MRI Anatomy Flashcards · Neuro

Brain Anatomy

Learn to identify every labeled structure on a Brain MRI, plane by plane.

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Brain anatomy, structure by structure

Brain MRI is the foundation of neuroimaging, and reading it starts with knowing the normal anatomy cold. This reference walks through every structure in our brain flashcard deck across the three standard planes (sagittal, coronal, and axial), with a plain-language definition, how each structure looks on MRI, and the pathology you will actually run into at the scanner.

Cerebral lobes & cortex

The outer mantle of the brain. On the midline sagittal you orient front to back; on coronals you compare side to side.

Vertex

The highest point of the cerebral cortex, at the top of the brain near the midline where the two parietal lobes meet beneath the crown of the skull.

On MRI: Found at the most superior slice of a midline sagittal or coronal image, immediately beneath the inner table of the calvarium. Cortical gray matter sits at intermediate signal on both T1 and T2.

Common pathology: Parasagittal/vertex meningiomas and superior sagittal sinus thrombosis localize here; the vertex also marks the top of the superior sagittal sinus.

Tip: Scroll to the very top of a midline sagittal; the last sliver of brain under the skull is the vertex.

Frontal Lobe

The largest lobe, sitting in front of the central sulcus. It drives motor control, executive function, personality, and expressive speech (Broca area on the left).

On MRI: Occupies the anterior third of the brain on sagittal and the anterior slices on axial/coronal. Normal cortex is gray-matter signal with a thin bright rim of subcutaneous and marrow fat above it on T1.

Common pathology: Common site for gliomas, contusions from trauma (coup/contrecoup), and frontotemporal dementia volume loss.

Parietal Lobe

The lobe behind the central sulcus that handles sensation, spatial awareness, and integration of touch, proprioception, and vision.

On MRI: Lies between the frontal lobe and the occipital lobe, superior to the temporal lobe. Best appreciated on sagittal and axial images at the level of the lateral ventricles.

Common pathology: Watershed infarcts, metastases, and tumors causing neglect or sensory deficits frequently involve the parietal lobe.

Occipital Lobe

The most posterior lobe and the home of the primary visual cortex along the calcarine sulcus.

On MRI: Forms the back of the brain on sagittal and axial views, just above the cerebellum and tentorium. Look for the calcarine sulcus splitting it on midline sagittal.

Common pathology: Posterior cerebral artery infarcts (causing visual field loss), PRES, and occipital lobe epilepsy.

Temporal Lobe

The lobe below the lateral (Sylvian) fissure responsible for hearing, memory, and receptive language (Wernicke area on the left). It contains the hippocampus.

On MRI: Sits in the middle cranial fossa, best seen on coronal and axial images. Coronal is the workhorse plane for the medial temporal/hippocampal structures.

Common pathology: Mesial temporal sclerosis (epilepsy), herpes encephalitis (classic limbic/temporal involvement), and Alzheimer-related atrophy.

Limbic Lobe

A C-shaped ring of cortex on the medial surface (cingulate and parahippocampal gyri) central to emotion, memory, and behavior.

On MRI: Best traced on midline sagittal arching over the corpus callosum (cingulate gyrus) and curling down into the temporal lobe (parahippocampal gyrus).

Common pathology: Limbic encephalitis, herpes encephalitis, and degenerative memory disorders target this system.

Corpus callosum & commissures

The white-matter cables that connect the two hemispheres, best seen front-to-back on the midline sagittal.

Genu

The anterior, curved "knee" of the corpus callosum, the bundle of white matter connecting the frontal lobes.

On MRI: A bright, gently curved band at the front of the corpus callosum on midline sagittal T1; white matter is bright on T1 and darker than cortex on T2.

Common pathology: Diffuse axonal injury, callosal dysgenesis, and demyelination (MS plaques love the callosum).

Tip: On a midline sagittal the corpus callosum looks like a boomerang: the front bend is the genu, the back bulge is the splenium.

Splenium

The posterior, rounded end of the corpus callosum connecting the occipital and parietal lobes.

On MRI: The thick bulb at the back of the corpus callosum on midline sagittal, just above the pineal region and the tentorial apex.

