1. BRAIN PARENCHYMA, VENTRICLES AND CISTERNS

2. NORMAL MYELINATION Normal pediatric myelination
On T1-weighted images, the corpus callosum is isointense relative to white matter at birth and becomes progressively increased in signal until it reaches the intensity of the adult structure at approximately 7 to 8 months of age. On T2-weighted images, at birth the signal intensities of gray and white matter are the opposite of those in the adult brain. White matter is of lower intensity than gray matter on T1-weighted images, and of higher signal intensitiy than gray matter on T2-weighted. This persists until approximately the age of 6 months. After this the white matter becomes progressively brighter than the gray matter on T1 and darker than gray matter on T2 until the adult pattern is reached. With the exception of the peritrigonal regions and peripheral subcortical fibres (terminal zones), the adult pattern of myelination is normally present by 18 months of age. It is important to differentiate the terminal zones from periventricular leukomalacia.

3. NORMAL MYELINATION Normal pediatric myelination
Craneal MR. SE T1 IR of a 3-month-old boy
Craneal MR. TSE T2 of a 3- month-old boy

4. NORMAL HYPERINTENSITIES
Hyperintense posterior limb of the internal capsule on FLAIR images. Increased signal in the posterior limbs of the internal capsule, related to lack of myelination in this region is a normal variant (A).
Hyperintense signal around the occipital horns on FLAIR image can be found in asymptomatic subjects (B). A B
There are some normal structures, such as the corticospinal tracts (arrow) or the choroid plexi, which show high intensity on diffusion weighted images (C). C

5. NORMAL HYPERINTENSITIES
Falcine lipoma: small lipomas are quite frequent in the falx cerebri and less usual, but also possible, in the straight sinus and the corpus callosum.

6. NORMAL HYPERINTENSITIES
Age-related white matter hyperintensities: Cerebral white matter hyperintensities on FLAIR and on T2-weighted images of the brain are a frequent finding in elderly people and the prevalence of these lesions rises steadily as age increases. There is still some debate about the clinical significance of these silent lesions. Larger lesions tend to be ischemic in origin, however, small lesions may be due to perivascular dilatation, demyelination, previous traumatic event or sequelae of neurologic infections.

7. SELLA AND PITUITARY GLAND
Elongated sella: Increased craniocaudal dimension of the sella turcica could be seen as a normal variant.
Empty sella. Sagittal T1-weighted images through the midline demonstrate complete absence of pituitary tissue within the sella turcica.
Partially empty sella: Sagittal T1-weighted images show a tiny, peripherally positioned pituitary gland within the sella turcica.

8. SELLA AND PITUITARY GLAND
Asymmetric pituitary gland can be seen in the absence of pathology. Sometimes the infundibulum is shifted. The dynamic pituitary imaging showed no evidence of adenoma.
Ectopic posterior pituitary gland: Posterior positioning of the posterior lobe (neurohypophysis) of the pituitary gland within the floor of the third ventricule should be reported since it could be associated with multiple endocrine deficiencies. Fat-suppressed images will allow differentiating of this entity from dermoid tumor or lipoma.

9. ENLARGED PERIVASCULAR SPACES
Enlarged perivascular spaces or Virchow-Robin spaces:
The perivascular space (PVS), also known as Virchow-Robin space, is an invagination of the subarchnoid space that surrounds the vessel wall as it courses from the subarachnoid space through the brain parenchyma. On imaging studies most of them appear as smoothly demarcated fluid-filled cysts, typically less than 5 mm in diameter, and often occur in clusters within the basal ganglia or the midbrain. On CT they are often mistaken for lacunar infarcts.

10. ENLARGED PERIVASCULAR SPACES
Enlarged perivascular spaces or Virchow-Robin spaces:
MR imaging features include round or oval shape, a well-defined, smooth margin, location along the path of penetrating arteries, isointensity relative to CSF (A, B, C) and lack of enhancement following contrast agent injection (D). C A B D

11. ENLARGED PERIVASCULAR SPACES
Enlarged perivascular spaces or Virchow-Robin spaces:
Giant PVS (2–3 cm in diameter) have been reported as a normal variant. Giant PVS differ from the typical ones in that they are larger in size and may show a mass effect. In addition, giant PVS may associate T2 signal changes in the surrounding white matter. T2
FLAIR
T1 Gd

12. VENTRICLE VARIANTS
Asymmetric lateral ventricle size: Asymmetry of the lateral ventricles is a common finding, usually more evident in the occipital horns. It can be considered a normal variant if not other abnormality is present.
Shifted septum:. Axial FLAIR image demonstrate incidental shift of the septum to the left of midline.

