Neurologic Imaging

atherosCLerotiC disease Slim sign: collapse of ICA above stenosis
atherosCLerotiC disease
atherosCLerotiC disease Color Doppler flow imaging of carotid arteries
• High-grade stenosis with minimal flow (string sign in angiography) is detected more reliably than with conventional Doppler US.

CT
• To determine complete occlusion versus a string sign (near but not complete occlusion), delayed images must be obtained immediately after the initial contrast images.
Bifid post-CS sign (85%) Bifid post-CS sign (85%)
cap sign • T2W: hyperintense. 20%-33% of ependymomas demonstrate the “cap sign,” a rim of extreme hypointensity (hemosiderin) seen at the poles of the tumor on T2W images. Most cases (60%) also show evidence of cord edema around the masses.
Classification of Plain Radiographic
Abnormalities of the Infant Skull
Variations in skull density
Decreased density: generalized or localized
Increased density: generalized or localized

Variations in skull size
Decreased size (microcephaly)
Increased size (macrocephaly)

Abnormal head shape

Calvarial defects

Acquired conditions
Posttraumatic abnormalities
Neoplasia
delta sign Primary (sinus occlusion)
• Clot in sinus is hyperdense on noncontrast CT and hypodense on contrast-enhanced CT.
• Dural enhancement of sinus margin: delta sign
• MRI
Bright sinus on T1W and T2W (depending on stage)
Absence of flow void
• Pearl: If bilateral thalamic infarcts or infarcts do not conform to an arterial territory, suspect venous thrombosis.

venous sinus thrombosis
dense MCA sign Early CT signs of cerebral infarction include:
Loss of gray-white interfaces (insular ribbon sign)
Sulcal effacement
Hyperdense clot in artery on noncontrast CT (dense MCA sign)
empty thecal sac sign • Clumping of nerve roots within the thecal sac
(intrathecal pseudomass); blunting of caudal
nerve root sleeves; nerve roots may also clump
peripherally (empty thecal sac sign)
eye of tiger sign Hallervorden-Spatz disease (eye of tiger sign — gliosis (white) surrounded by iron deposit (black) on T2W images)

t2w hyperintense basaL gangLia Lesions
Hot cross bun sign  • “Hot cross bun” sign in the pons on axial T2/FLAIR

parkinson pLus syndromes (patients who respond poorLy to antiparkinson's mediCation)
Multisystem Atrophy (MSA)
Hummingbird sign Volume loss of the midbrain — Hummingbird sign
Progressive Supranuclear Palsy (PSP)
Insular ribbon sign Early CT signs of cerebral infarction include:
Loss of gray-white interfaces (insular ribbon sign)
Sulcal effacement
Hyperdense clot in artery on noncontrast CT (dense MCA sign)
Intraparietal sulcus intersects the post-CS (99%) Intraparietal sulcus intersects the post-CS (99%)
Ivy sign • MRI: multiple tiny flow voids on T2W images, which are collaterals; engorged collaterals may produce FLAIR bright sulci (Ivy sign)
large lipid peak • Sign suggesting metastasis over primary brain tumor: large lipid peak
Leptomeninges insinuate into cerebral sulci Leptomeninges insinuate into cerebral sulci, which is a sign that helps distinguish a leptomeningeal
process from a dural one.

Carcinomatous meningitis
Leptomeningeal metastases are more common than
dural metastases, although the two may coexist.
• Common primary neoplasms that cause carcinomatous
meningitis include breast, lung, and skin
(melanoma).
• MRI is more sensitive than CT for detection.
• Leptomeninges insinuate into cerebral sulci,
which is a sign that helps distinguish a leptomeningeal
process from a dural one.
• Subarachnoid tumor may be detected early by
careful examination of cisternal segment of CN V
and intracanalicular segment of CNs VII and VIII
Macrocephaly Hydrocephalus
Subdural fluid collection
Neurofibromatosis
Achondroplasia
Tuberous sclerosis
Metabolic storage disease
Alexander disease, Canavan disease
Sotos syndrome
Mickey Mouse ears” Ballooning of temporal horns (“Mickey Mouse ears”) is a sensitive sign.

nOnCOmmuniCating hyDrOCephaluS
Microcephaly Causes of Microcephaly
Severe hypoxic-ischemic injury
Trisomy 21
Trisomy 13
Fetal alcohol syndrome
TORCH* syndrome
Rubinstein-Taybi syndrome
Seckel dwarfism
Midline sulcus sign (70%) Midline sulcus sign (70%)
• Most prominent convexity sulcus that reaches
the midline is the CS.
MRA string sign Arterial dissection
• CTA is preferred first study of choice—see intimal flap and caliber change
• MRI/MRA can also be performed.
T1W bright hematoma in vessel wall (sequence:
T1W with fat saturation): must be interpreted in conjunction with MRA
MRA string sign

Neptune's trident sign Trigeminal artery: cavernous ICA to basilar artery (most common), Neptune's trident sign on angiography
Neuroparenchymal Involvement in osteogenesis imperfecta Intracranial
hemorrhages are attributed to the development
of moyamoya disease with subsequent subarachnoid
hemorrhage as well as to vertebral artery
damage, vascular fragility, spontaneous intracranial
hypotension, and friction between multiple
bone fragments in the skull
Pars bracket sign (96%) Pars bracket sign (96%)
• Paired pars marginalis at or behind the CS
Sigmoidal hook sign Sigmoidal hook sign (89%-98%)
• Hooklike configuration of the central sulcus
corresponding to the motor hand area
Signet sign Signet sign: eccentric vessel lumen with surrounding
thrombus
Giant aneurysm
Sulcus/pre-CS sign Superior frontal sulcus/pre-CS sign (85% specific)
• The posterior end of the superior frontal sulcus joins the pre-CS
Thin post-central gyrus sign (98%) Thin post-central gyrus sign (98%)
toothpaste sign  MRI Extruded disk material gives rise to the toothpaste sign (disk material is extruded from disk into the spinal canal like toothpaste); the material may be continuous with the disk (simple herniation) or be separated (free fragment herniation).

Posterior disk herniation 
tramtrack sign” • Linear bands of enhancement (nerve within tumor): “tramtrack sign”

optiC nerve MeningioMa
vacuum sign Plain films
• The diagnosis of herniation is not possible by plain film.
• All findings of degenerative joint disease (e.g., narrowing of disk space, spurring, eburnation, vacuum sign) may appear in patients
with or without herniation.

Posterior disk herniation
White cerebellum sign • White cerebellum sign: sparing of brainstem in comparison with hemispheres
diFFuse CerebraL edema

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