Medical Term Glossary
Plain-language explanations of the medical terms that appear on CT, MRI and X-ray reports — what each one means, when it matters, and what to ask your doctor.
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Basal ganglia
A cluster of structures sitting deep inside the brain, on both sides, that help coordinate smooth, planned movements and certain types of learning and habit. They are routinely checked on every brain scan because they are a common site for small strokes, mineral deposits, and changes seen in some long-standing conditions.
Also: caudate putamen globus pallidus, deep brain nuclei, deep gray matter
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Brainstem
The stalk-like lower part of the brain that connects the larger brain above to the spinal cord below. It runs the basic, automatic functions the body cannot live without — breathing, heart rate, blood pressure, swallowing, and the level of wakefulness. Every brain scan checks this region carefully because of how vital it is.
Also: brain stalk, brain stem, lower brain stalk
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Calvarium
The dome-shaped top part of the skull — the smooth bony cap that covers and protects the brain. It does not include the bones of the face or the base of the skull. Radiologists use the word to point specifically at the upper skull bone when describing its thickness, shape, or any findings within it.
Also: calvaria, cranial vault, dome of the skull
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Cerebellopontine angle
A small, fluid-filled space deep in the skull where the cerebellum, brainstem, and hearing/balance nerves all come together on each side. It is checked closely on brain and ear MRI because it is the classic location for an acoustic neuroma.
Also: CP angle, CPA angle, acoustic neuroma region
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Cerebellum
The smaller, rounded part of the brain tucked under the back of the larger hemispheres, just above where the neck meets the skull. It coordinates balance, posture, and the smooth timing of movements. Radiologists mention it routinely on brain imaging because it is one of the standard structures they check on every scan.
Also: balance center of the brain, cerebellar, hindbrain coordinator
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Cerebral aneurysm
A weak, bulging spot in the wall of an artery inside the brain, shaped like a small balloon or berry. Most are small, found by chance on a scan done for another reason, and never cause a problem. The report will describe its size and location, which drive the decision to watch it or treat it.
Also: berry aneurysm, brain aneurysm, cerebrovascular aneurysm
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Cerebral atrophy
A general shrinking of brain tissue, with widened grooves on the surface and slightly larger fluid spaces in the centre. A small amount is a normal part of getting older. Larger amounts, or shrinkage that does not match a person's age, can be linked to specific neurological conditions and are usually viewed alongside symptoms.
Also: age-related atrophy, brain atrophy, brain shrinkage
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Cerebral edema
Extra water inside or around the brain tissue, making part of the brain look swollen on a scan. It is a reaction to many things — a bruise, a stroke, an infection, a tumour, or surgery — rather than a diagnosis by itself. How much swelling there is, and what is causing it, decides how worrying it is.
Also: brain edema, brain swelling, cerebral oedema
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Cerebral microbleed
A tiny spot of old bleeding in the brain, only a few millimeters across, visible on specialized MRI sequences but far too small to have caused any symptoms on its own. Microbleeds become more common with age and are linked to small blood vessel changes, high blood pressure, or past head trauma.
Also: brain microbleed, cerebral microbleeds, microbleed
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Chiari malformation
A structural finding where the lowest part of the cerebellum extends slightly below the base of the skull into the top of the spinal canal. Many people have a mild version with no symptoms at all, discovered only by chance on a scan done for another reason.
Also: Arnold-Chiari malformation, cerebellar tonsillar ectopia, chiari 1 malformation
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Circle of Willis
A ring-shaped network of arteries at the base of the brain that connects the major vessels supplying blood to both hemispheres. Radiologists check it on MRA or CTA scans mainly to look for aneurysms or narrowing, and a normal, symmetric circle is a reassuring finding.
Also: arterial circle of the brain, cerebral arterial circle, circle of Willis anatomy
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Corpus callosum
A thick band of nerve fibers running front to back through the middle of the brain, connecting the left and right hemispheres so they can share information. Radiologists check its shape and signal routinely, and it is a key structure looked at in multiple sclerosis.
Also: brain bridge, callosal body, callosum
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Demyelination
Loss or damage of myelin, the fatty insulating layer that wraps around nerve fibers and helps signals travel quickly. Seen as bright spots on brain MRI, it has many possible causes, ranging from small-vessel changes related to aging to conditions like multiple sclerosis.
Also: demyelinating lesions, foci of demyelination, myelin loss
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Developmental venous anomaly (DVA)
A cluster of small veins that drain normally into one larger vein in a spoke-like pattern, resembling the branches of a tree or an umbrella on contrast imaging. This is the most common blood vessel variation found in the brain and is considered a normal variant that essentially never causes problems.
