ABR Neuroradiology cheat sheet

Acute infarct: DWI hyperintensity with matching ADC hypointensity appears within minutes; ADC pseudonormalizes at roughly 7-10 days, so a subacute lesion may be bright on both DWI and ADC.

Hemorrhage on MRI follows oxyhemoglobin (T1 iso, T2 hyper) to deoxyhemoglobin (T1 iso, T2 dark) to methemoglobin (T1 bright; intracellular T2 dark, extracellular T2 bright) to hemosiderin (T1/T2 dark).

CT hyperdense MCA sign reflects thrombus in the proximal MCA; a hyperdense dot sign is the same clot seen in cross-section in an M2/M3 branch.

ASPECTS scores 10 regions on two axial CT levels (ganglionic and supraganglionic); each involved region subtracts 1 point, and a score of 6 or less generally predicts poor outcome.

Ring-enhancing lesion with restricted diffusion in the wall favors abscess; elevated rCBV, elevated choline, and reduced NAA favor high-grade glioma.

PRES: vasogenic edema of white matter, typically parieto-occipital and often bilateral, with T2/FLAIR hyperintensity and little or no restricted diffusion.

Cerebral amyloid angiopathy: lobar microbleeds, cortical superficial siderosis, and lobar hemorrhage in older patients; deep gray and brainstem sparing distinguishes it from hypertensive microangiopathy.

Herpes simplex encephalitis: asymmetric T2/FLAIR hyperintensity of medial temporal lobes, insula, and inferior frontal lobes with sparing of basal ganglia, often with restricted diffusion and enhancement.

Hydrocephalus decision rule: transependymal edema, enlarged temporal horns, and bowing of the corpus callosum favor obstructive or communicating hydrocephalus over ex vacuo ventricular enlargement.

Cord signal abnormality with brain-like T2 hyperintensity and swelling spanning multiple segments suggests transverse myelitis, infarction, or neuromyelitis optica; enhancement favors active inflammation.

Spondylodiscitis: disc space narrowing, endplate irregularity, and T2 hyperintensity of disc and adjacent marrow; epidural or paraspinal fluid collections and enhancement increase concern for abscess.

Modic changes: type 1 is T1 dark/T2 bright (edema, often painful), type 2 is T1 bright/T2 bright (fat), type 3 is T1 dark/T2 dark (sclerosis).

Cord compression from degenerative disease is best judged on axial T2 images, where the cord is assessed for flattening, deformation, and loss of surrounding CSF.

Cauda equina syndrome: urgent MRI when there is saddle anesthesia, bowel or bladder dysfunction, or bilateral leg weakness; look for a large disc extrusion or epidural collection.

Myelomeningocele versus meningocele: both show a posterior bony defect, but only myelomeningocele contains neural placode tissue within the sac.

Osteoporotic compression fracture: preserved posterior cortex, low-signal fracture line, and band-like marrow edema; pedicle involvement or epidural soft tissue favors pathologic fracture.

Syrinx: central CSF-intensity cavity on T1 and T2 within the cord, often with an associated Chiari malformation or tethered cord; it does not enhance.

Neck spaces: the parapharyngeal space is fat-filled and displaces to show origin; prestyloid masses are typically salivary or fat, whereas poststyloid masses are usually neurogenic or vascular.

Juvenile nasopharyngeal angiofibroma: adolescent male with epistaxis, centered at the sphenopalatine foramen, avid enhancement, and flow voids; it extends into the pterygopalatine fossa and widens it.

Squamous cell carcinoma nodal staging: nodes larger than 3 cm in greatest dimension are N2, and any node larger than 6 cm is N3; extranodal extension upstages further.

Thyroid nodule ultrasound: irregular margins, microcalcifications, taller-than-wide shape, and marked hypoechogenicity raise suspicion, with fine-needle aspiration guided by size and risk features.

Orbital cellulitis versus preseptal cellulitis: postseptal involvement, proptosis, and restricted extraocular movement indicate orbital cellulitis, which risks cavernous sinus thrombosis and abscess.

Cholesteatoma: middle ear soft tissue with bony erosion, often scutum or ossicular, and restricted diffusion on non-EPI DWI; it does not enhance centrally.

Parotid mass: pleomorphic adenoma is well circumscribed and T2 bright; Warthin tumor is often bilateral, cystic, and located in the parotid tail; malignancy shows ill-defined margins and perineural spread.

Perineural spread follows cranial nerves V and VII; look for nerve thickening, enhancement, and widening of the foramen ovale or stylomastoid foramen.