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*Medicine: Cellular Pathology > Gastrointestinal pathology (2) > Flashcards

Gastrointestinal pathology (2) Flashcards

1
Q

What is peritonitis?

A
  • inflammation of the peritoneum
  • peritoneum is a thin delicate layer of cells that covers external surfaces of all abdominal + pelvic organs
  • in certain circumstances, terms serosa and adventitia are used almost interchangeably w/ peritoneum
  • however, by convention, the term peritonitis is usually used rather than serositis to adventitis
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2
Q

Remember that inflammation represents the body’s response to cell damage. In the case of peritonitis, the peritoneum is usually damaged by bacterial infection.

The bacteria may gain access to the peritoneum via a number of routes, such as?

A
  • from exterior eg. a penetrating wound, peritoneal dialysis
  • from abdominal viscera eg. perforation of an inflamed appendix, perforation of an inflamed diverticulum, post-op leak from an intestinal suture line/anastomosis, bowel infarction
  • from the blood stream as part of a septicaemia
  • from female genital tract eg. PID or puerperal infection
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3
Q

Give examples of leakage of sterile body fluids into the peritoneal cavity and what the consequence of this is?

A
  • gastric contents from perforated peptic ulcer
  • pancreatic secretions secondary to pancreatitis
  • the contents of a ruptured ovarian mature cystic teratoma

these will also damage the peritoneum and initiate peritonitis. It is important to note that while these body fluids are sterile at first, they frequently become infected once they leak out of their organ, leading to bacteria peritonitis within 24-48hrs.

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4
Q

What does this image show?

A
  • generalised peritonitis
  • acute inflammatory exudate covers surface of abdominal viscera
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5
Q

What are complications of bacterial peritonitis?

A
  • sepsis
  • septic shock
  • death
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6
Q

What is the link between sterile abdominal surgery and peritonitis?

A
  • sterile abdo surgery causes localised or minimal generalised peritonitis
  • typically resolves spontaneously
  • but may heal to leave fibrotic adhesions
  • important cause of small bowel obstruction
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7
Q

What are the clinical features (signs and symptoms) of peritonitis?

A
  • increasing tachycardia and pyrexia
  • constant abdo pain due to peritoneal inflammation
  • abdominal tenderness + guarding
  • rebound tenderness
  • localised pain during distant palpation (tender spot hurts when one presses a distant non-tender part)
  • absence of bowel sounds (with tender, rigid abdomen)

as peritonitis progresses, the pt becomes more unwell w/ inc tachycardia and pyrexia, moist/cold/cyanosed skin and abdo distension (due to accumulation of free fluid).

Clinical features relating to underlying cause of the peritonitis may also be repsent and so should be sought (eg. features related to acute appendicitis or a perforated duodenal ulcer)

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8
Q

Peritonitis is primarily a clinical diagnosis and so investigations are usually of limited value.

What are the relevant investigations for peritonitis?

A
  • FBC -> marked leucocytosis, reflecting inflammation
  • serum amylase -> acute pancreatitis + prevent unnecessary surgery
  • an erect chest radiograph -> free gas under diaphragm (in cases of perforation)
  • an abdo radiograph -> free gas, or another cause
  • CT -> pinpoints cause of peritonitis
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9
Q

What is the basic principle sof management of peritonitis?

A

patient will likely need:

  • IV fluid + electrolyte replacement
  • antibiotic therapy
  • pain relief
  • gastric aspiration to prevent further distension

surgery is indicated if the source of peritonitis can be removed or closed (eg. repair of perforated duodenal ulcer or removal of gangrenous perforated appendix), or the underlying cause of peritionitis is not clear

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10
Q

What is intestinal obstruction?

A

refers to a restriction of normal passage of intestinal contents along the intestines

two main types:

  • mechanical obstruction - luminal contents cannot pass through the intestine bc the lumen is physically blocked, either completely or partially
  • paralytic obstruction (=ileus) - luminal contents cannot pass through the intestine bc of cessation of normal gut peristalsis (usually there is paralysis) - some call this functional obstruction
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11
Q

What are the ways to classify a mechanical obstruction?

A
  1. speed of onset
  2. anatomical site
  3. simple vs strangulating
  4. open vs closed loop
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12
Q

What is meant by the speed of onset?

A
  • ie. acute, chronic or acute-on-chronic
  • in acute obstruction - onset is rapid and symptoms severe
  • in chronic - symptoms are insidious and slowly progressive (eg. large bowel carcinoma)
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13
Q

What is meant by the anatomical site?

