Incidental findings on brain magnetic resonance imaging (MRI) in adults: a review of imaging spectrum, clinical significance, and management

Abstract

Utilization of brain MRI has dramatically increased in recent decades due to rapid advancement in imaging technology and improving accessibility. As a result, radiologists increasingly encounter findings incidentally discovered on brain MRIs which are performed for unrelated indications. Some of these findings are clinically significant, necessitating further investigation or treatment and resulting in increased costs to healthcare systems as well as increased patient anxiety. Moreover, management of these incidental findings poses a significant challenge for referring physicians. Therefore, it is important for interpreting radiologists to know the prevalence, clinical consequences, and appropriate management of these findings. There is a wide spectrum of incidental findings on brain MRI such as asymptomatic brain infarct, age-related white matter changes, microhemorrhages, intracranial tumors, intracranial cystic lesions, and anatomic variants. This article provides a narrative review of important incidental findings encountered on brain MRI in adults with a focus on prevalence, clinical implications, and recommendations on management of these findings based on current available data.

Figure 1.

Age-related white matter changes. Axial FLAIR images of three different patients who underwent brain MRI for unrelated indication. There are three patterns of deep/subcortical white matter changes based on extent of the lesions, including (A) punctate, (B) early confluent, and (C) confluent white matter changes. Punctate changes are typically of non-ischemic origin, whereas early confluent and confluent changes represent progressive ischemic lesions. FLAIR, fluid attenuated inversion recovery.

Figure 2.

Incidental low-grade glioma A 39-year-old female undergoing brain MRI for intermittent headaches. Patient denied any focal neurological deficits. Axial FLAIR (A) and axial contrast-enhanced T ₁WI (B) demonstrate a small ill-defined non-enhancing lesion in the left frontal lobe (arrows). Arterial spin labelling (C) and dynamic susceptibility contrast-enhanced MR perfusion (D) show no evidence of increased perfusion within the lesion (arrows). Multivoxel MR spectroscopy (TE = 144 ms) (E) shows decreased NAA peak, indicative of neuronal loss. There is no abnormal elevation of choline peak to indicate significantly increased cellular proliferation. Findings are concerning for low-grade neoplasm. Patient subsequently received surgical resection, with final pathology showing IDH-mutant, WHO Grade II glioma. FLAIR, fluid attenuated inversion recovery; IDH, isocitrate dehydrogenase; NAA, N-acetylaspartate; T ₁WI, T ₁ weighted imaging; TE, echo time.

Figure 3.

MVNT. A 60-year-old female undergoing brain MRI for ear pressure and retro-orbital pressure sensation. Axial (A) and coronal (B) FLAIR images demonstrate a cluster of multiple small FLAIR hyperintense foci in the left parietal lobe primarily involving superficial subcortical white matter and adjacent deep cortical gray matter (arrows)—characteristic imaging features of MVNT. Lesions show no restricted diffusion or contrast enhancement (not shown). No mass effect or abnormal gyral expansion noted. FLAIR, fluid attenuated inversion recovery; MVNT, multinodular and vacuolating neuronal tumor.

Figure 4.

Incidental meningioma. A 69-year-old female undergoing brain MRI for right tinnitus and intermittent vertigo. Axial (A) and coronal (B) contrast-enhanced T ₁WI demonstrate a dural-based enhancing extra-axial mass at the right posterior parietal convexity with focal invasion into the superior sagittal sinus, findings most consistent with meningioma. Patient was managed conservatively, and the tumor has been stable on serial follow-up MRI for 9 years.

Figure 5.

Incidental subependymoma. A 48-year-old female undergoing brain MRI for imaging surveillance of multiple sclerosis. Axial T ₂WI (A), contrast-enhanced T ₁WI (B), FLAIR (C), and coronal FLAIR (D) demonstrate a circumscribed non-enhancing mass in the left lateral ventricle. There were no symptoms attributed to the mass. Patient underwent surgical resection, with final pathology showing subependymoma (WHO Grade I). Note multiple T2 hyperintense white matter lesions in relation to underlying demyelinating disease (arrowheads on C and D). FLAIR, fluid attenuated inversion recovery.

