Not a straightfoward answer, but I would say that bleed of the adrenal glands occurs at the same frequency of bleeding in any internal organ. There is nothing particular about the adrenals that makes them more or less prone to bleed. Factors that can cause spontaneous bleeding include malignancy (or alternatively, clotting), blood thinning medications such as coumadin,plavix, aspirin or medications that affect those medications' actions. Blunt trauma, of course.