Question 1: Based on the clinical presentation and initial ultrasound findings, what is the most likely diagnosis?

The first ultrasound image shows a blind-ending, sausage-like structure with alternating hyperechoic and hypoechoic layers, including an outermost hypoechoic layer. The fluid-distended lumen measures 12 mm in diameter consistent with appendicitis. On color Doppler there is increased blood flow (hyperemia) in the appendiceal wall.

Image 3: Transverse ultrasound image RLQ

Question 2: What is marked on the above image?

Discussion:

Acute appendicitis is one of the most common causes of acute abdominal pain in children. The pathophysiology typically involves luminal obstruction, most commonly due to lymphoid hyperplasia in children, leading to increased intraluminal pressure, ischemia, and subsequent inflammation of the appendix. If untreated, this can progress to gangrene, perforation, and generalized peritonitis. Ultrasound is often performed as the first-line imaging in patients where there is a suspicion of appendicitis, particularly in children, due to its non-invasive nature and lack of ionizing radiation. Classic ultrasound findings include a non-compressible, blind-ending tubular structure in the RLQ with a diameter exceeding 6 mm. Additional findings, such as periappendicular fluid, increased echogenicity of the surrounding fat, or the presence of an appendicolith, can further support the diagnosis. In our case the lack of widespread fluid or systemic symptoms ruled out diffuse inflammatory processes, helping to guide prompt management.

Radiologists must differentiate appendicitis from other conditions such as mesenteric adenitis or ovarian torsion, which can present similarly. Careful interpretation of ultrasound findings, combined with clinical history, ensures accurate diagnosis and timely management, particularly when complications like abscess or perforation are suspected.

This case underlines the importance of a systematic ultrasound evaluation in the right lower quadrant, understanding key anatomical landmarks, and recognizing the sonographic signs of appendicitis. Radiologists must also know when further imaging, such as CT or MRI, is needed in ambiguous cases, particularly when non-operative management is considered.

Question 3: When performing an ultrasound examination for suspected appendicitis in a pediatric patient, what is the most important factor in choosing the appropriate transducer?

Image 4: Image from C1-6 transducer (GE Ultrasound, 1-6 MHz). The appendix is faintly visible

Image 5: Image from ML 6-15 transducer (GE Ultrasound, 6-15 MHz). The appendix is clearly visible

Additional discussion

When selecting a transducer for pediatric ultrasound, particularly for visualizing structures like the appendix, the frequency of the transducer is a critical factor. Higher-frequency transducers provide better resolution for superficial structures, such as the appendix, allowing clearer visualization of inflammation, fluid, and other diagnostic features. While lower-frequency transducers are better suited for imaging deeper structures, they may lack the resolution needed to accurately assess smaller or superficial anatomy, making them less ideal for pediatric purposes.

Image 6: Periappendicular fluid with septa and debris (arrow)

Question 4:  What is the most likely explanation for the fluid collection around the appendix in this patient with suspected appendicitis?