Acute Appendicitis: Ultrasound as the First Line of Accurate Diagnosis

Dr. Segnini
Dec 23, 2025
3 min read

Dr. Segnini acute appendicitis ultrasound diagnosis

The Dilemma of Acute Abdominal Pain

Acute abdominal pain in the right lower quadrant is one of the most frequent reasons for emergency room visits. Acute appendicitis is the leading cause of emergency abdominal surgery. However, its clinical diagnosis can be misleading, especially in children, women of childbearing age, and the elderly. This is where abdominal ultrasound emerges as a critical, accessible, and safe tool to confirm or rule out appendicitis, avoiding unnecessary surgeries and reducing diagnostic time.

Why is ultrasound the first choice in many cases?

Compared to other techniques such as Computed Tomography (CT), ultrasound offers decisive advantages for this diagnosis:

Absence of Ionizing Radiation: This is the absolute advantage , especially crucial in children and pregnant women , where it is the first-line imaging technique.
Dynamic and Targeted Evaluation: The radiologist can apply pressure with the transducer directly over the patient's point of pain ( McBurney 's sign). ultrasound guided ), which increases sensitivity.
Accessibility and Speed: Available 24/7 in most emergency services, allowing a diagnosis in minutes.
Differential Diagnosis: Not only does it look for the appendix, but it can also identify other common causes of similar pain (see below).

Ultrasound Criteria for the Diagnosis of Acute Appendicitis

Ultrasound is used to directly visualize the inflamed appendix. A normal appendix is often not visible. Signs of appendicitis include:

1. Primary (Direct) Findings:

Visible and Non-Compressible Appendix : The fundamental finding is to visualize a tubular, blind structure that originates from the cecum.
- Increased Diameter: The cross-section is key. An external diameter > 6 mm is highly suggestive. In the longitudinal section, it appears as a "tube" or "worm" structure.
- Non-Compressible: When firm pressure is applied with the transducer, a normal appendix or bowel loop collapses. An inflamed appendix does not compress due to edema and inflammation of the wall.
- Thickened and Edematous Wall: The wall of the appendix appears thickened (>2 mm) and often in a "double layer" or stratified.

2. Secondary (Indirect) Findings:

"Target" or "Target Sign": In cross-section, the inflamed appendix shows a hyperechoic center (lumen with pus or fecalith) surrounded by a hypoechoic ring (edematous wall) , and sometimes a hyperechoic outer halo (mesenteric fat).
Hypervascularization on Color Doppler : The appendix wall shows increased blood flow (vascularization), a sign of active inflammation.
Echogenic Mesenteric Fat (" Fat " Wrapping ": The fat surrounding the appendix becomes brighter ( hyperechoic ) and unstructured, indicating periappendiceal inflammation and infiltration .
Impacted Fecalith: A bright, hyperechoic structure within the lumen that casts a posterior acoustic shadow (black area). It is a risk factor for perforation.
Free Fluid Periappendicular or in Right Iliac Fossa: Anechoic (black) collection around the appendix, suggesting peritoneal irritation.

Ultrasound in Differential Diagnosis: Its Added Value

Pain in the right iliac fossa can be caused by many other conditions. Ultrasound can identify them.

In women: Ruptured or hemorrhagic ovarian cyst, adnexal torsion , pelvic inflammatory disease, ectopic pregnancy.
In all: Mesenteric lymphadenitis (swollen lymph nodes), cecal diverticulitis , ileocecal Crohn's disease, right renal/ ureteral colic.
In children: Intussusception (identified by the "target" sign in a different area).

Being able to visualize a healthy ovary with a corpus luteum, an ovarian cyst, or a ureter dilated by a stone completely changes management and avoids unnecessary surgery.

Limitations and When to Proceed to Computed Tomography (CT)

Ultrasound is operator-dependent . Its limitations include:

Patients with a lot of intestinal gas or obesity, which makes visualization difficult.
Retrocecal or atypically located appendicitis .
perforated appendicitis , where the anatomy is distorted.
Uncertain diagnosis despite a well-performed ultrasound.

In these cases, or when clinical suspicion is high and the ultrasound is negative/inconclusive, an abdominal CT scan with contrast is performed , which has higher sensitivity and specificity and a panoramic view.

Conclusion: An Effective Guardian in the Emergency Room

Ultrasound for the diagnosis of acute appendicitis represents the paradigm of precision medicine in emergency medicine . It is an extension of the stethoscope and the surgeon's hands. By providing direct, dynamic, and safe visualization of the appendix, it allows for:

confirm appendicitis and expedite surgery.
Rule out appendicitis with high reliability in many cases.
Diagnose an alternative pathology that explains the symptoms.

Its standardized use reduces negative appendectomies (operating without appendicitis) and, most importantly, minimizes radiation exposure , especially in the most vulnerable populations. It is an indispensable tool for safe and efficient decision-making.