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[[Image:Small intestine low mag.jpg|thumb|250px|right|Small bowel mucosa. [[H&E stain]].]]
The '''small intestine''', also '''small bowel''', is a relatively well-behaved piece of machinery from the perspective of [[pathology]].  It is uncommonly affected by malignancies, relative to its length when compared to the [[colon]] and [[rectum]].   
The '''small intestine''', also '''small bowel''', is a relatively well-behaved piece of machinery from the perspective of [[pathology]].  It is uncommonly affected by malignancies, relative to its length when compared to the [[colon]] and [[rectum]].   


=Normal=
=Normal small bowel=
==Anatomy==
*[[AKA]] ''normal small intestine''.
===Anatomy===
Consists of three segments:
Consists of three segments:
*Duodenum (which can be divided into four parts).
*[[Duodenum]] - can be divided into four parts.
*Jejunum.
*Jejunum.
*Ileum.
*Ileum.
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The later two parts keep ''general surgeons'' awake at night (quite literally) 'cause they get obstructed and need urgent operations.
The later two parts keep ''general surgeons'' awake at night (quite literally) 'cause they get obstructed and need urgent operations.


==Histology==
====Length====
*Normal length of small bowel = 3-8 metres.<ref name=pmid10422101>{{Cite journal  | last1 = Nightingale | first1 = JM. | title = Management of patients with a short bowel. | journal = Nutrition | volume = 15 | issue = 7-8 | pages = 633-7 | month =  | year =  | doi =  | PMID = 10422101 }}</ref>
 
"Short":
*Less than 200 cm = ''short bowel syndrome''.<ref name=pmid20709285>{{Cite journal  | last1 = Donohoe | first1 = CL. | last2 = Reynolds | first2 = JV. | title = Short bowel syndrome. | journal = Surgeon | volume = 8 | issue = 5 | pages = 270-9 | month = Oct | year = 2010 | doi = 10.1016/j.surge.2010.06.004 | PMID = 20709285 }}</ref><ref name=pmid16207689>{{Cite journal  | last1 = Matarese | first1 = LE. | last2 = O'Keefe | first2 = SJ. | last3 = Kandil | first3 = HM. | last4 = Bond | first4 = G. | last5 = Costa | first5 = G. | last6 = Abu-Elmagd | first6 = K. | title = Short bowel syndrome: clinical guidelines for nutrition management. | journal = Nutr Clin Pract | volume = 20 | issue = 5 | pages = 493-502 | month = Oct | year = 2005 | doi =  | PMID = 16207689 }}</ref>
**Less than 100 cm usu. requires parenteral nutrition.<ref name=pmid11873098>{{Cite journal  | last1 = Sundaram | first1 = A. | last2 = Koutkia | first2 = P. | last3 = Apovian | first3 = CM. | title = Nutritional management of short bowel syndrome in adults. | journal = J Clin Gastroenterol | volume = 34 | issue = 3 | pages = 207-20 | month = Mar | year = 2002 | doi =  | PMID = 11873098 }}</ref>
 
===Histology===
{{main|Gastrointestinal pathology}}
{{main|Gastrointestinal pathology}}
The ''[[Gastrointestinal pathology]]'' article covers basic histology of the GI tract.
The ''[[Gastrointestinal pathology]]'' article covers basic histology of the GI tract.


==[[Immunohistochemistry]]==
===[[Immunohistochemistry]]===
*Normal small intestine is CK20 +ve... while adenocarcinoma of the small bowel may be CK20 -ve.<ref>{{cite journal |author=Chen ZM, Wang HL |title=Alteration of cytokeratin 7 and cytokeratin 20 expression profile is uniquely associated with tumorigenesis of primary adenocarcinoma of the small intestine |journal=Am. J. Surg. Pathol. |volume=28 |issue=10 |pages=1352–9 |year=2004 |month=October |pmid=15371952 |doi= |url=}}</ref>
*Normal small intestine is CK20 +ve... while adenocarcinoma of the small bowel may be CK20 -ve.<ref>{{cite journal |author=Chen ZM, Wang HL |title=Alteration of cytokeratin 7 and cytokeratin 20 expression profile is uniquely associated with tumorigenesis of primary adenocarcinoma of the small intestine |journal=Am. J. Surg. Pathol. |volume=28 |issue=10 |pages=1352–9 |year=2004 |month=October |pmid=15371952 |doi= |url=}}</ref>


