IMAGING APPROACH IN ACUTE ABDOMEN

Dr.Parvathy S Nair

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

Role of imaging

• Indicated management may vary from emergency surgery to reassurance of the patient. So misdiagnosis may easily result in delayed necessary treatment or unnecessary surgery.

• The clinical presentation of patients with an acute abdomen is often nonspecific. Both surgical and nonsurgical diseases may present with a similar clinical history and symptoms.

• Laboratory findings (leucocyte count, erythrocyte sedimentation rate, CRP) are equally nonconclusive.

CAUSES

Self-limiting• Gastroenteritis• Lymphadenitis• Epiploic

appendagitis

AppendicitisCholecystitis

SalpingitisSigmoid diverticulitis

Life Threatening• Aortic

aneurysm rupture

• Pancreatitis• Perforated

peptic ulcer• Perforated

diverticulitis

• Before imaging, clinical history, physical examination findings, top diagnosis and possible differentials have to be obtained.

• This helps in choosing the appropriate imaging modality as well as narrows down the area to be concentrated

Plain Radiographs

• Important initial imaging modality• Non-specific• Normal radiograph do not rule out illeus or

other pathology• Greatest value in cases of hollow viscus

perforation and intestinal obstruction

• Abdomen erect including both diaphragm • Abdomen supine films• Left lateral decubitus or cross-table lateral

view in ill patients– Air between the liver and the abdominal wall is

seen easily• Right lateral decubitus in colonic obstruction

Perforation• RT upper quadrant gas Perihepatic Subhepatic Morrison’s pouch Ligament visualisation - falciform,umbilical• Rigler’s sign(double wall sign)• Triangular air indicating lateral umbilical ligament• Cupola sign-under surface of the central part of

diaphragm is seen• Foot ball sign –large quantity of air filling the

peritoneal cavity

Cupola sign

Intestinal obstruction

• Dilated gas filled bowel loops with air-fluid levels proximal to the obstruction

• Paralytic ileus-both SB and LB are dilated• “String of beads” sign-Mechanical obstruction• Thumb printing due to sub mucosal edema-

Ischemia• Intramural air-Necrotizing enterocolitis• “Coffee bean” appearance- Sigmoid volvulus

Appendicitis• Fluid levels localized to the caecum and terminal ileum,

indicating inflammation in the right lower quadrant• Localized ileus with gas in the cecum, ascending colon

and terminal ileum• Increased soft tissue density of the right lower quadrant• Blurring of the right flank stripe and presence of a

radiolucent line between the fat of the peritoneum and tansverus abdominis

• Fecolith in the right iliac fossa• Gas filled appendix• Blurring of the psoas shadow on the right side.

Other conditions

• Gangrenous cholecystitis -intraluminal and intramural air

• Sentinel loop, gasless abdomen and colon cutoff sign in Pancreatitis

• Extraluminal mottled gas in Abdominal abscess• Gas in perinephric region – Emphysematous

pyelonephritis• Ureteric colic – Urolithiasis

USG and CT

USG and CT

• An ileus may not be appreciated on a plain abdominal film if bowel loops are filled with fluid only without intraluminal air.

• Alternatively if a plain abdominal film does indicate an ileus then sonography or CT are usually needed to identify its cause.

Appendicitis

• A normal appendix has a maximum diameter of 6 mm, is surrounded by homogeneous non-inflamed fat, is compressible and often contains intraluminal gas.

• An 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.

Appendicitis

Sigmoid diverticulitis

• If 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.

Cholecystitis

• As gallstones are often occult on CT, sonography is the preferred imaging method for the evaluation of cholecystitis

• GB wall thickening• Hydropic GB

Small Bowel Obstruction

• Small bowel obstruction (SBO) accounts for approximately 4% of all patients presenting with an acute abdomen.

• The 'Small Bowel Feces Sign' (SBFS) is a very useful sign as it is seen at the zone of transition thus facilitating identification of the cause of the obstruction.

• The SBFS has been defined as gas and particulate material within a dilated small-bowel loop that simulates the appearance of feces.

Mesenteric 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.

Epiploic Appendagitis

• Epiploic appendages are small adipose protrusions from the serosal surface of the colon.

• An epiploic appendage may undergo torsion and secondary inflammation causing focal abdominal pain that simulates appendicitis when located in the right lower quadrant or diverticulitis when located in the left lower quadrant.

• The characteristic ring-sign corresponds to inflamed visceral peritoneal lining surrounding an infarcted fatty epiploic appendage.

Urolithiasis

Ruptured Aneurysm• Most abdominal aortic aneurysms rupture into the left

retroperitoneum 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.

A/c pancreatitis

• Early stages-USG is preferred• USG reveals enlarged hypoechoic pancreas with

peripancreatic fluid,+/- cholelithiasis• Also in follow up of fluid collection or

pseudocyst formation.• CECET – modality of choice- for diagnosis,detect

extrapancreatic,intras abdomial pathology• For staging of severity-CTSI

MRI

• Recent improvements in resolution and faster breath hold sequences have drastically increased usage of MRI in abdomen.

• But not routinely used in a/c abdomen except in situations where contrast cannot be administered or in pregnant patients

• Most important objective of imaging in a/c abdomen is– Identify most common causes– Choose the modality of imaging appropriately– Diagnose or exclude common conditions