The document discusses the acute abdomen and various imaging modalities used to evaluate it. It covers: 1) The causes of acute abdomen including perforation, obstruction, inflammation and others. 2) The imaging modalities used including plain films, ultrasound, CT and their roles in evaluating specific causes. 3) How different conditions present on imaging including bowel obstruction, perforation, appendicitis and others.

1. The Acute abdomen
Presented by: Dr. Mahesh Chaudhary
Resident MD Radiology, BSMMU
Dhaka, Bangladesh

2. • The 'acute abdomen' is a clinical condition characterized by severe abdominal
pain, requiring the clinician to make an urgent therapeutic decision.
 Role of imaging
• To help surgeon decide whether or not a patient with acute abdomen needs to
have a surgery
• Whether operation needs to be done immediately or time can be spent on
further investigations
• To support the clinical findings.

3.  Causes of acute abdomen
• Perforation
• Intestinal obstruction
• Paralytic ileus
• Inflammatory causes
• Renal colic
• Leaking abdominal aneurysm
• Acute gynecological disorder

4.  Imaging modalities
• Plain radiographs
• Ultrasound
• CT-scan of abdomen
• Barium enema

5. Plain abdominal film
Erect Chest Supine abdomen Erect abdomen Left lateral decubitus
Demonstrates-
-Small pneumoperitoneum
-Chest abnormalities
-Acute abdomen complicated
by chest pathology
-Acts as a baseline
Shows-
-Distribution of gas
-Caliber of bowel
-Displacement of bowel
-Obliteration of fat lines
Shows air-fluid level If patient cannot sit or stand
-Free gas between liver and
lateral abdominal wall
-Gas filled duodenal loop
-Calcification in aortic
aneurysm

7.  Role of USG in acute abdomen
• Real time USG allows confirmation of palpable masses and focal point of tenderness
• Evaluation of visible gas and fluid
• Perienteric soft tissue
• Evaluation of peristalsis
• Acute appendicitis
• Acute cholecystitis

8. Focused assessment with sonography for trauma ( FAST)
• Rapid bedside ultrasound examination performed by surgeons, emergency
physicians as a screening test for blood around the heart (pericardial
effusion) or abdominal organs (hemoperitoneum) after trauma.
• The four classic areas (4P) that are examined for free fluid are -
Perihepatic space (also called Morison's pouch or the hepatorenal recess)
Perisplenic space
Pericardium
Pelvis
• With this technique it is possible to identify the presence of intraperitoneal
or pericardial free fluid.
• In the context of traumatic injury, this fluid will usually be due to bleeding.

9.  Role of CT scan
• Most sensitive method for the detection of peritoneal free gas
• Confirm the diagnosis of intestinal obstruction
• H/O previous abdominal malignancy
• Extra luminal disease
• In acute pancreatitis, renal colic, leaking abdominal aneurysm, Intra abdominal
abscess

10. Bowel perforation
• The radiological hall mark of hollow viscus perforation is the presence of air and
fluid in the peritoneal cavity.
 Causes
• Peptic ulcer disease
• Inflammatory bowel disease
• Blunt or penetrating trauma
• Foreign body
• Neoplasm
• Obstruction
• Pancreatitis

11. Supine abdominal radiograph
• Oval/linear collection of gas
- Subhepatic space
- Morrison’s pouch
• Beneath the diaphragm(the cupola sign)
• In the center of the abdomen over a fluid collection(the football sign)
• Visualization of the outer as well as the inner wall of loop of bowel
(Rigler’s sign)
• Visualization of falciform ligament, medial and lateral umbilical ligament
and the urachus.
• In the fissure of ligamentum teres
11

12. • Erect chest film-

13. Supine abdominal radiograph

14. Rigler’s sign

15.  CT scan
• Most sensitive method for detecting peritoneal gas
• Gas tends to collect over the liver anteriorly, mid abdomen and peritoneal recess.

