Classic Neuroimaging Signs

Every subspecialty has its visual shorthand, but neuroradiology may be the most fun of all. Generations of trainees have learned to spot a hummingbird hiding in the midbrain, a giant panda glaring out of the tegmentum, and a tiger's eye buried in the globus pallidus. These "buzzword" signs are more than mnemonic party tricks — they encode real pathology into a single recognizable picture, and on board exams (and at the scanner at 2 a.m.) they earn their keep. Below is a curated, accuracy-first tour of the classics, grouped by category, each paired with its disease and the modality where it lives.

Stroke and vascular signs

• Hyperdense MCA sign — increased attenuation of the middle cerebral artery on non-contrast CT, reflecting acute intraluminal thrombus. Among the earliest visible markers of MCA occlusion.
• Insular ribbon sign — loss of the normal gray–white distinction and hypoattenuation of the insular cortex on CT, an early indicator of MCA-territory ischemia.
• Empty delta sign — on contrast-enhanced CT/CTV, enhancing dura surrounds a non-enhancing central filling defect in the superior sagittal sinus, indicating dural venous sinus thrombosis.
• Cord sign — a hyperdense, thrombosed cortical vein or dural sinus on non-contrast CT, another fingerprint of cerebral venous thrombosis.
• String of beads ("string and pearls") — alternating segments of stenosis and dilation on angiography, classically fibromuscular dysplasia and seen in some vasculitides.
• Ivy sign — leptomeningeal hyperintensity following the sulci on FLAIR / post-contrast MRI, representing slow-flow collaterals in moyamoya.

Neurodegenerative and movement-disorder signs

• Hummingbird (penguin) sign — midbrain tegmental atrophy with a preserved pons gives the brainstem a bird-in-profile silhouette on sagittal MRI, characteristic of progressive supranuclear palsy.
• Hot cross bun sign — a cruciform T2 hyperintensity in the pons from selective degeneration of transverse pontocerebellar fibers on axial T2 MRI, seen in multiple system atrophy (cerebellar type).
• Face of the giant panda sign — high T2 signal in the midbrain tegmentum with sparing of the red nuclei and substantia nigra creates a panda's face on axial T2 MRI, a hallmark of Wilson disease.
• Eye of the tiger sign — a central T2 hyperintensity surrounded by low-signal iron deposition in the globus pallidus on axial T2 MRI, classically pantothenate kinase–associated neurodegeneration (PKAN), a form of NBIA.

Demyelinating, prion, and related signs

• Dawson's fingers — periventricular demyelinating plaques oriented perpendicular to the lateral ventricles (along deep medullary veins) on sagittal FLAIR MRI, typical of multiple sclerosis.
• Cortical ribboning — gyriform restricted diffusion (cortical DWI hyperintensity) seen in Creutzfeldt–Jakob disease on DWI MRI.
• Pulvinar sign — symmetric high signal in the posterior (pulvinar) thalami on T2/FLAIR/DWI MRI, classically associated with variant CJD.
• Open-ring (incomplete-ring) enhancement — an enhancing rim that is interrupted on the gray-matter side on post-contrast MRI, a feature favoring demyelination (e.g., tumefactive MS) over tumor or abscess.

Other memorable signs

• Molar tooth sign — elongated, thickened, horizontally oriented superior cerebellar peduncles plus a deep interpeduncular fossa give the midbrain a molar-tooth appearance on axial MRI, the imaging signature of Joubert syndrome.
• Owl's eye (snake-eye) sign — bilateral, symmetric T2 hyperintensities in the anterior horn gray matter on axial cord T2 MRI, seen with anterior spinal cord infarction and cervical spondylotic myelopathy.

Quick-reference table

A word of caution

These signs are suggestive pattern-recognition aids, not diagnoses. Most are sensitive but non-specific, and several overlap across very different entities — a "hot cross bun" can rarely appear outside MSA, a "pulvinar sign" has mimics beyond variant CJD, and an "eye of the tiger" can be seen in other NBIA subtypes. Always read the sign back against the clinical story, the rest of the study, and the time course before letting a buzzword drive the diagnosis.