Choroidal detachment results when fluid or blood accumulates in the sub-choroidal space. Features that distinguish it from a retinal detachment include:
choroidal detachment tends to spare the region of the optic nerve and the posterior third of the globe. In contrast retinal detachment has its apex at the optic disc.
choroidal detachment may extend further more anteriorly than the ora serrata (site of retinal attachment at 2 and 10 o'clock). In contrast retinal detachment is limited by this anterior site of attachment.
on axial imaging, choroidal detachment has a shape reminiscent of a tennis ball*. A retinal detachment is typically V shaped.
* Note: the tennis ball analogy is a descriptive term only. To the best of my knowledge, there is no published literature describing a "tennis ball sign" of choroidal detachment, and an online search of the terms "tennis ball" and "choroidal detachment" yields results pertaining to etiology rather than radiologic description.