Radiology in acute abdomen
The acute abdomen is defined as a life threatening situation that is produced by a variety of intraperitoneal pathologic conditions and that requires expeditious and accurate diagnosis, and, in most instances, emergency surgical intervention
Imaging
Erect chest radiograph: o Small pneumoperitoneum can be detected o Various chest conditions may mimic an acute abdomen. o Acute abdominal conditions may be complicated by chest pathology o Acts as a valuable baseline
Abdominal radiographs: (kv:60-65, short exposure time) o Supine abdominal radiograph- distribution of gas calibre of bowel displacement of bowel obliteration of fat lines
o Erect abdominal radiograph- fluid level and free gas o Horizontal-ray films( erect or lateral decubitus)- free intra- abdominal air, fluid levels
o Lateral abdominal radiograph- demonstrate calcification in an aortic aneurysm
Ultrasonography- extremely effective in conditions like acute cholecystitis, appendicitis, gynaecological disease, intraperitoneal fluid etc
CT- modality of choice in acute abdominal cases as it is not hampered by overlying gas, bone or adipose tissue
IVU- in a case presenting with a renal colic - in renal trauma
Angiography- helps to define anatomy and globally assess
MRI
major organ and vascular structures
Nuclear medicine
Conditions presenting as an acute abdomen
Pneumoperitoneum
Presence of free gas in the peritoneal cavity always indicates perforation of a viscus Commonest cause is peptic ulcer perforation, less common causes are diverticulitis and malignant tumours.
Imaging Erect chest radiograph & left lateral abdominal radiograph Signs of free gas on the supine radiographo Morison’s pouch air o Perihepatic air o Rigler’s(double wall) sign o Falciform ligament o Umbilical ligament o Urachus o The cupula o Football or air-dome C.T.-most sensitive.
Free air under the diaphragm
Rigler’s sign
Pneumoperitoneum
Intestinal obstruction
Gastric dilatation Causeso Paralytic ileus Post operative Trauma Peritonitis Pancreatitis , Cholecystitis Diabetic & hepatic coma o Mechanical gastric outlet obstruction Peptic ulceration Antral carcinoma Extrinsic duodenal compression o Gastric volvulus o Air swallowing o Intubation o Secondary to intestinal obstruction o Drugs
Distended stomach with fluid and gas
Massive fluid filled stomach with little or no bowel gas beyond
Gastric volvulus
o Twisting of the stomach around its longitudinal or mesenteric axis o Laxity of the gastro-colic, gastrohepatic & gastro-lienal ligament predisposes to gastric volvulus o In organo-axial volvulus, the stomach twists either anteriorly or posteriorly around its longitudinal axis with two points of luminal obstruction Contrast studies reveal complete obstruction at the lower end of oesophagus/no passage beyond the obstructed pylorus
o In mesentero-axial volvulus, the stomach twists around the mesentery, so that the antrum and pylorus lie above the gastric fundus o Can cause complete obstruction, strangulation and perforation o The fluid and air containing dilated stomach is identified as a spherical viscus displaced upward and to the left with little or no gas beyond
Mesentero-axial volvulus
Organo-axial volvulus
Small bowel obstruction
Extrinsic causes - adhesions - hernias - masses - congenital malrotations Intramural causes - inflammatory strictures - ischaemia - primary small bowel tumours Intraluminal causes - gall stones -foreign bodies
Imaging Plain film o Signs appear after 3-5 hours, marked after 12 hours o Supine abdominal X-rays- dilated gas filled loops, identified as sausage shaped, oval or round soft tissue densities o Erect films- multiple fluid level o Horizontal ray films- ‘string of beads’ sign
Dilated small bowel loops
Multiple air-fluid levels
Contrast studies- 100ml of non-ionic contrast given orally
& further film taken at 4 hours. If no contrast in caecum- high likelihood for surgery USG - dilated fluid-filled loops
- peristaltic activity can be assessed C.T.- bowel calibre
- fluid filled loops - Level & cause of obstruction - ascitis
Strangulating obstruction o Occurs when two limbs of a loop are incarcerated by a band or in a hernia, compromising the blood supply o Plain radiograph- soft tissue mass or pseudotumour - gas filled loops separated by thickened walls may resemble a large coffee bean - if gangrene occurs, lines of gas seen in the wall of the small bowel
C.T.- small bowel dilatation - V shaped or radial fluid filled loops - mesenteric vessels converging towards the point of obstruction - stangulation- thickened loop with venous congestion of the mesentery locally - haemorrhage- increased attenuation of bowel wall - necrosis- gas in the bowel wall
