Appendix pathology

  • Finding the appendix is highly user and patient dependant.
  • A methodical approach and patience is required.
  • Always consider differential diagnoses.


Ultrasound signs of appendicitis

  • Hyperaemia of the appendix
  • Sono tenderness at McBurneys point (or focal appendix tenderness with probe pressure) 
  • Thickened appendix: > 6mm transverse diameter
  • Loss of wall stratification ie loss of the ‘target appearrance)
  • Free fluid around the appendix

Important: Depending on the degree of inflammation and timing of the scan since onset of symptoms, as to how many of these signs may be present. A hyperaemic aptender appendix should be considered as suspicios even without other sono-signs.

Ultrasound image- The appendix can be found from the groin, to the umbilicus or even high up under the liver,and rarely midline or in the left iliac fossa.

Ultrasound image- Appendicitis can be diagnosed when the outer diameter of the appendix measures greater than 6 mm.

Ultrasound image- Echogenic inflammatory periappendiceal fat change.

Ultrasound image- Appendicitis and omental thickening.

Ultrasound image- The abnormal appendix is draped around the iliac vessels.

Ultrasound image- The thickened appendix at the caecal junction. Some content is visible in the appendocele canal.

Ultrasound image- Transvaginal scan:
The thickened appendix with lobulated irregular margins is seen in the Pouch of Douglas.
Complex free fluid is also present (top left of the image)

Ultrasound image- Transvaginal scan:
Transverse view of the ruptured appendix and surrounding oedema in the Pouch of Douglas.
Increased vascularity is readily seen with power doppler.


  • A calcificationis often seen within the lumen of the appendix.
  • The presence of an appendicolith does not indicate appendicitis.

Appendicocoele or appendiceal mucocele

  • An appendocoele is a fluid filled cystic dilatation (mucocele) of or arising from the appendix.

Ultrasound image- An appendocoele is a fluid filled cystic dilatation of or arising from the appendix.

A case of a giant appendiceal mucocele in 90 year old male with intermittent RLQ pain for 3 years. 

Longitudinal ultrasound image of the appendix demonstrating diffuse cystic dilation.  

Image courtesy of Callum Linehan.

Transverse ultrasound image of a giant appendiceal mucocele.

Image courtesy of Callum Linehan.

Longitudinal colour Doppler image of a giant appendiceal mucocele.

The accumulated mucin presents as both homogenous hypoechoic and anechoic contents within the distended appendix.

Image courtesy of Callum Linehan.

Longitudinal ultrasound image of a giant appendiceal mucocele demonstrating the blind end of the appendix.

Image courtesy of Callum Linehan.

Longitudinal ultrasound image of a giant appendiceal mucocele at the ileocecal junction. No cecal extension or appendicolith is seen.  

Careful investigation for an appendicolith and any mass must be undertaken in cases of a mucocele to identify any sources of an obstruction or underlying malignancy. 

Image courtesy of Callum Linehan.

Transverse colour Doppler image of a giant appendiceal mucocele.

Image courtesy of Callum Linehan.

Differential Diagnoses

  • There are a plethora of differential diagnoses for abdominal pain suspicious for appendicitis.
  • Below are some that can be identified on ultrasound.

Rectus Abdominus Tear

Ultrasound image- Rectus Abdominis Muscle tear.
This patient had not had any memory of a muscle strain.
They felt a burning in the Right iliac fossa.

Ultrasound image- Rectus Abdominis Muscle Hypertrophy.

Crohn’s Disease

Crohn’s disease is an idiopathic inflammation of the bowel wall.
It affects primarily the small bowel but can involve anywhere.
Approximate involvement:

Only small bowel (especially the distal ileum)………30%
Small bowel and colon…………………………………………..40%
(REF: Farmer RG, Hawk WA, Turnbull RB Jr. Clinical patterns in Crohn’s disease: a statistical study of 615 cases. Gastroenterology. Apr 1975;68(4 Pt 1):627-35.)

Ultrasound image- Crohn’s disease can be mistaken for the appendix. Be sure to watch for any peristalsis.

Ultrasound image- Transverse view of Crohn’s disease in the bowel.
It has a similar target appearance to the appendix.