A
  • ie. small or large bowel (which is roughly synonymous to high and low obstruction)
  • small bowel obstruction is much more common than large bowel obstruction + is often rapid in onset
  • large bowel obstruction may be gradual or intermittent in onset
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14
Q

What is meant by simple vs strangulating obstruction?

A
  • simple refers to bowel obstruction without compromise to blood supply of the involved segment of intestine, it may be:
    • complete (total occlusion of lumen)
    • incomplete (partial occlusion, permitting distal passage of some fluid/air)
  • strangulating refers to bowel obstruction with compromise to blood supply of involved segment of intestine (as may occur, for example, in strangulated hernia, volvulus, inussusception or when a loop of intestine is occluded by a band). Strangulation may lead to bowel infarction, perforation and peritonitis. Strangulation usually implies that the obstruction is complete but some forms of partial obstruction can also be complicated by strangulation.
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15
Q

What is an open loop obstruction?

A

occurs when intestinal flow is blocked but proximal decompression is possible through vomiting

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16
Q

What is a closed loop obstruction?

A
  • obstruction occurs when inflow AND outflow from obstructed loop of bowel are both blocked
  • this results in accumulation of gas and secretions in the obstructed segment
  • without a means to decompression
  • bowel wall dilates resulting in increased pressure in wall
  • this stretches + compresses the blood vessels within wall
  • compromises the blood supply to affected segment, resulting in strangulation + its consequences
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17
Q

What are examples of closed loop obstruction?

A
  • torsion of a loop of small intestine around an adhesion
  • incarceration of bowel in a hernia
  • volvulus
  • large bowel obstruction with a competent ileocaecal valve
    • competent ICV means it closely completely
    • so therefore obstruction cannot decompress
    • causes bowel wall to distend (most pronounced at caecum)
    • other hand, an incompetent ICV will decompress large bowel obstruction
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18
Q

The common causes of small and large bowel obstruction in adults are different.

What are the common causes of small bowel obstruction?

A
  • adhesions (usually post-op)
  • hernias
  • intussusception
  • volvulus
  • Crohn’s stricture
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19
Q

What are common causes of large bowel obstruction?

A
  • colorectal cancer (adenocarcinoma)
  • diverticular strictures
  • sigmoid volvulus
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20
Q

What is the most common cause of bowel obstruction in the UK?

A

adhesions

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21
Q

What is an adhesion and when do they form? How do they result in bowel obstruction?

A
  • band of fibrous (scar) tissue that binds together normally separate anatomical structures
  • the scar tissue forms as part of healting by repair following inflammation
  • an important cause of localised peritoneal inflammation is the handling + manipulation of bowel during surgery which causes damage to delicate peritoneum -> inflammation + scarring -> post-operative adhesions
  • less commonly, adhesions may form secondary to ther causes eg. healing of infective peritonitis, post-radiotherapy
  • adhesions can kink, twist or pull intestines out of place causing small bowel obstruction. Acute large bowel obstruction due to post-op adhesions usually does not occur bc the large bowel is mostly retroperitoneal unlike the small bowel which gets easily kinked on its loose mesentery
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22
Q

What are abdominal hernias? How do they result in bowel obstruction?

A
  • hernias second most common cause of bowel obstruction in UK (but most common cause worldwide)
  • hernias are abnormal protrusions of peritoneal-lined sacs through defects in the abdominal wall
  • eg. inguinal and femoral canals, umbilicus, surgical scars
  • if a segment of bowel protrudes into the sac and becomes trapped, it may lead to a closed loop strangulating bowel obstruction and consequent infarction
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23
Q

What is intussusception and how does it cause bowel obstruction?

A
  • occurs when segment of small bowel prolapses into immediately adjoining bowel
  • prolapsing bowel is called the intussusceptum
  • different portions of intestine may form apex of intussusception
  • commonest form is ileocolic - extends through the ileocaecal valve into the colon
  • over 95% cases occur in infancy or young children in whom there is no obv cause
  • in adults, it’s usually associated w/ an intraluminal mass (such as the base of a Meckel’s diverticulum, a polyp or tumor) that serves as the initiating point of traction
  • the intussusceptum has its blood supply cut off by direct pressure of the outer layer and by stretching of its supplying mesentery resulting in strangulating obstruction
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24
Q

What is a volvulus and how can it lead to obstruction?

