Small intestine

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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 small bowel

  • AKA normal small intestine.

Anatomy

Consists of three segments:

  • Duodenum - can be divided into four parts.
  • Jejunum.
  • Ileum.

The later two parts keep general surgeons awake at night (quite literally) 'cause they get obstructed and need urgent operations.

Histology

Main article: Gastrointestinal pathology

The Gastrointestinal pathology article covers basic histology of the GI tract.

Immunohistochemistry

  • Normal small intestine is CK20 +ve... while adenocarcinoma of the small bowel may be CK20 -ve.[1]

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SMALL BOWEL, BIOPSY:
- SMALL BOWEL MUCOSA WITHIN NORMAL LIMITS.

TERMINAL ILEUM, BIOPSY:
- SMALL BOWEL MUCOSA WITHIN NORMAL LIMITS.

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

The segments

Duodenum

Main article: Duodenum

The duodenum is often biopsied by gastroenterologists.

Common reasons for biopsy:

  • Suspected giardia.
  • Suspected celiac sprue.
  • Is this cancer?
  • Looks normal... want to dot the i's and cross the t's.

Jejunum

  • Uncommonly seen by pathologists.
  • May be seen in the context of a resection done for a bowel obstruction.

Ileum

Specific conditions

Small bowel obstruction

  • Abbreviated SBO.

General

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:[2][3]

  • Adhesions > hernias > neoplasms.

In the context of bowel obstructions and IBD, pathologists often see resected stomas (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

Features:

  • +/-Adhesions (serosal).
    • 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:

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SMALL BOWEL, RESECTION:
- SMALL BOWEL WITH FIBROUS ADHESIONS (EXTENSIVE) ASSOCIATED WITH FOCAL LUMINAL
  NARROWING.
- NEGATIVE FOR DYSPLASIA AND NEGATIVE FOR MALIGNANCY.

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

Ischemic changes

SMALL BOWEL, RESECTION:
- SMALL BOWEL WITH ISCHEMIC CHANGES, FIBROUS ADHESIONS, FOCAL SEROSITIS AND MURAL
  MICROABSCESS FORMATION.
- NO SIGNIFICANT VASCULAR PATHOLOGY APPARENT.
- NEGATIVE FOR MALIGNANCY.

Small bowel neoplasms

Ileal nodular lymphoid hyperplasia

  • AKA nodular lymphoid hyperplasia of the terminal ileum.

General

  • An uncommon diagnosis.
  • May be associated with hypogammaglobulinemia.[5]

Gross

  • Mucosal nodularity.

Microscopic

Features:

  • Lymphoid nodules +/- germinal centre formation.

DDx:

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 lesions.

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TERMINAL ILEUM, BIOPSY:
- SMALL BOWEL MUCOSA WITH LYMPHOID NODULES WITH GERMINAL CENTRE
  FORMATION -- NO SIGNIFICANT PATHOLOGY.
- NEGATIVE FOR ILEITIS.

TERMINAL ILEUM, BIOPSY:
- SMALL BOWEL MUCOSA WITH LYMPHOID HYPERPLASIA -- NO SIGNIFICANT PATHOLOGY.

Micro

The sections show small bowel mucosa with lymphoid hyperplasia.

Immunostains for CD3, CD20 show a mixed population of lymphocytes. CD23 show follicular dendritic cells. Cyclin D1 is negative.

Multiple lymphomatous polyposis

  • Abbreviated MLP.
  • AKA lymphomatous polyposis.

General

Microscopic

Features:

  • Lymphoid nodules consisting of (small) atypical lymphocytes with an abnormal architecture.

IHC

See small cell lymphomas.

Small bowel diaphragm disease

  • AKA diaphragm disease.

General

  • Strictures associated with chronic NSAID use.[8]
  • Usu. mid to distal ileum.

Microscopic

Features:[8]

  • Focal submucosal fibrosis.
    • +/-Distortion of adjacent muscularis propria.
    • +/-Adjacent mucosal erosions/granulation tissue.

