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1. VASCULAR MALFORMATIONS OF CNS

2. AVM

3. Dural Arteriovenous Fistula Etiology Unlike parenchymal AVMs, adult dAVFs are usually acquired (not congenital). Although the precise etiology is controversial, upregulated angiogenesis in the wall of a thrombosed dural venous sinus is the most commonly cited mechanism Location. Most dAVFs are found in the posterior fossa and skull base. Between 1/3 and 1/2 occur at the transverse/sigmoid sinus junction peak age is 40-60 years, roughly 20 years older than the peak age for AVM

4. Imaging CT Findings Parenchymal hemorrhage is uncommon in the absence of CVD. An enlarged dural sinus or draining vein can sometimes be identified on NECT scans. Dilated transcalvarial channels from enlarged transosseous feeding arteries can occasionally be seen on bone CT images in patients with pulsatile tinnitus Contrast-enhanced scans may demonstrate enlarged feeding arteries and draining veins. The involved dural venous sinus is often thrombosed or stenotic .

5. MR Findings. A thrombosed dural venous sinus containing vascular appearing “flow voids” is the most common finding (7-9C) (7-9D). Thrombus is typically isointense with brain on T1 and T2 scans and “blooms” on T2* sequences. Chronically thrombosed, fibrotic sinuses may enhance.

6. Carotid-Cavernous Fistula Carotid-cavernous fistulas (CCFs) are a special type of arteriovenous shunt that develops within the CS divided into two subgroups, direct and indirect fistulas.

7. Imaging CT Findings NECT scans may demonstrate a prominent CS with enlarged superior ophthalmic vein (SOV). CECT scans often nicely demonstrate an enlarged SOV and CS CTA shows engorgement of the ophthalmic vein and CS

8. MR Findings. T1WIs may show a prominent “bulging” CS and SOV as well as “dirty” orbital fat. High-flow CCFs may show too many CS “flow voids” on T2WIs. Strong, uniform enhancement of the CS and SOV is typical. Angiography. Direct CCFs typically demonstrate rapid flow with very early CS opacification (7-13B). A single-hole fistula is usually present, typically between the C4 and C5 ICA segments

9. MR Findings. T1WIs may show a prominent “bulging” CS and SOV as well as “dirty” orbital fat. High-flow CCFs may show too many CS “flow voids” on T2WIs. Strong, uniform enhancement of the CS and SOV is typical. Angiography. Direct CCFs typically demonstrate rapid flow with very early CS opacification . A single-hole fistula is usually present, typically between the C4 and C5 ICA segments

10. Differential Diagnosis The major differential diagnosis with CCFs is cavernous sinus thrombosis (CST). Both CCF and CST may cause proptosis , intraorbital edema, enlarged extraocular muscles, and the appearance of “dirty” fat. In CST, the CS may appear enlarged, but prominent filling defects are present on T1 C+ MR

11. Vein of Galen Aneurysmal Malformation VGAM is essentially a direct AVF between deep choroidal arteries and a persistent embryonic precursor of the vein of Galen, the median prosencephalic vein (MPV) of Markowski

12. Imaging CT Findings. NECT scans show a well-delineated hyperdense mass at the tentorial apex, usually compressing the third ventricle and causing severe obstructive hydrocephalus. Variable encephalomalacia, hemorrhage, &/or dystrophic calcification in the brain parenchyma are often present. CECT scans show strong uniform enhancement

13. CVMs Without Arteriovenous Shunting Developmental Venous Anomaly-Developmental venous anomaly (DVA), also called venous “ angioma ” or “venous malformation,” is an umbrella-shaped congenital cerebral vascular malformation composed of angiogenically mature venous elements . Dilated, thin-walled venous channels lie within (and are separated by) normal brain parenchyma. Imaging General Features. DVAs are composed of radially arranged medullary veins that converge on a transcortical or subependymal large collector vein. The classic appearance is that of a Medusa head or upside-down umbrella

