Possible Differential diagnoses include
- Appendicitis
- Terminal ileitis
- Intussusception
- Crohn’s disease
- Abscesses
- Mesenteric adenitis
- Diverticulitis
- Caecal carcinoma
- Infectious colitis
- Hernias (inguinal/femoral/surgical/ventral)
- Vascular causes (AAA/ iliac aneurysms)
- Testicular (tortion/ epididimitis)
- Gyne/obstetric (ectopic, hydrosalpinx/ovarian cyst rupture/ endometriosis)
- Biliary colic
- Renal colic, UTI
- Psoas abscess
- Herpes Zoster
- Ascites/ free fluid/ pancreatitis
US technique
- Examine the patient first in the supine position to identify areas of tenderness and area of maximum tenderness.
- Use a curvilinear probe at first (1 – 5 MHz) change to a linear probe if pathology visualised and not deep.
- For the small bowel : “mow the lawn” technique in the supine position Start in the RLQ with the transducer in the transverse position and sweep up towards the RUQ, then sweep down again and repeat in parallel, overlapping lines until the entire abdomen has been examined.
- For the large bowel : repeat but follow the ascending, transverse, descending and sigmoid colon in transverse (transducer more laterally placed when swept down or up than when examining the small bowel)
- Use graded compression to displace gas.
- Repeat in area of tenderness in the longitudinal plane and obliquely if pathology best identified in this plane
- Identify any abnormalities : bowel obstruction, bowel wall thickening (attention to gut signature – serosa, muscularis propria, submucosa, muscularis mucosa, mucosa ) pseudokidney sign, free fluid, masses, aorta, nodes. “Creeping fat” ie hyperechoic mesentery
- Return to RIF. Identify the area of maximum tenderness . Scan slowly and carefully through this region.
- To check for a retrocaecal appendix if not visualised with patient in the supine position, turn patient into left lateral decubitus position and scan posterolaterally
- If no abnormality found in RIF, check for other pathology. Full abdominal ultrasound (liver/GB/kidneys/spleen/pancreas/aorta)
- CT to confirm pathology and complications
Ultrasound findings of appendicitis
- Identify caecum (haustra/dirty shadow of gas) Appendix lies at the base of the caecum
- Point of tenderness over the appendix
- Appears as a noncompressible, fluid filled, blind ended tubular structure.
- If inflamed the appendix > 6mm in diameter.
- Little or no peristalsis
- +/- appendicolith (in 30% of patients) within the appendix which appears as a hyperechoic area with posterior shadowing (due to calcification)
- Hyperaemic walls with colour Doppler or Power Doppler if not necrotic ( colour scale set on low)
- Target sign in transverse with increased thickness of muscularis propria and +/- destruction of gut signature
- Peri appendiceal mesentary fat is hyper echoic ” creeping fat”
- May have an associated abscess formation with or without gas or a complex peri appendiceal mass
- RIF free fluid
- +/mesentery adenopathy
- If perforated – may have associated ileus
Ultrasound findings of Crohn’s disease
- Bowel wall thickening ( > 3mm) of distal ilium and or colon
- Intestinal lumen is narrowed
- Target sign in transverse
- “skip areas” where there is normal bowel
- Loss of gut signature.
- Reduced peristalsis
- Surrounding hyperechoic mesentery fat and omentum which may be noncompressible
- Enlargement of mesentary nodes
- +/- fistulas (hypoechoic tracts with hyperechoic gas inclusions)
- +/- abscess formation (poorly defined , mostly hypoechoic focal masses which may contain hyperechoic gas and associated ring down or dirty shadow)
- +/- bowel obstruction (dilated loops of bowel with to and fro movement of bowel contents)
- +/- stenosis
- +/- perforation (rare)