Incidental Findings on Brain Magnetic Resonance Imaging (MRI)
Essentials
Magnetic resonance imaging (MRI) of the brain is indicated if a disorder such as a brain tumour, cerebrovascular disorder or infection or inflammatory disease of the central nervous system (CNS) is suspected.
The rates of incidental findings on MRI of the brain reported in the literature vary greatly. Nevertheless, it can be said that they are quite common.
Most of the changes are benign. Their prevalence increases with age and with more advanced imaging sequences.
Imaging just for the purpose of reassurance easily leads to benign incidental findings further leading to a circle of check-ups, unnecessary costs and stress.
It is the clinician's task to determine the significance of the finding relative to the patient's age, disorders, symptoms and other examination results.
To avoid unnecessary imaging:
make a working diagnosis
consider whether findings will lead to any interventions in this case
remember that imaging must be based on a medical indication!
Incidental finding
An abnormal observation unrelated to the problem being examined
Three classes:
Clinically insignificant finding - this is the largest group
Finding requiring monitoring
Significant finding requiring further examinations and interventions
A meta-analysis (n = 19 559) showed:
neoplasms in 0.7% of patients
non-neoplastic changes in 2% (excluding white matter hyperintensities, silent infarcts and microbleeds).
According to the literature, the need for further imaging or other further assessment varies by research population and reporting method.
In cohort studies of patients older than 70 years, 2.6-4.5% had potentially significant findings.
In studies including people of all ages, 2.2-3% had potentially significant findings.
In younger age groups, the threshold for further imaging and follow-up is lower.
Medical benefit from imaging (= incidental finding leading to either some intervention or change in medication benefiting the patient) was reported in 0-1% of patients.
Typical incidental findings
Neoplasms
Found in many studies in 1-2% of patients, in older age groups even more frequently.
Usually benign
Meningiomas are the most common.
Incidental pituitary findings
Adenomas, various types of cysts and unspecific foci
Asymptomatic foci less than 1 cm in size rarely grow, and even then, only slowly.
Intracranial cysts
Very common, several types
Arachnoid cyst
Asymptomatic cysts need not normally be monitored unless particularly large or expansive. Paediatric patients should be monitored more readily.
Pineal cyst (cyst in the pineal gland)
No need for routine check-ups at least if the cyst is ≤ 1 cm in size and has thin walls. Even cysts larger than this very rarely grow if there are no other suspicious findings, such as wall thickening or solid component.
Plexus cysts and xanthogranulomas need not be monitored.
Ependymal and neuroglial cysts are usually clinically insignificant.
Normal variation: expanded perivascular cerebrospinal fluid-filled spaces, cavum septum pellucidum (et vergae)
Vascular pathology
Aneurysm (most common, in 1-2%)
Basic principle: at least those exceeding 2 mm in size and occurring in patients below the age of 75 years should be treated.
However, there are other factors affecting the decision: underlying diseases, risk factors, number, site and morphology of the aneurysms.
Vascular imaging of asymptomatic patients is indicated if at least two of their first-degree relatives have been diagnosed with a brain aneurysm.
A normal brain MRI finding obtained using basic sequences will not exclude an aneurysm.
Cavernoma
Histologically, cavernomas are vascular hamartomas consisting of thin-walled sinusoids with slow flow
Removal of symptomatic (bleeding or epilepsy) or large superficial changes should be considered.
Developmental venous anomaly, DVA (venous angioma)
Monitoring or interventions are not indicated.
Cavernoma and DVA are interassociated.
Capillary telangiectasia does not require monitoring.
Stenoses should be assessed considering the clinical situation (age, symptoms, primary diseases, medication).
White matter changes
Part of normal ageing
Even children may have small foci of T2 signal intensification but these become significantly more frequent after the age of 50 years.
There are numerous causes, the most common aetiology being vascular.
In a cohort of people aged 73 years, 22% of subjects showed moderate or pronounced changes.
Asymptomatic cerebral infarction
The incidence increases with age, being 12% in a cohort of people aged 73.
Vascular imaging may be necessary.
(Micro)bleeds
Cannot necessarily be seen on ordinary MRI sequences.
History and location: Trauma? Amyloid angiopathy? Hypertension? Sequelae of infarction? Sequelae of subarachnoid haemorrhage?
Atrophy
Cerebral sulci and ventricles expand with age in people over the age of 65 years; the degree of atrophy usually remains low even in older age groups.
In a cohort study in people over the age of 70 years, 25% showed more than average atrophy.
In a person with few or no symptoms, a memory disorder cannot be diagnosed based on imaging alone.
Other intracranial incidental findings
Inflammatory changes
E.g. in radiologically isolated syndrome, the risk of becoming ill with multiple sclerosis is increased. The need for monitoring is assessed case-specifically.
Structural abnormalities, such as Chiari I malformation
Hydrocephalus
Chronic subdural haematoma or hygroma
Should be assessed considering the patient's history, symptoms and age.
Other random findings in the area of the head
Thickened mucosa, cysts and fluid accumulation in paranasal sinuses are very common and of no significance unless the patient has symptoms.
Orbital dermoid/epidermoid cysts: if asymptomatic and typical looking, do not usually require monitoring but late follow-up may sometimes be necessary to exclude a tendency to grow.
Salivary gland tumour (other than a simple cyst or lymph node): ultrasound-guided thin needle biopsy
Atheromas and typical lipomas of the scalp are insignificant
Bone changes must be assessed considering the clinical situation and the patient's age; e.g. fibrous dysplasia, haemangioma, suspected malignancy (metastases, myeloma).
References
Morris Z, Whiteley WN, Longstreth WT Jr et al. Incidental findings on brain magnetic resonance imaging: systematic review and meta-analysis. BMJ 2009;339:b3016. [PubMed]
Sandeman EM, Hernandez Mdel C, Morris Z et al. Incidental findings on brain MR imaging in older community-dwelling subjects are common but serious medical consequences are rare: a cohort study. PLoS One 2013;8(8):e71467. [PubMed]
Boutet C, Vassal F, Celle S et al. Incidental findings on brain magnetic resonance imaging in the elderly:the PROOF study. Brain Imaging Behav 2016. [PubMed]
Katzman GL, Dagher AP, Patronas NJ. Incidental findings on brain magnetic resonance imaging from 1000 asymptomatic volunteers. JAMA 1999;282(1):36-9. [PubMed]
Orme NM, Fletcher JG, Siddiki HA et al. Incidental findings in imaging research: evaluating incidence, benefit, and burden. Arch Intern Med 2010;170(17):1525-32. [PubMed]