16. Gastric dilatation
Causes
• Paralytic ileus
• Mechanical bowel obstruction
• Gastric volvulus
• Air swallowing
X-ray abdomen-supine
Intestinal obstruction

17. Small bowel obstruction
Extrinsic Bowel wall Intraluminal
Adhesions Neoplasia Intussusception
Hernia Stricture Foreign body
Volvulus Intestinal ischemia Gallstone ileus
Abscess Bezoar
Peritoneal deposits
Causes

18.  Goals of imaging in a patient with suspected intestinal obstruction
• To confirm that it is a true obstruction and to differentiate it from an ileus
• To determine the level of obstruction
• To determine the cause of the obstruction
• To look for findings of strangulation
• To allow good management either medically or surgically by laparotomy or laparoscopy

19. On Plain films
• Dilated gas filled loops of small bowel.
• Multiple fluid level
• Dilated small bowel almost completely filled with fluid with small bubbles of gas
trapped in rows between the valvulae conniventes-”string of beads” sign.
• Dilated fluid-filled loops of small bowel may be identified as oval or round soft
tissue densities.
• Absent or little air in large bowel

20. Supine abdominal radiograph-shows multiple dilated loops of gas filled small bowel

21. Erect abdominal film-shows multiple fluid levels

22. Erect abdomen “string of beads “ sign

23.  Role of USG in bowel obstruction
• Presence of abundant gas produces images of non diagnostic quality
USG evaluation of potential MBO
• GIT caliber
• Content of dilated loop
• Peristaltic activity
• Site of obstruction
• Gut wall morphology
• Extrinsic soft tissues

24. US Sagittal image of right flank

25.  Role of CT scan
• CT can confirm the diagnosis of SBO, indicate the location of the obstruction
• Fluid filled levels clearly visible on CT
• Indicated with H/O –
- previous abdominal surgery
- extra luminal disease
• Effective at detective hernias
• A focal calibre change from dilated to collapsed bowel, the transition point,
indicates the level of obstruction.
• The small bowel is considered dilated when its diameter is greater than2.5 cm.

26.  Simple bowel obstruction
• Dilated small bowel leads into a mass at the point of transition to collapsed
small bowel

27.  Closed loop obstruction
• Two points in the segment of bowel is
obstructed
• When blood supply is compromised its
called strangulation
• CT is the imaging of choice
• A U-shaped loop of bowel is seen with a
transition point at either end.
• In severe cases, gas may be seen within the
bowel wall and within the portal venous
system

28. • U-Shaped or C-shaped loop
• Beak appearance at the point of obstruction

29.  SBO due to hernia
External hernia Internal hernia
Inguinal
Femoral
Umbilical
Incisional
Spigelian
Paraduodenal
Transmesenteric

30.  CT findings
• Free fluid collection within hernia sac
• Bowel wall thickening
• Abnormal bowel wall enhancement(hypo or hyper attenuating)
• Proximal bowel dilatation
• Herniated bowel segment and involved mesentery are shorter in length

31. CT scan showing midline incisional hernia containing a bowel loop

32. SBO due to gall stone ileus
• Is mechanical bowel obstruction due to gall stone/s in the intestine
• 2% of SBO
Signs of gall stone ileus
• Gas within the bile ducts or the gall bladder
• Complete or incomplete SBO
• Abnormal location of gall stone
• Change in position of gall stone

33. Supine film:

34. Appendicular abscess

35. Intussusception
 Characteristics
Invagination or prolapse of a segment of intestinal
tract ( intussusceptum) into the lumen of the
adjacent intestine ( intussuscipiens).
90% are ileocolic and ileo-ileocolic.
 Clinical features
• Severe colicky pain and vomiting.
• Initial stools passed at the start of symptoms
are unremarkable; blood and mucus
(‘redcurrant jelly’) stools are passed after 24
hours

36. Cont.
 Adult intussusception
• The majority arise from a pathological lead point.
• Causes include lipomas, carcinomas, metastases and lymphoma.
 Paediatric intussusception
• 90% of all paediatric intussusceptions have no pathological lead point and are
thought to be associated with lymphoid hyperplasia in Peyer’s patches of the
ileum.
• 10% have a lead point, which include a Meckel’s diverticulum, polyps and
duplication cysts.
• Intussusception usually occurs within the first 2 years.

