IF the context is a CT scan (information which was not actually given in the OP, nor is it flagged [med]) I would take it to mean the same as flüssigkeitsisodense, i.e. with a density the same as that of fluid.
> This liquid shows a kind of equal density überall in itself, it is in a way homogeneous in terms of density, right?
Not quite. It may well be homogeneous but it means that the density of the lesion (in HU, as wienergreissler suggested) is the same as that of the reference tissue or structure – in this case the lesion has the same density as fluid (0-20 or 0-30 HU, depending on source).
I don’t think that “fluid-isodense” is commonly used by NES radiologists.
“Computed tomography findings will show a popliteal artery being compressed by a mass with the same density as fluid but will not show the true multilocular nature of the cyst due to the lower tissue resolution when compared with magnetic resonance imaging.4 “
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC...
NB: Fluid is usually hypodense to surrounding solid tissues but of similar density to fluid in other parts of the body:
“Fluid on CT is relatively hypodense (dark). It can be compared to fluid in the gallbladder or stomach.”
https://radiopaedia.org/articles/free-intrape...
Also check out “fluid attenuation”, e.g.
"In general, simple renal cysts have simple fluid attenuation (0–20 HU)"
https://www.ajronline.org/doi/pdf/10.2214/AJR....
"Simple cysts are the most common type of cystic liver lesion and are seen in approximately 2.5% of the population 1 ; they are developmental, arising from a defect in bile duct formation. On ultrasound, they are anechoic with posterior acoustic enhancement, while on CT they are of fluid attenuation (Figure 1)."
https://www.appliedradiology.com/articles/ima...
"Dabei zeigte sich eine große paratracheale, teils flüssigkeitsisodense Raumforderung ([Abb.1]).
[…]
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https://www.thieme-connect.com/products/ejour...
"Although many bronchogenic cysts manifest as homogeneous fluid attenuation lesions at multidetector CT …”
https://www.webcir.org/revistavirtual/articul...
