Acute Abdomen Imaging

IMAGING IN
ACUTE ABDOMEN
DR. WAN NAJWA ZAINI WAN MOHAMED
RADIOLOGIST, HOSPITAL QUEEN ELIZABETH II
Emergency And Trauma Imaging: Recognizing The Basics, 9 – 11 Nov 2018

CONTENTS
• INTRODUCTION
• IMAGING TOOLS
• RADIOLOGICAL SIGNS
 PLAIN RADIOGRAPH
 ULTRASOUND
 CT SCAN
• CONCLUSION

INTRODUCTION

DEFINITION
“Any sudden non-traumatic disorder whose chief
manifestation is in the abdominal area and for which urgent
operation may be necessary”
A clinical syndrome “sudden onset of severe abdominal pain
requiring emergency medical or surgical treatment”

In a review of 30,000 patients with acute abdomen
1. Acute Cholecystitis
2. Acute Renal Colic
3. Acute Appendicitis
4. Acute Pancreatitis
5. Hepatic Abscess
6. Intestinal Obstruction/
Intussusception
7. Psoas Abscess
8. Abdominal Trauma
9. Ob/Gyn Emergency
appendicitis
small-bowel obstruction
no cause
(non
specific
abdominal
pain)
acute cholecystitis
AJR 2000; 174:901-913

ROLE OF IMAGING
• To narrow down the differential diagnosis
 Prompt and accurate diagnosis essential to minimize
morbidity and mortality
• To help surgeon decide whether patient requires surgery or
not, and if so, how soon?

IMAGING TOOLS

IMAGING TOOLS
• PLAIN RADIOGRAPH
• ULTRASOUND
• CT SCAN

PLAIN RADIOGRAPH
• Long established as essential imaging method
• Often less specific; low diagnostic yield (10– 20%)
• Overutilization of AXR in AE setting (42.7 – 55.8%) due to
inappropriate requests  lower diagnostic accuracy
• Despite technical advances, plain radiography should be the
first imaging study for suspected cases of bowel perforation
or obstruction
• Remote setting without CT Scan facility: remains main
modality for initial investigation in acute abdomen

PLAIN RADIOGRAPH
• Views: Supine AXR, Erect
CXR
• Added views: Erect AXR, Left
Lateral Decubitus AXR,
Horizontal AXR
• Erect CXR – Best for small
pneumoperitoneum (air under
diaphragm), valuable pre-op
baseline

PLAIN RADIOGRAPH
TABLE 1: Royal College of Radiologists (RCR),London

ULTRASOUND
• Commonly used as primary screening tool
• Improvements in US resolution and probe technology – first
modality in assessing paediatric or female patients with O&G
problems.
• Advantage: widely available, low cost, absence of radiation
exposure
• Drawback – operator dependent, presence of ileus obscuring
area of interest which commonly accompanies acute abdomen
• Technique: B-mode (grey scale), curvilinear probe
• Need to: fast for gallbladder pathology, full bladder for O&G cases
& bladder/ pelvic assessment.

ULTRASOUND
 Indications:
Acute cholecystitis, choledocholithiasis
Renal colic/ Obstructive uropathy
Intraabdominal abscess/ collection – e.g. liver, kidney, psoas
Acute pancreatitis
Acute appendicitis
Intussusception
O&G emergency, e.g., ectopic gestation, adnexal torsion, and
hemorrhagic ovarian cyst
Abdominal aortic aneurysm
Abdominal trauma

CT SCAN
• Better detection and higher accuracy rates (almost 95%)
• Most beneficial in patients who present with confusing or
conflicting clinical signs and symptoms
• Useful in diagnosing, detecting and characterizing the full
extent of disease
• Technique:
 Scans obtained from diaphragm to beneath the symphysis
pubis
 Collimation of 5-7 mm and a pitch of 1.0-1.5
 Data reconstructed at intervals of 3-7 mm, depending on the
clinical indication

CT SCAN
• Use of contrast media depends on indication/working
diagnosis, time and local setting
• IV contrast
 Opacifies the abdominal vasculature and provides useful
information regarding enhancement of the parenchymal organs
and intestine
 Exceptions include evaluation of suspected ureteral colic
 Carries risk of nephrotoxicity and potential contrast material
reaction.
 Volume: 125 – 150 ml, rate: 2 – 3 ml/sec
 Scans obtained during portal venous phase at 60 – 70 sec
delay