Common pathology: Cytotoxic lesions of the splenium (CLOCCs), ischemia, and lymphoma; a frequent MS and DAI location.

Anterior Commissure

A small white-matter tract crossing the midline anterior to the fornix columns, linking the temporal lobes.

On MRI: A tiny round dot of white matter on midline sagittal, sitting at the front wall of the third ventricle, one anchor of the AC-PC line.

Common pathology: Mainly a landmark, but its position helps localize on functional and stereotactic planning.

Posterior Commissure

A small fiber bundle crossing the midline at the junction of the midbrain and third ventricle, involved in the pupillary light reflex.

On MRI: A subtle band at the back of the third ventricle on midline sagittal, just above the cerebral aqueduct, the posterior anchor of the AC-PC line.

Common pathology: Dorsal midbrain (Parinaud) syndrome involves this region; otherwise primarily a reference landmark.

AC-PC Line

The reference line connecting the anterior and posterior commissures, the standard plane used to align and prescribe brain imaging.

On MRI: Drawn on the midline sagittal between the two commissures; axial slices are angled parallel to it for reproducible, symmetric brain images.

Common pathology: A prescription landmark rather than a pathology site, but getting it right keeps studies comparable over time.

Tip: Set your axial angle along the AC-PC line so both sides of the brain are matched slice-for-slice; radiologists expect it.

Fornix

A curved white-matter tract carrying signals from the hippocampus to the mammillary bodies, a key memory pathway.

On MRI: A thin arching band beneath the corpus callosum on sagittal, forming the roof of the third ventricle.

Common pathology: Damaged in normal-pressure hydrocephalus, Wernicke-Korsakoff, and after colloid cyst surgery, causing memory loss.

Deep gray matter

Central relay and memory structures surrounding the third ventricle.

Thalamus

The paired egg-shaped relay station of deep gray matter that routes nearly all sensory and motor information to the cortex.

On MRI: Forms the lateral walls of the third ventricle, best seen on axial and coronal at the level of the basal ganglia. Gray-matter signal on all sequences.

Common pathology: Deep (lacunar) infarcts, deep venous thrombosis (bilateral thalamic edema), and thalamic gliomas.

Hippocampus

A seahorse-shaped structure in the medial temporal lobe that is central to forming new memories.

On MRI: Best evaluated on thin coronal images angled perpendicular to its long axis; compare right vs left size and signal.

Common pathology: Mesial temporal sclerosis (atrophy + T2 bright signal) in epilepsy; early volume loss in Alzheimer disease; herpes encephalitis.

Tip: Dedicated seizure/memory protocols add high-resolution coronal T2/FLAIR through the hippocampi; angle them off the temporal lobes.

Ventricles & CSF spaces

The fluid-filled chambers. CSF is dark on T1 and bright on T2, the single most useful signal rule in the brain.

Lateral Ventricles

The two large C-shaped CSF chambers, one in each hemisphere; their choroid plexus produces the cerebrospinal fluid that then circulates through the ventricular system.

On MRI: Paired, symmetric fluid spaces: dark on T1, bright on T2, suppressed (dark) on FLAIR. The frontal horns and atria are the easiest landmarks on axial.

Common pathology: Enlarged in hydrocephalus and atrophy; asymmetry can indicate mass effect; periventricular FLAIR signal in MS and small-vessel disease.

Third Ventricle

A thin, midline CSF cavity between the two thalami that connects the lateral ventricles to the fourth ventricle.

On MRI: A slit-like midline fluid space on axial and coronal; follows CSF signal. The massa intermedia may cross it.

Common pathology: Colloid cysts at the foramen of Monro (obstructive hydrocephalus), and tumors of the pineal/suprasellar region distort it.

Fourth Ventricle

The diamond-shaped CSF space in the posterior fossa between the brainstem (in front) and the cerebellum (behind).

On MRI: A midline CSF space on sagittal sitting against the back of the pons; on axial it is a tent-shaped fluid pocket between brainstem and cerebellum.

Common pathology: Obstructed in posterior fossa masses; ependymomas arise within it; effaced by Chiari malformation and tonsillar herniation.

