TABLE 2.

Definitions of the incidental findings.

Imaging diagnosis	Definition based on MRI characteristics
White matter hyperintensities	WMH commonly locate in both periventricular or subcortical areas with hypointense on T1-weighted images and hyperintense on T2-weighted and FLAIR images.
Brain atrophy	Overall brain volume decreases with advancing age, and cerebral spinal fluid increases relatively.
Enlarged perivascular space	Enlarged perivascular space is also called Virchow–Robin space (VRS). VRS is commonly linear or lobulated in shape with hypointense on T1-weighted images and hyperintense on T2-weighted and FLAIR images.
Cerebral microbleeds	CMB is a hypointense foci on SWI images with maximum size up to 5 or even 10 mm.
Paranasal sinusitis	Unilateral or bilateral mucoperiosteal thickness or hydrops in the paranasal sinus.
Retention cysts of the maxillary sinus	Retention cysts of the maxillary sinus are rounded or dome-shaped lesions originating from the wall of the sinus with hypointense on T1-weighted images and hyperintense on T2-weighted image.
Calvarial thickening	Widened skull width.
Mastoiditis	Increased fluid signal in the mastoid air cells on T2-weighted images.
Pineal cyst	Cystic lesions in Pineal region with hypointense on T1-weighted images and hyperintense on T2-weighted images.
Asymptomatic brain infarct	Asymptomatic brain infarct is a focal parenchymal lesion with hypointense on T1-weighted images, hyperintense on T2-weighted images and with a hyperintense rim on FLAIR images.
Falx cerebri ossification	Falx cerebri ossification demonstrates signal intensity similar to fatty marrow on T1-weighted and T2-weighted images and hypointense on SWI images.
Empty Sella	Pituitary surface is concave, and the height of the pituitary is less than 3 mm.
Rathke’s cleft cyst	Rathke’s cleft cyst commonly locate between anterior and posterior pituitary lobes with hypointense on T1-weighted images and hyperintense on T2-weighted images.
Hydrocephalus	Ventricular enlargement out of proportion to sulcal atrophy.
Cysts of the septum pellucidum	A cystic structure between lateral ventricles whose walls are 10 mm apart or greater.
Subdermal cyst	Cystic lesions in subdermal with hypointense on T1-weighted images and hyperintense on T2-weighted images.
Enlarged cisterna magna	With more rostral extension in the posterior fossa close to the occipital squama than normal.
Venous malformation	Venous malformation is comprised of one or more atypically shaped veins and is hypointense on SWI images and/or flow-voids on T1-weighted and T2-weighted images.
Cavernous malformation	Cavernous malformations are usually hypointense on SWI images and with a hypointense hemosiderin rim and a core of variable signal intensity on T2-weighted images.
Meningioma	Meningioma is an extra-axial lesion with isointense or hypointense on T1-weighted images, variable signal intensities on T2-weighted images. Calcifications sometimes (hypointense on all images) within lesion.
Osteoma	Dense lesions usually involve outer table with hypointense on all images.
Arachnoid cyst	Arachnoid cyst is a well-defined cystic lesion with hypointense on T1-weighted images and hyperintense on T2-weighted images.
Bone cyst	Cystic lesion on skull with hypointense on T1-weighted images and hyperintense on T2-weighted images.
Craniopharyngiomas	A cystic or calcified tumor usually locate in suprasellar region with variable intensities.
Pituitary adenoma	Normal pituitary gland may not be identified. Signal intensities of pituitary adenoma are isointense to gray matter on all sequences but sometimes show cystic changes.
Metastasis	Multiple skull osteoclasia. Whole-body CT scan also showed multiple bone destruction surrounded by soft tissue masses.
Aneurysm	Aneurysms are well delineated focal arterial out-pouching with a saccular shape, usually located in cavernous internal carotid artery or circle of Willis. Aneurysms are visualized as flow voids (black) on T2-weighted images and could be well identified on magnetic resonance angiography.
Chronic subdural hematoma	Crescent-shaped fluid collection with hypointense on T1-weighted images and hyperintense on T2-weighted images. Extra-axial fluid collection could cross sutures.
Acute subdural hematoma	Crescent-shaped lesion with hyperintense on T1-weighted and T2-weighted images. Extra-axial lesion could cross sutures.

WMH, white matter hyperintensities; EPVS, enlarged perivascular space; CMBs, cerebral microbleeds.