Year : 2006 | Volume
: 16 | Issue : 4 | Page : 463--468
Msct in acute small gut obstruction: A pictorial assay
G Mahajan, A Kapoor, A Kapoor, VP Lakhanpal
Consultant Radiologists. Advanced Diagnostics and Institute of Imaging, 17/8 Kennedy Avenue, Amritsar 143001, Punjab, India
Advanced Diagnostics and Institute of Imaging, 17/8 Kennedy Avenue, Amritsar 143001, Punjab
|How to cite this article:|
Mahajan G, Kapoor A, Kapoor A, Lakhanpal V P. Msct in acute small gut obstruction: A pictorial assay.Indian J Radiol Imaging 2006;16:463-468
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Mahajan G, Kapoor A, Kapoor A, Lakhanpal V P. Msct in acute small gut obstruction: A pictorial assay. Indian J Radiol Imaging [serial online] 2006 [cited 2019 Nov 16 ];16:463-468
Available from: http://www.ijri.org/text.asp?2006/16/4/463/32247
Acute small bowel obstruction (SBO) is a common cause of pain abdomen and forms 20% of surgical emergencies. SBO can be self limiting or life threatening and therefore requires an accurate and a prompt diagnosis which can reduce the mortality & morbidity. Conventional radiology has a low sensitivity of 40-60% for diagnosing acute SBO  and gives little information about the site and cause of obstruction. The use of oral contrast in a setting of acute pain abdomen can not only be unwise but dangerous as it can precipitate an attack of colic. With the advent of multislice imaging techniques, isotropic imaging with high z- axis resolution and multiplanar reformations, a gapless speedy assessment of the entire abdomen can be done in matter of a few seconds allowing the entire small bowel to be studied for the cause and site of obstruction and also the viability of the wall . It also allows the use of fluid present in the lumen of the small bowel as a inherent contrast which can be used as an alternative to the traditional concept of giving oral contrast for small bowel evaluation.
We archived our institutional records of six years from the year 2000-2006 of 250 patients with suspected acute bowel obstruction and reviewed the imaging findings on MSCT and describe the imaging technique without the use of oral contrast in the form of a pictorial assay and illustrate that MSCT can be used to diagnose different patterns SBO along with its causes.
Since patients with acute SBO have a natural oral contrast due to the fluid in the obstructed gut so no oral contrast was given in the technique used by us. The studies were done on a MSCT( Volume zoom, Siemens, Forchheim, Germany AG) using 120 KV and 145mas, pitch of 1.2 with collimation of 2.5 mm and 100-120cc of intravenous nonionic iodinated contrast ( Iopromide 300mg/ml(ultravist 300, Schering Germany, AG ) given through power injector(Med cad USA) at the rate of 3 ml/sec with a delay of 50 seconds. Single breath hold scan of the entire abdomen was done in a 5-10 seconds and the patient was sent back to the hospital. The source images were then post processed on Siemens Wizard work console using thick multiplanar and curvilinear processing protocols.
SBO is diagnosed when the small bowel is dilated with a calibre more than 2.5cms and also shows a zone of narrowing or transition On the basis of the patterns of small bowel obstruction it is classified into simple SBO and Closed loop SBO. In simple SBO there is narrowing of the small bowel at one or more points along with proximal dilatation [Figure 1]. The vessels along with the mesentry however appear normal. In closed loop obstruction the small bowel gets obstructed like a closed loop between two points of narrowing with the mesentry and the vessels supplying it also getting involved thus leading to small bowel ischemia or strangulation[Figure 2].
The various causes of simple and closed loop obstruction are summarized in Table 1. It is important from management viewpoint to differentiate between the two conditions as the line of management changes from being conservative to surgical if it is a closed loop obstruction.
With MSCT by using the present technique the diagnosis of acute SBO can be established and its etiology be assessed. We enumerate and discuss various etiological pattern of SBO observed on MSCT.
Bowel adhesions form the commonest cause of acute SBO -50-70% and in majority of the patients there is history of previous surgery. The pattern of acute SBO seen is of simple type with proximally dilated loops of small bowel alongwith a zone of transition with no surrounding mass lesion or wall thickening. This zone of transition is usually adjacent to the incision line of the previous surgery in patients with past history of laprotomy. Other cause for adhesions can be due to chronic inflammatory pathology due to previous abdominal infections in which there may be more than zones of transitions or adhesions [Figure 3]
They are abnormal peritoneal reflections which may be fibrous in nature and may have few small blood vessels in their substance and are associated with a high incidence of acute intestinal obstruction ,. On imaging it is difficult to visualise the band however the dilated proximal dilated loop shows an abrupt cutoff or narrowing at a suspected site or location. The diagnosis is also suggested on imaging by ruling out other causes of extrinsic obstruction. The common sites of presence of congenital bands are juxtaduodenal, mid gut or in the terminal ileum with intestinal malrotation being the most common associated finding. The SBO may be due to the band itself or due to associated volvulus. Imaging by helical CT will show abrupt narrowing or abrupt cut off.[Figure 4]a,b.