Also: DVA, benign venous anomaly, caput medusae pattern
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Diffuse axonal injury
Widespread, microscopic stretching or tearing of the brain's nerve fibers caused by strong rotational forces, typically from a car accident or a serious fall. It is a significant traumatic brain injury best seen on MRI, and its severity varies widely from mild to profound.
Also: DAI, axonal shearing injury, diffuse traumatic axonal injury
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Diffusion restriction
An imaging pattern on certain MRI sequences that shows where water molecules are moving less freely than normal inside tissue, most often because cells have been injured. It is the earliest and most sensitive MRI sign of a new stroke, sometimes visible within minutes of onset.
Also: DWI positive lesion, DWI restriction, acute diffusion abnormality
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Diffusion-weighted imaging (DWI)
A special MRI sequence that measures how freely water molecules move inside tissue. When water movement is blocked — for example, in the first minutes of a stroke or inside very dense tissue — the area lights up brightly on the scan. It is one of the most sensitive tools in emergency brain imaging.
Also: ADC map, DWI, DWI sequence
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Fazekas scale
A simple grade radiologists give to the small bright spots that show up in the brain's white matter on MRI, usually from tiny blood-vessel wear. It runs from 0 (none) to 3 (large, merging areas). Higher grades are common with age and high blood pressure and are often mild.
Also: fazekas grade, fazekas grade 1, fazekas grade 2
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FLAIR hyperintensity
A bright spot or patch on a specific type of MRI image that is good at picking up subtle tissue changes. The brightness itself simply means the tissue holds a little more water than its neighbours. Such spots are extremely common, often age-related, and only meaningful when read together with their pattern, size, and the person's symptoms.
Also: FLAIR bright lesions, FLAIR hyperintensities, T2 FLAIR hyperintensity
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Flow void
A dark, signal-free area on MRI created by blood moving quickly through a vessel, rather than by any tissue problem. It is a completely normal and expected finding within arteries and veins, and its presence is often reassuring evidence that a vessel is open.
Also: flow gap, flow-related signal loss, flowvoid
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Hemosiderin deposition
A dark residue left behind in tissue after old bleeding has broken down, made of iron-storing protein released from blood cells. On brain MRI it marks the site of a prior bleed, however minor, and can linger visibly for years or permanently after the bleeding itself has fully resolved.
Also: blooming artifact from hemosiderin, chronic hemorrhage residue, hemosiderin deposits
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Hippocampal atrophy
Shrinkage of a small seahorse-shaped structure deep in the brain's temporal lobe that plays a central role in forming new memories. It is a common finding on brain MRI in older adults and is strongly associated with Alzheimer's disease, though it can also occur with normal aging or other conditions.
Also: hippocampal sclerosis, hippocampal shrinkage, hippocampal volume loss
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Hydrocephalus
A build-up of cerebrospinal fluid inside the brain's fluid chambers, making them larger than normal. It can develop slowly or come on quickly, and the cause matters far more than the word itself. Treatment ranges from watchful waiting to a small surgical drain, depending on how much pressure the extra fluid creates.
Also: CSF build-up, NPH, communicating hydrocephalus
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Infarct
An area of brain tissue that has been injured or has died because its blood supply was cut off, usually by a blocked artery. On imaging it shows up as a patch of tissue that no longer looks like its healthy neighbours. The size and location decide how the symptoms appear and how the team responds.
Also: brain attack, cerebral infarct, infarction
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Internal auditory canal
A narrow bony tunnel inside the skull that carries the hearing and balance nerve and the facial nerve from the brainstem to the inner ear. It is routinely checked on ear and brain MRI, often abbreviated IAC or IAM in reports.
Also: IAC, IAM, auditory canal internal
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Intracranial
An adjective meaning inside the skull. It describes the location of something — a structure, a finding, or a process — rather than what that thing is or whether it is a problem. The word appears constantly in brain reports because radiologists use it to point at where something sits.
Also: inside the brain cavity, inside the skull, intracranial compartment
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Intracranial hemorrhage
Blood that has leaked inside the skull, either into the brain tissue itself or into one of the spaces wrapped around it. It is an important and time-sensitive finding because fresh blood takes up room the brain does not have to spare. Exact location, size, and cause shape how urgently it has to be treated.
Also: ICH, bleeding in the brain, brain bleed
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Labyrinthitis
Inflammation of the inner ear's balance and hearing organ, usually from a viral infection, causing sudden vertigo, nausea, and often hearing loss on one side. It is usually a clinical diagnosis, but MRI can show enhancement in the affected inner ear.
