A perforation but where?

Ultrasound Findings

• The biliary system appears normal, as does the liver.
• Just inferior to the liver in the region of interest is a trace of free fluid.
• Deep to this there is echogenic mesenteric and retroperitoneal fat with some hypoechoic oedematous stranding.
• Small amounts of retroperitoneal fluid track toward the right kidney.
• Several highly echogenic focci with dirty posterior acoustic shadowing are seen directly adjacent to a poorly defined loop of bowel.

In this case an elongated appendix passing retrocaecally, then up to the right upper quadrant, had become necrotic and perforated. The appendix is shown to contain a faecolith seen on CT scan.

Take home messages

• Inflamed fat is generally echogenic on ultrasound. This can be seen with mesenteric fat surrounding an inflamed appendix, or the fat around an inflamed diverticulum. In more superficial tissues it can be seen in cellulitis and lymphangitis.
• The stranding around inflammatory masses seen on CT often correlates with fluid tracking through the tissues that can be seen on ultrasound. Examples include the stranding around the kidney with renal colic, or around the pancreas with pancreatitis, or in this case.
• Small foci of free gas appear as highly echogenic areas with dirty posterior acoustic shadowing. Gas within bowel tends to move with peristalsis and have a thin layer of hypoechoic bowel wall around it. These findings of free gas are typical of what occurs with a ruptured hollow viscus.