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• 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.
Causes of acute abdomen• Perforation• Intestinal obstruction
• Paralytic ileus• Inflammatory causes
• Renal colic• Leaking abdominal aneurysm• Acute gynecological disorder
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
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
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.
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
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
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
CT scan• Most sensitive method for detecting peritoneal gas• Gas tends to collect over the liver anteriorly, mid abdomen and peritoneal recess.
Gastric dilatation
Causes
• Paralytic ileus• Mechanical bowel obstruction• Gastric volvulus• Air swallowing
X-ray abdomen-supineIntestinal obstruction
Small bowel obstruction
Extrinsic Bowel wall Intraluminal
Adhesions Neoplasia Intussusception
Hernia Stricture Foreign body
Volvulus Intestinal ischemia Gallstone ileus
Abscess Bezoar
Peritoneal deposits
Causes
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
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
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
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.
Simple bowel obstruction
• Dilated small bowel leads into a mass at the point of transition to collapsed small bowel
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
SBO due to hernia
External hernia Internal hernia
InguinalFemoral UmbilicalIncisionalSpigelian
ParaduodenalTransmesenteric
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
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
Intussusception
CharacteristicsInvagination 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
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.
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
Plain film
• There are multiple gas filled loops of dilated small bowel
• Soft tissue mass in right iliac fossa
Small-bowel obstruction due to a small-bowel melanoma metastasis which has caused jejunal intussusception.
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
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.
• 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.
Axial Sagittal and coronal images demonstrating gas within the bowel wall and portal venous system consistent with ischaemic small bowel
Large bowel obstruction
Etiology• Carcinoma• Volvulus• Diverticular disease
3 types of patterns of obstruction
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
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.
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).
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
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
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
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
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
Inflammatory conditions
• Intra-abdominal abscess
• Acute appendicitis
• Acute cholecystitis
• Emphysematous cholecystitis
• Acute pancreatitis
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
• Subphrenic space• Subhepatic
• Omental bursa • Pericolic• Pelvic
• Posterior pararenal• Anterior pararenal• Liver abscess
Specific anatomic sites of abscess formation
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
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
CT Scan• Subphrenic abscess containing fluid and air
• A mass (15-35 HU)• Ring enhancement after I.V contrast is
characteristic
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.
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
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
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
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
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..
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
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
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.
Axial and coronal images showing a thick-walled distended gallbladder with pericholecystic stranding in keeping with acute cholecystitis .
Acute pancreatitis
Etiology
• Gall stones• Ethanol abuse• Neoplasm• Infection• Traumatic• Iatrogenic
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
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.
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
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
CT grading-identifies subgroup of individuals at risk for morbidity and mortality
Percentage of necrosis
Severity index
A. Normal pancreas 0 0 oB. Focal or diffuse pancreatic enlargement 1 0 1C. 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 declinesGrade D and E: F/up scan needed at 7 to 10 days :At the time of discharge
• Fluid collection• Pancreatic necrosis• Haemorrhage• Pseudocysts• Pseudoaneurysms• Venous thrombosis
.Complications
Acute colitis• Acute inflammatory colitis• Toxic megacolon• Pseudomembranous colitis• Ischemic colitis
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
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
Ischemic colitis-Etiology• Vascular insufficiency
-C/F• Sudden onset of severe abdominal pain followed by bloody diarrhoea• Splenic flexure and descending colon preferentially involved
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
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
Imaging
Plain film• Central soft tissue mass which may obscure psoas
outline on the left• Frequently curvilinear calcification• Obscured renal outline
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
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.
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.
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
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.
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
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.
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.
ImagingThe role of imaging is to confirm urolithiasis, identify the location and degree of obstruction and identify potential complications.
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.
CT Scan
Findings• Hydronephrosis / hydroureter down to the level of a ureteric
calculus.• perinephric stranding and nephromegaly.