ABR Neuroradiology key terms

A calibrated CT attenuation value in which water is 0 and air is about -1000; dense bone and acute blood are strongly positive, while fat and fluid are negative. It lets readers compare tissue density across scanners.

A calculated map derived from diffusion-weighted imaging that quantifies how freely water molecules move; low ADC values indicate restricted diffusion such as acute infarction or high cellularity, while high values suggest free diffusion.

Reduced water mobility shown as bright signal on high b-value diffusion-weighted images with corresponding low values on the ADC map, typical of acute ischemia, abscess pus, and densely cellular tumors.

High signal on diffusion-weighted images caused by very long T2 relaxation rather than truly restricted diffusion; the ADC map is not low, which distinguishes it from genuine restriction.

Focal high attenuation along the proximal middle cerebral artery on noncontrast CT, reflecting acute thrombus; it is an early sign of large-vessel occlusion and predicts a poor outcome without reperfusion.

A 10-point grading system applied to noncontrast head CT in which points are subtracted for each of ten middle cerebral artery territory regions showing early ischemic change; lower scores indicate larger infarcts.

Hypoperfused but still viable brain tissue surrounding an infarct core; it is the target of reperfusion therapy and is often inferred when perfusion maps show delayed transit with preserved cerebral blood volume.

The volume of blood within a given mass of brain tissue per unit time; it is relatively preserved in ischemic penumbra but falls sharply in infarcted core, helping separate salvageable from dead tissue.

The average time blood takes to pass through a tissue region, calculated from perfusion imaging; it lengthens when perfusion pressure drops and is a sensitive marker of hemodynamically significant stenosis or occlusion.

Local signal loss and geometric distortion near materials that alter the magnetic field, such as blood products, calcium, air, or metal; it is prominent on gradient-echo and echo-planar sequences and can obscure adjacent anatomy.

A high-resolution gradient-echo MRI technique that emphasizes phase differences from paramagnetic substances, making venous blood, microbleeds, and calcification appear dark and conspicuous.

Apparent enlargement of a susceptibility source beyond its true size, seen on gradient-echo sequences; hemorrhage therefore looks larger on these images than on spin-echo or CT.

A small, round focus of chronic hemosiderin deposition in brain parenchyma, dark on susceptibility-sensitive MRI; lobar distribution suggests amyloid angiopathy, while deep locations suggest hypertensive small-vessel disease.

Deposition of amyloid-beta protein in cortical and leptomeningeal vessel walls, causing lobar microbleeds, cortical superficial siderosis, and lobar hemorrhage in older adults; it is a major cause of recurrent lobar bleeding.

A thin rim of hemosiderin coating the pial surface of the brain or spinal cord, appearing dark on susceptibility-sensitive sequences; it results from chronic subarachnoid bleeding and may cause ataxia and hearing loss.

A mass with peripheral contrast enhancement and a nonenhancing center, seen with abscess, tumor, and demyelination; wall thickness, diffusion signal, and clinical context help distinguish among these causes.

A technique that measures metabolite concentrations in a selected brain volume, producing peaks such as choline, creatine, N-acetylaspartate, and lactate; peak ratios help characterize tumors, infection, and metabolic disease.

An increase in the choline resonance on MR spectroscopy relative to creatine, reflecting accelerated cell membrane turnover; it is typical of neoplasms and can also occur in demyelination and inflammation.

A triangular filling defect within the dural venous sinus on contrast-enhanced imaging, outlined by enhancing dura, indicating dural venous sinus thrombosis; it is best seen on coronal or sagittal postcontrast images.

Brain injury caused by impaired venous drainage, often from dural sinus thrombosis; it frequently involves the parasagittal cortex or thalami, may be hemorrhagic, and does not respect arterial territory boundaries.

A small enhancing focus within a dilated perivascular space or cyst, representing a vessel traversing the space; it helps identify a perivascular space and distinguish it from other cystic lesions.

A fluid-filled channel surrounding penetrating cerebral vessels, visible on MRI as a small cyst-like structure that follows CSF signal and does not enhance; enlarged spaces are common and usually benign.

Contrast enhancement along the pia and arachnoid, following the surface of the brain and sulci; it suggests meningitis, carcinomatosis, or leptomeningeal spread of tumor and requires CSF correlation.

Thick enhancement of the dura mater that spares the sulci and follows the inner skull table or falx; causes include intracranial hypotension, postoperative change, and granulomatous disease.

A low cerebrospinal fluid pressure state, often from a dural leak, producing orthostatic headache, sagging brain, subdural collections, and diffuse smooth pachymeningeal enhancement on contrast MRI.

Deposition of calcium salts in tissue, appearing bright on CT and variably dark on MRI; its pattern helps identify tumors, metabolic disease, and prior infection or hemorrhage.

Signal alteration of vertebral endplates and adjacent marrow on MRI, classified into types reflecting edema, fatty replacement, and sclerosis; it is associated with degenerative disc disease and back pain.

Displacement of nucleus pulposus material beyond the normal limits of the intervertebral disc, which may compress nerve roots or the spinal cord; location and morphology guide surgical planning.

Narrowing of the neural foramen by disc material, osteophytes, or ligamentous hypertrophy, impinging on the exiting nerve root; it produces radicular symptoms that correlate with the affected level.

Forward or backward displacement of one vertebral body relative to the one below, often from degenerative change or a pars defect; grade and motion on flexion-extension views influence management.

A defect or fracture of the pars interarticularis, best detected on oblique radiographs or CT as a break in the bony ring; it can lead to slippage of the vertebra.

Abnormal high T2 signal within the spinal cord, indicating edema, demyelination, ischemia, or tumor; its length, location, and enhancement pattern narrow the differential diagnosis.

Clinical dysfunction of the spinal cord from compression, inflammation, vascular insult, or metabolic disease, often accompanied by T2 hyperintensity and cord swelling or atrophy on MRI.

A tumor arising from ependymal cells that may occur in the spinal canal, often centered in the central canal with a cystic component and hemorrhage; it is a common intramedullary tumor in adults.

Compression of the lumbosacral nerve roots causing saddle anesthesia, bladder or bowel dysfunction, and lower limb weakness; it is a surgical emergency requiring urgent imaging.

Inflammation of the optic nerve producing pain with eye movement and visual loss; MRI shows nerve enhancement and T2 hyperintensity, and it may be the first sign of demyelinating disease.

Tumor tracking along the sheaths of cranial nerves away from the primary site, seen as nerve thickening and enhancement; it changes staging and surgical planning in head and neck cancer.

An enlarged node with a nonenhancing low-attenuation center and a thick enhancing rim, suggesting metastatic squamous cell carcinoma, tuberculosis, or another aggressive process rather than simple reactive change.

Spread of tumor through a lymph node capsule into surrounding fat, shown as irregular nodal margins and stranding; it upstages head and neck cancer and worsens prognosis.

An expanding collection of keratinizing squamous epithelium in the middle ear or mastoid that erodes bone; it shows restricted diffusion on MRI and requires surgical removal.

A bony defect over the superior semicircular canal, best shown on high-resolution CT, that allows pressure transmission and causes sound- or pressure-induced vertigo and conductive hearing loss.