Posterior Inferior Cerebellar Artery Aneurysms


Posterior Inferior Cerebellar Artery Aneurysms

Posterior inferior cerebellar artery (PICA) aneurysms are relatively uncommon. Most PICA aneurysms can be treated endovascularly, but we have encountered a high rate of aneurysm recurrence associated with coiling procedures. As a result, surgical consideration should be given to PICA aneurysms, particularly those with wider necks. The classic PICA aneurysm arises at the takeoff of the PICA from the vertebral artery. These aneurysms can be challenging because of the great variability of the local vascular anatomy. At times, the aneurysm can be located along the anterolateral surface of the medulla and even as high as the cerebellopontine angle. We have found it useful to study the preoperative angiogram to determine the location of the aneurysm relative to the skull base when deciding how difficult the surgical exposure will be ( Fig. 8.1 ).

Many PICA aneurysms occur close to the point where the vertebral artery penetrates the dura not far above the craniocervical junction. These cases can be exposed in straightforward fashion, and distal control of the vertebral artery can be achieved without difficulty ( Fig. 8.2 ). In our experience, when the PICA takes origin from the vertebral artery low on its vertical segment, the aneurysm will generally be closer to the foramen magnum. On the other hand, when the PICA arises at the turn of the artery where it becomes horizontal or along its horizontal segment just before the vertebrobasilar junction, the surgeon can anticipate a more challenging exposure ( Fig. 8.3 ).

We use a far lateral suboccipital approach for these lesions ( Figs. 8.4, 8.5 ). The patient can be prone, lateral, or three-quarters prone, depending on the surgeon’s preference. As part of the exposure, we drill down the condyle aggressively to optimize visualization of the critical intradural anatomy. The vertebral artery is readily exposed extradurally along the lateral aspect of the C1 arch, where hemostatic agents may be useful in controlling bothersome venous bleeding from the vertebral venous plexus. Once the dura is opened, the intradural vertebral artery can be traced to the PICA origin, offering early proximal control ( Fig. 8.6 ). Gentle retraction of the cerebellar tonsil may be helpful with exposure. When the distal vertebral artery communicates normally with the vertebrobasilar junction, retrograde bleeding from the opposite vertebral artery can be problematic should the aneurysm rupture intraoperatively. Therefore, in the setting of a recent rupture, we expose the vertebral artery distal to the PICA origin to obtain proximal and distal control prior to dissection of the aneurysm.

(A) Vertebral arteriogram demonstrates a somewhat fusiform aneurysm (arrow) arising just distal to the PICA origin (small white star) on the PICA itself (larger white star). The PICA origin is low on the vertical portion of the vertebral artery (arrowhead), presumably close to the location where the artery becomes intradural. This suggests an easier exposure. (B) Postoperative arteriogram demonstrates clip occlusion of the aneurysm.
(A) Artist’s photographic overlay reveals a low-lying PICA aneurysm visible immediately after dural opening without cerebellar retraction. (B) A more common situation is shown, in which a PICA aneurysm is initially hidden by the cerebellum.
Vertebral arteriogram demonstrates recurrent PICA aneurysm (white arrowhead) with a coil mass (white arrow) displaced upward within the aneurysm. The PICA (black arrow) arises at the aneurysm neck. Note the location of the aneurysm high on the vertebral artery, where the artery has become horizontal and is curving to reach the vertebrobasilar junction. This was treated through a far lateral suboccipital approach and was technically more difficult than the case shown in Fig. 8.1 .
(A) A far lateral suboccipital approach has been completed. The dura is reflected back and an excellent exposure of the lower medulla with its associated anatomy is provided. By gently elevating the cerebellum, the vertebral artery (proximal and distal to the PICA) is seen along with the aneurysm (star), the PICA itself (arrow), and lower cranial nerve rootlets. (B) In this magnified view, the proximal intradural vertebral artery (star) is appreciated. (C) The aneurysm has been repaired with a single clip.
(A) A large, atheromatous PICA aneurysm (star) is exposed (A) with a more normal-appearing PICA (arrow) emerging from its base. (B) The aneurysm is reflected upward to reveal the underlying vertebral artery and PICA origin.

While exposing a PICA aneurysm, the surgeon will typically work past the fine and delicate lower cranial nerve rootlets ( Fig. 8.7 ). In the unruptured setting, these can be easily identified and preserved, but in the setting of a subarachnoid hemorrhage (SAH), it can be more difficult to protect these rootlets when they are encased in thick subarachnoid clot. In all instances, the nerves should be carefully protected during surgery, and we generally test patients for ipsilateral swallowing difficulty prior to initiating a regular diet postoperatively.

Artist’s illustration depicting a far lateral suboccipital approach. The dura has been opened to reveal a PICA-origin aneurysm along the lateral aspect of the medulla. Lower cranial nerves are seen crossing the field.
A PICA aneurysm (star) and the associated PICA (black arrow) have been exposed with cranial nerve XI as well as fine rootlets of the other lower cranial nerves crossing the field. The vertebral artery (white arrow) has been exposed proximal to the PICA origin.

We have included several examples of PICA aneurysms in this series to illustrate their surgical treatment ( Figs. 8.8, 8.9 ).

It should be noted that if formal digital subtraction angiography is planned as an intraoperative measure during the treatment of a PICA aneurysm, the preoperative placement of a long femoral sheath is strongly recommended, as the patient is typically positioned such that it would be awkward or impossible to place the sheath once the procedure is under way ( Table 8.1 ).

(A) Vertebral angiography demonstrates a PICA aneurysm (star) arising high on the vertebral artery (arrow) at the start of its horizontal intracranial segment. The PICA (arrowhead) is readily appreciated. (B) The aneurysm has been occluded with a fenestrated clip. The treatment of this lesion is shown in .
(A) Preoperative vertebral arteriogram shows a small PICA aneurysm (arrowhead) in a young patient with multiple aneurysms. The PICA (arrow) arises from the base of the aneurysm. (B) The lesion is exposed through a far lateral suboccipital approach, and the proximal vertebral artery (arrow), aneurysm (star), and PICA (arrowhead) are readily seen. The treatment of this lesion is shown in .

PICA Aneurysm Pearls and Pitfalls

Use the far lateral suboccipital approach.

Remove adequate amount of the occipital condyle for visualization.

Identify intradural vertebral artery for proximal control.

Trace vertebral artery to PICA origin.

Expose distal vertebral as well for complete control of aneurysm.

Watch for exposed mastoid air cells to avoid delayed CSF fistula or infection.

Gently elevate cerebellar tonsil as needed.

Carefully protect fine lower cranial nerve rootlets; injury to rootlets may cause dysphagia or dysphonia.

Be particularly cautious with rootlets encased in thick subarachnoid clot.

Be aware of high-lying aneurysms, which can be difficult to reach.

PICA infarct can result in Wallenberg syndrome: ataxia, dysphagia, dysarthria, vertigo, nystagmus, Horner syndrome, sensory disturbance.

Place long femoral sheath preoperatively if an intraoperative digital subtraction angiogram is planned.

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Jun 30, 2020 | Posted by in NEUROSURGERY | Comments Off on Posterior Inferior Cerebellar Artery Aneurysms
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