Aneurysms

1-Incidence: 1-14% of population.

2-Causes

-Congenital 97%.

-Infectious 3%.

-Others as arteriosclerotic, traumatic, neoplastic, fibro-muscular disease.

3-Most common site is at circle of willis, sylvian fissure, basilar tip and at the anatomic site of posterior cerebral artery.

4-It could be multiple in 20-25% of patient, if there is rupture, it should be considered coming from the biggest one.

5-Sizes larger than 5-15 mm is more liable to rupture.

6-The most common site to be ruptured is anterior communicating artery(commenest area for rupture).

7-The area of most biggest hemorrhage is indicating to the artery ruptured.

8-Giant aneurysm is the aneurysm more than 2.5 cm in diameter and has an incidence like that of multiplicity.

9-CT appearance:

-Without contrast rarely to be seen.

-Could be seen as faint hyper dense lesion due to calcification or sub arachnoid hemorrhage.

-CECT shows intense homogenous enhancement.

10-Carotid Cavernous Fistula:

-Is an abnormal communication between internal carotid artery and cavernous sinus.

-Appears on CT as marked enlargement and enhancement of the affected cavernous sinus + dilatation of the superior ophthalmic vein.

11-In case of basilar artery tip aneurysm, we can differentiate between aneurysm and meningioma by looking to the basilar artery if you can see it, it is meningioma, if not , so it will be aneurysm.

By MRI with contrast, the aneurysm does not enhance as the contrast is moving inside it, and in non contrast MRI you can find signal voids as whorls.

12-Partially thrombosed aneurysm is not that common in belly aneurysms, and it is seen as a black ball containing a white ball as described by PR.DR. Mamdouh Mahfouz, this white ball could be central or eccentric inside the black one.

13-By development of multi detector CT, you can do reconstruction on the line of the artery, so you can see the carotid artery along its course, you can diagnose easly the aneurysm.

14-By MRI:

-If the lumen of the aneurysm is patent, the aneurysm will be seen as signal void or whorly appearance in T2 image.

-If the lumen is thrombosed, you will see laminated thrombus with mixed stages.

-If there is bleeding, you will see peri aneurysmal hemorrhage and edema.

15-Very important rule by PR.DR.Mamdouh that if you find a hyper intense lesion in T1, it should be considered as bleeding untill prove otherwise.