Clean vs. Dirty Shadowing

Greetings Scan Squad! 

This week I want to talk about another common question: clean versus dirty shadowing. 

Shadowing can be called ‘clean’ when there is complete dropout with sharp edges to the shadow. This occurs due to complete absorption of the ultrasound waves. It is typically caused by stones (any location), bone (rib, pelvis etc.) and foreign bodies. 

On the other hand, ‘dirty’ shadowing has a hazy appearance. It is due to complete reflection of the ultrasound waves. It is typically caused by gas or air. 

The most important thing to remember is that there is overlap between the two types of shadowing. Just because there is a dirty shadow, does not mean you can rule out a foreign body! 

Happy scanning! 

A clean, strong shadow (arrow) produced by a foreign body in the jejunum. You can see a dilated (measuring 1.43cm in height) segment of jejunum to the right of the foreign body. It contains echogenic liquid ingesta within the lumen.

Dirty shadowing at the ileo-colic junction (ICJ). Shadowing is present in both the colon (arrow on the left) and the ileum (arrow on the right). The shadowing is caused by gas (remember the hyperechoic line at the mucosal interface) in the lumen.