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.

Small bowel mucosa. H&E stain.

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.

Length

  • Normal length of small bowel = 3-8 metres.[1]

"Short":

  • Less than 200 cm = short bowel syndrome.[2][3]
    • Less than 100 cm usu. requires parenteral nutrition.[4]

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.[5]

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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 morphologically benign lymphoid aggregates, negative for significant pathology.

Roux-en-Y gastric bypass

Small Bowel, Excision During Roux-en-Y Gastric Bypass:
- Small bowel wall within normal limits.

Block letters

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.
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.

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:[6][7]

  • 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

Mechanical small bowel perforation

See mechanical bowel perforation.

Ileal nodular lymphoid hyperplasia

  • AKA nodular lymphoid hyperplasia of the terminal ileum.

General

  • An uncommon diagnosis.
  • May be associated with hypogammaglobulinemia.[9]

Gross

  • Mucosal nodularity.

Microscopic

Features:

  • Lymphoid nodules +/- germinal centre formation.

Note:

  • Tingible body macrophages suggest an aggregate is benign.

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:

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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 and CD20 show a mixed population of lymphocytes. A CD23 immunostain shows follicular dendritic cell networks. A cyclin D1 immunostain is negative.

Alternate

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.

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.[12]
  • Usu. mid to distal ileum.

Microscopic

Features:[12]

  • 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.[14]
    • 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:[14]

  • 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.[15]
  • 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.
Main article: Autoimmune enteropathy

See also

References

  1. ↑ Nightingale, JM.. "Management of patients with a short bowel.". Nutrition 15 (7-8): 633-7. PMID 10422101.
  2. ↑ Donohoe, CL.; Reynolds, JV. (Oct 2010). "Short bowel syndrome.". Surgeon 8 (5): 270-9. doi:10.1016/j.surge.2010.06.004. PMID 20709285.
  3. ↑ Matarese, LE.; O'Keefe, SJ.; Kandil, HM.; Bond, G.; Costa, G.; Abu-Elmagd, K. (Oct 2005). "Short bowel syndrome: clinical guidelines for nutrition management.". Nutr Clin Pract 20 (5): 493-502. PMID 16207689.
  4. ↑ Sundaram, A.; Koutkia, P.; Apovian, CM. (Mar 2002). "Nutritional management of short bowel syndrome in adults.". J Clin Gastroenterol 34 (3): 207-20. PMID 11873098.
  5. ↑ 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.
  6. ↑ URL: http://www.emedicine.com/EMERG/topic66.htm. Accessed on: 19 April 2011.
  7. ↑ Greenwald, J.; Heng, M. (2007). Toronto Notes for Medical Students 2007 (2007 ed.). The Toronto Notes Inc. for Medical Students Inc.. pp. GS21. ISBN 978-0968592878.
  8. ↑ 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.
  9. ↑ 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.
  10. ↑ 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.
  11. ↑ URL: http://www.pathmax.com/gilymph.html. Accessed on: 1 April 2012.
  12. ↑ 12.0 12.1 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/.
  13. ↑ Chung, SH.; Jo, Y.; Ryu, SR.; Ahn, SB.; Son, BK.; Kim, SH.; Park, YS.; Hong, YO. (Jun 2011). "Diaphragm disease compared with cryptogenic multifocal ulcerous stenosing enteritis.". World J Gastroenterol 17 (23): 2873-6. doi:10.3748/wjg.v17.i23.2873. PMID 21734797.
  14. ↑ 14.0 14.1 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.
  15. ↑ Nakase, H. (Jul 2008). "[Ischemic enteritis].". Nihon Rinsho 66 (7): 1330-4. PMID 18616124.
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