37. Ultrasound
• A mass is usually demonstrated in the right upper quadrant adjacent to the
gallbladder, in ileocolic intussusceptions, which are the most common type in
paediatric patients.
• Transverse section through the mass reveals concentric alternating hyperechoic and
hypoechoic rings, representing compressed mucosal and serosal surfaces and
oedematous bowel wall respectively (target/doughnut sign).
• A longitudinal section through the mass demonstrates a hypoechoic mass with an
appearance very similar to a kidney (pseudo-kidney sign) .
Radiological features

38. Plain film
• There are multiple gas filled loops of dilated
small bowel
• Soft tissue mass in right iliac fossa

39. Small-bowel obstruction due to a small-bowel melanoma metastasis which has caused
jejunal intussusception.

40. Mesenteric ischemia
• Due to thrombosis or embolism of SMA or vein.
 Plain films
• Gas filled slightly dilated loops of bowel with multiple fluid levels
• Thumb printing sign(20-30 %)
• Occasionally air in the intestinal wall
• Thickened valvulae conniventes

41.  CT Scan
• Low-density filling defects within an enhancing artery confirms the
presence of thrombus. Reduced or non-enhancement suggests
thrombosis or atherosclerotic narrowing.
• The bowel wall may demonstrate either low attenuation due to oedema
or high attenuation due to mural haemorrhage.
• Bowel-wall enhancement may be poor with a sharp cut-off between
normal and abnormal colon at the boundary of vascular territories.
• In complete occlusion there can be absent of enhancement of bowel wall.

42. • Dilated bowel loops with air fluid levels
• In severe cases gas may be seen within the bowel wall appearing as
intramural locules of low attenuation.
• Gas may also be seen in the portal venous system as branching
peripheral low attenuation usually in the left lobe of the liver .
• CT angiography allows the assessment of the coeliac axis, superior
and inferior mesenteric arteries
Contd.

43. Gas in portal vein Pneumatosis intestinalis

44. Axial Sagittal and coronal images demonstrating gas within the bowel
wall and portal venous system consistent with ischaemic small bowel

45. Large bowel obstruction
Etiology
• Carcinoma
• Volvulus
• Diverticular disease
3 types of patterns of obstruction

46.  Plain film signs of large bowel
• Depends on the state of competence of ileo caecal valve
• Few in number
• Large: above 5.0 cm diameter
• Tend to be peripheral
• Haustra : thick and widely separated and may or may not extend right
across the bowel

48. CT-Scan
• CT confirms obstruction with a colonic diameter of >5.5 cm (9 cm in
the caecum) considered abnormal.
• Identification of a transition point indicates the level of obstruction.
• CT clearly demonstrates intramural gas, perforation and abscess
formation.

49. Colonic carcinoma
• Focal irregular bowel-wall thickening with proximal dilatation.
• There may be inflammatory stranding in the adjacent fat.
Axial and coronal images demonstrating large-bowel obstruction (asterix)
secondary to a colonic carcinoma in the distal descending colon (arrow).

50.  Contrast enema maybe helpful:
• To differentiate pseudo-obstruction and may be indistinguishable on
plain film from mechanical of obstruction
• To localize the point of obstruction
• To diagnose the cause of obstruction e.g. tumour, inflammatory mass

51. Large bowel volvulus
• Prerequisite :Long and freely mobile mesentery must be present
 Sigmoid volvulus
• Common in old , mentally ill and instituionalised people
• Twisting occurs around the mesenteric axis

52.  Identification of loop in sigmoid volvulus
• Ahaustral margin
• Left flank overlap sign
• Apex at or above T10 level
• Apex under the left hemidiaphragm
• Inferior convergence on the left
• Liver overlap sign

53. Sigmoid volvulus. Supine film.

54.  Caecal volvulus
• Associated with degree of malrotation
• Accounts for less than 2% of adult intestinal obstruction
• Age -30-60 years
Diagnosis
• Pole of the caecum and the appendix lie in LUQ(50%)
• Caecum twists in axial plane and lies in the RLQ(50%)
• One or two haustral markings can usually be identified
• Seen as large gas filled or fluid filled viscus
• Identification of adjacent gas filled appendix confirms the diagnosis
• Left half of colon is usually collapsed

