Chin Med J (Taipei) 1998;61:S186.

Ultrasonography of the Acute Abdomen

Yi-Hong Chou, M.D

Department of Radiology, Veterans General Hospital -Taipei, R.O.C.

Abstract

Acute abdomen, being still one of the most frequent, most dangerous, and most challenging ailments to a radiologist, is a syndrome of sudden onset that affects the abdominal cavity. It is generally accompanied by pain and other abdominal signs and symptoms with varying severity which frequently requires prompt surgical intervention or medical treatment. The role of imaging in the evaluation of patients with acute abdominal condition is twofold, first, to guide the referring physician to establish a precise diagnosis with shorter time, second, to aid in planning an appropriate approach of treatment.

The main goal of imaging in the acute abdomen is to narrow down the differential diagnoses enabling the clinician to undertake an appropriate and prompt treatment without much delay. Since the advent of modern cross-sectional imaging modalities such as computed tomography (CT) and state-of-the-art ultrasound (US), the value of imaging study has been enhanced significantly. The precise diagnosis of intraabdominal pathologies can frequently be made. US, usually used as an imaging modality following plain abdominal radiograph, remains the primary screening tool for evaluating the acute abdomen.

One of the major drawbacks of US is the occurrence of ileus which often accompanies the intraabdominal pathology. A keen knowledge of abdominal anatomy and pathology is essential. Scanning technique and experience, as well as confidence in interpreting US studies are also vital.

The most commonly encountered acute abdominal pathologies in dayly practice are:
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, and 9. Ob/Gyn emergency, e.g., ectopic gestation, adnexal torsion, and hemorrhagic ovarian cyst.

Acute Cholecystitis/ The US manifestations of acute cholecystitis are: (a) Presence of gall stones with positive sonographic Murphy's sign, (b) A distended gall bladder ( > 4cm) with internal echoes indicating sludge or pus, (c) Diffuse thickening of the gall bladder wall ( > 3.5mm), and (d) Pericholecystic fluid collection. Acute Renal Colic/ US can demonstrate dilatation of the pelvicalcyeal system and the ureter proximal to the obstruction. However, it has been observed in a few cases that there may not be significant pelvicalyceal system dilatation on US. Acute Appendicitis/ The US manifestations of acute appendicitis are: (a) A noncompressible appendix, (b) Outer diameter > 7mm, (c) Presence of appendicolith, (d) A hypoechoic periappendicular mass suggesting appendicular perforation. and (e) Peritoneal fluid in perforation. Acute Pancreatitis/ The US appearances include: (a) The pancreas may be in normal appearance, (b) A diffusely enlarged hypoechoic pancreas, (c) Indistinct borders of the pancreas, (d) A dilated pancreatic duct, (e) A focal hypoechoic area commonly seen in the head of the pancreas indicating focal involvement, (f) A phlegmon of the pancreas presenting as a hypoechoic mass, and (h) Splenic vein thrombosis. Hepatic Abscess/ The typical US features of an abscess are: (a) A well defined hypoechoic area with distal enhancement, (b) Oval or rounded shape, (c) Predilection for the right lobe, (d) May be solitary or multiple, (e) No significant wall echoes, (f) Right pleural effusion, and (g) Hepatomegaly. Intussusception/ US appearances: "pseudo-kidney" appearance, "doughnut" sign, "hay-fork" sign, and hypoechoic concentric rings corresponding to the oedematous walls of the intussusceptum and intussuscipien. Psoas Abscess/ An enlarged psoas muscle which is markedly hypoechoic indicating presence of (echogenic) fluid. Acute Ob/ Gynecological Condition/ Transvaginal sonography along with B-HCG evaluation are the procedures of choice in the valuation of ectopic pregnancy. Common US findings of ectopic gestation: (a) A thickened endometrium with absence of an intrauterine gestational sac, (b) A small echogenic ring structure in the adnexa that is clearly separate from the ovary, (c) Presence of a live embryo and/or a yolk sac, (d) A rim of colour around the ectopic ring structure and trophoblastic flow on Colour Doppler, and (e) Presence of echogenic, fluid in the abdomen suggesting haemorrhage. The US appearances of a hemorrhagic ovarian cyst are: (a) A well defined adnexal mass, (b) Heterogeneous echotexture, (c) Presence of debris and septations, (d) Posterior enhancement, and (e) Serrated margin. The US manifestations of adnexal torsion are: (a) An enlarged ovary (solid or cystic), (b) with or without "tumor" within it. Color Doppler US may be of limited value in the diagnosis.

[Chin Med J (Taipei) 1998;61:S186.]