Educational diagnostic ultrasound images demonstrating acute appendicitis in longitudinal (a) and transverse (b) planes. Image (a) shows a longitudinal view of a distended, non-compressible appendix with an anteroposterior diameter of 0.94 cm and mural thickening of 0.14 cm. Hypoechoic free fluid is visible surrounding the structure. Image (b) shows the appendix in a transverse cross-section, displaying the classic 'target sign' (bull’s eye appearance), characterized by alternating hyperechoic and hypoechoic concentric rings representing the fluid-filled lumen, mucosa/submucosa, and muscularis layers. The transverse diameter is measured at 0.64 cm. These findings—specifically a total diameter greater than 6 mm, wall thickening, and periappendiceal fluid—are key diagnostic ultrasound criteria for acute appendicitis. The images serve as an educational example of graded-compression sonography for gastrointestinal pathology.

This diagnostic image displays Tissue Harmonic Imaging (THI) sonography of the right iliac fossa (RIF) demonstrating signs of acute appendicitis. The content is divided into two views: (a) a longitudinal scan and (b) a transverse scan, both acquired using a high-frequency (7.5 MHz) linear transducer. In the longitudinal view (a), the appendix appears as a blind-ended, aperistaltic, and non-compressible tubular structure with a significantly thickened wall and a total diameter exceeding 6 mm. In the transverse view (b), the inflamed appendix exhibits the characteristic 'target sign' or 'bull's-eye' appearance, consisting of concentric layers with alternating echogenicity, which corresponds to the histological layers of the appendiceal wall. These findings are hallmarks of appendiceal inflammation. The high-resolution THI technology enhances the visualization of these tissue interfaces compared to conventional ultrasound, aiding in definitive diagnosis for medical students and clinicians.

**Imaging Modality:** Abdominal Ultrasound (Greyscale sonography). **Anatomical Region:** Right lower quadrant of the abdomen. **Observed Pathology:** Acute appendicitis. **Characteristic Visual Features:** - **Transverse View:** The image displays a cross-sectional ("target" or "bullseye") appearance of the appendix. - **Morphology:** There is a non-compressible, blind-ending tubular structure with an enlarged outer diameter measuring 11 mm (exceeding the standard diagnostic threshold of 6–7 mm). - **Wall Features:** Circumferential wall thickening is visible with a central hypoechoic lumen. - **Extra-appendiceal Findings:** Prominent hyperechoic (echogenic) periappendiceal fat is observed surrounding the structure, indicative of secondary inflammatory changes (fat stranding). - **Secondary Cues:** On-screen calipers provide measurement verification of the distended structure. **Key Diagnostic Features:** Dilated appendix (>6 mm) in the transverse plane combined with increased echogenicity of the surrounding mesenteric fat, classic sonographic hallmarks of acute inflammation.

**Imaging Modality:** B-mode Ultrasound (Sonography) **Anatomical Region:** Right lower quadrant of the abdomen **Observed Pathology:** Acute appendicitis with appendicolith. **Characteristic Visual Features:** * **Transverse View:** The image displays a cross-section of the vermiform appendix appearing as a non-compressible, blind-ending tubular structure. * **Target Sign:** A classic "target" or "bull’s-eye" appearance is visible, characterized by concentric layers of varying echogenicity representing the inflamed appendiceal wall layers (mucosa, submucosa, and muscularis propria). * **Appendicolith:** A distinct, highly echogenic (hyperechoic) foci is located within the lumen of the appendix, associated with subtle posterior acoustic shadowing, indicative of a fecalith or appendicolith. * **Wall Changes:** There is evidence of mural thickening and luminal distension. * **Surrounding Tissue:** Increased echogenicity of the periappendiceal fat is noted, suggestive of secondary inflammatory changes (fat stranding). **Key Diagnostic Features:** The combination of a dilated appendiceal diameter, the presence of an intraluminal obstructing appendicolith, and the distinct target sign in the transverse plane are definitive sonographic markers for acute obstructive appendicitis.

**Imaging Modality:** Ultrasound (Grayscale B-mode sonography). **Anatomical Region:** Right lower quadrant (RLQ) of the abdomen. **Observed Pathology:** Acute appendicitis. **Characteristic Visual Features:** The image displays a longitudinal view of a blind-ending, tubular structure in the right iliac fossa, consistent with the vermiform appendix. Key sonographic findings include: * **Increased Caliber:** Significant thickening and distension of the appendiceal diameter. * **Wall Thickening:** Distinct mural thickening with preservation of gut signatures (hypoechoic and hyperechoic layers). * **Luminal Distension:** The lumen appears fluid-filled and non-compressible. * **Periappendiceal Changes:** There is a surrounding zone of increased echogenicity in the adjacent mesenteric fat, indicative of inflammatory fat secondary to the infection. **Diagnostic Features:** The combination of a non-compressible, blind-ending tubular structure exceeding 6mm in diameter with surrounding hyperechoic inflammatory fat is highly diagnostic of acute appendicitis. The orientation and anatomical marker on the UI confirm the probe placement over the McBurney's point region.

This diagnostic image is a B-mode grayscale abdominal ultrasound focusing on the right lower quadrant (RLQ). The image demonstrates a cross-sectional view of the vermiform appendix (labeled 'A'), appearing as a tubular, hypoechoic structure within the peritoneal cavity. A yellow measurement caliper ('D') indicates an outer diameter of 6 mm. Adjacent to the appendix, a small, localized periappendiceal fluid collection ('FL') is visible as an anechoic to hypoechoic area, suggesting localized inflammatory changes. The image quality allows for the differentiation of the appendix from surrounding soft tissue and bowel loops. This visual is clinically significant for the assessment of acute abdominal pain and the diagnostic evaluation of appendicitis. It serves as an educational example of RLQ sonography, illustrating target signs and fluid presence associated with inflammatory processes in the iliac fossa.