30 Small bowel obstruction
Fig. 30.1A The radiograph shows several abnormally dilated small bowel loops in small bowel obstruction.
Background
Small bowel obstruction is a very common emergency presentation and as plain films are still the first-line modality for diagnosis, accurate interpretation is important to enable prompt, accurate management of these patients.
Causes may be mechanical or functional (due to a paralysis of the bowel wall). The commonest two causes of mechanical obstruction are adhesions and hernias. Tumours (of the small bowel or caecum, or metastatic) are also a common cause. The finding of small bowel obstruction should prompt the assessing physician to elicit a history of malignancy or previous surgery (adhesions) and examine the groins (for hernias).
Functional obstruction most commonly follows abdominal surgery, which should be clear clinically. Pseudo-obstruction is a condition that has several underlying causes such as electrolyte disturbances and fractures. It is difficult to differentiate this from mechanical obstruction on radiological grounds alone.
Be aware of the complication of perforation – longstanding small bowel obstruction leads to bowel ischaemia and necrosis which may initially manifest as pneumatosis intestinalis (see Chapter 37). Do not forget to request an erect CXR in patients with suspected obstruction and look for the signs of perforation (see Chapters 27 and 45).
Clinical features
Symptoms
The main symptoms are colicky central abdominal pain, vomiting, absolute constipation and abdominal distension.
Signs
Signs include a distended tympanic abdomen and increased, tinkling bowel sounds on auscultation, as distinct from ileus or functional obstruction where bowel sounds are absent. Look for scars indicating previous surgery and hernias.
Peritonism may suggest perforation, which may complicate obstruction.
In very late presentation small bowel obstruction, bowel sounds may be decreased or absent.
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