55. Caecal volvulus. Supine.

56. Paralytic ileus
• It occurs when intestinal peristalsis ceases and fluid and gas accumulate in the
bowel loops.
• Postoperative
• Peritonitis
• Inflammation
• Trauma
• Drugs
• CHF , Renal Failure
• Leaking abdominal aortic aneurysm
• Hypokalemia
• General debility or infection
• Vascular occlusion
• Pneumonia
 causes

57. Paralytic ileus. Supine film.

58. Inflammatory conditions
• Intra-abdominal abscess
• Acute appendicitis
• Acute cholecystitis
• Emphysematous cholecystitis
• Acute pancreatitis

59.  Intra-abdominal abscesses
• Abscess are mass lesions of soft tissue density
• Displacement of bowel or organ from their usual position
• Effacement of fat lines
• May contain gas

60. • Subphrenic space
• Subhepatic
• Omental bursa
• Pericolic
• Pelvic
• Posterior pararenal
• Anterior pararenal
• Liver abscess
Specific anatomic sites of abscess formation

61.  Sub-phrenic and Subhepatic abscess
On Chest X-ray
-raised hemidiaphragm(80%)
-Basal consolidation(70%)
-Pleural effusion(60%)
Other signs
• Decreased diaphragmatic movement
• Generalized or localized paralytic ileus
• Scoliosis toward the lesion
• Decreased organ mobility

62.  USG
• an effective test for abdominal collections, being sensitive for fluid collections or
gas–fluid collections.
• It can also be used for guided percutaneous drainage.
• Occasionally deep collections may be obscured by overlying bowel gas

63.  CT Scan
• Subphrenic abscess containing fluid and air
• A mass (15-35 HU)
• Ring enhancement after I.V contrast is
characteristic

64. Retroperitoneal abscess in the anterior and posterior pararenal spaces.

65.  Leucocyte scanning
• 111In-labelled leucocyte scans have been shown to have sensitivity ad specifity
greater than 90 % in the localization of intra abdominal sepsis
• Can identify sepsis at any site including prosthetic grafts and pre-exiting cysts.

66.  Acute appendicitis
• Appendix calculus(.5-6.0 cm)
• Sentinel loop
• Dilated caecum
• Widening of the properitoneal fat
• Blurring of the properitoneal fat
• Right lower quadrant haze due to fluid and edema
• Right lower quadrant mass indenting the caecum
• Blurring of right psoas outline
• Gas in the appendix-rare
On plain films---Signs of acute appendicitis

67.  USG signs
• Blind ending tubular structure at the point of tenderness
• Non-compressible
• Diameter 7mm or greater
• No peristalsis
• Appendicolith casting acoustic shadow
• High echogenicity non-compressible surrounding fat
• Surrounding fluid or abscess
• Edema of caecal pole

68. Ultrasound images showing an anechoic blind-ending tubular structure measuring 10mm in
diameter in the right iliac fossa (RIF): this was found to be non-peristaltic and non-
compressible.
An echogenic round body, with posterior acoustic shadowing seen within the tubular
structure, in keeping with an Appendicolith.
APP = dilated appendix, OMEN = surrounding echogenic inflamed omentum, BLD = bladder

69.  CT findings of acute appendicitis
• 90% diagnostic accuracy to detect acute appendicitis
• Failure of appendix to fill with oral contrast
• Tubular structure 6 mm in diameter or greater with a thickened wall
• Appendicolith
• Surrounding inflammatory changes

70. Acute appendicitis. CT showing
an appendix which contains a
dense Appendicolith
Appendix inflammatory mass. CT shows soft-
tissue density in the right iliac fossa containing an
Appendicolith..

71.  Acute cholecystitis
• Gallstones
• Duodenal ileus
• Ileus of hepatic flexure of colon
• Right hypochondrial mass due to
enlarged gallbladder
• Gas within the biliary system
Signs of acute cholecystitis

72.  Ultrasound : The mainstay of imaging in cholecystitis
• Gallbladder wall thickening (>3 mm), which may be poorly defined.
• Impacted calculi in the gallbladder neck or cystic duct. Gallstones are visualized
as echogenic foci with posterior acoustic shadowing.
• Biliary sludge may be seen as echogenic debris layering in the gallbladder.
• Pericholecystic fluid.
• Positive ultrasound Murphy’s sign

73. USG

74.  CT is not routinely required but may be utilized as part of the investigation of
nonspecific abdominal pain or to assess for secondary complications of
cholecystitis.
• Gallbladder wall thickening (>3 mm).
• Biliary calculi may be visualized as foci of high attenuation within the gallbladder.
• Inflammatory stranding in the pericholecystic fat
• Pericholecystic fluid/focal enhancing collections will appear as a low-attenuation
collection surrounding the gallbladder.
• Locules of free gas adjacent to the gallbladder secondary to necrosis/perforation.
• Cholecystoenteric fistulae are rare.

