Small Bowel

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Small Bowel

• Vithal Vernenkar, D.O.
• St. Barnabas Hospital
• Dept. Surgery

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Structural and Functional Anatomy

• 280cm long
• Jejunum begins at LOT, no clear demarcation to
  ileum
• Jejunum has long vas recta, large plicae, thick
  walls, transparent mesentery
• Ileum has short vasa, small plicae, thin walls,
  fat in the mesentery.

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Structural and Functional Anatomy

• Mesentery attaches the small intestine to the
  posterior abdominal wall.
• Contains nerves, blood vessels, lymphatics, lymph
  nodes, and fat.

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Structural and Functional Anatomy

• Lymph tissues known as Peyers patches are
  abundant.
• SMA supplies the midgut structures (duodenum
  distal to the ampulla, pancreas, small intestine,
  ascending and transverse colon.)

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Histology

• Four layers
• Mucosa turns over every 3-7 days
• Submucosa contains vessels, nerves, lymph,
  Meissners plexus. This layer provides the major
  strength when suturing
• Muscularis outer long layer, inner circ layer
• Adventitia is a layer of visceral peritoneum

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Physiology (CHO)

• Daily CHO load is 350g of starch, lactose,
  sucrose
• Initial enzyme digestion is by pancreatic and
  salivary amylase
• CHO broken down to monosaccharides by microvilli

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Physiology (Protein)

• The jejunum is responsible for 80-90 of protein
  absorption
• Proteins are converted by acid and pepsin from
  stomach to polypeptides
• Acid is neutralized and pepsin is inactivated as
  chyme enters the duodenum

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Physiology (Protein)

• Trypsinogen is activated from pancreas to trypsin
  by enterokinase in the duodenum
• Trypsin activates chymotrypsin and elastase,
  further digesting polypeps
• Amino acids and dipeptides are absorbed

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Physiology (Fats)

• Emulsification begins in the stomach
• Fat enters the duodenum, where pancreatic and
  biliary secretions mix
• Lipase breaks down fats in to monoglycerides,
  which are absorbed by diffusion

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Physiology (Fats)

• In epithelial cells, triglycerides are
  resynthesized, chylomicrons are formed and enter
  the lymphatic system thru small lacteals
• Bile salts are reabsorbed in the ileum
• Most of the excreted fat comes from desquamated
  cells and bacteria

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Physiology (H2O, Lytes, Minerals, Vitamins)

• Iron is absorbed mainly in the duodenum
• Most minerals and water soluble vitamins absorbed
  in jejunum
• B12 is absorbed only in terminal ileum
• Of the 5-10 liters entering the small bowel, only
  500cc enter the colon.

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Consequences of Small Bowel Resection

• Frequently improve with time
• Can often be adequately treated with dietary
  changes and antiperistaltic medications

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Consequences of Small Bowel Resection

• Diarrhea can result from water overload in colon
• Malabsorption (Steatorrhea)
• Irritation of colonic mucosa by bile salts that
  haven't been reabsorbed by terminal ileum

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Consequences of Small Bowel Resection

• Bacterial overgrowth in the small intestine may
  occur after resection of the ileocecal valve
  (ileal brake) and can lead to deconjugation of
  bile salts in the small intestine
• Alterations in H2O and lytes absorption lead to
  net secretion instead of absorption.
• Fermentation of CHO leads to gas production
• These lead to bloating, diarrhea, and steatorrhea

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Consequences of Small Bowel Resection

• Nutritional deficiencies- B12 supplementation
  should be provided after resection terminal ileum
• Cholelithiasis may result from bile acid
  malabsorption after ileal resection
• Renal stones- fat malabsorption leads to calcium
  binding of fat in the colon. This leaves oxalate
  free to form water soluble absorbable salts
  excreted in the urine.

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Short Bowel Syndrome

• Inadequate length of intestine
• Generally occurs when more than 50 of the small
  intestine is resected or if less than 100cm
  remains.
• Leads to diarrhea, steatorrhea, weight loss,
  nutritional deficiencies, hypergastrinemia
• If the terminal ileum and valve are retained, 70
  can be resected.

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Motility

• Is inhibited by epinephrine
• Is increased by acetylcholine
• Migrating myoelectric complex (MMC) results in
  cyclic contractions occurring every three minutes
  during fasting
• These contractions are thought to clean the
  intestine, prevent overgrowth, regulated by
  motilin

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Motility

• The order of recovery of bowel function after
  surgery is
• Small bowel
• Colon
• Stomach

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Crohns Disease

• Chronic, transmural, inflammatory process
  primarily affecting young individuals
• Also known as regional enteritis, terminal
  ileitis, and granulomatous ileocolitis
• Incurable condition requiring ongoing medical
  management and frequent surgical interventions
• Long term pain and disability

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Frequency

• 5.3 cases per 100,000, incidence increasing in
  adults and children
• Males and females equally affected
• Peak age of onset is between 2nd and fourth
  decades, but 5 of cases under 5y

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Frequency

• More common in Ashkenazi Jews, white populations
• Positive family history in 10-15, suggesting a
  genetic predisposition
• Relative risk of first degree relatives of these
  patients developing the disease is 10-21 times
  greater than general population

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Etiology

• Unknown, but many hypotheses
• Likely multifactorial, involving an infectious
  agent, environmental exposure activating an
  immune response in a genetically susceptible host

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Etiology

• The first gene locus linked to Crohns was the
  IBD1 gene on Chr 16
• Bacterial agents have long been thought to be
  involved in the pathogenesis of the disease
  although none identified as of yet.

