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Editors
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]