brain edema vs hydrops

brain edema and hydrops both are nouns.

Word	Noun	Adjective	Verb	Adverb
brain edema	Yes	No	No	No
hydrops	Yes	No	No	No

As nouns, hydrops is a hypernym of brain edema; that is, hydrops is a word with a broader meaning than brain edema:

brain edema: swelling of the brain due to the uptake of water in the neuropile and white matter
hydrops: swelling from excessive accumulation of watery fluid in cells, tissues, or serous cavities

Other hypernyms of brain edema include dropsy, edema, oedema.

brain edema (noun)	hydrops (noun)
swelling of the brain due to the uptake of water in the neuropile and white matter	swelling from excessive accumulation of watery fluid in cells, tissues, or serous cavities