Choroid Plexus

The vascular, frond-like tissue inside the ventricles that produces cerebrospinal fluid.

On MRI: Lines the atria of the lateral ventricles; enhances avidly with contrast and frequently calcifies (dark) with age.

Common pathology: Choroid plexus cysts, papillomas/carcinomas (especially in children), and a common site of physiologic calcification.

Brainstem & posterior fossa

The midbrain, pons, and medulla column and the cerebellum behind it, the heart of the midline sagittal.

Midbrain

The uppermost brainstem segment, connecting the cerebrum to the pons and carrying the cerebral aqueduct, cranial nerves III–IV, and the substantia nigra.

On MRI: On axial it shows the classic "Mickey Mouse"/heart shape; on midline sagittal it sits between the thalamus above and the pons below.

Common pathology: Top-of-basilar infarcts, Parinaud syndrome, and the "hummingbird" tectal atrophy of progressive supranuclear palsy.

Pons

The bulky middle segment of the brainstem that relays signals between the cerebrum and cerebellum and houses cranial nerves V–VIII.

On MRI: The rounded bulge on the front of the brainstem on midline sagittal; gray/white signal with the basilar artery seen as a dark flow void grooving its anterior surface.

Common pathology: Central pontine myelinolysis, pontine infarcts/hemorrhage, and diffuse intrinsic pontine glioma (DIPG) in children.

Medulla Oblongata

The lowest brainstem segment, controlling breathing, heart rate, and blood pressure, continuous with the spinal cord at the foramen magnum.

On MRI: The narrowing tail of the brainstem on midline sagittal as it passes through the foramen magnum into the spinal cord.

Common pathology: Lateral medullary (Wallenberg) syndrome, tonsillar herniation, and craniocervical junction lesions.

Cerebellum

The "little brain" in the posterior fossa behind the brainstem that coordinates balance, posture, and fine movement.

On MRI: Shows its finely folded folia behind the fourth ventricle on sagittal and axial; the vermis is the midline portion.

Common pathology: Cerebellar infarcts and hemorrhage (can compress the fourth ventricle), tonsillar ectopia/Chiari I, and metastases.

Spinal Cord

The continuation of the medulla below the foramen magnum that carries motor and sensory tracts to and from the body.

On MRI: A smooth band of cord on the lower midline sagittal, surrounded by bright CSF on T2, descending out of the foramen magnum.

Common pathology: Cervical cord compression, demyelination (MS), and syrinx are evaluated where the cord exits the skull base.

Sella & skull base

Midline bone and gland landmarks at the base of the brain.

Pituitary Gland

The "master gland" sitting in the sella turcica below the optic chiasm; it controls growth, metabolism, and reproduction.

On MRI: A small soft-tissue structure in the sella on midline sagittal; the posterior lobe is normally bright on T1 ("posterior bright spot"). Dedicated pituitary protocols use thin dynamic coronals.

Common pathology: Microadenomas and macroadenomas, Rathke cleft cysts, and apoplexy, a common reason for a dedicated sella study.

Clivus

The sloping skull-base bone (part of the sphenoid and occipital bones) behind the sella, in front of the brainstem.

On MRI: A bright fatty-marrow ramp on midline sagittal T1 just behind the sphenoid sinus and in front of the pons.

Common pathology: Chordoma, metastases, and skull-base fractures; marrow signal change can be an early clue.

Foramen Magnum

The large opening at the base of the skull through which the brainstem becomes the spinal cord.

On MRI: The bony ring at the bottom of the midline sagittal where the medulla transitions to cord; assess the cerebellar tonsil position relative to it.

Common pathology: Chiari I malformation (tonsils >5 mm below the foramen), foramen magnum meningiomas, and basilar invagination.

Vascular structures

Flowing arteries are dark "flow voids" on standard spin-echo MRI.

Internal Carotid Arteries

The paired major arteries that supply the anterior circulation of the brain, entering through the skull base into the cavernous sinus.

On MRI: Round dark flow voids on either side of the sella on axial spin-echo images; bright on time-of-flight MRA.