=Clinical=
===Sign out===
==Small bowel obstruction==
<pre>
*Abbreviated ''SBO''.
Small Bowel, Biopsy:
===General===
- Small bowel mucosa within normal limits.
*Radiologic/clinical diagnosis
</pre>
 
<pre>
Terminal Ileum, Biopsy:
- Small bowel mucosa within normal limits.
</pre>
 
<pre>
Terminal Ileum, Biopsy:
- Small bowel mucosa with morphologically benign lymphoid aggregates, negative for significant pathology.
</pre>


The usual causes of bowel obstruction (large & small) are (mnemonic) ''SHAVING'':
====Roux-en-Y gastric bypass====
*Strictures (think [[IBD]]).
{{Main|Obese}}
*Hernias.
{{Main|Roux-en-Y gastric bypass}}
*Adhesions.
*[[Volvulus]].
*Intussusception.
*Neoplasia.
*Gallstone ileus.


The top three are:<ref>URL: [http://www.emedicine.com/EMERG/topic66.htm http://www.emedicine.com/EMERG/topic66.htm]. Accessed on: 19 April 2011.</ref><ref>TN 2007 GS21</ref>
====Block letters====
* Adhesions > hernias > neoplasms.
<pre>
SMALL BOWEL, BIOPSY:
- SMALL BOWEL MUCOSA WITHIN NORMAL LIMITS.
</pre>


In the context of bowel obstructions and IBD, pathologists often see resected [[stoma]]s (that were put in place emergently).  These specimens are usually fairly straight forward.
<pre>
TERMINAL ILEUM, BIOPSY:
- SMALL BOWEL MUCOSA WITHIN NORMAL LIMITS.
</pre>


<pre>
TERMINAL ILEUM, BIOPSY:
- SMALL BOWEL MUCOSA WITH MORPHOLOGICAL BENIGN LYMPHOID AGGREGATES, NO SIGNIFICANT PATHOLOGY.
</pre>


=The segments=
=The segments=
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==Ileum==
==Ileum==
*This is seen occasionally -- often in the context of IBD and more specifically [[Crohn's disease]].
*This is seen occasionally -- often in the context of [[IBD]] and more specifically [[Crohn's disease]].
*Crohn's disease (and [[ulcerative colitis]]) is discussed in the ''[[colon]]'' article.
**[[Crohn's disease]] and[[ulcerative colitis]] are discussed in their respective articles.


===Ileal nodular lymphoid hyperplasia===
=Specific diagnoses=
*[[AKA]] ''nodular lymphoid hyperplasia of the terminal ileum''.
==Ileitis==
====General====
:''Active ileitis'' and ''acute ileitis'' redirect here.
*An uncommon diagnosis.
:This deals with nonspecific ileitis.
*May be assoc. with hypogammaglobulinemia.<ref name=pmid8782302>{{cite journal |author=Yamaue H, Tanimura H, Ishimoto K, Morikawa Y, Kakudo K |title=Nodular lymphoid hyperplasia of the terminal ileum: report of a case and the findings of an immunological analysis |journal=Surg. Today |volume=26 |issue=6 |pages=431-4 |year=1996 |pmid=8782302 |doi= |url=}}</ref>
===General===
*Common.
 
===Microscopic===
Features:
*Intraepithelial [[neutrophil]]s.
 
DDx:
*[[Crohn's disease]].
*Infectious ileitis.
**[[Tuberculosis]].
*Benign ileum - may have focal intra-epithelial lymphocytes associated with lamina propria lymphoid nodules.
*[[NSAID enteropathy]].<ref name=pmid20532706>{{Cite journal | last1 = Dilauro | first1 = S. | last2 = Crum-Cianflone | first2 = NF. | title = Ileitis: when it is not Crohn's disease. | journal = Curr Gastroenterol Rep | volume = 12 | issue = 4 | pages = 249-58 | month = Aug | year = 2010 | doi = 10.1007/s11894-010-0112-5 | PMID = 20532706 }}</ref>
 
====Images====
<gallery>
Image: Mild ileitis -- very low mag.jpg | Ileitis - very low mag. (WC)
Image: Mild ileitis -- low mag.jpg | Ileitis - low mag. (WC)
Image: Mild ileitis -- intermed mag.jpg | Ileitis - intermed. mag. (WC)
Image: Mild ileitis -- high mag.jpg | Ileitis - high mag. (WC)
</gallery>


====Microscopic====
===Sign out===
features:
<pre>
*Prominent lymphoid follicles.
Terminal Ileum, Biopsy:
- Small bowel with moderate active inflammation, marked villous blunting, basal plasmacytosis
  and prominent eosinophils, see comment.
- NEGATIVE for granulomas.
- NEGATIVE for dysplasia.


