1. DR. ABDULLATEEF AL-BAYATI
Al-Mustansiriyah University
College of Medicine - Department of Medicine
Division of Radiology
IMAGING OF ACUTE ABDOMEN
DR. ABDULLATEEF AL-BAYATI
Teaching Board Member
CABMS-RAD 5

2. Perforation of the gastrointestinal tract
Perforation of the gastrointestinal tract may be due to:
Peptic ulceration
Inflammation including acute diverticulitis and appendicitis
Blunt or penetrating injury including iatrogenic trauma.
Perforation of the stomach, small intestine and most of the colon produces free gas in the peritoneal cavity.
Perforation of the duodenum and posterior rectum results in free retroperitoneal gas.
Radiographic signs of free gas:
Erect CXR: gas beneath diaphragm (crescent shape).
Supine abdomen: gas outlines anatomical structures, such as the liver, falciform ligament and spleen; bowel walls are seen as white lines outlined by gas on both sides, i.e. inside and outside the bowel lumen (Rigler's sign).
Free gas is also identified on erect abdomen film.
If the patient is too ill to stand then either decubitus or shoot-through lateral films can be performed.

4. Small bowel obstruction
The clinical presentation of small bowel obstruction (SBO) may include abdominal pain and vomiting, progressing to acute abdomen with abdominal distension and tenderness.
Causes of SBO in adults include:
Adhesions due to previous surgery, trauma or infection
Strangulated hernia
Small bowel neoplasm
Gallstone ileus.
In children, causes of SBO include strangulated hernia, congenital malformation, intussusception and malrotation.
Abdominal x-ray (AXR) is the primary investigation of choice in suspected small bowel obstruction.

5. Signs of small bowel obstruction on AXR:
Dilated small bowel loops, which have the following features
Central location.
Numerous
2.5–5.0 cm diameter
Small radius of curvature
Valvulae conniventes, seen as white lines that are thin, numerous, close together and extend right across the bowel.
Do not contain solid feces.
Multiple fluid levels on the erect AXR
‘String of beads’ sign on the erect AXR due to small gas pockets trapped between Valvulae conniventes.
Absent or little air in the large bowel.

7. Paralytic ileus
Differential diagnosis of dilated small bowel loops on AXR is paralytic ileus.
Paralytic ileus may be generalized or localized.
Localized ileus refers to dilated loops of bowel (‘sentinel loops’), usually small bowel, overlying a local inflammation:
Right upper quadrant: acute cholecystitis
Left upper quadrant: acute pancreatitis
Lower right abdomen: acute appendicitis.
Generalized ileus refers to non-specific dilatation of small and large bowel, which may occur postoperatively or with peritonitis.
Scattered irregular fluid levels are seen on the erect X-ray.

9. Strangulated hernia
The term ‘hernia’ refers to abnormal protrusion of intra-abdominal contents, usually peritoneal fat and bowel loops.
Inguinal hernia accounts for about 80 per cent of abdominal wall hernias.
Femoral hernia is more common in females.
Other types of external hernia include umbilical hernia and hernia related to previous surgery, either incisional or parastomal.
Most hernias present with an inguinal or abdominal wall mass that increases in size when the patient stands or strains.
Occasionally, hernias may become strangulated and present with localized pain and intestinal obstruction.
Radiographic signs of strangulated hernia:
Gas-containing soft tissue mass in the inguinal region may have a fluid level on the erect view
Gas in the bowel wall within the hernia indicates incarceration and bowel wall infarction.

11. Gallstone ileus
Gallstone ileus refers to small bowel obstruction secondary to gallstone impaction. Gallstone ileus usually occurs in a setting of chronic cholecystitis where a large gallstone erodes through the inflamed gallbladder wall to enter the duodenum.
The gallstone then becomes impacted in the distal small bowel causing small bowel obstruction.
Radiographic signs of gallstone ileus:
Small bowel obstruction
Gas in the biliary tree seen as a branching pattern of gas density in the right upper quadrant
Calcified gallstone lying in an abnormal position is occasionally seen.

13. CT of small bowel obstruction
CT is the investigation of choice for suspected SBO when clinical and AXR assessments are inconclusive.
CT is highly accurate for establishing the diagnosis of small bowel obstruction, defining the location and cause of obstruction, and diagnosing associated strangulation.
CT signs of SBO include dilated small bowel loops measuring >2.5 cm in diameter, with an identifiable transition from dilated to non-dilated or collapsed bowel loops.

14. Large bowel obstruction
Subacute to chronic presentation with abdominal pain and distension and constipation (colorectal carcinoma).
Acute presentations of LBO may be seen with sigmoid volvulus, cecal volvulus and diverticulitis.
Signs of large bowel obstruction on AXR:
Dilated large bowel loops, which have the following features
Peripheral location
Few in number
Large: above 5.0 cm diameter
Wide radius of curvature
Haustra, seen as thick white lines that are widely separated, and may or may not extend right across the bowel (compare these features with those of the small bowel valvulae conniventes described above).
Contain solid faeces
Small bowel may also be dilated if the ileocecal valve is ‘incompetent’
Depending on which large bowel loops are dilated, an approximate level of obstruction may be suggested on AXR.
With respect to the cause of LBO, AXR appearances are generally non-specific and non-diagnostic.
Cases where a specific diagnosis may be made with AXR include cecal volvulus and sigmoid volvulus.

17. Cecal volvulus
Cecal volvulus refers to twisting and obstruction of the caecum.
Cecal volvulus occurs most commonly in patients aged 20–40 and is associated with an abnormally long mesentery and malrotation.
Radiographic signs of cecal volvulus:
Markedly dilated caecum containing one or two haustral markings
The dilated caecum may lie in the right iliac fossa or left upper quadrant
Attached gas-filled appendix
Small bowel dilatation
Collapse of left half of colon.

19. Sigmoid volvulus
Sigmoid volvulus refers to twisting of the sigmoid colon around its mesenteric axis with obstruction and marked dilatation.
Sigmoid volvulus occurs in elderly and psychiatrically disturbed patients.
Radiographic signs of sigmoid volvulus:
Massively distended sigmoid loop in the shape of an inverted ‘U’, which can extend above T10 and overlap the lower border of the liver.
Usually has no haustral markings.
The outer walls and adjacent inner walls of the ‘U’ form three white lines that converge towards the left side of the pelvis.
Overlap of the dilated descending colon: ‘left flank overlap’ sign (good differentiating feature from cecal volvulus in which the remainder of the large bowel is not dilated).
Contrast enema may be helpful to localize the location of LBO and to diagnose its cause, e.g. tumor or inflammatory mass.
CT may be used for the assessment of difficult or equivocal cases of large bowel obstruction.
In the majority of cases, CT will diagnose the location and cause of obstruction.
CT may also diagnose other relevant findings, such as liver metastases in the case of an obstructing tumor.

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