CT SCAN
Arterial phase imaging useful in suspected hemorrhage, bowel
ischemia, and arterial thrombosis cases
Delayed scans can reveal renal and bladder mass/disease that
might be overlooked during earlier phases
• Oral contrast
Used primarily to differentiate bowel loops from abdominal and
pelvic masses and abscesses
May obscure the diagnosis of bowel hemorrhage or ischemia
Exceptions – high-grade small bowel obstruction, ureteral colic
In suspected gastric disease or gastrointestinal bleeding, water
can be used

CT SCAN
Volume: 800-1000 ml of oral diluted water-soluble contrast
material at least 1 hr before scanning
Practical difficulties – time consuming, randomness of contrast
opacification, inability of sick patients to consume and retain
sufficient quantities
• Rectal contrast
Not routinely used
Advocated by some to optimize the detection of appendicitis,
diverticulitis, and epiploic appendagitis
Volume: 400-600 ml of a 3% solution of water-soluble contrast
material administered rectally by gravity through a soft rubber
rectal catheter.

PLAIN RADIOGRAPH
RADIOLOGICAL SIGNS
PLAINNEARAUVERSby
VANGOGH

Analyzing AXR
A. Bowel Loops (Intraluminal Air)
B. Extra Luminal Air
C. Soft Tissue
D. Calcification

• Stomach
Relatively large amount of gas
Gastric rugae (supine)
Long air fluid level in
fundus (erect)
• Small bowel
Central position, valvulae
conniventes
Calibre 2.5cm, usu. small amt
of gas
> 2 fluid levels & dilated –
abnormal
• Large bowel
Peripheral position, haustra
Calibre:
 Transverse colon : 5.5 cm
 Caecum >9 cm - danger of
perforation
 Fluid levels – common, 3-5
fluid levels (< 2.5 cm in
length) may be seen esp. in
right lower quadrant

Case courtesy of Dr Jeremy Jones, Radiopaedia.org, rID: 34067

Abnormal Site/Distribution
Lumen Size /Content
Wall Appearance
I. Gasless Abdomen
II. Bowel Dilatation
a. Gastric Dilatation
b. Mechanical Obstruction
c. Pseudo-obstruction
d. Paralytic Ileus
III. Mucosal Wall
Abnormality

I. Gasless Abdomen
• Total paucity of gas – rare
• Fluid filled bowels, common in
children
• Highly suggestive of high
obstruction
• Other causes: excessive
vomiting, diarrhea, early
stages of appendicitis,
Addisonian crisis (adrenal
crisis), cerebral depression

a. Gastric Dilatation
• Mechanical/ gastric outlet obstruction
 Duodenal ulcer, antral carcinoma, extrinsic compression
 Huge fluid-filled stomach with little or no bowel gas beyond
• Paralytic ileus
 “acute gastric dilatation”
 Fluid & electrotrolyte disturbance
 > in old people, high mortality
• Gastric volvulus
 Grossly dilated, air-filled stomach
 Spherical, left upward
 Elevated diaphragm

b. Mechanical Obstruction

Small Bowel Obstruction
• Causes – adhesion,
strangulated hernias,
intussusception, volvulus, tumor,
gallstone ileus
• 3 signs highly suggestive:
two or more air–fluid levels
air–fluid levels wider than 2.5
cm
air–fluid levels differing more
than 5 mm from one another in
the same loop of small bowel

Large Bowel Obstruction
• Left > right
• Depends on site of obstruction/ patency of ileocaecal valve
• Common causes:
• Tumor, Abscess, Diverticular ds, Volvulus
• Extrinsic compression by pelvic tumor
• Both small & large bowels dilated ~ mimic paralytic ileus

Pseudo-obstruction
• Symptomatically, clinically and radiologically mimic intestinal
obstruction
• May be acute & self limiting
• Pneumonia, sepsis, drugs, DM, collagen & neurologic
disorders, amyloid ds or idiopathic
• Gastric, small or large bowel distension with fluid levels
• Contrast study

