Sonography of abdominal fat
A question for you. Free fluid appears hypoechoic (dark) on ultrasound. Normal abdominal fat is relatively hypoechoic too. Why then, when abdominal fat becomes oedematous does it become hyperechoic (brighter)?
https://www.mdpi.com/2076-3417/13/1/432
This appears to be the answer. It’s all about interfaces -in this case on a microscopic scale.
‘Both pure water and fat appeared to be echo-free. Pure water displayed acoustic enhancement, while fat displayed acoustic shadowing. However, the emulsion appeared to be hyperechoic because of the difference in acoustic impedance between water and fat.’
In radiography (x-ray and CT) the term ‘misty mesentery’ is used to describe attenuation of the mesentery. In layman’s terms the abdominal fat acquires a hazy ‘white’ appearance.
https://ajronline.org/doi/pdf/10.2214/ajr.167.1.8659422
Causes of misty mesentery include oedema, inflammation, fibrosis and infiltration.
In contrast (no, not that kind of contrast!), oedematous mesentery appears hyperechoic on ultrasound whereas, as the fat becomes replaced by solid tissue or inflammatory infiltrates the affected mesentery becomes hypoechoic. So, ‘misty mesentery’ isn’t really a terminology that translates into sonography.
I’m not aware of a catchy sonography name for irregular hypoechoic areas within the mesentery. Usually us sonographers are ready with a ‘sign’ name!
This is what we’re talking about: pyogranulomatous inflammation of the mesentery in a young cat with FIP manifesting as hypoechoic ‘cords’ through the (normal) hyperechoic fat of the mesentery.
..and from the same patient.
I guess you could just call this infiltration of the mesentery and you wouldn’t be wrong. I’d call it ‘two-tone mesentery’:
https://www.creativereview.co.uk/2-tone-records/
…the black/white aesthetic fits nicely.
More examples:
Infiltrated mesentery deep to the spleen in a cat with sclerosing encapsulating peritonitis (SEP)
More detail from the same patient
The same SEP patient: a dramatic spider’s web of adhesions
This kind of thing is the hallmark of SEP. Bunched viscera, tightly bound together.
Dogs get two-tone mesentery too:
Septic peritonitis resulting from a GI perforation in a dog
Sadly, in many patients with two-tone mesentery the infiltration is neoplastic:
The archetypal ‘two-tone mesentery’: pancreatic carcinoma in a dog spreading in cords through the omentum
A similar pancreatic carcinoma in a cat
