C.N.S.Intracranial Aneurysms

Mohamed Zaitoun

Assistant Lecturer-Diagnostic Radiology Department , Zagazig University Hospitals

EgyptFINR (Fellowship of Interventional

Neuroradiology)-Switzerlandzaitoun82@gmail.com

Knowing as much as possible about your enemy precedes successful battle

and learning about the disease process precedes successful management

Aneurysm1-Presentation2-Incidence3-Diagnosis4-Types

1-Presentation :a) Sudden onset of severe headacheb) Mass effectc) Thromboembolic events

a) Sudden onset of severe headache :-Sudden onset of severe headache +/- neurological

signs + /- reduced level of consciousness with scan findings of :

1-Subarachnoid Hemorrhage2-Parenchymal Hemorrhage (usually with

associated SAH )3-Intraventricular Hemorrhage (most often

secondary to bleeding in the general subarachnoid space , occasionally primary)

b) Mass effect :1-Cranial nerve palsies (especially 3rd nerve palsy

with PCOM aneurysms)2-Horner’s syndrome3-Brainstem dysfunction4-Hydrocephalus

c) Thromboembolic events

2-Incidence :-Incidence in general population is 2-3 %-Overall risk of rupture = 0.5-1.5 % per annum ,

variable according to size and position of aneurysm , sex , smoking , etc

3-Diagnosis :a) CT & CTAb) MR & MRAc) Catheter Angiography

a) CT & CTA :-Extra-axial mass in subarachnoid space-Enhances if patent-May be thrombosed and / or have calcification

(especially giant aneurysms)-CTA demonstrates site and morphology of

aneurysm and may allow planning of treatment (neurointervention versus surgery) without need for catheter angiography

Nonenhanced CT scan of a middle-aged man with headaches, the patient had a giant aneurysm of the LT ICA in its intracavernous segment, this aneurysm is densely calcified and is easily depicted

CTC shows a basilar tip aneurysm

Coronal reformatted MIP images from a CTA demonstrates a 5 mm aneurysm (straight arrow) of the anterior communicating artery (arrowhead)

RT MCA aneurysm seen on both CTA and MRA), A, Coronal section on CTA reveals aneurysm in RT MCA bifurcation, B, MRA also displays aneurysm with less definition, C, 3D reconstruction of CTA better defines saccular appearance of this aneurysm

A, Catheter angiography lateral view, following left ICA injection, shows aneurysm originating from supraclinoid portion of ICA, B, CTA axial source image reveals lobulated aneurysm (arrow)

CTA obtained on day 6 after occurrence of aneurysmal subarachnoid hemorrhage shows severe spasm of the right MCA (arrows) and a midline hematoma surrounding a thrombosed aneurysm of the anterior communicating artery

b) MR & MRA :-Patent aneurysm will show flow void -Giant or partially thrombosed aneurysms can

show complex flow patterns with heterogeneous signals on standard sequences

-Not reliable for treatment planning

T1 of a middle-aged woman with progressive headaches, aphasia, and right-sided hemiparesis, a large intracerebral mass with a significant amount of surrounding edema is depicted, the lesion is a giant internal carotid artery aneurysm

T2 of a middle-aged woman with progressive headaches, aphasia, and right-sided hemiparesis, the lesion is a giant internal carotid artery aneurysm, note the flow void, the blood breakdown products within the layers of mural thrombus, and calcification within the aneurysm that produces a marked hypointense signal, significant surrounding edema is depicted

T2 shows 7-mm basilar artery terminus aneurysm (arrow)

MRA shows basilar tip aneurysm (arrow) and very small (1.5 mm) P1 segment aneurysm (arrowhead)

Coronal T2 through the chiasmatic cistern , the optic chiasm is displaced to the left (arrow) and the anterior cerebral arteries elevated by a large right carotid-ophthalmic aneurysm , this patient present with visual disturbance and examination revealed an ipsilateral temporal quadrantanopia

(a) Axial T2 and (b) oblique frontal intra-arterial digital subtraction angiography showing a giant aneurysm of the intrapetrous right carotid artery , this patient presented complaining of deafness and was treated by balloon occlusion of the carotid artery

c) Catheter Angiography :-Invasive with 0.1-0.5 % inherent stroke risk-Still considered gold standard but may soon be

superimposed by CTA

Left oblique cerebral angiogram in a patient with multiple intracranial aneurysms shows an anterior communicating aneurysm and a middle cerebral artery aneurysm

