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Intestinal obstruction 
Dr.Husen 18.11.2014 tue> 

Intestinal obstruction may be classified into two types: 
• Dynamic, in which peristalsis is working against a mechanical obstruction. It 
may occur in an acute or a chronic form. 
• Adynamic, in which there is no mechanical obstruction; peristalsis is absent or 
inadequate (e.g. paralytic ileus or 
pseudo-obstruction). 

Causes of intestinal obstruction 

Dynamic 

 Intraluminal 

Faecal impaction 
Foreign bodies 
Bezoars 
Gallstones 

Adynamic  

 Paralytic ileus 
 Pseudo-obstruction  
 

PATHOPHYSIOLOGY 

Irrespective of aetiology or acuteness of onset, in dynamic 
(mechanical) obstruction the bowel proximal to the obstruction dilates and the 
bowel below the obstruction exhibits normal peristalsis and absorption until it 
becomes empty and collapses. Initially, proximal peristalsis is increased in an 
attempt 
to overcome the obstruction. If the obstruction is not relieved, the bowel continues 
to dilate, ultimately there is a reduction in peristaltic strength, resulting in flaccidity 
and paralysis.   
The distension proximal to an obstruction is caused by two factors: 
• 

Gas

: there is a significant overgrowth of both aerobic and anaerobic organisms, 

resulting in considerable gas production. 
Following the reabsorption of oxygen and carbon dioxide, the majority is made up 
of nitrogen (90 per cent) and hydrogen sulphide. 
• 

Fluid:

 this is made up of the various digestive juices (saliva 500 mL, bile 500 mL, 

pancreatic secretions 500 mL, gastric secretions 1 litre – all per 24 hours). This 
accumulates in the gut lumen as absorption by the obstucted gut is retarded. 
 
 
 

Dehydration and electrolyte loss are therefore due to: 

1.  reduced oral intake; 

Intramural 

Stricture 
Malignancy 
Intussusception 
Volvulus 

 

Extramural 

Bands/adhesions 
Hernia 

 


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2.  defective intestinal absorption; 
3.  losses as a result of vomiting; 
4.  sequestration in the bowel lumen; 
5.  transudation of fluid into the peritoneal cavity.  

 

STRANGULATION 

When strangulation occurs, the blood supply is compromised and the bowel 
becomes ischaemic. 

Causes of strangulation 

1. 

Direct pressure on the bowel wall 

2. 

Hernial orifices 

3. 

Adhesions/bands 

4. 

Interrupted mesenteric blood flow 

5. 

Volvulus 

6. 

Intussusception 

7. 

Increased intraluminal pressure 

8. 

Closed-loop obstruction 

 

Distention of the obstructed segment of bowel results in high pressure within the 
bowel wall. This can happen when only 
part of the bowel wall is obstructed as seen in Richter’s hernias. 
Venous return is compromised before the arterial supply. The resultant increase in 
capillary pressure leads to impaired local 
perfusion and once the arterial supply is impaired, haemorrhagic infarction occurs. 
As the viability of the bowel is compromised, translocation and systemic exposure 
to anaerobic organisms and 
endotoxin occurs.  
 
The morbidity and mortality associated with strangulation are largely dependent 
on the duration of the ichaemia and its 
extent. Elderly patients and those with comorbidities are more vulnerable to its 
effects. Although in strangulated external hernias the segment involved is often 
short, any length of ischaemic bowel can cause significant systemic effects 
secondary to 
sepsis and obstruction proximal to the obstruction can result in significant 
dehydration. When bowel involvement is extensive circulatory failure is common.  
 
 
 

Closed-loop obstruction 


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This occurs when the bowel is obstructed at both the proximal 
and distal points. A classic form of closed-loop obstruction is seen in the presence 
of a malignant stricture of the colon with a competent 
ileocaecal valve (present in up to one-third of individuals). This 
can occur with lesions as far distally as the rectum. The inability 
of the distended colon to decompress itself into the small bowel results in an 
increase in luminal pressure, which is greatest at the caecum, with subsequent 
impairment of blood flow in the wall. Unrelieved, this results in necrosis and 
perforation  

SPECIAL TYPES OF MECHANICAL 

INTESTINAL OBSTRUCTION 

Internal hernia 

Internal herniation occurs when a portion of the small intestine 
becomes entrapped in one of the retroperitoneal fossae or in a 
congenital mesenteric defect. 
The following are potential sites of internal herniation (all 
are rare): 
• the foramen of Winslow; 
• a defect in the mesentery; 
• a defect in the transverse mesocolon; 
• defects in the broad ligament; 
• congenital or acquired diaphragmatic hernia; 
• duodenal retroperitoneal fossae – left paraduodenal and right 
duodenojejunal; 
• caecal/appendiceal retroperitoneal fossae – superior, inferior 
and retrocaecal; 
• intersigmoid fossa. 

Obstruction from enteric strictures 

Small bowel strictures usually occur secondary to tuberculosis or 
Crohn’s disease. Malignant strictures associated with lymphoma 
are uncommon, whereas carcinoma and sarcoma are rare. 
Presentation is usually subacute or chronic. Standard surgical 
management consists of resection and anastomosis. Resection 
is important to establish a histological diagnosis as this can be 
uncertain clinically. In Crohn’s disease, strictureplasty may be 
considered in the presence of short multiple strictures without 
active sepsis. 
 
 

Bolus obstruction 


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Bolus obstruction in the small bowel may be caused by gallstones, 
food, trichobezoar, phytobezoar, stercoliths and worms.  

Gallstones 

This type of obstruction tends to occur in the elderly secondary 
to erosion of a large gallstone directly through the gall 

bladder into the duodenum. Classically, there is impaction 

about 60 cm proximal to the ileocaecal valve. The patient 
may have recurrent attacks as the obstruction is frequently 
incomplete or relapsing as a result of a ball-valve effect. The 
characteristic radiological sign of gallstone ileus is Rigler’s  
triad, comprising: small bowel obstruction, pneumobilia and 
an atypical mineral shadow on radiographs of the abdomen. 
The presence of two of these radiological signs has been considered 
pathognomic of gallstone ileus and is encountered in 
40–50 per cent of the cases  

Food 

Bolus obstruction may occur after partial or total gastrectomy 
when unchewed articles can pass directly into the small bowel. 
Fruit and vegetables are particularly liable to cause obstruction.  

Trychobezoars and phytobezoars  

These are firm masses of undigested hair ball and fruit/vegetable 
fibre, respectively. The former is due to persistent hair chewing 
or sucking, and may be associated with an underlying psychiatric 
abnormality. Predisposition to phytobezoars results from a 
high fibre intake, inadequate chewing, previous gastric surgery, 
hypochlorhydria and loss of the gastric pump mechanism.  

Stercoliths  

These are usually found in the small bowel in association with a 
jejunal diverticulum or ileal stricture. Presentation and management 
are identical to that of gallstones.  

Worms 

Ascaris lumbricoides may cause low small bowel obstruction, 
particularly in children .An attack may follow the initiation 
of antihelminthic therapy., If worms are not 
seen in the stool or vomitus, the diagnosis may be indicated by 
eosinophilia or the sight of worms within gas-filled small bowel 

loops on a plain 
radiograph 
 

Done by: Diaa Abdulfatah M 

 




رفعت المحاضرة من قبل: Mohammed Musa
المشاهدات: لقد قام 9 أعضاء و 125 زائراً بقراءة هذه المحاضرة








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