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Small intestine (view source)

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====Roux-en-Y gastric bypass====
====Roux-en-Y gastric bypass====
<pre>
{{Main|Obese}}
Small Bowel, Excision During Roux-en-Y Gastric Bypass:
{{Main|Roux-en-Y gastric bypass}}
- Small bowel wall within normal limits.
</pre>


====Block letters====
====Block letters====
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**[[Crohn's disease]] and[[ulcerative colitis]] are discussed in their respective articles.
**[[Crohn's disease]] and[[ulcerative colitis]] are discussed in their respective articles.


=Specific conditions=
=Specific diagnoses=
==Small bowel obstruction==
==Ileitis==
*Abbreviated ''SBO''.
:''Active ileitis'' and ''acute ileitis'' redirect here.
:This section gives an overview of SBOs. Its primary focus is benign causes of SBO that have nonspecific pathologic findings. Specific causes definitively identified by pathology, e.g. [[adenocarcinoma]], are dealt with separately.
:This deals with nonspecific ileitis.
===General===
===General===
*Radiologic/[[clinical diagnosis]].
*Common.
 
The usual causes of bowel obstruction (large & small) are (mnemonic) ''SHAVING'':
*Strictures (think [[IBD]]).
*Hernias.
*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>{{Ref TN2007 |GS21}}</ref>
* Adhesions > hernias > neoplasms.
 
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.
 
===Radiology===
*Air-fluid levels.
 
===Gross===
*+/-Adhesions.
*+/-Bowel contorted.
*+/-Luminal narrowing +/-proximal dilation.
*+/-Serosal exudate.
**Suggestive of perforation.


===Microscopic===
===Microscopic===
Features:
Features:
*+/-Adhesions (serosal).
*Intraepithelial [[neutrophil]]s.
**Dense fibrous tissue replaces the adipose tissue.
**+/-Increased vascularity.
*+/-Submucosal fibrosis.
*+/-[[Serositis]] - seen in small bowel perforation.
*+/-Foreign body-type granuloma - due to previous surgical intervention.


DDx:
DDx:
*Small bowel [[adenocarcinoma]] - most important differential diagnosis.
*[[Crohn's disease]].
*Metastatic adenocarcinoma - classically on the serosal aspect.
*Infectious ileitis.
*[[Signet ring cell carcinoma]].
**[[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>


===Sign out===
===Sign out===
<pre>
<pre>
SMALL BOWEL, RESECTION:
Terminal Ileum, Biopsy:
- SMALL BOWEL WITH FIBROUS ADHESIONS (EXTENSIVE) ASSOCIATED WITH FOCAL LUMINAL
- Small bowel with moderate active inflammation, marked villous blunting, basal plasmacytosis
   NARROWING.
   and prominent eosinophils, see comment.
- NEGATIVE FOR DYSPLASIA AND NEGATIVE FOR MALIGNANCY.
- NEGATIVE for granulomas.
</pre>
- NEGATIVE for dysplasia.


<pre>
Comment:
SMALL BOWEL, RESECTION:
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.
- SMALL BOWEL WITH FIBROUS ADHESIONS (EXTENSIVE), FOCAL LUMINAL NARROWING AND A
  FOREIGN BODY-TYPE GRANULOMA.
- NEGATIVE FOR DYSPLASIA AND NEGATIVE FOR MALIGNANCY.
</pre>
</pre>


====Ischemic changes====
==Small bowel obstruction==
<pre>
*Abbreviated ''SBO''.
SMALL BOWEL, RESECTION:
{{Main|Small bowel obstruction}}
- SMALL BOWEL WITH ISCHEMIC CHANGES, FIBROUS ADHESIONS, FOCAL SEROSITIS AND MURAL
  MICROABSCESS FORMATION.
- NO SIGNIFICANT VASCULAR PATHOLOGY APPARENT.
- NEGATIVE FOR MALIGNANCY.
</pre>


==Small bowel neoplasms==
==Small bowel neoplasms==
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===IHC===
===IHC===
*CD20 and CD3 - mixed population of lymphocytes.
*[[CD20]] and CD3 - mixed population of lymphocytes.
*[[CD23]] - follicular dendritic cells.
*[[CD23]] - follicular dendritic cells.
*Cyclin D1 -ve.
*Cyclin D1 -ve.
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==Meckel diverticulum==
==Meckel diverticulum==
===General===
{{Main|Meckel diverticulum}}
*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:
*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:
*[[Appendicitis]].
 
===Gross===
*Antimesenteric attachement, i.e. a ''Meckel's diverticulum'' hangs off the side opposite of the mesentery.
 
Image:
*[http://commons.wikimedia.org/wiki/File:Meckel%27s_Diverticulum_AFIP.jpg Meckel diverticulum - (AFIP/WC)].
 
===Microscopic===
Features:<ref name=pmid15026601/>
*Small bowel mucosa.
*+/-Gastric mucosa:
**Foveolar epithelium: champagne flute-like columnar epithelium.
**Oxyntic mucosa: parietal cells (pink) and chief cells (purple).
*+/-Pancreatic epithelium:
**Pancreatic acini.
 
Images:
*[http://radiographics.rsna.org/content/24/2/565/F12.expansion.html Gastric foveolar epithelium in a MD (radiographics.rsna.org)].
*[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==
==Ischemic enteritis==
===General===
{{Main|Ischemic enteritis}}
*Typically elderly and due to [[atherosclerosis]].
*Rare.
*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===
Features:
*See ''[[ischemic colitis]]''.
 
DDx:
*Infection.
*[[Crohn's disease]].
*[[Radiation changes]].
*Drugs/toxins.


=Weird stuff=
=Weird stuff=
Michael
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