Ischemic injury would be like a very tiny stroke, I think. Very slight bleeding. My first neuro issue was diagnosed for a while as a Temporary Ischemic Attack (TIA), and felt like (I'm told) a stroke.
As for your second question, I think there is no difference between small vessel disease and small vessel changes. And I've been told by a number of doctors that small vessel damage in the brain is fairly common in MRIs, particularly in older people.
Small vessel ischemic disease or small vessel disease or white matter disease occurs due to blockade of small vessels in the brain resulting in minute areas of brain damage.
This can occur in patients with long standing history of headaches, migraines, smoking, alcoholism, diabetes, high BP, brain infections, or stroke.
It is important to correlate these findings with your symptoms. Also there is evidence that patients with small vessel ischemic disease have increased risk of stroke.