A
  • an abnormal twisting of a segment of the bowel around its site of mesenteric attachment
  • resulting in closed loop obstruction
  • there is also occlusion of the main vessels at base of involved mesentery -> strangulation
  • precipitating factors include
    • abnormally mobile loop of intestine (eg. long sigmoid loop)
    • abnormally loaded loop eg. chronic constipation
    • a loop fixed at its apex by adhesions, around which it rotates
    • a loop of bowel with a narrow mesenteric attachment
  • volvulus most commonly occurs in the sigmoid colon but it may also occur in the caecum and small intestine
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25
Q

How might volvulus be treated?

A
  • by passing a long soft rectal tube through sigmoidoscope
  • advancing it into sigmoid colon
  • this often untwists an early volvulus and is accompanied by passage of vast amounts of flatus + liquid faeces
  • if this fails, the volvulus is untwisted at laparotomy and bowel is decompressed via a rectal tube threaded up from anus
  • if infarction/gangrene has occurred, affected segment is resected and two open ends are brought out as a double-barreled colostomy which is later closed
26
Q

Describe the presentation of colorectal cancer as bowel obstruction

A
  • bowel cancer (almost always adenocarcinoma) may present as large bowel obstruction
  • this is more common with left-sided tumours because the bowel contents are more solid by the time they reach left side
  • the obstruction may be chronic w/ insidious onset and slowly progressive symptoms
  • a chronic obstruction may develop acute symptoms as the obstruction suddenly becomes complete
  • this is often termed acute-on-chronic obstruction
  • don’t forget that colorectal cancer presents as an emergency (such as bowel obstruction) in around 20 cases
27
Q

Describe how Crohn’s disease can cause bowel obstruction

A
  • transmural inflammation heals by fibrosis
  • results in stricture formation
  • presents as bowel obstruction
  • Crohn’s disease most commonly affects terminal ileum
  • so typically causes small bowel obstruction rather than large bowel obstruction
28
Q

Why does absolute constipation occur in bowel obstruction?

A
  • when bowel is obstructed by a simple occlusion
  • the intestine distal to obstruction exhibits normal peristalsis
  • enabling any residual content to be passed out
  • the bowel empties and collapses
  • results in absolute constipation as neither faltus nor faeces are passed
29
Q

Why does a colickly pain occur in bowel obstruction?

A
  • bowel proximal to obstruction exhibits increased peristalsis
  • in an attempt to overcome obstruction
  • results in colickly pain
30
Q

Why does abdominal distension occur in bowel obstruction?

A
  • bowel proximal to obstruction gradually becomes dilated
  • dilation due to a combo of:
    • accumulation of gas (swallowed air mainly)
    • accumulation of intestinal secretions due to breakdown in normal fxn of mucosa, the accumulation of fluid and electrolytes in the bowel lumen represents a third space loss
31
Q

Why does vomiting occur in bowel obstruction?

A
  • due to ejection of accumulated intestinal secretions + contents
32
Q

What happens to the blood supply in the intestine as it distends?

A
  • as bowel distends, pressure in wall increases
  • as a consequence, vessels in wall collapse
  • resulting in compromise to blood supply to intestine
  • ie. obstruction is now strangulating
  • the veins collapse first leading to interference w/ venous drainage
  • as bowel distends further, intraluminal pressure rises, arteries collapse -> intereference w/ arterial supply
  • if unrelieved, bowel infarction, perforation + peritonitis can develop
33
Q

What is the definition of gangrene?

A
  • infarction w/ superimposed bacterial invasion and putrefaction of tissue
34
Q

What are the cardinal clinical features of mechanical bowel obstruction?

A
  • colickly abdominal pain (a severe gripping pain that comes and goes in waves; small bowel colic is felt in the central part of the abdomen and large bowel colic felt in lower third of abdomen)
  • abdominal distension
  • vomiting
  • absolute constipation

not all 4 cardinal features are necessarily present in every case, the severity and time of onset of each of these symptoms will depend on level of obstruction

35
Q

What are other clinical features of bowel obstruction?

A
  • bowel sounds: at first hyperactive/loud/frequent, then as bowel distends sounds become more resonant and high-pitched and eventually tinkling
  • dehydration + loss of skin turgor
  • hypotension, tachycardia
  • empty rectum on PR exam
  • pulse and temp are frequently normal (a raised tempt + tachycardia suggests strangulation)
36
Q

What features is it important to look for on examination for the most common causes of bowel obstruction?

A
  • hernias
  • abdominal scars (indicating prev surgery + therefore post-op adhesions)
  • a palpable mass (eg. caecal mass representing a caecal cancer)
37
Q

How do you distinguish between a simple and strangulating obstruction?

