MRI for brain structure, blood vessels

DEAR DR. ROACH » In 2016, I had a brain MRI without contrast, which showed chronic small-vessel brain disease and a remote lacunar infarct in the right cerebellum. This brain MRI was done because I was experiencing insomnia, along with dizzy spells, brain fog, poor judgment and difficulty walking and driving.

In May 2017, I had a brain CT scan because my blood pressure was high and I was having some pain on the left side of my head. (For years, I had experienced migraines or cluster headaches on the right side, but they ceased about eight years ago.) The brain CT scan was read as “normal.”

Why would the CT scan not show the damage that the MRI showed a year ago? I was told that the damage was permanent. I still can tell a difference in my thinking and memory skills, which were the result of the stroke that the MRI showed. — P.J. DEAR READER » An MRI is a much more sensitive test than a CT scan for looking at the brain structure and its blood vessels. The back part of the brain, called the posterior fossa, contains the cerebellum, and that area in particular is very difficult for the CT to show.

A CT scan is quick and useful for making sure there is no bleeding inside the head. But an MRI simply has much better resolution of the soft tissues, necessary to see small-vessel disease.

“Lacuna” is Latin for “pool” (the word “lagoon” comes from the same root), so a lacunar infarct is a small stroke that looks like a pit or pool. High blood pressure is a common underlying cause. Keeping the blood pressure down is the single most important factor in preventing another stroke.

DEAR DR. ROACH » I read that if you think you are having a heart attack, you should chew an aspirin tablet while waiting for the ambulance. Why is that? Should the aspirin then be swallowed? — K.S. DEAR READER » For people suspected of a heart attack, who do not have a reason not to take aspirin (such as allergy or active stomach bleeding), taking aspirin immediately can save lives. Chewing regular (not the enteric-coated) aspirin greatly speeds its absorption. The aspirin must be swallowed, as it is not absorbed well through the mouth. DEAR DR. ROACH » Should an otherwise healthy 63-year-old female who has had genital herpes for 28 years still get the shingles vaccine? Wouldn’t there be some immunity built up in her system, as she has regular occurring outbreaks, six times or more annually? — C.S. DEAR READER » Genital herpes usually is caused by herpes simplex virus 2 (it can rarely be caused by HSV-1), which is related to the virus that causes shingles, varicella-zoster. Unfortunately, the two viruses are different enough that a history of genital herpes doesn’t protect you from developing shingles. So, the vaccine is recommended for all adults over 60, unless there is a reason not to get it, such as a deficiency in the immune system due to recent chemotherapy.

Herpes viruses (there are eight in total) are very good at evading the immune system, and the vaccines for herpes viruses have so far been disappointing; only the shingles and chickenpox vaccines are effective (and even they are not as effective as we’d like). There are new vaccines in development that hopefully will give more complete and longer-lasting protection.