KEY FACTS Terminology Pilocytic astrocytoma (PA): Well-circumscribed, slow-growing tumor, often with cyst and mural nodule Imaging Cystic cerebellar mass with enhancing mural nodule Arises from cerebellar hemisphere and compresses 4th ventricle Enlarged optic nerve/chiasm/tract with variable enhancement Cerebellum (60%) > optic nerve/chiasm (25-30%) > adjacent to 3rd ventricle > brainstem Well circumscribed with little to no edema Aggressive appearance (enhancement and MRS) of tumor is misleading…

KEY FACTS Terminology Diffusely infiltrating malignant astrocytoma with anaplasia, marked proliferative potential Imaging Infiltrating mass that predominately involves white matter with variable enhancement T2 heterogeneously hyperintense Neoplastic cells almost always found beyond areas of abnormal signal intensity May involve and expand overlying cortex Usually no enhancement; focal, nodular, homogeneous, patchy enhancement less common Ring enhancement is suspicious for glioblastoma (GBM) MRS: Increased Cho/Cr ratio, decreased N…

KEY FACTS Terminology Well-differentiated but infiltrating neoplasm, slow growth pattern Primary brain tumor of astrocytic origin with intrinsic tendency for malignant progression, degeneration into anaplastic astrocytoma (AA) Imaging Focal or diffuse nonenhancing white matter mass T2 homogeneously hyperintense mass May expand adjacent cortex Usually no enhancement Enhancement suggests progression to higher grade MRS: High choline, low NAA typical but not specific Perfusion: Relatively lower rCBV compared…

Introduction The most widely accepted classification of brain neoplasms is sponsored by the World Health Organization (WHO). A working group of world-renowned neuropathologists periodically convenes for a consensus conference on brain tumor classification and grading. The results are then published. An update to the 2007 edition of the so-called “Blue Book” is scheduled for early 2017. Brain tumors are both classified and graded. Although this is…

KEY FACTS Terminology Brain capillary telangiectasia (BCT) Cluster of enlarged, dilated capillaries interspersed with normal brain parenchyma Imaging General features Common sites: Pons, cerebellum, spinal cord Usually < 1 cm CT Usually normal MR T1WI usually normal T2WI – 50% normal on T2WI – 50% show faint stippled foci of hyperintensity Large BCTs may show ill-defined FLAIR hyperintensity Moderately hypointense on GRE; profoundly hypointense on SWI…

KEY FACTS Terminology Cavernous malformation (CM) Benign vascular hamartoma Contains masses of closely apposed immature blood vessels (“caverns”), no neural tissue Intralesional hemorrhages of different ages Imaging General: Locules of variable size with blood at different stages of evolution Variable appearance depending on hemorrhage/stage CMs vary from microscopic to giant (> 6 cm) Classic MR: Popcorn-ball appearance with complete hypointense hemosiderin rim on T2WI MR DSA:…

KEY FACTS Terminology Congenital cerebral vascular malformation with mature venous elements May represent anatomic variant of otherwise normal venous drainage Imaging General features Umbrella-like collection of enlarged medullary (white matter) veins (“Medusa head”) At angle of ventricle Numerous linear or dot-like enhancing foci Converge on single enlarged “collector” vein “Collector” vein drains into dural sinus/deep ependymal vein Usually solitary, variable size (< 2-3 cm) Hemorrhage may…

KEY FACTS Imaging Location: Dural sinus wall Posterior fossa >> supratentorial Can involve any dural sinus (transverse/straight sinus most common) NECT Usually normal; ICH if outlet vein thrombosed or flow-related aneurysm, venous pouch ruptures Bone CT Dilated transosseous calvarial vascular channels, ± enlarged foramen spinosum MR Isointense thrombosed sinus ± flow voids on T1/T2WI Thrombosed dural sinus blooms on T2* May show parenchymal hemorrhage in dAVF…

KEY FACTS Terminology Pial vascular malformation of brain Artery → vein shunting, no intervening capillary bed Imaging General features Supratentorial (85%), posterior fossa (15%) CT/CTA Iso-/hyperdense serpentine vessels ± Ca++ Arterial feeders, nidus, draining veins enhance MR “Bag of worms”/tangle of serpiginous “honeycomb” flow voids No intervening normal brain in arteriovenous malformation (AVM) nidus Minimal/no mass effect ± high signal (gliosis) on FLAIR T2* GRE “blooming”…

General Considerations Cerebrovascular malformations (CVMs) of the brain are a heterogeneous group of disorders that represent morphogenetic errors affecting arteries, capillaries, veins, or various combinations of vessels. The presentation, natural history, and management approaches to CVMs depend on their type, location, size, and hemodynamic characteristics. Some CVMs, such as venous or capillary malformations, are almost always clinically silent and therefore usually identified at imaging or autopsy.…