13. VENTRICLE VARIANTS Cavum septum pellucidum:
It consists in a elongated finger-shaped CSF collection between frontal horns of lateral ventricles. It is due to a fetal septum pellucidum obliteration failure. Its appear in all the premature newborn, 85 % of term infants and 1-15% of adults. (figure A).
Coronal T2-weighted image demonstrates, developmental cerebrospinal fluid filled space between the frontal horns as a normal variant (figure B). A B
Cavum septum vergae
It is similar to Cavum septum pellucidum, but the midline collection has a posterior continuation between fornices. It could be found on 100% of 6 month fetal, 30% term infants and less than 1% of adults (figure C)
Cavum vellum interpositum.
Cavum vellusm interpositum is a triangular CSF space between lateral ventricles, below fornix, above third ventricle and behind foramen of Monro. It is due to a cystic dilatation of the cistern of the velum interepositum. A rare association with hydrocephalus have been descrived. It is usually asymptomatic. C

14. VENTRICLE VARIANTS
Choroid plexus cysts are the most common of all intracranial cysts. Most are bilateral and located in the lateral ventricular atria. Except in very rare cases, are asymptomatic. Peripheral calcification is common. Most choroid plexus cysts are xanthogranulomas
Ring-shaped lateral ventricular nodules less than 1 cm in diameter are occasionally seen during routine brain MR, specially in the roof of body or frontal horn of the lateral ventricles. These nodules may be of nonaggressive nature.

15. NORMAL INTRACRANIAL CALCIFICATION
The presence of physiological intracranial calcifications is usual on cranial studies, increasing its frequency with aging.
Pineal gland calcification (A) usually measures less than 1 cm, it is rare under the age of 8 years and gradually increases with age.
Habenular calcification (B) is identifiable just anterior to the pineal gland. Often mistaken for pineal gland, it is characteristically V-shaped on axial CT. A B
Calcification in the choroid Plexus (C) also increases in frequency and extent with age. It is most common in choroid plexus of lateral ventricle and at the lateral recess of the fourth ventricle. C

16. NORMAL INTRACRANIAL CALCIFICATION
Dural calcification (arrow) may occur any where but it is more frequently seen in the falx and tentorium cerebelli, usually without clinical significance independently of the amount of calcium.
Calcification of the basal ganglia: Usually it is bilateral, symmetrical and confined to the globus pallidus. Its frequency also increases with age. We must keep in mind that this finding has been associated with several nosologic entities, especially if in young patients or if not confined to the globus pallidus..

17. NORMAL AGING BRAIN
Brain volume: Overall brain volume decreases with advancing age, as the CSF volume and spaces increases.
10 days-old
10 years-old
94 years-old

18. NORMAL AGING BRAIN
A thin periventricular high signal rim visible on FLAIR and T2 sequences, without white matter hyperintensities, could be considered a “successfully aging brain". Focal or confluent white matter hyperintensities are quite common after 50-years-old (see normal hyperintensities slide). Ferric iron deposition it could be normal in GP, but it is abnormal in thalamus.
Remember that on gradient echo T2 sequences, presence of "black dots" is not normal irrespective of age, and could be a sing of long-standing hypertension or amyloid angiopathy.

19. NORMAL AGING BRAIN
On diffusion-weighted images, there is a small but significant increased water diffusibility. ADC increases and anisotropy decreased on diffusion tensor imaging.
29-years-old
30-years-old
40-years-old
71-years-old
74-years-old

20. NORMAL AGING BRAIN
On spectroscopy imaging, there are also variations with age. Choline (Cho) and creatine (Cr) increases with aging. N-acetyl aspartate (NAA) Increases during brain development and
decreases in old age. Consequently, NAA/Cho and NAA/Cr decreases with aging, specially in cortex, centrum semiovale, and temporal regions.

21. CISTERNS AND FISSURES Benign enlargement of the subarachnoid spaces.
Benign enlargement of the subarachnoid spaces is believed to be a benign entity of developmentally normal infants. Normal values for the frontal subarachnoid space in infancy were published as 0–4 mm. Benign enlargement of the subarachnoid spaces appears to be related to normal variations in CSF absorptive capacity, and the imaging findings should follow an anticipated time line to resolution by 24 months of age.
Imaging features include enlarged lateral and third ventricles, and a subarachnoid space that is wider than normal in the frontal region, anterior interhemispheric fissure, and Sylvian fissure, bilateral symmetrical fluid on both sides of the falx, lack of mass effect, and no internal membranes. The degree of dilatation of the lateral ventricles is approximately proportional to the width of the frontal subarachnoid space. Symmetry of the extraparenchymal fluid is an important finding.
Genetic disorders, such as mucopolysaccharidoses and glutaric aciduria type I, and cerebral atrophy must be considered in the differential diagnosis.
For the differentiation from subdural hygroma remember that in benign enlargement of the subarachnoid spaces veins are recognized as curvilinear structures adjacent to the inner table of the calvarium, and course directly into the superior sagittal sinus; however, in subdural collections, the veins are displaced away from the inner table by asymmetrical fluid collections

22. CISTERNS AND FISSURES Enlarged cisterna magna or mega cisterna magna.
Cisterna magna is the subarachnoid space localized between the cerebellum and the posterior surface of the medulla oblongata. Variation in size is a normal variant and if large, it is termed megacisterna magna. In megacisterna magna the vermis is intact and the cerebellar hemispheres are normally formed. If particularly enlarged, it can cause prominent scalloping of the occipital squamae. In such cases, it may be difficult to distinguish from posterior fossa arachnoid cyst.

23. CISTERNS AND FISSURES Hippocampal cyst.
Hippocampal cyst (arrow) are sulcal remnants, a normal developmental variant as a result of a failure of normal hippocampal sulcus involution.
Choroidal fissure asymmetry and cyst.
Choroidal fissure could be asymmetric as a normal variant (A). Also consider that asymptomatic cyst in choroidal fissure may distort normal hippocampus (B and C). It follows CSF signal in all sequences. A B C