75. Axial and coronal images showing a thick-walled distended gallbladder with
pericholecystic stranding in keeping with acute cholecystitis .

76.  Acute pancreatitis
Etiology
• Gall stones
• Ethanol abuse
• Neoplasm
• Infection
• Traumatic
• Iatrogenic

77.  Role of USG
• To detect gallstones as a cause of acute pancreatitis
• Detect bile duct calculus and obstruction
• Diagnosis of unsuspected acute pancreatitis or confirm diagnosis
• Guide aspiration and drainage
• Enlargement of the gland
• Decreased gland echogenicity
• Peripancreatic inflammation
• Pancreatic duct dilatation
• Rarely echogenicity may increase due to hemorrhage
USG features

78. Acute pancreatitis . Transverse image shows
heterogeneous pancreas with focal hypoechoic area
Transverse image shows acute inflammation ventral
to the pancreas and ventral to the splenic vein–
superior mesenteric vein confluence . The pancreas
is enlarged and heterogeneous.

79.  Role of CECT
• Necrosis cannot be definitely diagnosed by USG .CECT is the modality of choice.
• Detect complications
• Diagnose unsuspected or confirm acute pancreatitis
• Diagnose conditions mimicking acute pancreatitis
• Guide aspiration and drainage

80.  CT findings
• Enlarged gland
• Low or heterogeneous glandular attenuation
• Peripancreatic fat-normal or hazy
• Focal areas of decreased or no enhancement represents areas of necrosis

81. CT grading-identifies subgroup of individuals at risk for morbidity and
mortality
Percentage
of necrosis
Severity
index
A. Normal pancreas 0 0 o
B. Focal or diffuse pancreatic enlargement 1 0 1
C. Inflammation of pancrease or
Peripancreatic fat
2 <30 %(2) 4
D. Single ill defined Peripancreatic fluid
collection
3 30-50%(4) 7
E. 2 or more Peripancreatic fluid collection 4 >50%(6) 10
Grade A –C: F/Up recommended only if clinical condition declines
Grade D and E: F/up scan needed at 7 to 10 days
:At the time of discharge

82. Acute pancreatitis.

83. Severe pancreatitis.

84. • Fluid collection
• Pancreatic necrosis
• Haemorrhage
• Pseudocysts
• Pseudoaneurysms
• Venous thrombosis
.
Complications

85. Acute colitis
• Acute inflammatory colitis
• Toxic megacolon
• Pseudomembranous colitis
• Ischemic colitis

86.  Plain film can assess
• the extent of the colitis
• the state of mucosa
 State of colonic mucosa can be assessed from :
- the faecal residue
- the width of the bowel lumen
-the mucosal edge
-the haustral pattern

87. Toxic megacolon
• A fulminating form of colitis with transmural inflammation, extensive &
deep ulceration & neuromuscular degeneration.
• Most often involves the transverse colon
• Radiological Findings:
Mucosal islands (=pseudopolyps) & dilatation (>5.5 cm)
Haustra will be effaced or blunted
• Common complication:
Perforation in the sigmoid & peritonitis

88. Supine film. Toxic megacolon in Crohn's disease.

90. Chron’s disease Ulcerative colitis

91. Ischemic colitis
-Etiology
• Vascular insufficiency
-C/F
• Sudden onset of severe abdominal pain followed by bloody diarrhoea
• Splenic flexure and descending colon preferentially involved

92. X-ray: Ischemic colitis

93.  CT scan
• Best diagnostic modality
• Mural thickening and peri-colonic stranding
• Thickening and mucosal hyper density
• Heterogeneous enhancement
• Loss of colonic Haustra
• Colon contour is shaggy
• Lumen dilated
• +/- gas in the bowel wall, portal vein and mesentery

