Appendicitis - Xray, Ultrasound and CT scan

Clinical Characteristics

• A common cause of an acute appendicitis with a peak incidence in the 2nd and 3rd decades.
• The aetiology is probably related to the luminal obstruction, often by lymphoid hyperplasia or a foecolith.
• Typically presents with RIF pain, nausea, vomiting, fever and evidence of inflammation such as raised WBC and CRP.
• However 1/3 may have an atypical presentation.
• Complication include localised perforation, abscess formation and generalised peritonitis. Rarely an obstructed appendix becomes distended by abnormal accumulation of mucus, forming an appendix mucocoele.

Radiological Features

Xray  Examination of Appendicitis

• In xray examination it is neither sensitive nor specific but can provide clues on a radiograph.
• The presence of a calcified appendicolith in the right lower quadrant, combined with abdominal pain, has a high positive predictive value for acute appendicitis.
• Other signs are less specific and include caecal wall thickening, small bowel ileus and decreased small bowel gas in the RIF.
• Free peritoneal fluid can lead to loss of the psoas outline, loss of the fat planes around the bladder and loss of definition the inferior liver outline.

Plain Abdominal Xray Appendicolith

A coronal CT reformat on picture below demonstrate the presence of a RIF appendicolith (arrows). The CT demonstrate free fluid within abdomen and pelvis and several dilated loops of small bowel, secondary to ruptured appendicitis with an associated ileus.

Ultrasound Scan of the Appedicitis

Ultrasound of the appendix is the initial imaging of choice if there is a diagnostic uncertainty.

It can identify other causes of RIF pain such as ovarian torsion and mesenteric adenitis.

Ultrasound findings that suggest appendicitis include:

• Visualization of a blind ending, non peristaltic, non compressible appendix.
• A diameter of greater than 6mm.
• Presence of an appendicolith, and distention of lumen.
• Peri-appendiceal free fluid.
• NB a negative ultrasound does not exlude appendicitis; if there is a high degree of clinical suspicion this should not preclude further imaging or laparoscopy. 

Raptured appendicitis on arrows. Note the presence of an ill defined mottled gas pattern within the RIF, with an air-fluid level, caused by the raptured appendix. 

Contrast Enhanced CT scan

Contrast enhances CT is increasingly being used. However, it is not a first line investigation owing to the radiation dose incurred by the patient.

Tends to be used where there is diagnostic delimma such as with an atypical presentation.

Findings include in CT Images:

• A thickened appendix plus an appendicolith
• Inflammatory stranding in the adjacent fat.
• An inflammatory appendix mass.
• A local collection
• Local lymphadenopathy.

Appendicitis. Dilated tubular appendix containing an appendicolith (arrow).

Thickened tubular appendix, with inflammatory stranding seen at its tip (arrow).