Also: acute labyrinthitis, inner ear infection, inner ear labyrinthitis
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Lacunar infarct
A small area of dead brain tissue caused by the blockage of one of the tiny, deep arteries that supply the brain's interior. These small strokes are a common incidental finding on brain MRI, especially with increasing age, and many cause no noticeable symptoms.
Also: lacunar infarction, lacunar ischemic stroke, lacunar stroke
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Larynx
The voice box — the structure in the front of the neck that holds the vocal cords and sits at the top of the windpipe. It lets you speak, guards the airway when you swallow, and routes air to the lungs. Radiologists name it to locate findings in this part of the throat.
Also: Adam's apple, laryngeal region, throat voice box
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Leptomeningeal enhancement
A pattern seen on contrast MRI where the thin membranes covering the brain and spinal cord light up abnormally after dye injection, rather than staying invisible as they normally do. It can signal infection such as meningitis or spread of cancer cells along these surfaces, and always needs prompt medical evaluation.
Also: carcinomatous meningitis, leptomeningeal carcinomatosis, leptomeningeal disease
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Mass effect
A phrase radiologists use when something inside the skull is taking up extra room and pushing on the brain tissue or fluid spaces nearby. It is a description of crowding, not a diagnosis on its own. The cause — swelling, bleeding, a tumour, or a fluid pocket — and how much pressure it creates is what matters most.
Also: compression effect, local mass effect, mass-like effect
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Mastoid air cells
Tiny honeycomb-like air pockets inside the bone just behind each ear, connected to the middle ear. They normally contain air and help regulate pressure in the ear. Because they sit right next to the brain, every head CT or MRI looks at them and notes whether they are clear or contain fluid.
Also: ear bone air spaces, mastoid, mastoid bone
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Midline shift
A sign on brain imaging that something on one side is pushing the brain's central structures over toward the other side. It almost always points to swelling, bleeding, or a mass that needs attention soon. The amount of shift, measured in millimetres, is one of the strongest cues to how urgent the situation is.
Also: brain shift, deviation of the midline, mass effect with midline shift
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MR angiography (MRA)
A specialized MRI technique that highlights blood vessels rather than surrounding tissue, often without any injected dye. Radiologists use it to check for narrowing, blockages, aneurysms, or malformations in arteries and veins, most commonly in the brain and neck, using the same scanner as a standard MRI.
Also: MR angio, MRA, MRA brain scan
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Multiple sclerosis
A condition in which the immune system mistakenly attacks the protective coating around nerve fibers in the brain and spinal cord, leaving scattered patches of damage. It is a leading cause of demyelinating plaques found on brain MRI in younger adults, and it is manageable, not untreatable.
Also: MS, MS lesions, demyelinating disease
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Nasopharynx
The space at the very back of the nose, above the roof of the mouth, where the nasal passages meet the top of the throat. Air passes through it on its way from the nose to the lungs. Radiologists name it to pinpoint findings in this upper throat region behind the nose.
Also: back of nose, behind the nose, post-nasal space
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Neurovascular compression
A blood vessel pressing against or touching the root of a cranial nerve as it exits the brainstem, sometimes irritating the nerve's function over time. It is a well-known cause of conditions like trigeminal neuralgia or one-sided ringing in the ear.
Also: microvascular compression, nerve root compression by vessel, neurovascular conflict
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Normal pressure hydrocephalus (NPH)
Enlarged fluid-filled ventricles inside the brain that develop despite pressure readings staying in the normal range, most common after age 60. The condition classically causes a triad of gait trouble, memory decline, and bladder urgency, and is one of the few treatable causes of dementia-like symptoms.
Also: Hakim's triad, Hakim-Adams syndrome, NPH
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Orbits
The bony eye sockets in the front of the skull, holding the eyeballs along with the muscles, nerves, fat, and blood vessels that surround them. They sit right next to the sinuses and the front of the brain, so head and brain scans routinely include them and comment on what is inside.
Also: bony orbit, eye socket, eye sockets
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Oropharynx
The middle part of the throat that sits directly behind the mouth — the area you can partly see when you open wide and say 'aah'. It includes the back of the tongue, the tonsils, and the soft palate. Radiologists name it to locate findings in this central throat region.
Also: back of mouth, back of throat, middle throat
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Paranasal sinuses
Air-filled spaces in the bones of the face around the nose, lightening the skull and warming and moistening the air you breathe. They sit in the forehead, behind the cheeks, between the eyes, and deep inside the head, and they all drain into the nose. Brain and head scans routinely include and comment on them.
