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

Main article: Obese
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 diagnoses

Ileitis

Active ileitis and acute ileitis redirect here.
This deals with nonspecific ileitis.

General

  • Common.

Microscopic

Features:

DDx:

  • Crohn's disease.
  • Infectious ileitis.
  • Benign ileum - may have focal intra-epithelial lymphocytes associated with lamina propria lymphoid nodules.

Images

  • Ileitis - very low mag. (WC)

  • Ileitis - low mag. (WC)

  • Ileitis - intermed. mag. (WC)

  • Ileitis - high mag. (WC)

Small bowel obstruction

  • Abbreviated SBO.
Main article: Small bowel obstruction

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.[7]

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.[10]
  • Usu. mid to distal ileum.

Microscopic

Features:[10]

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

DDx:

Meckel diverticulum

Main article: Meckel diverticulum

Ischemic enteritis

General

  • Typically elderly and due to atherosclerosis.
  • Rare.
  • High mortality.[12]
  • 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. ↑ 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.
  7. ↑ 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.
  8. ↑ 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.
  9. ↑ URL: http://www.pathmax.com/gilymph.html. Accessed on: 1 April 2012.
  10. ↑ 10.0 10.1 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/.
  11. ↑ 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.
  12. ↑ Nakase, H. (Jul 2008). "[Ischemic enteritis].". Nihon Rinsho 66 (7): 1330-4. PMID 18616124.
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