Imaging of acute abdomen

Imaging of Acute Imaging of Acute AbdomenAbdomen

Dr . Mohammed Bawazir Radiology Department

The 'acute abdomen' is a clinical condition characterized by severe abdominal pain, requiring the clinician to make an urgent therapeutic decision.

Imaging techniquesImaging techniquesClinical assessment is often difficult and laboratory investigations are often non specific.

Plain X-rayUltrasonographyCT examinationsContrast studies

Abdominal XrayAbdominal XrayPlain radiographs of the abdomen, is of significant diagnostic limitations, It is the initial radiological approach.

Two views are usually taken : supine and an erect.

If the patient is unable to stand, a decubitus view

AXR - IndicationsAXR - IndicationsSuspected bowel obstruction Suspected perforationSuspected foreign bodyModerate to severe undifferentiated abdominal pain

Renal tract calculi follow-up

Abdominal Ultrasound - Abdominal Ultrasound - IndicationsIndicationsTrauma survey and follow up (FAST)Suspected acute cholocystitisSuspected acute pyelonephritis –

single kidney, transplant, immunocompromised, abnormal renal function, DM, cong anomalies, recurrent/failed to respond to AB, equivocal

RIF pain – young femalesAscites localization

Abdominal CT - IndicationsAbdominal CT - IndicationsAppendicitisColitis (Inflammatory, infective,

ischaemic), DiverticulitisPerforation – Normal erect CXR

strong clinical suspicionStrong suspicion of bowel

obstruction on AXR – further investigation (If not for urgent surgery), uncertainty about the site of obstruction

Urolithiasis AAA/rupture

Confirm or exclude the Confirm or exclude the most common diseasemost common diseaseMany disorders may cause an acute abdomen, but fortunately only a few of these are common and clinically important. Focus on confirming or excluding these frequent disorders

AppendicitisAppendicitisAn inflamed appendix has a diameter larger than 6 mm, and is usually surrounded by inflamed fat. The presence of a fecolith or hypervascularity on power Doppler strongly supports inflammation

DiverticulitisDiverticulitisIf the pain is located in the LLQ main concern is sigmoid diverticulitis.In diverticulitis sonography and CT show diverticulosis with segmental colonic wall thickening and inflammatory changes in the fat surrounding a diverticulum.

Complications of diverticulitis such as abscess formation or perforation, can best be excluded with CT.

CholecystitisCholecystitisCholecystitis occurs when a calculus

obstructs the cystic duct. The trapped bile causes inflammation of the gallbladder wall. As gallstones are often occult on CT, sonography is the preferred imaging method for the evaluation of cholecystitis, also allowing assesment of the compressiblity of the gallbladder. 

Screen for general signs Screen for general signs of pathologyof pathologyAfter excluding these frequent disorders, search for signs of any other pathology, by systematically screening the whole abdomen.Look for inflamed fat, bowel wall thickening, ileus, ascites and free air.

Inflamed fatInflamed fat

Bowel wall thickeningBowel wall thickening

Thickening of bowel wall indicates inflammation or tumor, and has an extensive differential diagnosis. Thickening of small bowel loops usually indicates regional inflammation, as small bowel tumors (carcinoid, lymphoma, GIST) are relatively infrequent. In patients with local colonic wall thickening a carcinoma is a prime concern.

ileusileusPathologic distention of bowel

loops may be caused by obstruction or paralysis. Firstly determine which parts of the gut are affected: small bowel, large bowel, or both. Look for normal nondistended bowel loops, which, if present, strongly suggest an obstructive cause for the ileus.

Alternatively, an ileus without any normal bowel loops strongly suggests a paralytic cause. This is usually a response to general peritonitis, wich may have many possible causes of the inflammation.

VolvolusVolvolusThe sigmoid colon is more prone to twisting than other segments of the large bowel because it is 'mobile' on its own mesentery, which arises from a fixed point in the left iliac fossa (LIF).

Sigmoid Volvolus (Coffee Sigmoid Volvolus (Coffee bean sign)bean sign)

Whirlpool signWhirlpool signThe whirlpool sign, also known as the whirl sign, is seen when structures twist on itself. It is most commonly described in the abdomen bowel rotates around its mesentery, with mesenteric vessels creating the whirls but is also seen in ovarian torsion.

Whirlpool sign Whirlpool sign It is seen in a number of settings:Malrotation complicated by midgut

volvoluscaecal volvulussigmoid volvulusclosed loop bowel obstruction enteritis: similar pattern, but in the

opposite direction has been described on ultrasound  

omental torsion

AscitisAscitis

Free air Free air PNEUMOPERITONEUM PNEUMOPERITONEUM

The presence of free intraperitoneal air is proof of bowel perforation, and indicates a surgical emergency. A pneumoperitoneum has only two frequent causes:

- Perforation of a gastric ulcer- Perforation of colonic diverticulitis

Free air is usually not seen in perforated appendicitis).Always examine the images in lungsetting for better detection of free intraabdominal air 

RT upper quadrant gas Perihepatic Subhepatic Morrison’s pouch Ligament visualisation - falciform,umbilicalRigler’s sign(double wall sign)Triangular air indicating lateral umbilical ligamentCupola sign-under surface of the central part of diaphragm is seenFoot ball sign –large quantity of air filling the peritoneal cavity

Rigler’s SignRigler’s SignRigler's sign refers to the appearance

of the bowel wall on plain film when it is outlined by intraluminal and extraluminal air .The extra luminal air is free peritoneal gas

The Cupola SignThe Cupola SignFree air beneath the central

tendon of diaphragm

Decubitus XrayDecubitus XrayThere is evidence of free air between

the abdominal wall and the liver (white arrow). There is also evidence of free fluid in the peritoneum (black arrow).

Football sign(Massive Football sign(Massive pneumoperotineuam)pneumoperotineuam)

Diffrential DiagnosisDiffrential DiagnosisA complete list of all possible causes of an acute abdomen is of little use in daily practice, therefore here are some imaging examples of several frequent causes of acute abdominal pain

Mesentric Lymphadenitis Mesentric Lymphadenitis A common mimicker of appendicitis. It is the second most common cause of

right lower quadrant pain after appendicitis.

It is defined as a benign self-limiting inflammation of right-sided mesenteric lymph nodes without an identifiable underlying inflammatory process, occurring more often in children than in adults.

This diagnosis can only be made confidently when a normal appendix is found, because adenopathy also frequently occurs with appendicitis.

UrolithiasisUrolithiasisUrolithiasis often causes flank pain,

but an ureteral stone (arrowhead) may occasionally present with clinical signs simulating appendicitis, cholecystitis or diverticulitis.Appendicitis on the other hand may cause hematuria, pyuria and albuminuria in up to 25% of patients because of ureteral inflammation from an adjacent inflamed appendix.

Pancreatitis Pancreatitis

Ruptured AneurysmRuptured AneurysmMost abdominal aortic aneurysms rupture into

the left retroperitoneum (4). Clinically this may simulate sigmoid diverticulitis or renal colic due to impingement of the hematoma on adjacent structures. However most patient will present with the classic triad of hypotension, a pulsating mass and back pain. Continuous leakage will lead to rupture into the peritoneal cavity and eventually death.Sonography is a quick and convenient modality, but it is much less sensitive and specific for the diagnosis of aneurysmal rupture than CT.The absence of sonographic evidence of rupture does not rule out this entity if clinical suspicion is high.

Ovarian TorsionOvarian Torsion