KEY FACTS Terminology Atherosclerotic vascular disease fusiform aneurysm (ASVD FA) ASVD → abnormal dilation, tortuosity of intracranial arteries Aneurysms with separate inflow, outflow ostia Imaging Exaggerated arterial ectasia(s) + focal fusiform/saccular enlargement Long segment irregular fusiform or ovoid arterial dilatation Usually large (> 2.5 cm), may be giant Vertebrobasilar > carotid circulation CT: Hyperdense, Ca++ common May present as CPA mass MR: Signal varies flow, presence/age…

KEY FACTS Terminology Extensive ectatic, elongated vertebrobasilar artery (VBA) Usually associated with decreased blood flow velocity Imaging General findings Irregular, elongated, tortuous VBA Usually 6-12 mm, can be giant (> 2.5 cm) Focal arterial dilatation = fusiform aneurysm CT Hyperdense tortuous enlarged vessel, Ca++ common Enlarged lumen enhances, intramural thrombus does not MR Signal varies with flow, presence/age of thrombus Dynamic CE MRA best 3D TOF…

KEY FACTS Terminology Intracranial saccular aneurysm (SA) Outpouching affecting only part of arterial circumference Lacks internal elastic lamina ± tunica media Imaging Round/lobulated arterial outpouching Usually arises from bifurcations of circle of Willis (COW), supraclinoid internal carotid and middle cerebral arteries 90% occur in anterior circulation 10% posterior circulation: Basilar tip, cerebellar arteries (posterior inferior cerebellar artery most common) Rare (< 1%): Trigeminal artery, vertebrobasilar junction…

KEY FACTS Terminology Unique type of subarachnoid hemorrhage (SAH) Localized to sulci over top (“convexity”) of brain Imaging NECT: Hyperdensity in 1 or several adjacent dorsolateral convexity sulci Spares basal, perimesencephalic cisterns MR Sulcal cerebrospinal fluid (CSF) replaced by isointense fluid in convexity sulcus (“dirty CSF”) Hyperintense sulcus on FLAIR GRE, SWI show “blooming” in affected sulci Top Differential Diagnoses Aneurysmal SAH Perimesencephalic nonaneurysmal SAH Traumatic…

KEY FACTS Terminology Subarachnoid hemorrhage (SAH) centered immediately anterior to midbrain ± pons No source demonstrated at CTA/DSA/MRA Imaging NECT: Hyperdense prepontine, perimesencephalic cerebrospinal fluid (CSF) Often involves interpeduncular, ambient, quadrigeminal cisterns ± thin extension into posterior suprasellar, proximal sylvian/interhemispheric fissures Does not extend into distal sylvian, interhemispheric fissures CTA used to exclude basilar tip aneurysm MR T1: Iso- to hyperintense T2 variable (iso- to hyper-)…

KEY FACTS Terminology Subarachnoid hemorrhage (SAH) caused by ruptured aneurysm (aSAH) Saccular aneurysm (SA) > > dissecting aneurysm (DA) Imaging CT/CTA Hyperdense sulci on NECT Distribution varies with aneurysm location Suprasellar cistern (IC-PCoA, ACoA aneurysms) Sylvian fissure (middle cerebral artery bifurcation) Prepontine, cerebellopontine angle cisterns (posterior inferior cerebellar artery, blood blister artery bifurcation SA or vertebral DA) CTA 90-95% positive if aneurysm ≥ 2 mm MR/MRA…

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KEY FACTS Terminology Thrombotic occlusion of deep cerebral veins Usually affects both internal cerebral veins (ICVs) ± vein of Galen (VOG), straight sinus (SS) May occur with more widespread dural sinus thrombosis Imaging NECT Hyperdense ICV ± VOG, SS Hypodense thalami/basal ganglia (BG), loss of gray matter-white matter (WM) interfaces – Variable loss of deep gray-white interfaces; thalami seem to “disappear” into background WM hypodensity ±…

KEY FACTS Terminology Cortical/cerebral venous thrombosis (CVT) Dural sinus thrombosis (DST) CVT with DST > isolated CVT without DST Imaging NECT Cord sign (hyperdense vein) Involved veins usually enlarged (distended with clot), irregular ± petechial parenchymal hemorrhage, edema CECT If DST, empty-delta sign (25-30% of cases) CTV: Thrombi may be seen as filling defects MR Acute thrombus isointense on T1WI Hypointense on T2WI (can mimic flow…

KEY FACTS Terminology Cavernous sinus (CS) Blood clot in CS Imaging CT Bone CT – Look for sinus infection, erosive changes CECT – Nonenhancing filling defects (clot) inside enhancing dural walls of cavernous sinus (CS) – CS margins convex (not flat/concave) CTA/CTV – Filling defects in 1 or both CSs MR T1WI – Convex, enlarged CS (isointense to gray matter) – Orbits: ± “dirty fat,” enlarged…