Psoas Muscle abscess / haematoma

A psoas abscess or haematoma can have variable presentations including RIF and back pain.

If a psoas abnormalitity is suspected, assess superioly through the ipsilateral kidney.

Also look in the groin at the iliopsoas tendon and bursa.

Mesenteric cysts

  • Mesenteric cysts can be anywhere in the abdomen including the right iliac fossa.

Ultrasound image- This is a mesenteric cyst inferior to the left kidney.

Mesenteric Adenitis

Enlarged Lymph nodes in the mesentery are common with appendicitis. Children commonly also have enlarged lymph nodes with viral illness.
The process may be acute or chronic, depending on the cause.
It causes a clinical presentation that may be difficult to differentiate from acute appendicitis.

Ultrasound image- Mesenteric Adenitis is the inflammation of lymph nodes within the mesentry.


  • This patient was experiencing lower abdominal pains. He was focally tender at the inflamed bowel.
    Diverticula of the sigmoid colon are hypoechoic peripherally but centrally echogenic because of the gas or faeces they contain.

Ultrasound image- When the bowel is abnormal the wall increases in thickness. This is muscular hypertrophy which has a hypoechoic outer layer.

Ultrasound image- The normal wall is not seen posteriorly. There is gas in the lumen causing shadowing .

Ultrasound image- The Omentum is inflamed around the site of the abscess. The echogenicity increases in the fat.

CT confirms the diverticulitis and , abscess and omental inflammation.

Quadratus Lumborum Sarcoma

This patient experienced right iliac fossa pain radiating to the back and hip

Ultrasound image- Quadratus Lumborum Sarcoma

Ultrasound image- Internal Vascularity in the mass.



  • Focal RIF pain
  • Rebound tenderness
  • Pelvic pain
  • Elevated WCC (white cell count)


Bowel gas and patient habitus are the biggest limiting factors to visualising the appendix.

Up to 60% of appendix’ are retrocaecal and thus may be obscured. Not identifying an appendix does NOT exclude appendicitis.

Use of a high resolution probe (7-15MHZ) is essential. Beam steering or compounding can help to overcome anisotropy in linear structures such as tendons. Good colour / power / Doppler capabilities. Be prepared to change frequency output of probe (or probes) to adequately assess both superficial and deeper structures.

Scanning Technique

Finding the appendix is highly sonographer dependent. They must have a good skill level to undertake this examination.

Begin by placing the transducer in a transverse position and applying deep graded compression to the displace the gas and bring the bowel closer to the probe.

  • Beginning at the hepatic flexure the bowel is traced down to the caecum.
  • The patient should point to the location of pain .
  • It is a good idea to have a protocol which includes the entire pelvis of all females with right lower quadrant pain and scanning the renal and biliary systems of all patients with a normal appendix.
  • Sometimes the external iliac artery and vein can provide a good landmark for finding the appendix because of the location and pulsatility, compressible, and having Doppler flow.

Ultrasound Criteria to Diagnose Appendicitis

In order to demonstrate all the possible presentations of appendicitis it is important that the entire appendix is visualized-

  • When the outer diameter of the appendix measures greater than 6 mm
  • Echogenic inflammatory periappendiceal fat change
  • The wall thickness can measure almost 3 mm or greater
  • Progressed appendicitis can demonstrate a gangrenous appendix. The lumen distends tremendously sometime upwards to 2 cm and is not compressible. An appendicolith may be present which will cast an acoustic shadow.
  • An appendicolith may be present which will cast an acoustic shadow
  •  A perforated appendix is demonstrated when the appendicular wall has ruptured producing fluid or a newly formed abscess. The appearance is hyperechoic with an echo-poor abscess surrounding the appendix. There may be a reflective omentum around the appendix, a thickened bowel, and enlarged lymph nodes. Asymmetrical wall thickening may indicate perforation.
  • Free fluid in the periappendiceal region

Differential Diagnoses Visible on Ultrasound

  • Ovarian abnormality
  • Mesenteric adenitis
  • Renal calculi
  • Psoas Muscle Abscess
  • Mesenteric Cyst

Basic Hard Copy Imaging

Document the normal anatomy. Any pathology found in 2 planes, including measurements and any vascularity.