Paralytic Ileus
• Occurs when intestinal
peristalsis ceases, fluid and
gas accumulation in bowel
• Occurs most freq. in
inflammatory conditions,
peritonitis & post operative
• Local inflammation – ileus of
1 or 2 loops of small bowel
“sentinel loops”
• Gas Distribution: Generalized
presence of gas throughout
all quadrants
• Bowel Dilatation: The degree
of bowel dilatation is
proportional
• Arrangement of Loops:
Disorderly arrangement “a
bag of popcorn”

MECHANICAL OBSTRUCTION PARALYTIC ILEUS
Gas distribution
Too much air in the small bowel (and not
much gas in the large bowel) or too much air
in the large bowel (and not much gas in the
small bowel).
Poor gas distribution or gasless
Good gas distribution over most of the
abdomen
Too much air in both large and small bowel
* Warning: This could also appear in large
bowel obstruction with an incompetent
ileocecal valve, or in an early or intermittent
small bowel obstruction
Bowel dilatation
Smooth bowel walls (resembles sausages or
a hose)
Preferential dilatation of the bowel proximal
to the obstruction
Dilatation of the bowel in proportion to each
other, so that the colon remains larger than
the small intestine
 Look for sentinel loops
Air-fluid levels
Many dilated air-fluid levels in both limbs of a
given loop, at different heights (candy
canes)
Fewer and/or smaller (less dilated) air-fluid
levels scattered throughout the abdomen
Arrangement of loops
(supine only)
 Orderly arrangement of dilated loop
 “Stepladder" fashion from left upper
quadrant to right lower quadrant
 A bag of sausages
Disorderly loops scattered throughout the
abdomen
A bag of popcorn
Table 3: Comparison between Mechanical Obstruction and Paralytic Ileus

III. Mucosal Wall Abnormality
• Irregularity, thickening
inflammation, ischaemia (oedema, haemorrhage)
• Thumbprinting sign
Submucosal haemorrhage
• String of beads sign
Gas in between valvulae conniventes
• Intramural air
hypoxaemia, infection, emphysema, cystic pneumatosis

ANALYZING AXR
C. Soft Tissue
D. Calcification

B. Extraluminal Air
I. Intramural air
II. Pneumoperitoneum (Intraperitoneal air)
III. Pseudo-pneumoperitoneum
IV. Air in lumen – portal vein, biliary tree
V. Air in an organ

I. Intramural Air
• Cystic pneumatosis
May be due to gas leak
1-3cm cysts in subserosal and
submucosal layer
Interstitial emphysema
Sign of impending rupture in
toxic megacolon
• Gas forming infection
• Hypoxaemia due to infarction
or thrombosis

II. Pneumoperitoneum
• Perforated hollow viscus
Ulcer, neoplasm, bowel
obstruction, ischaemic bowel,
diverticulitis, surgical Cx
• Through the peritoneum
Penetrating injury
• Via Female Reproductive
System
Exercise, postpartum,
douching, intercourse
• From chest, retroperitoneum
• Signs:
Central Tendon
Double Wall Sign (Rigler Sign)
Football Sign
Falciform Ligament
Parahepatic Air
Umbilical Ligament, Urachus
Lucent Liver Sign

III. Pseudo-pneumoperitoneum

IV. Air in Lumen
Air in Portal Vein
• Aeroportia
• Associated with presence of
air within bowel wall
• E.g. Necrotizing enterocolitis,
bowel infarction
• Signify grave prognosis when
occur in bowel necrosis
DELICATE & PERIPHERAL

IV. Air in Lumen
Air in Biliary Tree
• Aerobilia
• Occur in patulous sphincter,
post ERCP/ sphincterectomy,
any fistulous communication
between biliary tree and
bowel
• Gas forming infection of the
gallbaldder
CHUNKY AND CENTRAL

V. Air in Organ
• Infection caused by gas
forming organism
• Collects within the organ wall
or cavity
• Linear lucency within wall or
confined lucency in the region
of involved organ
• Air fluid level may be seen