A

signs of strangulation are generally same as peritonitis:

  • toxic appearance w/ tachycardia + fever
  • colickly pain becoming continuous as peritonitis develops
  • tenderness, guarding and rebound tenderness
  • absent bowel sounds
38
Q

What is the medical management of mechanical bowel obstruction?

A
  • iv fluid/electrolyte replacement important
  • close monitoring also important (fluid balance chart, urinary catheter, regular review)
  • NG suction used to decompress gut, helps to decompress bowel and to lessen risk of inhalation of gastric contents during induction of anaesthesia - combo of nasogastric suction and iv fluids = ‘_drip and suck’_
  • iv antibiotics commenced if strangulation is suspected
  • investigations appropriate to identify likely cause requested eg. contrast CT
39
Q

Is surgery required for mechanical bowel obstruction?

A
  • depends on clinical scenario
  • small bowel obstruction due to adhesions may settle w/ conservative ‘drip and suck’ management without need for surgery
  • however, surgical intervention is indicated if clinical features of strangulation or peritonitis develop or there is failure to respond to conservative management
  • surgery may also be indicated in other cases of small + large bowel obstruction:
    • if underlying cause needs surgical treatment, eg. hernia, colonic carcinoma
    • if pt does not improve w/ conservative mgmt over 24-48hrs
    • if there are signs of strangulation and/or peritonitis
40
Q

What is paralytic ileus?

A
  • when luminal contentsf cannot pass through intestine
  • bc of cessation of normal gut peristalsis (usually there is paralysis)
41
Q

What is the aetiology (causes) of paralytic ileus?

A
  • post-operative state
  • generalised peritonitis of any cause eg. perforation, severe acute pancreatitis
  • drugs eg. opiates, anticholinergics
  • electrolyte imbalances eg. hypokalaemia, uraemia

n.b. ‘gallstone ileus’ is a complete misnomer since a gallstone causes a mechanical obstruction

42
Q

Why does paralytic ileus result in the post-operative state?

A
  • any handling of bowel at surgery will cause an ileus
  • this is main reason why pts are kept nil by mouth after abdo surgery until bowel regains function
  • ileus is a normal physiological event after abdo surgery
  • usually resolves spontaneously within 2-3 days of procedure
  • in this context, paralytic ileus is defined as ileus of the intestine persisting more than 3 days after surgery
  • in this context, another aetiological factor is prob present
43
Q

What is the pathophysiology of paralytic ileus?

A
  • effects of paralytic ileus are similar to those of simple mechanical obstruction
  • lack of coordinated peristalsis results in a functional obstruction
  • gas (mainly swallowed air) and fluid/electrolytes accumulate in bowel lumen
  • as bowel dilates, blood supply to bowel is compromised resulting in ischaemia
  • if not reversed, may result in infarction (gangrene) and perforation
44
Q

What are the clinical features of paralytic ileus?

A
  • mimics mechanical obstruction as also causes constipation + vomiting
  • however, ileus does not usually cause colickly pain since bowel not contracting
  • nevertheless, there is often pain (which is usually not colickly) due to underlying disorder causing ileus
45
Q

What is the difference between a colicky and constant abdominal pain?

A
  • colicky (visceral) abdo pain is caused by stretching or contracting of a hollow viscus eg. gallbladder, ureter, ileum
  • constant localised (somatic) pain is due to peritoneal irritation and indicates the presence of inflammation eg. pancreatitis, cholecystitis, appendictis
46
Q

What are important causes of bowel infarction?

A
  • strangulating bowel obstruction
  • occlusion of mesenteric artery by an embolus
  • occlusion of mesenteric artery by a thrombus
  • occlusion of mesenteric artery by an aortic dissection extending into mesenteric artery
  • compression of veins in bowel wall (due to bowel obstruction)
  • occlusion of a mesenteric vein by thrombus
  • vasculitis
  • non-occlusive infarction eg. shock
47
Q

Where might thromboemboli originate from?

A
  • left atrium in a pt w/ atrial fib
  • mural thrombus secondary to MI
  • a vegetation on a heart valve in a pt w/ infective endocarditis
  • an atheromatous plaque in aorta which ruptures
48
Q

Bowel infarction is difficult to recognise clinically and so clinicians must have a high index of suspicion and actively consider the diagnosis. What are the classical clinical symptoms?

A
  • acute colicky abdominal pain
  • rectal bleeding
  • shock (due to associated blood loss)
  • maybe abdo pain
  • signs of peritonism
49
Q

What is the management of bowel infarction?