Gallstone ileus o Mechanical intestinal obstruction due to impaction of gall stones in the intestine o Comprises about 2% of small bowel obstruction o Signs- gas within bile ducts/ the gall bladder - complete or incomplete small bowel obstruction - abnormal location of gallstone - change in position of gallstone o C.T.- small bowel dilatation - gas within the biliary tree - gallstone at the point of obstruction
Gall stone ileus
Intussusception •
It is the invagination of a segment of bowel ( intussusceptum) into the contiguous segment ( intussuscipiens)
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Commonly seen in children below 2 years
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Ileocolic segment involved in 90% cases, ileoileocolic, colocolic and ileoileal intussusception may also occur
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Usually commences in the ileum due to inflammation of the lymphoid tissue in Peyer’s patches
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Pathological lead points – 5‐ 10 % cases
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In adults – surgery/ tumour
Plain radiograph- absence of bowel gas in RIF - Soft tisssue mass, spherical or oval, surrounded by cresent of air -“Target sign”- two concentric circles of fat density - Small bowel obstruction
Contrast examination- Intraluminal crescentic filling defect - Outer surface may show a rim of barium similar to a “coiled spring” - reduction can be achieved
USG-mass with a central echogenic area surrounded by concentric sonolucent rings
CT- sausage shaped mass
Ileo-colic intussusception
Small intestinal infarction Caused by thrombosis or embolism of the superior mesenteric artery Plain film findings: - Gas and fluid filled dilated small bowel loops - Multiple fluid levels - Submucosal haemorrhage and oedema- Wall thickening - Gangrene-Linear gas streaks in bowel wall - Perforation- free gas -Gas in the portal vein-grave prognostic sign CT- Bowel wall thickening - Engorgement of mesenteric veins - Increased attenuation of mesenteric fat
Large bowel obstruction Common causes include tumour, abscess, diverticular disease, volvulus etc Plain radiographs- depends on the site of obstruction and the competency of the ileo-caecal valve
Type Ib
Type Ia
Type II
Large bowel volvulus
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Sigmoid colon and caecum ‐ most common sites
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Compound volvulus, involving interwining of two loops of bowel is rare
Caecal volvulus Seen when caecum & ascending colon are on a mesentery the caecum twists and inverts( 50%), in the other half the twist occurs in an axial plane Plain radiograph - large viscus filled with gas and fluid - 1 or 2 haustral markings - left side of the colon is collapsed
Sigmoid volvulus •
Twisting of the sigmoid loop around the mesenteric axis, axial torsion is rare
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Plain radiograph‐ northern exposure sign coffee bean sign white stripe sign three line sign
Sigmoid volvulus
Contrast enema-“ bird of prey” sign-smooth, curved tapering of the barium column -mucosal folds show a “cork screw “ pattern -In chronic casesshouldering
Bird of prey & cork screw app
Distinction between small and large bowel dilatation
Valvulae conniventes No. of loops Distribution of loops Haustra Diameter Radius of curvature Solid faeces
Small bowel
Large bowel
present in jejunum Many Central Absent 3-5 cm Small Absent
Absent Few Peripheral Present 5 cm+ Large Present
Paralytic ileus •
Occurs when intestinal peristalsis ceases and, as a result, fluid and gas accumulate in the dilated bowel
• Abdominal radiographs‐ ‐small and large bowel dilatation ‐ multiple fluid levels
Acute Colitis
Toxic megacolon
A fulminating form of colitis with trans-mural inflammation, extensive and deep ulceration and neuromuscular degeneration Plain abdominal radiographs- mucosal islands - dilatation(>5.5cm) -perforation : pneumoperitoneum
Ischaemic colitis Disorder caused by vascular insufficiency and bleeding into the wall of the colon Preferentially involves the splenic flexure Ischaemia causes oedema, haemorrhage & ulceration and fibrosis following transmural ischaemia may result in stricture formation Imaging- splenic flexure irregularity with mural thickening Barium studies : -Thumb printing - ulcerations - loss of haustra
Thumb printing
Inflammatory conditions
Acute appendicitis o Commonest acute surgical condition in the developed world o Radiological signs Appendix calculus(0.5-0.6)cm
Right lower quadrant mass indenting the caecum Dilated caecum Sentinel loop Widening / blurring extraperitoneal fat line Scoliosis concave to the right Right lower quadrant haze Gas in the appendix
Ultrasonography: Blind ending tubular structure Non compressible Diameter 7 mm or greater No peristalsis Appendiculolith High echogenicity non-compressible surrounding fat Surrounding fluid or abscess
