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.