===Multiple lymphomatous polyposis===
Comment:
*Abbreviated ''MLP''.
The inflammation is nonspecific; it could be due to infection, inflammatory bowel disease (especially Crohn's disease), ischemia, or therapy/drugs.  Clinical correlation is required.
*[[AKA]] ''lymphomatous polyposis''.
</pre>


====General====
==Small bowel obstruction==
*MLP is classically due to ''[[mantle cell lymphoma]]''.<ref name=pmid20206107>{{Cite journal  | last1 = Ruskoné-Fourmestraux | first1 = A. | last2 = Audouin | first2 = J. | title = Primary gastrointestinal tract mantle cell lymphoma as multiple lymphomatous polyposis. | journal = Best Pract Res Clin Gastroenterol | volume = 24 | issue = 1 | pages = 35-42 | month = Feb | year = 2010 | doi = 10.1016/j.bpg.2009.12.001 | PMID = 20206107 }}</ref>
*Abbreviated ''SBO''.
**May be due to other lymphomas, e.g. [[follicular lymphoma]].<ref>URL: [http://www.pathmax.com/gilymph.html http://www.pathmax.com/gilymph.html]. Accessed on: 1 April 2012.</ref>
{{Main|Small bowel obstruction}}


=Specific conditions=
==Small bowel neoplasms==
==Small bowel neoplasms==
*Adenocarcinoma - like colonic.
*Adenocarcinoma - like colonic.
*Adenosquamous carcinoma.
*[[Adenosquamous carcinoma]].
*[[Neuroendocrine tumour]].
*[[Neuroendocrine tumour]].
*[[GIST]].
*[[GIST]].
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**Classically have a ''peripheral lymphoid cuff''.<ref name=pmid15728600>{{cite journal |author=Levy AD, Quiles AM, Miettinen M, Sobin LH |title=Gastrointestinal schwannomas: CT features with clinicopathologic correlation |journal=AJR Am J Roentgenol |volume=184 |issue=3 |pages=797–802 |year=2005 |month=March |pmid=15728600 |doi= |url=http://www.ajronline.org/cgi/content/full/184/3/797}}</ref>
**Classically have a ''peripheral lymphoid cuff''.<ref name=pmid15728600>{{cite journal |author=Levy AD, Quiles AM, Miettinen M, Sobin LH |title=Gastrointestinal schwannomas: CT features with clinicopathologic correlation |journal=AJR Am J Roentgenol |volume=184 |issue=3 |pages=797–802 |year=2005 |month=March |pmid=15728600 |doi= |url=http://www.ajronline.org/cgi/content/full/184/3/797}}</ref>


==Small bowel diaphragm disease==
==Mechanical small bowel perforation==
*[[AKA]] ''diaphragm disease''.
:See ''[[mechanical bowel perforation]]''.
 
==Ileal nodular lymphoid hyperplasia==
*[[AKA]] ''nodular lymphoid hyperplasia of the terminal ileum''.
===General===
===General===
*Strictures associated with chronic [[NSAID]] use.<ref name=pmid1481311>{{cite journal |author=McCune KH, Allen D, Cranley B |title=Small bowel diaphragm disease--strictures associated with non-steroidal anti-inflammatory drugs |journal=Ulster Med J |volume=61 |issue=2 |pages=182–4 |year=1992 |month=October |pmid=1481311 |pmc=2448949 |doi= |url=}}</ref>
*An uncommon diagnosis.
*Usu. mid to distal ileum.
*May be associated with hypogammaglobulinemia.<ref name=pmid8782302>{{cite journal |author=Yamaue H, Tanimura H, Ishimoto K, Morikawa Y, Kakudo K |title=Nodular lymphoid hyperplasia of the terminal ileum: report of a case and the findings of an immunological analysis |journal=Surg. Today |volume=26 |issue=6 |pages=431-4 |year=1996 |pmid=8782302 |doi= |url=}}</ref>
 
===Gross===
*Mucosal nodularity.


===Microscopic===
===Microscopic===
Features:<ref name=pmid1481311/>
Features:
*Focal submucosal fibrosis.
*Lymphoid nodules +/- germinal centre formation.
**+/-Distortion of adjacent muscularis propria.
 