14. CT Findings. NECT scans are usually normal. Unilateral basal ganglia calcification has been reported in the drainage territory of some deep DVAs CECT scans and CTVs show numerous linear &/or punctate enhancing foci that converge on a well-delineated tubular collector vein In larger DVAs, perfusion CT may show a venous congestion pa ern with increased CBV, CBF, and MTT in the adjacent brain parenchyma

15. Differential Diagnosis A histologically mixed vascular malformation in which the DVA provides prominent venous drainage is common. The most common combination is a mixed cavernous-venous malformation (7-25). Unusually large (“giant”) capillary telangiectasias often have a dominant central collector vein and may therefore resemble a DVA

16. Sinus Pericranii Terminology Sinus pericranii (SP) is a rare benign venous anomaly that consists of an emissary intradiploic vein that connects an intracranial dural venous sinus with an extracranial venous varix (7-22). The dilated venous pouch hugs the external table of the skull.

17. Imaging CT Findings An SP shows strong uniform enhancement after contrast administration . The underlying calvarial defect varies in size but is typically well demarcated MR Findings. Most SPs are isointense on T1WI and hyperintense to brain on T2WI. “ Puddling ” of contrast within the SP on T1 C+ is typical unless the lesion is unusually large and flow is rapid. MRV is helpful in delineating both the intra- and extracranial components

18. Cerebral Cavernous Malformation

19. Imaging General Features A well-circumscribed mixed density/signal intensity mass surrounded by a complete hemosiderin rim (“ popcorn ball”) is the classic finding. CCMs can vary from microscopic to giant (> 6 cm) lesions. In rare circumstances, a CCM (often mixed with venous malformations) may occupy an entire lobe of the brain. CT Findings. Large CCMs appear hyperdense with or without scattered intralesional calcifications. Most CCMs are well delineated and do not exhibit mass effect unless there is recent hemorrhage .

20. MR Findings. Findings depend on the stage of evolution and pulse sequence utilized. CCMs have been divided into four types based on imaging appearance ( Zabramski classification). The classic CCM ( Zabramski type II) is a discrete reticulated or “popcorn ball” lesion caused by blood products contained within variably sized “caverns” or “ locules .” Fluid-fluid levels of differing signal intensities are common (7-25B). The mixed signal core is surrounded by a complete hemosiderin rim on T2WI that “blooms” on T2* sequences (7 25C). CCMs with subacute hemorrhage ( Zabramski type I) are hyperintense on T1WI and mixed hyper-/hypointense on T2WI T2* scans (GRE, SWI) should always be performed to look for additional lesions. Punctate microhemorrhages are seen as multifocal “blooming black dots” ( Zabramski type IV) in many cases with familial CCM If a CCM coexists with a DVA, the venous “ angioma ” may show strong enhancement

21. Differential Diagnosis The most common differential diagnosis is a mixed vascular malformation in which a CCM is the dominant component. Occasionally, a hemorrhagic or densely calcified neoplasm (such as a glioblastoma or oligodendroglioma , respectively) can mimic a CCM. Multifocal “black dots” on T2* scans can be seen in a number of lesions besides type IV CCMs. Chronic hypertensive encephalopathy, amyloid angiopathy, axonal stretch injury, and cortical contusions may have similar appearances. Hemangiomas are true benign vasoformative neoplasms and should not be mistaken for CCMs. Most are found in the skin and soft tissues of the head and neck. Hemangiomas within the CNS are rare and most commonly found in dural venous sinuses and cranial meninges, not the brain parenchyma

22. Capillary Telangiectasia A brain capillary telangiectasia (BCT) is a collection of enlarged, thin walled vessels resembling capillaries. The vessels are surrounded and separated by normal brain parenchyma

23. no mass effect is SEEN lack edema, do not incite surrounding gliosis, and neither hemorrhage nor calcify. CT Findings. Both NECT and CECT scans are usually normal unless the telangiectasia is unusually large

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