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Segments of PICA
The Posterior Inferior Cerebellar Artery a branch of the intracranial portion of the vertebral artery has 4 major segments. Each segment has certain anatomical consideration with respect to the cerebellum and supplies provide distinct arterial supply to the brainstem and the cerebellum. Those branches are:
- 1. Anterior Medullary segment.
- 2.Lateral MedullarysSegment: passes through fibers of 12, and then passes fibers of IX, X, XI.
- 3.Tonsillomedullary segment: caudal loop, rostral Loop (apex is Choroidal point).
- 4.Telovelotonsillar segment: apex is choroidal point.
- 5. Cortical segment
The first three segments do have important perforators that supply the brain stem, yet there are no important perforators beyond that region. Generally there is no significant vessels that do not arise distal to the choroidal point.
Three percent of intracranial aneurysms arise from PICA origin, which corresponded to 20% of Vertebrobasilar artery aneurysms. Among those 80% arise near PICA origin of the intracranial vertebral artery
- Patients with PICA aneurysms can present with 6th cranial nerve palsy or lower cranial nerve deficit.
- Distal PICA aneurysms can present with 4th ventricular or cerebellar intraparenchymal hemorrhage in addition to subarachnoid hemorrhage.
Patients with PICA aneurysms who are considered for treatment, and are not a good candidate for endovascular treatment (aneurysm anatomy) can be treated with surgical clipping. The surgical approach include the Far-Lateral approach for aneurysms located laterally off the midline with respect to bony landmarks, or midline suboccipital craniotomy for tonsilar segment PICA aneurysms.
For Far Lateral approaches, the patients are positioned laterally, with head tilted 30degrees up Straight ahead position (nose parallel with the floor). While for distal aneurysms near midline: the patients are positioned prone for suboccipital approach.
The skin incision is either reverse L- shaped or lazy-S shaped depending on the surgeon preference, this is started at level of Pinna 3 fingerbreadths medial to the mastoid and curved down to level of C2 in midline. This is followed by a tear drop craniotomy extending from Transverse-Sigmoid junction down to foramen magnum laterally. During the craniotomy the perivertebral plexus is packed or coagulated with bipolar coagulation. The posterior-medial third of atlantocondylar articulation can be drilled and removed to allows more medial exposure without need for brainstem/cerebellar retraction. The dura is opened with curve starting superolaterally and curving down towards midline. This will provide access to the PICA aneurysms, with minimal retraction.
Complications realated to the surgical clipping include, dysphagia, dysphonia, inability to swallow, surgical wound infection and Pseudo-meningocele.