Barium study: - mass indenting the caecum - displacement of caecum - partial filling or non filling of the appendix
C.T. : - Appendix measuring greater than 6mm in diameter - Failure of the appendix to fill with oral contrast / air upto its tip - Appendiculolith - Wall enhancement - The ‘arrow head’ sign
Acute cholecystitis Almost all cases of acute cholecystitis are associated with gall stones and most are caused by obstruction of the cystic duct Plain radiograph- normal in 2/3rd cases o Gall stones o Porcelein GB o Distended GB o Duodenal ileus o Hepatic flexure ileus o Gas within the gallbladder or biliary tree
Ultrasound- Mural thickening >3mm, with a hypoechoic halo - Pericholecystic abscess formation - Gallstones/ sludge - Positive sonographic Murphy’s sign
Acute pancreatitis Inflammation of the pancreas with release of various enzymes
Plain film changesChest x-rayo Left sided pleural effusion o Splinting of left hemidiaphragm o Basal atelactasis Abdominal filmo Duodenal ileus o Gasless abdomen o “colon cut off” sign o Renal “halo” sign o Absent left psoas shadow o Indistinct mottled shadowing o Sentinel loop o Intrapancreatic gas-abscess/ enteric fistula
Bone changeso Bone infarcts o Avasular necrosis o Lytic lesions
USGo Pancreatic enlargement, hypoechoic parenchyma o Fluid collections o Ascitis
CTo Demonstrates gland enlargement, necrosis, haemorrhage and presence of
solid parenchyma o Localisation of extrapancreatic fluid collection o Detect pseudocyst formation Balthazar et.al. devised the following grading system based on CT findingsGrade A : Normal pancreas Grade B : focal or diffuse enlargement of the gland Grade C : peripancreatic oedema and intrinsic abnormalities of grade A Grade D : single, ill-defined fluid collection or phlegmon Grade E : two or more fluid collections or presence of gas
Intra‐abdominal abscess Abscesses are collections of pus that may displace adjacent structures following their involvement by inflammatory process
Subphrenic abscess •
Nearly always occurs as a result of surgery
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Chest X‐ray‐ raised hemidiaphragm ‐ basal consolidation ‐ pleural effusion
Abdominal radiographs‐ gas/fluid level ‐ Irregular gas pocket ‐ Scoliosis towards the lesion ‐ localised paralytic ileus
Fluoroscopy‐ decrease diaphragmatic movement ‐ locates small gas‐fluid level/ irregular gas pockets
Barium studies- displacement of bowel - Presence of gas/fluid level outside the bowel
USG- helpful in detection of gas free abscesses CT- ill defined or partially encapsulated fluid collections with/ without gas foci
Radionuclide scanning – Indium-111 chelated to leucocytes with either oxine or tropolone
Sub-phrenic abscess
Trauma
Visceral injuries Pattern of injuries encountered at laparotomy following trauma Organ (i) Spleen (ii) Liver (iii) Mesentery (iv) Urologic (v) Pancreas (vi) Small bowel (vii) Colon (viii) Duodenum (ix) Vascular (x) Gall bladdder
Relative incidence 46% 33% 10% 09% 09% 08% 07% 05% 04% 02%
Splenic trauma •
Most commonly injured organ
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Lesions may be‐ ‐ subcapsular/intrasplenic haematomas ‐ splenic lacerations
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USG‐ normal appearing spleen with free intraperitoneal fluid ‐ curved/cresenteric subcapsular haematoma ‐ round, linear or irregular intrasplenic haematomas ‐ non‐homogenous splenic echotexture Lacerated splenic injury
CT- modality of choice o Subcapsular haematomas- low attenuation collections that indent the splenic margin o Intrasplenic haematoma- diffuse hypoattenuating lesions o Splenic lacerations- low attenuation defects o Complex interconnecting lacerations- shattered spleen Angiography- determines presence of active extravasation
Splenic laceration
Fractured spleen
Benya’s grading of splenic injury(1995) Grade I- superficial laceration & subcapsular haematoma (3 cm deep) or foci of devascularized spleen
Hepatic trauma •
2nd most injured organ in blunt abdominal trauma
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Right lobe> left lobe
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USG: haematomas‐ :subcapsular( lens shaped) :deep (linear, spherical, ovoid, irregular or branching)
o Bilomas‐ anechoic well defined intra/extrahepatic masses without any visible capsule
Hepatic laceration
CT: contrast enhanced CT remains the best investigative modality Contusions- illdefined areas of low attenuation Lacerations- low attenuation areas in linear or branching patterns - multiple radiating lacerations-“bear claw” appearance Haematomas –subcapsular: indents the liver margin - intraparenchymal: round/oval with central high attenuation Fractures- laceration extending from one surface to another
Subcapsular haematoma Bear claw appearance