Figure 6.

Incidental pineal tumor. A 59-year-old female undergoing brain MRI for headache after a mechanical fall. Sagittal high-resolution T ₂WI (A), sagittal (B) and axial (C) contrast-enhanced T ₁WI demonstrate a small extra-axial enhancing mass at the pineal region. There is no significant local mass effect or obstructive hydrocephalus. Patient was managed conservatively, and the mass has been stable on serial follow-up MRI for 2 years. It is favored to be benign tumor such as meningioma or pineocytoma.

Figure 7.

Rathke’s cleft cyst. A 38-year-old female undergoing brain MRI for postpartum headache. Sagittal T ₁WI (A) and coronal T ₂WI (B) demonstrate a small well-circumscribed cystic lesion centered in the pars intermedia of the pituitary gland (arrows). The lesion contains T1 hyperintense and T2 hypointense content likely secondary to high proteinaceous fluid content. Findings are most consistent with Rathke’s cleft cyst. The lesion has been stable on serial follow-up MRI.

Figure 8.

Incidental pituitary adenoma. A 51-year-old male undergoing MRI for surveillance for the left vestibular schwannoma previously treated with radiation therapy. Coronal contrast-enhanced T ₁WI with fat suppression (A) demonstrates a small hypoenhancing lesion centered in the right lateral aspect of pituitary gland (arrow), most consistent with pituitary adenoma. There was no evidence for endocrinological dysfunction on physical exam or laboratory work-ups. The lesion was presumed to be a non-functioning pituitary microadenoma. Note a small enhancing vestibular schwannoma in the left internal auditory canal and cerebellopontine angle cistern (arrowhead on Figure 8B).

Figure 9.

The American College of Radiology recommendations for management of incidental pituitary findings on CT or MRI. Reference: Hoang JK, Hoffman AR, Gonzalez RG, Wintermark M, Glenn BJ, Pandharipande PV, et al. Management of Incidental Pituitary Findings on CT, MRI, and (18)F-Fluorodeoxyglucose PET: A White Paper of the ACR Incidental Findings Committee. J Am Coll Radiol. 2018;15(7):966–72. The flow chart is reproduced with permission from the Journal of the American College of Radiology.

Figure 10.

Incidental pineal cyst. A 31-year-old female undergoing brain MRI for dizziness. Axial T ₂WI (A), FLAIR (B), contrast-enhanced T ₁WI (C) and sagittal contrast-enhanced T ₁WI (D) demonstrate a 2.0 cm cystic lesion centered in the pineal region (arrows). No abnormal solid component or solid enhancement is present. The cyst has been stable on serial follow-up MRIs for 4 years. FLAIR, fluid attenuated inversion recovery

Figure 11.

Incidental colloid cyst. A 37-year-old female undergoing brain MRI for concussion. Axial T ₁WI (A) and sagittal high-resolution T ₂WI (B) demonstrate a 1.0 cm cystic lesion centered in the foramen of Monro (arrows), most consistent with colloid cyst. No imaging evidence of obstructive hydrocephalus. The cyst has been stable on serial follow-up MRIs for 5 years. Incidentally noted small pineal cyst (arrowhead on image B).

Figure 12.

Neuroenteric cyst. A 37-year-old female undergoing brain MRI for headaches. Axial T ₁WI (A), axial T ₂WI (B), axial contrast-enhanced T ₁WI (C), axial DWI (D) and ADC maps (E) show a small extra-axial cystic lesion centered in the right cerebellomedullary cistern (arrows). The lesion is slightly hyperintense to CSF on T1 and isointense on T2, with no definite enhancement. There is no diffusion restriction. The lesion exerts minimal mass effect on the lower brainstem. The patient underwent surgical excision, with final pathology showing neuroenteric cyst. ADC, apparent diffusion coefficient; DWI, diffusion-weighted imaging.