Small intestine

The small bowel is a relatively well-behaved piece of machinery from the perspective of pathology. It is uncommonly affected by malignancies.

Anatomy

Consists of three segments:

• Duodenum (which 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.

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:

• 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.

Immunohistochemistry

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

Histology

Main article: Gastrointestinal pathology

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

• 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.

Nodular lymphoid hyperplasia

General

• An uncommon diagnosis
• Prominent lymphoid follicles
• May be assoc. with hypogammaglobulinemia.

Small bowel neoplasms

• Adenocarcinoma - like colonic.
• Adenosquamous carcinoma.
• Neuroendocine tumour.
• GIST.
• Schwannoma.
  • Classically have a peripheral lymphoid cuff.

See also

• Stomach.
• Gastrointestinal pathology.
• Colon.