:
*[http://www.flickr.com/photos/lunarcaustic/4615988256/ CMV colitis (flickr.com/lunar caustic)].
*[http://www.flickr.com/photos/lunarcaustic/4615988164/ CMV colitis (flickr.com/lunar caustic)]
===IHC===
*CMV +ve.
 
Others:
*HSV-1.
*HSV-2.
*VZV.
*[[EBV]].


==Intestinal spirochetosis==
==Intestinal spirochetosis==
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*[[AKA]] ''solitary rectal ulcer syndrome''.
*[[AKA]] ''solitary rectal ulcer syndrome''.
*''[[Mucosal prolapse syndrome]]'' may be used as a synonym; however, it encompasses other entities.<ref name=pmid22697798>{{Cite journal  | last1 = Abid | first1 = S. | last2 = Khawaja | first2 = A. | last3 = Bhimani | first3 = SA. | last4 = Ahmad | first4 = Z. | last5 = Hamid | first5 = S. | last6 = Jafri | first6 = W. | title = The clinical, endoscopic and histological spectrum of the solitary rectal ulcer syndrome: a single-center experience of 116 cases. | journal = BMC Gastroenterol | volume = 12 | issue =  | pages = 72 | month =  | year = 2012 | doi = 10.1186/1471-230X-12-72 | PMID = 22697798 }}</ref>
*''[[Mucosal prolapse syndrome]]'' may be used as a synonym; however, it encompasses other entities.<ref name=pmid22697798>{{Cite journal  | last1 = Abid | first1 = S. | last2 = Khawaja | first2 = A. | last3 = Bhimani | first3 = SA. | last4 = Ahmad | first4 = Z. | last5 = Hamid | first5 = S. | last6 = Jafri | first6 = W. | title = The clinical, endoscopic and histological spectrum of the solitary rectal ulcer syndrome: a single-center experience of 116 cases. | journal = BMC Gastroenterol | volume = 12 | issue =  | pages = 72 | month =  | year = 2012 | doi = 10.1186/1471-230X-12-72 | PMID = 22697798 }}</ref>
===General===
{{Main|Solitary rectal ulcer}}
*Clinically may be suspected to a malignancy - biopsied routinely.
*Mucosal ulceration.
*"Three-lies disease":<ref name=pmid18271667>{{cite journal |author=Crespo Pérez L, Moreira Vicente V, Redondo Verge C, López San Román A, Milicua Salamero JM |title=["The three-lies disease": solitary rectal ulcer syndrome] |language=Spanish; Castilian |journal=Rev Esp Enferm Dig |volume=99 |issue=11 |pages=663–6 |year=2007 |month=November |pmid=18271667 |doi= |url=http://www.grupoaran.com/mrmUpdate/lecturaPDFfromXML.asp?IdArt=459864&TO=RVN&Eng=1}}</ref>
# May not be solitary.
# May not be rectal -- can be in left colon.
# May not be ulcerating -- non-ulcerated lesions: polypoid and/or erythematous.
 
Note: Each of the words in ''solitary rectal ulcer'' is a lie.
 
====Epidemiology====
*Typically younger patients - average age of presentation ~30 years in one study.<ref name=pmid17139403>{{cite journal |author=Chong VH, Jalihal A |title=Solitary rectal ulcer syndrome: characteristics, outcomes and predictive profiles for persistent bleeding per rectum |journal=Singapore Med J |volume=47 |issue=12 |pages=1063–8 |year=2006 |month=December |pmid=17139403 |doi= |url=http://www.sma.org.sg/smj/4712/4712a7.pdf}}</ref>
*Rare.
 
====Clinical presentation====
*Usually presents as BRBPR ~ 85% of cases.<ref name=pmid17139403/>
*Abdominal pain present in approx. 1/3.<ref name=pmid17139403/>
**May be very painful.
 
Treatment:
*Usually conservative, i.e. non-surgical.
*Resection - may be done for fear of malignancy.
 
===Gross===
*Classically, anterior or anterolateral wall of the rectum.<ref name=pmid18271667/>
 
===Microscopic===
Features:<ref name=pmid18271667/><ref name=pmid2091997>{{Cite journal  | last1 = Malik | first1 = AK. | last2 = Bhaskar | first2 = KV. | last3 = Kochhar | first3 = R. | last4 = Bhasin | first4 = DK. | last5 = Singh | first5 = K. | last6 = Mehta | first6 = SK. | last7 = Datta | first7 = BN. | title = Solitary ulcer syndrome of the rectum--a histopathologic characterisation of 33 biopsies. | journal = Indian J Pathol Microbiol | volume = 33 | issue = 3 | pages = 216-20 | month = Jul | year = 1990 | doi =  | PMID = 2091997 }}</ref>
*Fibrosis of the lamina propria.
*Thickened muscularis mucosa with abnormal extension to the lumen.
*+/-Mucosa ulceration.
*+/-Submucosal fibrosis.
 
DDx:
*[[Inflammatory pseudopolyp]] (inflammatory polyp).
**Associated with [[inflammatory bowel disease]].
*[[Rectal prolapse]].
*Well-differentiated [[colonic adenocarcinoma|adenocarcinoma]].
 
===IHC===
*p53 -ve.
**May be used to help exclude adenocarcinoma.


==Rectal prolapse==
==Rectal prolapse==
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==Angiodysplasia==
==Angiodysplasia==
===General===
{{Main|Angiodysplasia}}
*Causes (lower) GI haemorrhage.
*Generally, not a problem pathologists see.
*May be associated with [[aortic stenosis]]; known as ''Heyde syndrome''.<ref name=pmid19652242>{{cite journal |author=Hui YT, Lam WM, Fong NM, Yuen PK, Lam JT |title=Heyde's syndrome: diagnosis and management by the novel single-balloon enteroscopy |journal=Hong Kong Med J |volume=15 |issue=4 |pages=301–3 |year=2009 |month=August |pmid=19652242 |doi= |url=http://www.hkmj.org/abstracts/v15n4/301.htm}}</ref>
 
Epidemiology:
*Older people.
 
Etiology:
*Thought to be caused by the higher wall tension of cecum (due to larger diameter) and result from (intermittent) venous occlusion/focal dilation of vessels.<ref name=Ref_PBoD854>{{Ref PBoD|854}}</ref>
 
===Gross===
*Cecum - classic location.
 
Note:
*[[Crohn's disease]] - may mimic angiodysplasia radiographically.<ref name=pmid3054852/>
 
===Microscopic===
Features:<ref name=pmid3054852>{{Cite journal  | last1 = Hemingway | first1 = AP. | title = Angiodysplasia: current concepts. | journal = Postgrad Med J | volume = 64 | issue = 750 | pages = 259-63 | month = Apr | year = 1988 | doi =  | PMID = 3054852 }}</ref>
*Dilated vessels in mucosa and submucosa.


==Drugs==
==Drugs==
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*[[Intestinal polyps]].
*[[Intestinal polyps]].
*[[Small bowel]].
*[[Small bowel]].
*[[Doughnuts]].


=References=
=References=
Michael
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