Pulmonary Infarction

Chest x-ray demonstrates a peripheral airspace opacity (arrows) that has a wedge-shaped configuration and a blunt medial apex pointing toward the hilum

Coronal-reformatted CT images confirm the presence of airspace opacity in the right middle lobe (arrows) with an embolus in the corresponding segmental pulmonary artery (arrowhead)

Facts: 

• Pulmonary embolic obstruction can occur with or without resultant pulmonary infarction
• In pulmonary embolism with infarction, process begins as "incomplete" infarct (intra-alveolar hemorrhage without necrosis of alveolar wall), which can go on to necrosis "infarct" especially in patients with underlying unhealthy lung
• On CXR, infarct is seen as a wedge-shaped, pleural-based consolidation with a rounded convex apex directing toward the hilum "Hampton hump"
• Often occurs in lower lobes
• Heals with scar formation

Reference

Dalen JE. Pulmonary embolism: what have we learned since Virchow? Chest 2002; 122:1440-1456.

Color Doppler Twinkling Artifact

Longitudinal images of the left kidney show a stone (arrow) in the lower pole with posterior acoustic shadowing and the color Doppler twinkling artifact (short arrows).

Facts:

• Rapidly alternating red and blue signal behind a highly reflective structure on color Doppler US
• Useful diagnostic signs especially for urinary calculi detection and improved diagnostic confidence
• Can also be seen in calcifications in various tissues, biliary stones, encrusted indwelling urinary stents, gallbladder adenomyomatosis and bile duct hamartomas
• Two proposed mechanisms:
• Phase jitter - intrinsic machine noise causing random fluctuation of acoustic waves
• Acoustic waves hitting a rough interface producing complex beam pattern with multiple reflections

Reference

Kim HC, et al. Color Doppler twinkling artifacts in various conditions during abdominal and pelvic sonography. J Ultrasound Med 2010; 29:621.

Emphysematous Cystitis

Sagittal-plane ultrasound image of the bladder shows a linear hyperechoic structure with posterior "dirty shadowing" in the anterior aspect of the urinary bladder. There is no recent bladder catheterization. Upon decubitus positioning, this abnormality is immobile, suggesting extraluminal location. 

Axial non-contrast CT of the same patient demonstrates gas within the anterior and posterior walls of the urinary bladder (arrows).

Facts:

• Rare bladder inflammation with gas in bladder wall and surrounding tissues
• Generally caused by E.coli, K.pneumoniae or anaerobic gas-forming organisms
• Pathology: numerous gas filled intramural cysts on mucosal surface
• Risk factors: diabetes, immunocompromised state, urinary tract obstruction
• Most patients have mild forms of disease and respond well to antibiotics. Some have severe inflammation, gangrene and sepsis

Imaging:

• X-ray and CT usually is diagnostic with gas in the bladder wall, surrounding tissues and in the lumen in the absence of prior catheterization
• Ultrasound may show gas in the wall as hyperechoic lesions with posterior dirty shadowing. Visualization of posterior wall of urinary bladder may be limited if gas is present in the anterior aspect of the bladder. Decubitus scan helps localizing gas, whether inside the bladder lumen or in the wall
• CT helps detecting complications such as perforation or emphysematous pyelonephritis

Reference

Gillenwater JY, et al. Adult and pediatric urology, volume 1, 2002.

Petersen RO, et al. Urologic pathology, 2009.