Brain shrinkage (atrophy) seen by chance on a brain scan

What the report means

Atrophy. Radiologists rate shrinkage of the inner part of the temporal lobes (medial temporal atrophy, MTA) and of the brain surface overall (global cortical atrophy, GCA) on simple visual scales. These work on both CT and MRI. (Wahlund 2017)
Wider fluid spaces. As the brain shrinks, the fluid-filled spaces inside it (the ventricles) look wider. Reports may call this no, mild, moderate or severe widening, compared with a healthy 25-year-old. (Wahlund 2017)
Judged against age. Experts advise that the radiologist describes the findings, then says whether they are abnormal taking the person's age into account, and relates them to the clinical picture. (Wahlund 2017) "Age-appropriate" means the change is what is usually seen at that age.
Not every finding is age-related. A third ventricle wider than 10 mm is abnormal at any age. (Wahlund 2017)

How much shrinkage is normal with age

A slow, steady loss. Across 56 long-term MRI studies of 2,211 healthy people, brain volume was stable or grew in early adulthood, then fell by about 0.2% a year after age 35. The loss sped up to about 0.5% a year by age 60. (Hedman 2012)
Healthy older people score higher. In a study of 184 people whose type of dementia was confirmed after death and 73 healthy controls, the older controls had higher atrophy scores than the younger controls. (Harper 2016) In 2,934 memory clinic patients, atrophy scores rose with age in people without dementia too. (Rhodius-Meester 2017)
Cut-offs rise with age. One large study proposed medial temporal atrophy cut-offs of 1.5 or more at ages 45 to 74, 2 or more at 75 to 84 and 2.5 or more at 85 to 94, on a 0 to 4 scale. (Ferreira 2015)(Rhodius-Meester 2017)

Why a scan alone does not diagnose dementia

No single test. A dementia diagnosis is based on several assessments together: a history, tests of memory and thinking, and blood tests. Brain scans on their own cannot diagnose dementia, and a scan without obvious changes does not mean someone does not have it. (NHS tests)
NICE wording. NICE starts with a history from the person and, if possible, someone who knows them well, then a physical examination, blood and urine tests, and a brief memory test. Imaging is used to rule out other causes and to help with the type of dementia. Alzheimer's disease should not be ruled out based only on CT or MRI. (NICE NG97)
Less telling with age. In the memory clinic study, atrophy ratings told people with Alzheimer's disease apart from people without it best under age 65. Medial temporal atrophy only did so under 75, and in people with mild memory problems it only predicted dementia in those over 75. (Rhodius-Meester 2017)
Dementia is not normal ageing. The NHS says dementia is not a natural part of ageing, which is why memory problems are worth raising with a GP. (NHS symptoms)
Worry is real. See after an abnormal screening result.

Which checks guidance lists

If you have memory or thinking symptoms

See a GP. The NHS advises seeing a GP if you keep having problems with your memory, or if memory problems affect daily life. (NHS memory loss) Forgetting things more often than others your age may be mild cognitive impairment. (MedlinePlus)
Early symptoms. The NHS lists memory loss, trouble concentrating, difficulty with familiar daily tasks, struggling to follow a conversation or find a word, confusion about time and place, and mood changes. (NHS symptoms)
The tests. A GP may use a short memory test and blood tests for liver, kidney and thyroid function, HbA1c (for diabetes), and vitamin B12 and folate, to look for other causes. (NHS tests) A normal score on a memory test does not on its own rule dementia out. (NICE NG97) See memory screening: Mini-Cog and MoCA scores.

If you have no symptoms

Memory screening. For adults 65 and older without signs or symptoms, the USPSTF found the evidence insufficient to judge the benefits and harms of routine screening for cognitive impairment. (USPSTF 2020)
Blood pressure and diabetes. The USPSTF recommends blood pressure screening for adults 18 or older (USPSTF blood pressure 2021), and screening for prediabetes and type 2 diabetes at 35 to 70 in people with overweight or obesity. (USPSTF diabetes 2021) The NHS Health Check, offered every 5 years from 40 to 74, looks at heart disease, diabetes, kidney disease and stroke risk; people over 65 are also told the signs of dementia. (NHS risk factors)
Hearing. The NHS lists hearing loss and untreated depression among risk factors for dementia. (NHS risk factors) For adults 50 and older who have not noticed hearing problems, the USPSTF found the evidence on routine hearing screening insufficient. (USPSTF hearing 2021) See hearing tests by age.

How it ties to your age-based checks

A report of brain shrinkage is a good moment to make sure your routine checks are up to date:

Other brain scan findings have their own pages: white matter changes on a brain MRI, small meningioma found by chance and pineal cyst found by chance.

Who it applies to

Adults told that a brain MRI or CT done for another reason shows mild or age-appropriate volume loss. People already being assessed for dementia, children and people with fluid build-up in the brain (hydrocephalus) are outside this page.

The NHS advises calling 999 (911 in the US) for signs of a stroke: a face that has dropped on one side, weakness in one arm, or slurred or confused speech, even if the symptoms stop. Other signs include sudden weakness or numbness down one side, loss of sight, confusion and memory loss, or a severe headache. (NHS stroke)

Routine age-based screening

A finding on a brain scan does not replace the routine screenings for your age. See screenings by age and gender.

Where they differ:

Memory checks without symptoms. The USPSTF found the evidence insufficient for routine cognitive screening at 65 and older. (USPSTF 2020) The NHS Health Check tells people over 65 the signs of dementia to look out for. (NHS risk factors)
Who needs a scan. NICE offers structural imaging during a dementia assessment unless dementia is well established and its type clear. (NICE NG97) The NHS says not everyone will need a brain scan, especially if tests already show dementia is likely. (NHS tests)
Where to draw the line. Earlier medial temporal atrophy cut-offs were 1 or more under 75 and 1.5 or more over 75; later work raised them to 1.5, 2 and 2.5 over 85. (Rhodius-Meester 2017)(Ferreira 2015) No age-specific cut-offs exist yet for some of the other scales. (Harper 2016)

Your doctor decides what your result means for you.

Questions people ask

Is some brain shrinkage normal with age?

Yes. A review of 56 MRI studies in healthy people found a steady loss of about 0.2% of brain volume a year after age 35, rising to about 0.5% a year by age 60. Healthy older people score higher on atrophy rating scales than healthy younger people. (Hedman 2012) (Harper 2016)

Does atrophy on my scan mean I have dementia?

No. The NHS says brain scans on their own cannot diagnose dementia; a diagnosis is based on a history, memory and thinking tests, blood tests and sometimes a scan together. NICE says Alzheimer's disease should not be ruled out based only on CT or MRI either. (NHS tests) (NICE NG97)

What does "age-appropriate" mean on the report?

Radiologists are advised to judge shrinkage against the person's age. Scores that would be unusual at 50 can be expected at 80, so cut-offs for the main rating scale rise with age. (Wahlund 2017) (Ferreira 2015)

Should I have a memory test?

If memory problems keep happening or affect daily life, the NHS advises seeing a GP. For people 65 and older without symptoms, the USPSTF found too little evidence to say whether routine memory screening helps. (NHS memory loss) (USPSTF 2020)

Which other checks are linked?

The NHS lists hearing loss and depression among dementia risk factors and offers a Health Check from 40 to 74 that looks at heart disease, diabetes, kidney disease and stroke risk. The USPSTF advises blood pressure screening from 18 and diabetes screening at 35 to 70 for people with overweight or obesity. (NHS risk factors) (USPSTF blood pressure 2021) (USPSTF diabetes 2021)