94. Leaking abdominal aortic aneurysm
Etiology
• Atherosclerosis
• Mycotic
• inflammatory
 Age: 65 yrs and older
 Site: below the origin of renal arteries
 C/F: prescence of pulsatile mass with sudden hypotension
: back pain

95. Imaging
Plain film
• Central soft tissue mass which may obscure psoas
outline on the left
• Frequently curvilinear calcification
• Obscured renal outline

96. Supine film.
Leaking aortic aneurysm.

97. CT scan
• Most common finding is retro peritoneal
hematoma(density>50 HU)
•Extension of blood into pararenal spaces and psoas
muscle
• On CECT active extravasation of the contrast

98. Axial NECT image

99. Axial and coronal arterial-phase images

100. Ectopic pregnancy
• Occurs in 2% of pregnancies and accounts for 9% of all pregnancy-
related deaths secondarily to venous thromboembolism.
• Many factors increase the risk of ectopic pregnancy by affecting the
migration of the embryo to the endometrial cavity.
• Usually presents by 7th week of pregnancy.
• Missed or delayed diagnosis can be devastating with massive
haemorrhage and possibly death.

101.  Risk factors
• pelvic inflammatory disease
• previous history of ectopic pregnancy
• prior tubal surgery
• assisted reproductive technology
• intra-uterine contraceptive devices,
• age >35 years and smoking.

102. Radiological features
• An extra-uterine sac containing a fetal pole or yolk sac with or without
cardiac motion is observed in <20% of cases and confirms an ectopic
pregnancy .
• A thick-walled cystic structure or a complex adnexal mass independent of
the ovary and uterus is also suggestive of ectopic pregnancy.
• Identification of a viable intra-uterine gestation sac virtually rules out an
ectopic pregnancy except in the rare circumstance of a heterotopic
pregnancy (incidence of 1 in 7,000 pregnancies)
 Ultrasound : The imaging modality of choice
Features

103. Cont.
• Other supportive findings include absence of an intra-uterine pregnancy at
6 weeks gestation pelvic free fluid or hyperechoic clot within the uterus,
hydro- or haematosalpinx or a thickened endometrium.
• A pseudogestational sac may be seen consisting of endometrial thickening
with an anechoic centre composed of haemorrhage.
• In cases of rupture, extensive anechoic intra-abdominal and pelvic
haemorrhage may be seen.

104. Longitudinal images demonstrating a normal uterus with no intra-uterine pregnancy .

105. Ovarian cyst torsion
• Commonest in women of childbearing age but can affect women of all ages.
• Caused by twisting of the vascular pedicle with associated venous or arterial
occlusion and subsequent infarction.
• Symptoms include lower abdominal pain, nausea , vomiting
• Risk factors include enlarged ovaries >6 cm, elongated ovarian ligaments

106.  USG
• Free fluid seen within the abdomen is suggestive of cyst rupture. In the absence
of a visible cyst, a review of previous ultrasound studies may be useful.
• Torsion is characterized by an heterogeneous enlarged ovary with internal echoes
and reduced or absent Doppler signal.

107. Ultrasound LA : Ovary

108. Renal colic
• Pain caused by the passage of a renal calculus through the ureter.
Clinical features
Renal colic: severe, spasmodic flank pain radiating to groin.
Imaging
The role of imaging is to confirm urolithiasis, identify the location and degree of
obstruction and identify potential complications.

109. Plain films
• Low sensitivity and specificity (45% and 75%) for urolithiasis limits its role in the
acute setting. Can provide a baseline for follow-up.
Intravenous urography (IVU)
• Traditionally the first-line imaging modality. Not ideal if there is poor renal
function.
Findings
• Direct visualization of a ureteric calculus.
• A delayed nephrogram and filling of the collecting system with a standing column
of contrast in the ureter to the level of the calculus which persists post
micturition.
• The length of delay in the appearance of contrast in the collecting system gives an
idea of the degree of obstruction.
• Affected kidney is modestly enlarged.

110. Nephrogram: IVU

111.  CT Scan
Findings
• Hydronephrosis / hydroureter down to the level of a ureteric
calculus.
• perinephric stranding and nephromegaly.

112. Thank you