(a) Axial CT showing acute SAH with intra parenchymal and intraventricular hemorrhage , (b, c) DSA by right (b) and left (c) ICA injection 2 days after the hemorrhage shows no evidence of vasospasm and only faint filling of a small saccular aneurysm of the anterior communicating artery on b (arrow) , (d, e) A repeat study was performed 4 days later and shows the aneurysm filling from the left side (e) and intense vasospasm of right (d) and left (e) anterior cerebral arteries

(a) Left carotid angiography showing a saccular ACOM aneurysm 24 h after rupture , (b) the aneurysm rebleed before treatment and a second angiogram 8 days later (immediately prior to coil embolisation) shows a daughter lobule at the fundus

(a) Very large aneurysm arising from the lCA distal to the ophthalmic artery origin ; pointing upwards and medially , aneurysms at this site are variously described as carotid-ophthalmic , paraclinoid or global ICA aneurysms , the neck is very wide and this lesion was treated by parent artery occlusion , (b) T1 showing the aneurysm filling the chiasmatic cistern with the chiasm displaced to the right , (c) T1 shortly after left ICA balloon occlusion , the aneurysm sac is substantially thrombosed

ICA DSA showing a small superior hypophyseal aneurysm arising from the supraclinoid artery and pointing medially , the aneurysm arises at the level of the superior hypophyseal artery , but this vessel is rarely visible on angiography

Oblique frontal angiograms of a large aneurysm of ICA , (a) before and (b) 6 months after coil embolisation , aneurysms at this site often have wide necks which increases the risk of recurrence after coil embolisation , a microcatheter has been positioned in the central part of the aneurysm sac in (a) , at follow-up (b) there is a small neck remnant (arrow) which will be monitored by further intra-arterial angiography

Lateral intra-arterial DSA showing a small aneurysm at the origin of the anterior inferior frontal artery , the angiogram was performed soon after SAH

Left MCA arising at the bifurcation , the orbitofrontal artery arises from the superior trunk (arrow) and its origin is intimately related to the aneurysm neck , an early branch of the M2 arteries such as this may be difficult to separate , on imaging , from the aneurysm neck

Basilar artery (BA) termination aneurysm on frontal (a) and oblique (b) intra-arterial DSA , this aneurysm points upwards and to the right side , lateral deviation of the aneurysm sac is due to asymmetry of the inflow , the bifurcation of the BA , in this case , is low relative to the dorsum sella and the P1 arteries are therefore directed vertically , the right P1 is obscured and oblique views (b) are used to show the relationship of the aneurysm neck to the posterior cerebral artery origins , note that both PCOMs fill and the proximity

Oblique lateral intra-arterial DSA following vertebral artery (VA) injection , there is a small saccular aneurysm arising from the PICA , the neck of the aneurysm is clearly separate from VA ; arising from the apex of the initial downward turn of the lateral medullary section of PICA , the aneurysm points upwards and medially

4-Types :a) Saccular aneurysmb) Fusiform aneurysmc) Dissecting aneurysmd) Mycotic aneurysme) Oncotic aneurysmf) Traumatic pseudoaneurysm

a) Saccular Aneurysm :1-Incidence2-Etiology3-Radiographic Features4-Complications5-Multiple aneurysms6-Giant aneurysm

1-Incidence >>-Present in approximately 2% of population ,

multiple in 20% , 25% are giant aneurysms (>25 mm)

-Increased incidence of aneurysm in :a) Adult dominant polycystic kidney disease

(ADPKD)b) Aortic Coarctationc) FMDd) Structural collagen disorders (Marfan syndrome ,

Ehlers-Danlos syndrome)e) Spontaneous dissections

2-Etiology :-Degenerative vascular injury (previously

thought to be congenital) > trauma , infection , tumor & vasculopathies

3-Radiographic Features :a) CT & CTAb) MR & MRAc) Catheter Angiography

a) CT & CTA :-See before

b) MR & MRA :-See before

c) Catheter Angiography :-Number of aneurysms : multiple in 20%-Location , 90% in anterior circulation-Size-Relation to parent vessels-Presence and size of aneurysm neck

4-Complications :a) Rupture >>-SAH-Parenchymal hematoma-Hydrocephalusb) Vasospasm >>-Occurs 4 to 5 days after rupture-Causes secondary infarctions-Leading cause of death / morbidity from rupture

c) Mass effect >>-Cranial nerve palsies-Headached) Death >> 30 %e) Rebleeding >>-50% rebleed within 6 months-50% mortality

5-Multiple Aneurysms :-In the presence of multiple aneurysms , one may identify

the bleeding aneurysm using the following criteria :a) Location of SAH or hematoma adjacent to or around

bleeding aneurysmb) Largest aneurysm is the one most likely to bleedc) Most irregular aneurysm is the one most likely to bleedd) Extravasation of contrast (rarely seen)e) Vasospasm adjacent to bleeding aneurysm