Is another common cause of extrinsic acute SBO and can be external or internal hernia.
External hernia is seen through a defect in the abdominal /pelvic wall and can be inguinal, femoral, spigelian, incisional or umblical. On imaging the dilated herniated gut coils alongwith the hernia sac and neck can be visualised to suggest acute SBO. These may or may not be associated with complications like closed loop obstruction. The second type of hernia is internal hernia which can be paraduodenal, transmesenteric, pericecal or at the foramen of winslow and is due to comgenital or acquired defects in the peritoneum, mesentry or omentu . On imaging the internal hernia appears as a sac like structure containing dilated small bowel loops with mesenteric vessels converging towards its orifice. Wall thickening of the entrapped loops may also be seen. Paraduodenal hernias on imaging may appear as a bunch of small gut coils between the stomach and pancreas, or as a sac like mass near the duodenum with encapsulation of small bowel loops [Figure 5] and may cause mass effect on the posterior wall of the stomach, with or without inferior displacement of the duodenojejunal flexure or left lateral displacement of the main mesenteric vessels.
Acquired internal hernia is commonly transmesenteric & is commonly related to previous surgery .On imaging clustering of the small bowel loops is seen just under the anterior abdominal wall without overlying omental fat with central, caudal & dorsal displacement of the colon & stretching of the mesenteric vessels .
Are mass lesions arising from the small bowel which appears thickened and on imaging presents as diffusely thickened solid soft tissue mass with or without enlarged lymph nodes and peritoneal fluid. The commonest type of small bowel masses are adenocarcinoma, carcinoid, GIST and lymphoma while secondaries from carcinoma ovaries, colon, stomach, pancreas and rarely lung can also present as small bowel solid neoplasms.[Figure 6]a,b 
Inflammatory pathologies leading to acute SBO can be acute or chronic. Imaging in acute inflammation of the gut shows simple wall thickening with surrounding areas of soft tissue inflammation or streaking involving the mesentry or the omentum while in chronic inflammation which is commonly due to tuberculosis in our country; imaging shows the bowel with an area of focal mural wall thickening and luminal narrowing -stricture formation; which can be single or multiple .There may be associated findings of mesenteric lymphadenopathy, ascites, mesenteric, omental thickening.[Figure 7]a,b The commonest site of involvement is ileal followed by jejunum & colon The differential diagnosis is from other common causes of chronic inflammation like crohns disease, which shows pseudodiverticulae formation along with strictures unlike tuberculosis.
Is the invagination of the proximal bowel with or without mesentry into the distal bowel.
Majority of the intussusceptions are secondary to tumors like polyps, lipomas, lymphoma, lymphoid hyperplasias. The multiplanar ability of the MSCT allows for accurate delineation of the type of the intussusception and also detects any secondary complications if present [Figure 8]a,b. Imaging shows intussusception as thickwalled bowel loops with a distended lumen having proximal bowel with or without mesenteric fat giving a target sign.
The causes for obturated type of acute SBO are impacted gall stones, foreign bodies, bezoar, meconium, polyps. Gallstone ileus is the commonest cause and is seen in the elderly females with hyperdense calculi in the gut at the point of obstruction.There may be associated findings of dilated small gut coils associated with a cholecystoduodenal fistula or air in the Gb fossa [Figure 9]a,b.
Closed loop obstruction
Closed loop obstruction results when a loop is obstructed at two points at a single site and is usually due to an adhesive band or an external /internal hernia  It is prone to produce a volvulus as it tends to involve the mesentry and is a common cause of strangulation.There may be A shaped, U shaped or Coffee bean shaped bowel loop with the mesenteric vessels converging towards the point of torsion. On imaging visualization of two adjacent collapsed loops with a beak sign or a whirl sign [Figure 10] at the site of obstruction is diagnostic of closed loop obstruction. Bowel ischemia is the dreaded complication of closed loop SBO and is seen in acute SBO in approximately 5-35% of cases with a high morbidity & mortality rate., Thus the challenge on imaging in such type of acute SBO is to rule out strangulation. The changes seen in ischemic gut on MSCT are wall thickening with lack of enhancement or delayed enhancement, regional mesenteric haze, mesenteric vascular congestion, and in the advanced cases pneumatosis intestinalis [Figure 11]a,b and air in the portal system .
The most significant advancement in the diagnosis acute SBO has been the development of the MSCT which not only assists in reaching the diagnosis but also helps in the early identification of patients requiring urgent operative decompression. A broad overview of the spectrum of findings seen in acute SBO has been discussed with use of the MSCT using oral water technique alongwith multiplanar reconstructions to show its usefulness in the detection of acute SBO and its related complications .
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