Also: ethmoid sinus, facial sinuses, frontal sinus
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Perivascular (Virchow-Robin) spaces
Tiny fluid-filled channels that surround small blood vessels as they dip into brain tissue, forming part of the brain's normal drainage system. They are visible on MRI in almost everyone and become more numerous with age, so their presence alone is not a sign of disease.
Also: VR spaces, Virchow-Robin spaces, cribriform state
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Periventricular
A descriptive term meaning "around the fluid-filled spaces in the middle of the brain." It points to the region of brain tissue that lies just next to the ventricles, where a finding has been seen. The word itself only marks the location — what matters is what is found there.
Also: around the brain's fluid spaces, around the ventricles, next to the ventricles
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Pineal cyst
A small fluid-filled sac in the pineal gland, a pea-sized structure deep in the middle of the brain that helps regulate sleep. These are extremely common incidental findings on MRI and almost always harmless, causing no symptoms in the vast majority of people who have one.
Also: benign pineal cyst, cyst of the pineal gland, pineal gland cyst
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Pituitary adenoma
A benign, non-cancerous growth on the pituitary gland, the small hormone-producing organ located just beneath the brain, near the crossing point of the eye nerves. Most are tiny and found by chance, but size and whether they produce extra hormones both shape what happens next.
Also: adenoma of the pituitary gland, benign pituitary tumor, pituitary gland growth
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Pituitary gland
A pea-sized gland at the base of the brain that controls many of the body's hormones. It sits in a small bony pocket behind the eyes and directs other glands — the thyroid, adrenals, and reproductive organs. Radiologists name it when describing its size, shape, or any spot within it.
Also: brain hormone gland, hypophysis, master gland
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Sella turcica
A small saddle-shaped hollow in the bone at the base of the skull that cradles the pituitary gland. Its Latin name means 'Turkish saddle' because of its shape. Radiologists mention it when describing the pituitary gland sitting inside it, or when commenting on the size and shape of the bony pocket itself.
Also: Turkish saddle, hypophyseal fossa, pituitary fossa
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Skull fracture
A break in one of the bones that make up the skull, usually caused by a direct blow or a fall. Most are simple and heal on their own, but the location and pattern matter because some types raise the chance of injury to the brain or its blood vessels underneath.
Also: basilar skull fracture, broken skull, calvarial fracture
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Small vessel disease
Wear and tear in the brain's tiniest blood vessels, which shows up on MRI as bright spots or patches in the deep brain tissue. It is very common with age and conditions like high blood pressure, and often causes no symptoms. Managing blood pressure and other risks is the main response.
Also: cerebral small vessel disease, chronic microvascular changes, chronic small vessel ischemic disease
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Subarachnoid hemorrhage
Bleeding into the thin, fluid-filled space that wraps around the brain, between two of its protective layers. It is a time-sensitive finding because the blood sits in the same space as the cerebrospinal fluid and can quickly affect the whole brain. The cause and the amount of bleeding decide how it is treated.
Also: SAH, aneurysmal bleed, bleed under the arachnoid
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Subdural hematoma
A collection of blood between the brain's surface and its tough outer covering, usually caused by a tear in a small bridging vein after a head injury. It can range from a thin, incidental film to a large collection that presses on the brain and needs urgent treatment.
Also: SDH, blood between brain and skull, brain bleed
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Sulci
The grooves on the outer surface of the brain, between the raised folds. They are a normal part of how the brain is built — the wrinkled surface packs a much larger sheet of tissue into the limited space of the skull. Radiologists describe how deep or wide these grooves look as part of every brain scan.
Also: brain folds, brain grooves, cerebral sulci
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Ventricles (brain)
The four connected, fluid-filled chambers in the centre of the brain. They make and circulate the clear cushioning fluid that bathes the brain and spinal cord. Their size and shape are routinely measured on scans because changes in either can hint at swelling, blockage, or natural shrinkage of the surrounding tissue.
Also: CSF spaces, brain fluid chambers, cerebral ventricles
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Ventriculomegaly
Enlargement of the brain's four fluid-filled cavities, called ventricles, beyond their typical size for a person's age. It can result from a blockage in fluid drainage, an underlying loss of brain tissue, or simply reflect normal variation, so the cause matters far more than the finding itself.
Also: cerebral ventriculomegaly, dilated ventricles, enlarged ventricles
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Vestibular schwannoma (acoustic neuroma)
A slow-growing, non-cancerous tumor arising from the nerve that carries hearing and balance signals from the inner ear to the brain. It typically causes gradual hearing loss on one side, ringing, or unsteadiness, and is usually monitored or treated well before it becomes dangerous.
Also: CPA tumor, acoustic neuroma, cerebellopontine angle tumor
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