Common pathology: Atherosclerosis, dissection, and aneurysms (especially the cavernous and supraclinoid segments).

Basilar Artery

The single midline artery formed by the two vertebral arteries that supplies the brainstem and posterior circulation.

On MRI: A midline dark flow void hugging the front of the pons on axial; bright on MRA.

Common pathology: Basilar tip aneurysms, basilar occlusion (a stroke emergency), and dolichoectasia.

Paranasal sinuses

Air-filled spaces around the skull base, normally signal-void (black) when aerated.

Sphenoid Sinus

The deepest paranasal sinus, sitting directly below the sella turcica and pituitary gland.

On MRI: An air-filled (dark) space beneath the sella on midline sagittal; mucosal thickening or fluid stands out as bright T2 signal.

Common pathology: Sinusitis, mucoceles, and the surgical corridor for trans-sphenoidal pituitary surgery.

Frontal Sinus

The paired air sinus within the frontal bone above the orbits and nasal bridge.

On MRI: An aerated dark space in the forehead on anterior sagittal slices; opacification appears bright on T2.

Common pathology: Sinusitis, mucoceles, and osteomas; relevant in trauma to the anterior skull base.

Ethmoid Sinuses

A honeycomb of small air cells between the orbits at the roof of the nasal cavity.

On MRI: Multiple small aerated cells (dark) between the eyes; thin bony septa separate them.

Common pathology: Sinusitis, polyps, and a route of spread for orbital/intracranial infection.

Maxillary Sinus

The largest paranasal sinus, in the cheekbone (maxilla) below each orbit.

On MRI: A large aerated dark space in the cheek; air-fluid levels and mucosal thickening are bright on T2.

Common pathology: Sinusitis, retention cysts, and the most common site of paranasal masses.

Coverings

The membranes and folds that wrap and partition the brain.

Falx Cerebri

The vertical sheet of dura that runs in the midline between the two cerebral hemispheres.

On MRI: A thin midline band on coronal and axial; it normally enhances and contains the superior sagittal sinus along its top edge.

Common pathology: Falcine meningiomas, midline (subfalcine) shift from mass effect, and dural-based metastases.

Meninges

The three protective membranes around the brain and cord: dura mater (outer), arachnoid (middle), and pia mater (inner).

On MRI: Normal meninges are thin; the subarachnoid space between arachnoid and pia is bright CSF on T2. Abnormal meninges enhance with contrast.

Common pathology: Meningitis and carcinomatosis (leptomeningeal enhancement), subdural/epidural collections, and dural thickening from low pressure.

Frequently asked questions

What structures are seen on a brain MRI?

A standard brain MRI shows the cerebral lobes (frontal, parietal, temporal, occipital, limbic), the corpus callosum and commissures, deep gray matter such as the thalamus and hippocampus, the ventricles and CSF spaces, the brainstem (midbrain, pons, medulla) and cerebellum, the pituitary and skull base, the major arteries, the paranasal sinuses, and the meninges. This page labels all 35 with their MRI appearance.

Which plane is best for studying brain anatomy?

The midline sagittal is the best single image for orientation: it shows the corpus callosum, brainstem, cerebellum, fourth ventricle, pituitary, and skull base in one view. Axial is best for the ventricles, basal ganglia, and vascular structures, while coronal is preferred for the hippocampi and medial temporal lobes.

How do you tell gray matter, white matter, and CSF apart on MRI?

On T1-weighted images, white matter is brightest, gray matter is intermediate, and CSF is dark. On T2-weighted images the order flips: CSF is brightest, gray matter is intermediate, and white matter is darkest. FLAIR keeps T2 contrast but darkens (suppresses) the CSF so periventricular lesions stand out.

What is the AC-PC line and why does it matter for technologists?

The AC-PC line connects the anterior and posterior commissures on the midline sagittal. Prescribing axial slices parallel to it produces symmetric, reproducible images that match prior studies and meet radiologist expectations; it is the standard alignment for brain MRI.

Do I need an account to use these brain MRI flashcards?

No. The interactive flashcards and this full labeled reference are open to use, with no account required to start. Creating an account lets you save your progress across devices and track which packs you have mastered.

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