CT grading (blunt abdominal trauma): Grade I-capsular avulsion, superficial lacerations(3 cm Grade IV- massive central/subcapsular haematoma >10 cm, lobar tissue destruction or devascularisation Grade V- Bilobar tissue destruction or devascularisation
Gall bladder & extrahepatic biliary tree trauma
Very rare
USG Perforation pericholecystic fluid collapsed GB ascites
CT ascitis localised fluid collection collapsed GB
Contusion
wall thickening with inhomogenous enhancement
Avulsion
wall thickening of GB biloma hemoperitoneum
biloma hemoperitoneum
GB haematoma
Renal injury •
Occurs in 8‐10% of all abdominal trauma
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Predisposing factors‐ anatomical variants like horse shoe, cross fused and pelvic or transplanted kidney
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IVU – confirm the presence of a functioning kidney on the contralateral side
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USG‐ acute retroperitoneal or renal haematoma appears hypoechoic, becoming more hyperechoic with time
CT is the gold standard in renal trauma with accuracy as high as 98% Contusions- ill-defined areas of low attenuation with irregular margins Traumatic segmental infarcts- well defined and wedge shaped Lacerations- linear disruption that may extend into the medulla, causing urinary extravasation Intra renal haematoma- expand the kidney Subcapsular haematoma- distort the renal contour
Angiography: to investigate delayed or protracted bleeding : treatment of CT detected traumatic vascular malformations
Classification of renal trauma according to severity (Federle’s classification): Category I(75-85%)-contusions and CM lacerations that donot communicate with the collecting system Category II(10-15%)-parenchymal lacerations communicating with the collecting system resulting in extravasation -perinephric/paranephric haematoma Category III(5%) -major renal lesions or damage to vascular pedicle -renal arterial avulsion/thrombosis -multiple fractures running across segmental blood vessels -Rarely, traumatic renal vein thrombosis -subcapsular rim sign-complete renal artery occlusion Category IV-ureteropelvic junction avulsion - laceration of renal pelvis -ureter may fail to fill but calyces are intact
Urinary Bladder trauma •
Susceptibility to trauma‐infant bladder ‐ distended/obstructed bladder
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Usually associated with pubic ramus fracture
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Classification‐ Extra‐peritoneal rupture‐ localised collection of contrast lying anterior & lateral to the bladder
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Intra‐peritoneal rupture‐ splillage of contrast around pelvic small bowel loops and in the paracolic gutters Combined intra & Extraperitoneal rupture Type I‐ bladder contusion Type II‐ intra‐peritoneal rupture Type III‐ interstitial bladder injury Type IV‐ extra‐peritoneal rupture Type V‐ combined bladder injury
Pancreatic injuries •
Accounts for 3‐12% of cases
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USG ‐diffuse swelling of the pancreas ‐ fluid collections
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CT‐ normal (40%) ‐ thickening of left anterior renal fascia ‐ lacerations & contusions seen as areas of low attenuation ‐ sequele like pseudocyst, abscess detected
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ERCP & MRCP‐ detects site of pancreatic duct rupture
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Angiography‐ detects sites of active bleeding/pseudoaneurysm
CT grading (blunt pancreatic injury): Grade I- minor contusion or laceration without duct injury Grade II- minor contusion or laceration without duct injury or tissue loss Grade III- distal transection or parenchymal injury with duct injury Grade IV- proximal transection or parenchymal injury involving ampulla Grade V- massive disruption of pancreatic head
Bowel and mesentery •
Occurs in 5% of blunt abdominal trauma cases
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Deceleration injuries occurs at the point of fixation of the bowel
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CT findings‐ ‐ oral contrast extravasation ‐ visualisation of the disrupted bowel ‐ extraluminal mesenteric gas ‐ pneumoperitoneum ‐ focal wall thickening ‐ abnormal bowel wall enancement ‐ free peritoneal fluid
Vascular injuries •
Very rare except at the junction of the hepatic vein & IVC
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Imaging plays little role
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In haemodynamically stable patients, CT, DSA, doppler studies can be done
• CT‐ o Caval injuries‐ lumen is irregular or compressed by haematoma ‐ active vascular contrast extravasation o Aortic injuries ‐ contrast extravasation ‐ Psoas or mesenteric haemorrhages ‐ Enhancing pseudoaneurysm
Angiography‐ gold standard
