Clinical Tools › Fetal Brain Development
Fetal Cortical Sulcation & Brain Development
Explore the appearance timeline of fetal sulci, gyri and key structures across anatomy / prenatal ultrasound / fetal MRI, distinguishing earliest visible from reliably visible. Enter a gestational age to read out whether each structure should be visible, with clinical significance and red flagsper structure (e.g. delayed central/convexity sulci → lissencephaly; absent CSP → callosal agenesis / septo-optic dysplasia). Covers Sylvian fissure + insular opercularization, parieto-occipital, calcarine, cingulate, central, superior temporal, frontal sulci, olfactory sulcus, hippocampal fissure, corpus callosum, cavum septi pellucidi, ventricular atrium and cerebellar vermis. Evidence-based on Toi 2004, Cohen-Sacher 2006, Chi 1977, Garel, Barkovich and the ISUOG guideline.
① Choose modality
② Gestational age (optional — per-structure read-out)
wk
Prenatal ultrasound · Developmental timeline
Hippocampal fissure / hippocampal inversionfissure
Medial temporal (limbic)
Earliest visible：16–18 wk · Reliably visible：Consistent from ≈20 wk · Plane：Coronal (temporal horn)
Sylvian fissure + insular opercularizationfissure + operculization
Lateral convexity / insula
Earliest visible：14–16 wk (shallow indentation) · Reliably visible：Sylvian fissure/insula 100% visible at 22 wk; operculization angle: obtuse ~20 wk, acute ~24 wk · Plane：Transthalamic axial / coronal
Cavum septi pellucidicavity
Midline (between septal leaves)
Earliest visible：16–18 wk · Reliably visible：Should be consistently visible at 18–37 wk (mandatory on the BPD plane); normally closes back-to-front after 37–40 wk · Plane：Transthalamic axial (BPD plane)
Lateral ventricle (atrial width + choroid plexus)ventricle
Supratentorial ventricles
Earliest visible：Measurable from 15–16 wk · Reliably visible：Atrial width normal <10 mm; 10–15 mm mild ventriculomegaly; ≥15 mm severe · Plane：Transventricular axial (inner-to-inner at atrium)
Parieto-occipital fissurefissure
Medial hemisphere (parieto-occipital)
Earliest visible：18.5 wk (Toi); some at 16–17 wk · Reliably visible：95% visible after 20.5 wk (Cohen-Sacher); 100% visible at 23 wk · Plane：Parasagittal / axial
Calcarine sulcussulcus
Medial occipital (visual cortex)
Earliest visible：18.5 wk (Toi) · Reliably visible：95% visible after 21.9 wk; 100% visible at 24–27 wk · Plane：Parasagittal
Corpus callosumcommissure
Midline commissure
Earliest visible：Transvaginal at 16–18 wk · Reliably visible：Fully demonstrated and measurable on the midsagittal plane at 18–20 wk (length increases with gestation) · Plane：Mid-sagittal (preferred) + coronal
Cerebellar vermis foliationcerebellum
Posterior fossa (midline cerebellum)
Earliest visible：Measurable on the transcerebellar axial plane (TCD) · Reliably visible：From 18–20 wk the vermis should completely cover the 4th ventricle; foliation (e.g. primary fissure) identifiable from 24 wk · Plane：Transcerebellar axial + vermian mid-sagittal
Cingulate sulcussulcus
Medial hemisphere (above corpus callosum)
Earliest visible：23.2 wk (Toi); cingulate may be seen as early as 18 wk · Reliably visible：After 24.3 wk (Toi); Slagle: first seen at a mean of 26 wk, branching at 30–34 wk; ~25% not seen until 24–25 wk · Plane：Mid/parasagittal
Central (Rolandic) sulcussulcus
Lateral convexity (fronto-parietal)
Earliest visible：~24–26 wk (a convexity sulcus) · Reliably visible：Convexity sulci consistently visible after 27.9 wk (Toi) · Plane：Convexity parasagittal/coronal
Superior temporal sulcussulcus
Lateral temporal lobe
Earliest visible：~26–28 wk · Reliably visible：After 28–30 wk · Plane：Temporal parasagittal/axial
Pre- and post-central sulci (convexity)sulci
Lateral convexity
Earliest visible：~26–28 wk · Reliably visible：After 28–30 wk · Plane：Convexity
Superior / inferior frontal sulcisulci
Dorsolateral frontal lobe
Earliest visible：~28–30 wk · Reliably visible：After 30–32 wk · Plane：Frontal coronal/parasagittal
Olfactory sulcus / bulbsulcus
Inferior frontal (orbital) surface
Earliest visible：Hard to demonstrate reliably on ultrasound · Reliably visible：Usually needs MRI; ultrasound has limited value · Plane：Frontal-base coronal (limited)
Gestational ages are consensus ranges and vary by method and individual; 'earliest' = first detectable in some fetuses, 'reliable' = visible in the great majority (>95%/100%). For licensed clinicians; does not replace clinical judgment and full neuroimaging assessment. Sources: Toi 2004, Cohen-Sacher 2006, Chi 1977, Garel AJNR 2001, Barkovich, and the ISUOG CNS guideline.