Reading Your MRI Report After Gamma Knife: What "Stable", "Increased" and "Loss of Enhancement" Usually Mean

After Gamma Knife, “stable” on an MRI report is usually good news, “loss of central enhancement” usually reflects the treatment acting on the target, and “increased in size” in the first year or two can be temporary swelling rather than growth; your team reads these phrases against the trend across all your scans, not one report alone. The point of radiosurgery is control, so a target that is still visible and has stopped growing is often exactly the outcome planned¹.

My six month report arrived in the patient portal on a Friday evening, three days before my appointment. It said my acoustic neuroma showed “central loss of enhancement” and was “not significantly changed in size”, and I spent the weekend convinced that “loss” was bad and that “not significantly” was hiding something. Both phrases turned out to be the result my consultant had hoped for. This is the glossary I wish I had had that weekend, with the clinical lines checked by our reviewer. It sits beside Gamma Knife results and follow-up, which covers the follow-up schedule and what success looks like.

Why the report reads the way it does

MRI reports are written by a radiologist for the doctors treating you, in a deliberately cautious language that compares this scan with earlier ones; they describe what is visible, not what it means for you. The meaning comes from your team putting the report together with your symptoms, your treatment plan and the full set of images.

Two things about that language catch people out. First, everything is relative: “increased”, “decreased” and “stable” are measured against a named comparison scan, which is usually the last one, sometimes the planning scan. Second, radiologists list possibilities rather than conclusions. “Cannot be excluded” and “suggest correlation with clinical findings” are routine phrases, not alarms. I learned to read my reports as careful descriptions handed to my consultant, not as verdicts handed to me.

Radiosurgery works gradually. The AANS notes that malignant targets may shrink within a couple of months, benign tumours over about 18 months to two years, and that an AVM can take up to two years to show the effect, which is why the scans go on for so long and why any one report is a single frame of a slow film².

”Stable” and “no significant change”

“Stable” or “no significant change” means the target is about the same size as on the comparison scan, and after radiosurgery for a benign tumour that is usually the intended outcome. Cleveland Clinic notes that many noncancerous tumours stop growing straight away but do not get smaller, while cancerous ones more typically become stable or shrink over weeks to months¹.

The word “significant” bothered me more than it should have. It is there because measurements on MRI vary by a millimetre or so between scans, depending on slice position and how the tumour is outlined, and radiologists do not want to call a change that is within that noise. “No significant change” means “no change we would act on”, not “a change we are not telling you about”.

If you have read anything on this site you will know the line by now: the tumour still being visible is not failure. Why that is, and how it felt to live with, is in radiosurgery and scanxiety.

”Loss of central enhancement”

Loss of central enhancement means the middle of the target is taking up less of the contrast dye than before, so it looks darker in the centre with a brighter rim; it is commonly seen in the first year after radiosurgery and is generally read as a treatment effect. A 2024 radiology primer on acoustic neuromas after radiosurgery shows near-complete loss of central enhancement at 6 months, and a controlled tumour of stable size despite considerable loss of central enhancement³.

Contrast dye, usually gadolinium, is injected during the scan and lights up tissue with an active blood supply. Many tumours enhance brightly before treatment. When the centre stops enhancing, it suggests the tissue there has changed in response to the dose. It is not a measurement of size, and it can happen while the tumour stays the same size or even swells a little.

That was my six month report exactly. My consultant called it “what we like to see at this stage” and moved straight on, which in hindsight was the most reassuring thing he could have done. Whether it means the same on your scan is a question for the person who can see the pictures.

”Increased in size” in the first year or two

An increase in size in the first year or two after radiosurgery can be temporary swelling, sometimes called pseudoprogression or transient enlargement, rather than the tumour growing; it is particularly recognised with acoustic neuromas. In one series in Neuro-Oncology, 23% of treated acoustic neuromas enlarged, almost all starting at around 6 months, and the authors concluded that enlargement in the first 24 months rarely meant the treatment had failed, while any change after 24 months pointed toward failure⁴.

That is why teams rarely act on a single larger scan in the first two years. They look for the shape of the trend: swelling that peaks and then settles or shrinks is the pattern of a treatment effect, and the 2024 primer shows a tumour that grew from 3.9 mL at planning to 4.4 mL at 6 months, then fell to 0.6 mL at 4 years. Steady growth across several scans, especially beyond about two years and especially with worsening symptoms, is the pattern that prompts a different conversation³.

The phrase that usually accompanies this on a report is something like “likely treatment-related change, recommend follow-up imaging”. It is a holding sentence. It means the radiologist cannot tell from one image and wants the next one before anyone decides. If your report says this, the most useful thing to ask is when the next scan is and what would change the plan. What happens if growth continues is covered in repeat Gamma Knife treatment.

”Oedema”, “radiation-induced change” and “necrosis”

“Oedema” means swelling of the brain tissue around the target, “radiation-induced change” is a general term for the tissue reacting to the dose, and “radiation necrosis” means an area of tissue damaged by radiation; all three are recognised delayed effects, usually appearing months rather than weeks after treatment. Reported rates of radiation necrosis vary widely between studies, from about 3% to 34%, and larger targets carry more risk⁵.

What matters most is not the words but whether you have symptoms. Plenty of people have oedema on a scan and feel nothing, and it is simply watched. When it causes headaches, weakness or the return of an old symptom, steroids are commonly used to settle it. The whole picture, including the steroid side effects, is in swelling after Gamma Knife.

One phrase deserves its own mention: “radiation necrosis versus tumour progression”. On standard MRI the two can look similar, so radiologists sometimes list both. Teams separate them with time, with repeat imaging and sometimes with specialist scan sequences. It is a sentence that starts a conversation, not one that ends it, and my own conversation about it is in radiation necrosis: what I learned.

Words you can usually skim

Reports often mention incidental findings that have nothing to do with your treatment: small white matter spots, sinus thickening, a “mucous retention cyst” or age-related changes; they are common on brain MRI and are usually noted for completeness. If one of them is new or the radiologist suggests following it up, your team will say so.

I wasted an evening on “mild mucosal thickening in the maxillary sinuses”, which turned out to mean I had a cold. Not every unfamiliar phrase is about the target. The paragraph to read closely is the one that names the treated lesion and compares it with the previous scan; the conclusion or “impression” at the end usually summarises it in one or two lines.

Questions to take to the appointment

The most useful questions about any post-radiosurgery report are about trend and action: what has changed since the last scan, how that fits the expected pattern, and what would make the team do something different. Bring the exact phrases that worried you, written down.

The ones I now ask every time:

• Compared with which scan, and how much has it changed in millimetres or volume?
• Is this the pattern you expected at this point after treatment?
• Is anything on this report a reason to change the plan or bring the next scan forward?
• What symptoms should make me ring you before the next scan?
• When is the next scan, and will we always compare with the same baseline?

If you find reading the report alone before the appointment makes the wait worse, it is reasonable to stop opening the portal and let the consultant tell you. I tried both. What helped most was going in with my list.

What a report cannot tell you

A report is a radiologist’s description of one moment, written for your team. It cannot tell you how you will feel, what your next scan will show, or whether a phrase that sounds ominous is ordinary for your type of target at your point in the timeline. The phrase that frightened me most on my own six month report turned out to be the one my consultant was most pleased by, and I only understood that once someone who could see the images explained it. What your own report means, and whether anything needs doing about it, is for the team who planned your treatment and can see every image side by side.