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Etiology

• Environmental factors such as smoking, second
  hand smoke have been linked to the development of
  Crohns
• HLA-DR2 and DRB1 associated with UC not Crohns

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Pathology

• Characteristically progresses in a discontinuous
  manner with affected bowel interspersed with
  normal bowel
• Mouth to anus

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Pathology

• Most common site terminal ileum (40), colon only
  (35), small bowel only (20), perianal (5).
  Appendix often involved. Rectum frequently spared
• Anal involvement may be characterized by fissures
  (most common), abscesses,or fistulae. Most are
  off midline, not the usual posterior midline.

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Pathology

• Endoscopically appears as patchy areas of
  inflammation separated by uninvolved bowel
  Skip. The earliest lesions are apthous ulcers,
  tiny erosions that typically occur over lymphoid
  follicles
• Progress to lineal ulcers, which cross over
  transverse folds causing the cobblestone
  appearance

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Ulcers
29
Ulcers
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Cobblestone
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Pathology

• Grossly, surgical specimens are rigid, thickened
  as a result of chronic inflammation and fibrosis
  during healing periods
• Mesentery is thickened and shortened, may
  surround the bowel creeping fat

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Pathology

• Because of the transmural nature of the disease,
  fistulous connections can occur to other bowel or
  organs.
• Non-caseating granulomas are found in lamina
  propria or submucosa in 50 of patients
• Fibrosis may lead to strictures

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Clinical Features

• Intestinal manifestations
• Diarrhea
• Pain
• Anorexia
• Nausea, weight loss
• Perirectal disease
• Bleeding is uncommon in comparison to UC

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Clinical Features

• Extraintestinal manifestations
• Arthritis
• Erythema nodosum, multiforme
• Pyoderma gangrenosum
• Sclerosing cholangitis, cholelithiasis
• Renal calculi
• Endocrine disorders (growth, amenorrhea), ocular
  disease

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Diagnosis

• Combination of laboratory, radiological,
  pathologic examinations
• Differential includes bacterial enteritis, viral
  enteritis, ulcerative colitis, among others.
• Labs may show anemia, malnutrition, increased ESR
• B12 anemia, iron deficiency, folic acid
  deficiency
• Deficiencies in copper, selenium, zinc common

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Work-up

• Colonoscopy
• UGI series with small bowel follow thru
• CT scan
• Barium enema
• Fistulogram
• Despite work-up, 10 will have indeterminate
  colitis, with features of both Crohns and UC

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Complications of Crohns

• Fistula (29)
• Pelvic abscess (20)
• Obstruction (30-50)
• Hemorrhage (2)
• Cancer (1)
• Perforation (1)
• Ureteral obstruction (1)

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Medical Management

• Aminosalicylates often 1st line, include
  sulfasalazine(old), mesalamine(Asacol, Pentasa),
  olsalazine, balsalazide
• The newer meds lack the sulfapyridine carrier, so
  better tolerated. Also come in enema form for
  colon symptoms
• 5-ASA blocks prostaglandin release, decreases
  inflammation

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Medical Management

• Corticosteroids for treating acuter disease, not
  long term or for achieving remission.
• Topical steroids used in colitis, as enema,
  without the side effects of systemic.

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Medical Management

• Flagyl most commonly used antibiotic
• Can heal perianal fistulas caused by Crohns to
  completion
• Cipro is the most common alternative

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Medical Management

• Immunosupressants such as Azathioprine and
  6-mercaptopurine used, especially to reduce time
  on steroids, effective in maintenance therapy
• Cyclosporine, oral treats active disease, used as
  bridge therapy until the above two start working,
  effects go on after stopping drugs for months

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Medical Management

• Biologic therapies against TNF-alpha
  (inflammatory cytokine)
• FDA approved infliximab (Remicade), an antibody
  that targets TNF-alpha
• Used for active disease, fistula

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Surgical Therapy

• Reserved for complications of the disease, and
  failure of medical management
• Most patients will require surgery during their
  lifetime
• Within 20y of the onset of their symptoms, 75
  require surgery, many multiple resections, so
  attempts to conserve bowel are a must to avoid
  SBS
• No surgical cure

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Surgical Therapy

• An alternative to bowel resection is
  stricuroplasty
• In cases of long strictures (12cm), or multiple
  strictures in close proximity, resection with
  primary anastamosis is required.
• Anastomotic leak around 9
• Recurrence is 2