6-Giant aneurysm :a) Definition :-Aneurysm > 25 mm in diameterb) C/P :-Mass effect (cranial nerve palsies , retro-orbital

pain )-Hemorrhage

c) Radiographic Features :1-Large mass lesion with internal blood

degradation products2-Signet sign : eccentric vessel lumen with

surrounding thrombus3-Curvilinear peripheral calcification4-Ring enhancement : fibrous outer wall

enhances after complete thrombosis

5-Mass effect on adjacent parenchyma6-Slow erosion of bone :*Sloping of sellar floor*Undercutting of anterior clinoid*Enlarged superior orbital fissure

b) Fusiform (Atherosclerotic) Aneurysm :1-Etiology & Incidence2-Radiographic Features3-Complications

1-Etiology & Incidence :-Elongated aneurysm caused by atherosclerotic

disease-Most located in the vertebrobasilar system-Often associated with dolichoectasia

(elongation and distention of the vertebrobasilar system)

2-Radiographic Features :-Vertebrobasilar arteries are elongated ,

tortuous and dilated-Tip of basilar artery may indent 3rd ventricle-Aneurysm may be thrombosed :CT: HyperdenseT1W: Hyperintense

3-Complications :a) Brainstem infarction due to thrombosisb) Mass effect (cranial nerve palsies)

c) Dissecting Aneurysm :1-Etiology2-Radiographic Features

1-Etiology :-Following a dissection an intramural hematoma

may organize and result in a saclike out pouching

-Causes : Trauma > vasculopathy ( SLE , FMD ) > spontaneous dissection

-Location: Extracranial ICA > vertebral artery

2-Radiographic Features :Elongated contrast collections extending beyond

the vessel lumenAngiography is sometimes required for imaging

of vascular detail (dissection site)

Patient presenting with SAH) due to rupture of a dissecting aneurysm of the right intracranial vertebral artery (VA) (arrow) , this is a common site for a dissecting aneurysm to cause SAH

(a) Diffusion shows lesion of restricted diffusion on the left side (arrow), which was consistent with acute posterior choroidal-artery infarction, (b) T2, (c) MRA and CTA (d) show a dilatation of the left posterior cerebral artery, with a double lumen, that is, a true circulating lumen (lower arrows) and a false noncirculating lumen (upper arrows) divided by an intimal flap (b, arrowheads), suggesting a dissecting aneurysm, (e) Angiography confirmed an aneurysm of the posterior cerebral artery , (f) shows the coiling of the aneurysm

d) Infectious (Mycotic Aneurysm) :1-Causes :-Bacterial endocarditis , IVDA (intravenous drug

abuse) 80 %-Meningitis , 10 %-Septic thrombophlebitis , 10 %

2-Radiographic Features :-Aneurysm itself is rarely visualized by CT-Most often located peripherally and multiple-Intense enhancement adjacent to vessel-Conventional angiography is the imaging study

of choice

Coronal CT angiography showing a large irregularly shaped presumed mycotic middle cerebral artery aneurysm

e) Oncotic aneurysm :-Is an aneurysm caused by neoplasm-A benign left atrial myxoma may predominantly

embolize and cause a distal oncotic aneurysm

Oncotic IAA in a 14-year-old girl with Maffucci syndrome and a skull base chondrosarcoma, (a) Axial T2 through the circle of Willis shows bulbous dilatation of the right ICA (arrow) where it abuts the skull base chondrosarcoma (arrowheads), (b) Axial CTA at the same level shows the aneurysmally dilated right ICA (straight arrow), mildly aneurysmal left ICA (curved arrow), and normal-caliber basilar artery (arrowhead)

f) Traumatic Pseudoaneurysm :-Aneurysms due to trauma are most commonly

pseudoaneurysms which don’t contain the typical three histologic layers of the vessel wall, usually the vessel wall exhibit abnormal luminal narrowing proximal to the aneurysm

-Similar to mycotic aneurysms, traumatic pseudoaneurysms tend to occur distally

-Arteries close to bony structures (such as the basilar & vertebral artery) are prone to dissecting aneurysms

(a) Preoperative T1+C shows a 3-cm tuberculum sellae meningioma encasing the ACOM, (b) Preoperative RT ICA angiogram shows elevation of the right A1 portion and occlusion of the left A1 portion, but no aneurysms (c) RT ICA angiogram, 1 month after surgery, shows a newly developed 3- × 5-mm aneurysm of the ACOM, (d) RT ICA angiogram, 2 months after surgery, shows a 6- × 8-mm aneurysm that enlarged progressively