![]() After the VA penetrates the dura, it courses laterally and then ventrally to join the contralateral VA to form the basilar artery. The posterior meningeal branch often originates from the middle portion of this VA segment. Bleeding from these branches should not be confused with bleeding from the VA itself. Along the transverse segment of the vertebral artery, there are usually muscular branches that anastomose with branches of the external carotid artery. After exiting through the foramen, it curves behind the atlantooccipital joint to lie horizontally along the posterior arch of C-1.Īs the vertebral artery courses medially, it curves rostrally and passes through the foramen magnum. At C-3, the artery turns laterally and enters the foramen of C-2. The vertebral artery originates as the first branch of the subclavian artery and enters the transverse foramen of the sixth cervical vertebral body. Midline aneurysms related to ectatic posterior circulation can be very challenging to reach microsurgically and endovascular options should be explored. In addition, it establishes the diagnosis of dissection that is not uncommon in this vascular territory.Ī CT angiogram is effective for demonstrating the relevant composition of the vasculature in relation to the corresponding posterior fossa bony anatomy, including the foramen magnum and clivus. Proximal fusiform aneurysms involving the perforating arteries may require revascularization, but distal ones can be treated with Hunterian ligation.Ĭatheter angiography provides superior imaging of proximal PICA perforating arteries and the robustness of collateral flow. In addition, the size of the posterior communicating arteries can determine if proximal VA occlusion is safe. Reduplicated PICA and dominant anterior inferior cerebellar arteries (AICA’s) supplying the PICA territory are also important factors in this tolerance. The morphology of the vertebral artery (VA) should be assessed, and a hypoplastic VA ending in PICA should be noted because this vascular variation is likely to affect the tolerance of distal neural territories to temporary or permanent VA occlusion. The occurrence of radiographic hydrocephalus after such an aneurysm rupture reaches 95%. Spontaneous fourth ventricular hemorrhage in the absence or presence of subarachnoid hemorrhage (SAH) requires a vascular study to rule out a PICA aneurysm. As always, the microsurgical experience of the treating clinician plays a central role in the offered choice of therapy. Patients with PICA aneurysms who are older, who have medical morbidities, and who harbor narrow-neck aneurysms should undergo endovascular management whereas young patients and those with wide-neck aneurysms should be considered for microsurgical clipping. Therefore, microsurgery remains a viable option for select patients. The small caliber of the PICA and the broad neck of the associated aneurysms place the PICA at some risk during coil embolization. The tradeoffs between minimally invasive coil embolization versus the more durable clip ligation continue to complicate decision making in aneurysm surgery. The clipping-versus-coiling debate continues to haunt neurosurgeons. Young age of the patient and irregular morphology of the sac all portend a higher rupture risk, and these factors should prompt treatment of aneurysms that are even as small as 5 mm. Nonetheless, most clinicians apply the natural history data from anterior circulation aneurysms to those of the posterior circulation. These studies have not targeted posterior circulation aneurysms adequately, and therefore the true natural history, including the hemorrhagic risk of PICA aneurysms, is unknown. Although natural history studies suggest a very low rupture risk for lesions under 7 mm, the majority of aneurysms that present with hemorrhage are indeed under 7 mm in size this phenomenon presents a conundrum for the neurosurgeon.
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