A
  • resusciated w/ IV fluids
  • given broad spectrum antibiotics
  • urgent laparotomy where any dead bowel resected
  • revascularisation by embolectomy or bypass may improve doubtfully viable bowel and allow primary anastomosis
50
Q

What is diverticular disease?

A
  • common condition in which many diverticula develop in the large bowel
  • almost always in the sigmoid colon
  • incidence rises with increasing age
  • particularly common in western world, occurring in 50% of ppl 60+
51
Q

What is a diverticulum?

A
  • plural: diverticula
  • a pouch of colonic mucosa that has herniated through the muscularis propria
  • and has come to lie in the subserosal (pericolic) fat outside the bowel wall
  • note the outer wall of diverticula is supported only by a thin layer of subserosal connective tissue
  • so diverticula are prone to perforation when they are obstructed and/or inflammed
52
Q

What are the 2 factors important for diverticula formation?

A
  • areas of weakness in the colonic wall:
    • there are natural defects in the circular muscle layer where blood vessels pass through to supply the submucosa and mucosa
  • raised intraluminal pressure due to insufficient dietary fibre:
    • fibre binds salt and water in the colon resulting in bulky, moist faeces that are easily propelled through colon
    • movement of faeces from a low fibre diet along colon requires increased muscular effort which results in muscular hypertrophy and inc intraluminal pressure. As a consequence, diverticula are more likely to form
53
Q

What is the most common site for diverticula formation and why?

A
  • sigmoid colon
  • has the smallest diameter of any portion of large bowel
  • therefore site where intraluminal pressure highest
54
Q

What is the difference between diverticulosis and diverticulitis?

A
  • osis = diverticula are present but asymptomatic
  • itis = an acutely inflammed diverticulum, the most common presentaton
55
Q

So how is acute diverticulitis initiated (pathophys)?

A
  • when faecal matter impacts and obstructs neck of diverticulum
  • this leads to trapping of bacteria
  • consequent bacterial replication in occluded lumen
  • -> infection and mucosal injury
  • local trauma (‘rubbing’) to mucosa by faecolith may also cause mucosal injury
  • mucosal injury initiates an acute inflammatory response, resulting in acute diverticulitis
56
Q

What are the clinical features of acute diverticulitis?

A
  • abdominal pain (usually LIF)
  • malaise
  • fever
  • localised tenderness
  • no peritonisim
57
Q

How does an abscess form from acute diverticulitis? What is an abscess?

A
  • an abscess is a localised collection of pus within a newly-formed cavity in the tissue
  • acute inflammatory response process may extend beyond diverticulum into surrounding subserosal tissue -> formation of a pericolic abscess
  • the cavity forms bc of breakdown and destruction of body’s tissue
  • pus consists of inflammatory cells (mainly neutrophils) admixed w/ cellular debris, fbirin and oedema fluid
58
Q

What can the pericolic abscess lead to?

A
  • pericolic abscess may perforate into the abdominal cavity
  • resulting in bacerial peritonitis
  • alternatively, an inflamed diverticulum may perforate directly into the abdominal cavity, also resulting in faecal peritonitis
  • inflamed diverticula are particularly prone to perforate bc the wall of the diverticulum is supported only by a thin layer of subserosal tissue
59
Q

Why might a fistula form from diverticulitis?

A
  • rarlely, as a consequence of inflammation
  • fistula is an abnormal connection between two epithelial surfaces
  • fistula may form between sigmoid colon and bladder
  • this presents clinically as faecaluria (passing faecal matter in urine)
  • fistulae may also form to the vagina
60
Q

Why might a stricture form as a consequence of diverticular disease?

A

because of:

  • smooth muscle hypertrophy and hyperplasia due to low fibre diet
  • fibrosis around diverticula (repeated episodes of inflammation heal by fibrosis)

both of these factors lead to a reduction in the diameter of the lumen ie. a stricture - they present with clinical features of bowel obstruction

61
Q

What important GI symptom is diverticular disease a common cause of?

A
  • lower GI bleeding
  • the small blood vessels are stretched over dome of diverticula
  • can rupture causing bleeding
  • bleeding from diverticula is typically painless and spontaneous
    • in most cases blood loss from diverticula is small
    • occasionally it may be massive
62
Q

What other disease may diverticular disease also mimic and how do we rule this out?

A
  • may clinically closely mimic colorectal cancer
  • intermittent abdo pain + altered bowel habit
  • both conditions affect broadly similar age groups
  • positive FOB and iron deficiency anaemia (due to ongoing bleeding from diverticula)

‘Diverticular’ strictures should be biopsied to rule out colon carcinoma

*Medicine: Cellular Pathology (16 decks)

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