Ultrasound Diagnosis of Acute Appendicitis in Children: Appendiceal Diameter and Incompressibility
Measurement Technique
The appendix is measured from outer to outer wall using maximum outer diameter (MOD), with and without compression. Measurements are performed in the plane with the most clearly defined wall, since in acute appendicitis the wall may be less distinct, "ragged", or accompanied by loss of normal intestinal wall layering (gut signature) (Hagen-Ansert, 2023).
Normal Findings
A normal appendix is easily compressible, with a lumen that may be empty or filled with gas or fecal material. Walls are not thickened; maximum normal wall thickness is less than 1.7 mm (range 1.1–2.7 mm). In children younger than 6 years, maximum wall thickness less than 3 mm may be considered normal. The appendix may be tortuous, which complicates visualization along its entire length (Hagen-Ansert, 2023).
Criteria for Acute Appendicitis
| Finding | Value |
|---|---|
| Compressibility | Acutely inflamed appendix is noncompressible |
| MOD on compression | 7 mm or greater — corresponds to appendicitis in children and adults |
| Wall thickness | >2 mm |
| Periappendiceal fat | Increased echogenicity |
| Wall | Loss of wall delineation |
In the clinical example presented, the noncompressible appendix had MOD of approximately 8 mm and wall thickness >2 mm, indicating appendicitis; increased echogenicity of periappendiceal fat and loss of wall delineation were also noted. The terminal ileum was visualized above the appendix in the transverse plane (Hagen-Ansert, 2023).
Assessment is performed in longitudinal and transverse (axial) planes. The finding of incompressibility and MOD ≥7 mm on compression are complementary criteria (Hagen-Ansert, 2023).
Frequently asked questions
What threshold appendiceal diameter indicates appendicitis in children?
MOD (maximum outer diameter) of 7 mm or greater on compression corresponds to appendicitis in both children and adults (Hagen-Ansert, 2023).
How should the appendix be measured correctly?
From outer to outer wall according to maximum outer diameter (MOD), with and without compression, in the plane with the most clearly defined wall (Hagen-Ansert, 2023).
What is the normal appendiceal wall thickness?
Less than 1.7 mm (range 1.1–2.7 mm). In children younger than 6 years, wall thickness less than 3 mm may be considered normal (Hagen-Ansert, 2023).
What does appendiceal incompressibility mean?
A normal appendix is easily compressible, whereas an acutely inflamed appendix is noncompressible — this is one of the key signs of appendicitis (Hagen-Ansert, 2023).
What additional ultrasound findings support the diagnosis?
Wall thickening >2 mm, increased echogenicity of periappendiceal fat, and loss of normal wall differentiation (stratification) (Hagen-Ansert, 2023).