Dolicoectasia with Basilar Aneurysm

NonContrast CT study of brain and Non contrast 3D TOF MR Brain Angiography show:
Left vertebro basilar Dolico Ectasia.
Basilar mid portion shows a saccular aneurysm with hyperdense thrombus in it.
High riding basilar tip and PCAs.
Dilated both the ICAs cavernous and supra clinoid portion with high riding bifurcation of ICA.

Vertebral Artery compressing Medulla

MRI Brain Axial T2w images at the level of medulla show tortuous dilated left vertebral compressing left half of medulla.
Tortuous intracranial arteries in the subarachnoid space may compress and distort the brain parenchyma, can cause direct compression or stretching of the cranial nerves.
Most intra cranial arterial compressive lesions are associated with dolichoectasia of vertebral-basilar system.
Compression of the medulla by dilated and tortuous vertebral arteries is rare and is a less well known clinical entity.
Compression most commonly occurs at the ventrolateral surface of medulla.
The clinical features can be transient or permanent, can be motor, cerebellar or vestibular.
In most of the cases poor correlation exists between the clinical findings and the severity of compression. In some cases it may not match at all to the patient’s clinical features.

Anatomical Variations of Vertebral

Left vertebral arising from arch of aorta near root of left subclavian 

Axial row images of same pt showing origin of left vertebral from arch of aorta near root of left subclavian  

Anatomical Variation of Vertebrals

Right vertebral artery may arise:
• from the first part of the subclavian, nearer than normal to the brachiocephalic or to the anterior scalene muscle;
• directly from the arch of the aorta;
• from the right common carotid, when the right subclavian arises from the aorta beyond the left subclavian;
• or from the brachiocephalic trunk. The right artery may pass behind the esophagus.

The left vertebral artery may arise :
• directly from the left common carotid;
• root of the subclavian, close to the aortic arch.
• or from the arch of the aorta.

There are occasionally two left vertebral arteries. In such case, one may from the arch of the aorta, the other from the left subclavian artery in the normal position.
The origin of the left vertebral artery from the aortic arch is a very common variation, but the origin of the vertebral artery from the right side of the arch is very rare.
The left and right vertebrals may be doubled with each vessel entering a different transverse foramen. In rare occasion either vertebral artery may arise from the thyrocervical trunk or from the costocervical trunk.

The two vertebrals are usually unequal in size, the right being smaller than the left. The dominant continues as basilar. Intra cranial portion of contra lateral vertebral may be hypoplastic or completely absent.

Very rarely the two vertebrals fail to unite to form the median basilar artey, hence the basilar may appear to be doubled. The two longitudinal trunks may be united by anastomoses between them.
The vertebral artey may exist as several vessels that eventually unite, or it may form an arterial ring traversed by the hypoglossal nerve.

Related post:
Duplication of vertebral 

On left side there are 2 separate origins of the vertebral artery from the corresponding subclavian, the duplicated vessels join together before continuing as one vessel in the foramina transversaria