DDx:

Meckel diverticulum

General

  • Most common congenital anomaly of the gastrointestinal tract.[9]
    • 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:

Gross

  • Antimesenteric attachement, i.e. a Meckel's diverticulum hangs off the side opposite of the mesentery.

Image:

Microscopic

Features:[9]

  • 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:

Ischemic enteritis

General

  • Typically elderly and due to atherosclerosis.
  • Rare.
  • High mortality.[10]
  • May occur together with ischemia of the colon, i.e. ischemic colitis, in which case it is known as ischemic enterocolitis.

Etiologies:

Microscopic

Features:

DDx:

Weird stuff

Autoimmune enteropathy

  • Abbreviated as AIE.

General

  • Considered a pediatric disease.
  • Super rare in adults - there are only ~11 reported cases in the literature.[11]

Diagnosis is clinico-pathologic:[11]

  1. Intact immune system.
  2. Autoantibodies.
    • Anti-enterocyte antibody.
    • Anti-goblet antibody.
  3. Lack of response to gluten-free diet.

Microscopic

Features:[11]

  • +/-Loss of goblet cells.
  • +/-Loss of paneth cells.
  • Villous blunting.

DDx:

See also

References

  1. ↑ Chen ZM, Wang HL (October 2004). "Alteration of cytokeratin 7 and cytokeratin 20 expression profile is uniquely associated with tumorigenesis of primary adenocarcinoma of the small intestine". Am. J. Surg. Pathol. 28 (10): 1352–9. PMID 15371952.
  2. ↑ URL: http://www.emedicine.com/EMERG/topic66.htm. Accessed on: 19 April 2011.
  3. ↑ TN 2007 GS21
  4. ↑ Levy AD, Quiles AM, Miettinen M, Sobin LH (March 2005). "Gastrointestinal schwannomas: CT features with clinicopathologic correlation". AJR Am J Roentgenol 184 (3): 797–802. PMID 15728600. http://www.ajronline.org/cgi/content/full/184/3/797.
  5. ↑ Yamaue H, Tanimura H, Ishimoto K, Morikawa Y, Kakudo K (1996). "Nodular lymphoid hyperplasia of the terminal ileum: report of a case and the findings of an immunological analysis". Surg. Today 26 (6): 431-4. PMID 8782302.
  6. ↑ Ruskoné-Fourmestraux, A.; Audouin, J. (Feb 2010). "Primary gastrointestinal tract mantle cell lymphoma as multiple lymphomatous polyposis.". Best Pract Res Clin Gastroenterol 24 (1): 35-42. doi:10.1016/j.bpg.2009.12.001. PMID 20206107.
  7. ↑ URL: http://www.pathmax.com/gilymph.html. Accessed on: 1 April 2012.
  8. ↑ 8.0 8.1 McCune KH, Allen D, Cranley B (October 1992). "Small bowel diaphragm disease--strictures associated with non-steroidal anti-inflammatory drugs". Ulster Med J 61 (2): 182–4. PMC 2448949. PMID 1481311. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2448949/.
  9. ↑ 9.0 9.1 Levy, AD.; Hobbs, CM.. "From the archives of the AFIP. Meckel diverticulum: radiologic features with pathologic Correlation.". Radiographics 24 (2): 565-87. doi:10.1148/rg.242035187. PMID 15026601.
  10. ↑ Nakase, H. (Jul 2008). "[Ischemic enteritis].". Nihon Rinsho 66 (7): 1330-4. PMID 18616124.
  11. ↑ 11.0 11.1 11.2 Akram, S.; Murray, JA.; Pardi, DS.; Alexander, GL.; Schaffner, JA.; Russo, PA.; Abraham, SC. (Nov 2007). "Adult autoimmune enteropathy: Mayo Clinic Rochester experience.". Clin Gastroenterol Hepatol 5 (11): 1282-90; quiz 1245. doi:10.1016/j.cgh.2007.05.013. PMC 2128725. PMID 17683994. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2128725/.
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