ANALYZING AXR
C. Soft Tissue
D. Calcification

C. Soft Tissue
• Fat lines: Posterior extraperitoneal fat pad
 Completely surround kidneys, psoas, post. borders of liver and
spleen
 Extends anteriorly and laterally to surround parietal peritoneum
(properitoneal fat)
 Responsible for visualisation of intraabdominal organs
• Can be displaced by organ enlargement or effaced by
inflammation or fluid
• May be blurred or not identified at all
 Spleen not be identified in 42%
 Right psoas blurred in 19%
 Properitoneal outlines lost in 18%

PSOAS ABSCESS INTUSSUSCEPTION
Soft tissue mass with air crescent sign

D. CALCIFICATION
Calcification Acute condition
Gallstones Cholecystitis
Pancreatitis
Biliary colic (stone may be close to spine)
Empyema of gallbladder
Gallstone ileus (stone in abnormal location)
Calcified gallbladder wall Cholecystitis
Limy bile Cholecystitis
Appendix calculus Appendicitis
Calculus in:
Meckels,jejunal & colonic diverticulum
Acute inflammation or perforation
Pancreatic calculi Pancreatitis
Ureteric calculus Renal colic
Calcified aneurysmsaortic, splenic, hepatic Rupture
Teeth or bone in ovarian dermoid Torsion

ULTRASOUND
RADIOLOGICAL SIGNS

Acute Cholecystitis
• Non compressible, tender
gallbladder distension
• Wall thickening > 3mm
• Pus/sludge content +/-
calculus
• Pericholecystic collection

Obstructive Uropathy
• Dilated pelvicalyceal system/
ureter
• Cortical thinning
• Renal or ureteric calculi

Acute Appendicitis
• Wall-to-wall diameter >6mm
• Surrounding inflamed fat
• Faecolith
• Hypervascularity

Acute Pancreatitis
• Hypoechogenicity
surrounding the
peripancreatic area
• Complex striated pattern with
hemorrhage

Liver Abscess
• Hypoechoeic collection with
posterior enhancement
• Moving pus/sediment within
• Perilesional hypervascularity

Acute Diverticulitis
• Diverticulosis with segmental
colonic wall thickening
• Inflammatory changes in the
fat surrounding a diverticulum

Bowel Dilatation/ Thickening
• Bowel Dilatation
 Distended loops of bowel
 Ileus – fluid filled
• Ileitis/Colitis
 Mural wall thickening, oedema

Ascites/ Free fluid

CT SCAN
RADIOLOGICAL SIGNS

Acute Appendicitis
• Diameter enlarged > 6cm
• Wall – thickened,
homogenous dense
enhancement
• Adjacent periappendiceal fat
streakiness/ inflammation
• Appendicolith

Acute Diverticulitis
• Inflammatory change in the
pericolic fat
• Mural wall thickening
• Phlegmon or frank abscess
formation
• Diverticula

Bowel Obstruction
• Dilated fluid filled bowels with
transition zone
• Causative agent : mass,
hernia, intussusception,
abscess, inflammatory
thickening vs adhesion
• Closed loop obstruction
 Strangulated bowel
 Twisted C or U-shaped loop
with converged mesenteric
vessels
 Engorged mesenteric
vasculature, edema, bowel
wall thickening

Bowel Ischaemia
• Causes :
vascular occlusion or
thrombosis from arterial/
venous disease
 hypoperfusion
• Mural thickening with target or
halo appearance
• Pneumatosis intestinalis
• Air in the bowel wall,
mesentery or portal venous
system – grave prognosis

GI Perforation
• Pneumoperitoneum, most
non dependent area –
anterior to liver surface
• Extravasation of oral contrast
• Loculated fluid and gas, focal
mesenteric or omental
infiltration, focal enhancement
of the parietal peritoneum can
help pinpoint site of
perforation

CONCLUSION

CONCLUSION
• In patients with an acute abdomen ‘the stakes are high’ –
important to recognize life-threatening conditions from self-
limiting causes
• Although AXR limited role, still valuable in remote/ district
hospitals and certain conditions
• Sonography and CT more accurate and rapid
• A systematic approach to radiological imaging:
 Confirm or exclude the most common diseases
 Screen the whole abdomen for general signs of pathology

Acute Abdomen Imaging

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