**+/-Adjacent mucosal erosions/granulation tissue.
Note:
*Tingible body macrophages suggest an aggregate is benign.


DDx:
DDx:
*[[Crohn's disease]].
*[[MALT lymphoma]].
*[[Mantle cell lymphoma]].
*Other lymphomas.
 
===IHC===
*[[CD20]] and CD3 - mixed population of lymphocytes.
*[[CD23]] - follicular dendritic cells.
*Cyclin D1 -ve.
 
Note:
*IHC should be used if there is:
**Clinical suspicion.
**Histologic suspicion - either:
***Sheets of lymphocytes without apparent germinal centre formation in a larger area (~ 2 mm).
***[[Lymphoepithelial lesion]]s.
 
===Sign out===
<pre>
TERMINAL ILEUM, BIOPSY:
- SMALL BOWEL MUCOSA WITH LYMPHOID NODULES WITH GERMINAL CENTRE
  FORMATION -- NO SIGNIFICANT PATHOLOGY.
- NEGATIVE FOR ILEITIS.
</pre>
 
<pre>
TERMINAL ILEUM, BIOPSY:
- SMALL BOWEL MUCOSA WITH LYMPHOID HYPERPLASIA -- NO SIGNIFICANT PATHOLOGY.
</pre>


==Meckel diverticulum==
====Micro====
===General===
The sections show small bowel mucosa with lymphoid hyperplasia.
*Most common congenital anomaly of the gastrointestinal tract.<ref name=pmid15026601>{{Cite journal  | last1 = Levy | first1 = AD. | last2 = Hobbs | first2 = CM. | title = From the archives of the AFIP. Meckel diverticulum: radiologic features with pathologic Correlation. | journal = Radiographics | volume = 24 | issue = 2 | pages = 565-87 | month =  | year =  | doi = 10.1148/rg.242035187 | PMID = 15026601 }}</ref>
**Remnant of the ''omphalomesenteric duct'' - a connection of the yolk sac and midgut.


The rule of 2s:
Immunostains for CD3 and CD20 show a mixed population of lymphocytes. A CD23 immunostain shows follicular dendritic cell networks. A cyclin D1 immunostain is negative.
*2 feet from the terminal ileum
*2% of the population
*2% symptomatic.
*2 inches long.
*2 year old.
*2 types of epithelium - gastric and pancreatic.


Main clinical DDx of a symptomatic Meckel diverticulum:
=====Alternate=====
*[[Appendicitis]].
Immunostains for CD3 and CD20 show a mixed population of lymphocytes, with CD20 cells predominating. A cyclin D1 immunostain is negative. A CD23 immunostain shows follicular dendritic cell networks.


===Gross===
==Multiple lymphomatous polyposis==
*Antimesenteric attachement, i.e. a ''Meckel's diverticulum'' hangs off the side opposite of the mesentery.  
*Abbreviated ''MLP''.
*[[AKA]] ''lymphomatous polyposis''.


Image:
===General===
*[http://commons.wikimedia.org/wiki/File:Meckel%27s_Diverticulum_AFIP.jpg Meckel diverticulum - (AFIP/WC)].
*MLP is classically due to ''[[mantle cell lymphoma]]''.<ref name=pmid20206107>{{Cite journal  | last1 = Ruskoné-Fourmestraux | first1 = A. | last2 = Audouin | first2 = J. | title = Primary gastrointestinal tract mantle cell lymphoma as multiple lymphomatous polyposis. | journal = Best Pract Res Clin Gastroenterol | volume = 24 | issue = 1 | pages = 35-42 | month = Feb | year = 2010 | doi = 10.1016/j.bpg.2009.12.001 | PMID = 20206107 }}</ref>
**May be due to other lymphomas, e.g. [[follicular lymphoma]].<ref>URL: [http://www.pathmax.com/gilymph.html http://www.pathmax.com/gilymph.html]. Accessed on: 1 April 2012.</ref>


===Microscopic===
===Microscopic===
Features:<ref name=pmid15026601/>
Features:
*Small bowel mucosa.
*Lymphoid nodules consisting of (small) atypical lymphocytes with an abnormal architecture.
*+/-Gastric mucosa:
**Foveolar epithelium: champagne flute-like columnar epithelium.
**Oxyntic mucosa: parietal cells (pink) and chief cells (purple).
*+/-Pancreatic epithelium:
**Pancreatic acini.


