sigmoid sinus vs sinus sigmoideus

sigmoid sinus and sinus sigmoideus both are nouns.

Word	Noun	Adjective	Verb	Adverb
sigmoid sinus	Yes	No	No	No
sinus sigmoideus	Yes	No	No	No

As nouns, sigmoid sinus and sinus sigmoideus are synonyms defined as:

sigmoid sinus and sinus sigmoideus: an S-shaped dural sinus on the temporal and occipital bones

sigmoid sinus (noun)	sinus sigmoideus (noun)
an S-shaped dural sinus on the temporal and occipital bones	an S-shaped dural sinus on the temporal and occipital bones