Images:
===IHC===
*[http://radiographics.rsna.org/content/24/2/565/F12.expansion.html Gastric foveolar epithelium in a MD (radiographics.rsna.org)].
See ''[[small cell lymphomas]]''.
*[http://radiographics.rsna.org/content/24/2/565/F15.expansion.html Gastric glands in a MD (radiographics.rsna.org)].
*[http://radiographics.rsna.org/content/24/2/565.long Pancreatic glands in a MD (radiographics.rsna.org)].


==Ischemic enteritis==
==Small bowel diaphragm disease==
*[[AKA]] ''diaphragm disease''.
===General===
===General===
*Typically elderly and due to [[atherosclerosis]].
*Strictures associated with chronic [[NSAID]] use.<ref name=pmid1481311>{{cite journal |author=McCune KH, Allen D, Cranley B |title=Small bowel diaphragm disease--strictures associated with non-steroidal anti-inflammatory drugs |journal=Ulster Med J |volume=61 |issue=2 |pages=182–4 |year=1992 |month=October |pmid=1481311 |pmc=2448949 |doi= |url=}}</ref>
*Rare.
*Usu. mid to distal ileum.
*High mortality.<ref name=pmid18616124>{{Cite journal | last1 = Nakase | first1 = H. | title = [Ischemic enteritis]. | journal = Nihon Rinsho | volume = 66 | issue = 7 | pages = 1330-4 | month = Jul | year = 2008 | doi = | PMID = 18616124 }}</ref>
*May occur together with ischemia of the colon, i.e. ''[[ischemic colitis]]'', in which case it is known as ''ischemic enterocolitis''.
 
Etiologies:
*[[Atherosclerosis]].
*[[Vasculitis]].
*Embolism.
*Thrombosis.


===Microscopic===
===Microscopic===
Features:
Features:<ref name=pmid1481311/>
*See ''[[ischemic colitis]]''.
*Focal submucosal fibrosis.
**+/-Distortion of adjacent muscularis propria.
**+/-Adjacent mucosal erosions/granulation tissue.


DDx:
DDx:
*Infection.
*Cryptogenic multifocal ulcerous stenosing enteritis.<ref>{{Cite journal  | last1 = Chung | first1 = SH. | last2 = Jo | first2 = Y. | last3 = Ryu | first3 = SR. | last4 = Ahn | first4 = SB. | last5 = Son | first5 = BK. | last6 = Kim | first6 = SH. | last7 = Park | first7 = YS. | last8 = Hong | first8 = YO. | title = Diaphragm disease compared with cryptogenic multifocal ulcerous stenosing enteritis. | journal = World J Gastroenterol | volume = 17 | issue = 23 | pages = 2873-6 | month = Jun | year = 2011 | doi = 10.3748/wjg.v17.i23.2873 | PMID = 21734797 }}</ref> (???)
*[[Crohn's disease]].
*[[Crohn's disease]].
*Radiation.
 
*Drugs/toxins.
==Meckel diverticulum==
{{Main|Meckel diverticulum}}
 
==Ischemic enteritis==
{{Main|Ischemic enteritis}}


=Weird stuff=
=Weird stuff=
==Autoimmune enteropathy==
==Autoimmune enteropathy==
*Abbreviated as ''AIE''.
*Abbreviated as ''AIE''.
===General===
{{Main|Autoimmune enteropathy}}
*Considered a pediatric disease.
*Super rare in adults - there are only ~11 reported cases in the literature.<ref name=pmid17683994>{{Cite journal  | last1 = Akram | first1 = S. | last2 = Murray | first2 = JA. | last3 = Pardi | first3 = DS. | last4 = Alexander | first4 = GL. | last5 = Schaffner | first5 = JA. | last6 = Russo | first6 = PA. | last7 = Abraham | first7 = SC. | title = Adult autoimmune enteropathy: Mayo Clinic Rochester experience. | journal = Clin Gastroenterol Hepatol | volume = 5 | issue = 11 | pages = 1282-90; quiz 1245 | month = Nov | year = 2007 | doi = 10.1016/j.cgh.2007.05.013 | PMID = 17683994 | PMC = 2128725 | URL = http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2128725/ }}</ref>
 
Diagnosis is clinico-pathologic:<ref name=pmid17683994/>
#Intact immune system.
#Autoantibodies.
#*Anti-enterocyte antibody.
#*Anti-goblet antibody.
#Lack of response to gluten-free diet.
 
===Microscopic===
Features:<ref name=pmid17683994/>
*+/-Loss of goblet cells.
*+/-Loss of paneth cells.
*Villous blunting.
 
DDx:
*[[Celiac disease]].


=See also=
=See also=
Michael
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