Double origin of the posterior inferior cerebellar artery
The posterior inferior cerebellar artery (PICA) frequently arises from the fenestrated segment of the intracranial vertebral artery (VA), and this common variation can be misinterpreted as or confused with a PICA of double origin. Rarely, a PICA of true double origin occurs when two branches of the PICA arise separately from the intracranial VA and fuse to form an arterial ring.
Uchino et al. discovered this rare variation incidentally while interpreting images of magnetic resonance angiography. This is the first report of MR angiographic findings of this rare variation 1).
For Lesley et al. double origin of the PICA is seen in 4.1% of patients with intracranial aneurysms and on 1.45% of catheter angiograms. The double origin of the PICA has an increased association with intracranial aneurysmal disease and may represent a risk factor for subsequent development of an intracranial aneurysm 2).
Posterior fossa arteriovenous malformations (AVMs), especially cerebellar arteriovenous malformations, are also not common. Consequently, the association of a Double origin of the posterior inferior cerebellar artery (DOPICA) with a cerebellar AVM is even rare.
Rodriguez-Calienes et al. presented a rare case of a pediatric cerebellar AVM supplied by a branch of a DOPICA which was treated endovascularly with NBCA. Total obliteration was achieved in the immediate controls and at 1-year follow-up.
Navigation through tortuous and long branches from a DOPICA is technically feasible. Although NBCA cure rates are relatively low, when the microcatheter can no longer navigate through the feeding artery, a correct dilution of NBCA with lipiodol can provide adequate penetration of this embolic agent, to obliterate the AVM nidus completely 3).
A cadaveric specimen was prepared for dissection. A far lateral craniotomy was performed on the right side. While exploring the right cerebellomedullary cistern, two separate origins of PICA were found from the vertebral artery (VA) as the caudal and rostral trunks that joined to form the distal PICA trunk at the tonsillomedullary segment. Microscopic and endoscopic illustrations are provided.
To the best of the authors' knowledge, this is the first anatomic report on the DOPICA. Cadaveric illustration of this variant helps with understanding its anatomical relationship with adjacent neurovascular structures of the cerebellomedullary cistern including the perforating arteries and the lower cranial nerves 4).
Cho et al. demonstrated the first case of double origin of the posterior inferior cerebellar artery (PICA) with juxta-proximal fenestration of the caudal component, which was misunderstood as triple origin, combined with an unruptured middle cerebral artery aneurysm. The caudal component of the PICA originated from the atlanto-occipital portion and it was fenestrated shortly after origin. The cranial component originated from the intracranial vertebral artery and converged with the superior branch of the caudal component, and then met the inferior branch of the caudal component distally 5).
Two cases of anatomical variation of the PICA that they have called its double origin, one of which gave rise to an aneurysm. The first patient was a 36-year-old man who presented with a subarachnoid hemorrhage related to the rupture of a PICA aneurysm. The aneurysm was treated by the endovascular route. Selective and super selective studies showed that the PICA origin was low on the fourth segment of the vertebral artery (VA). The aneurysm was located on an anastomosis between the PICA and a small upper arterial branch originating from the VA. Embolization was performed through the small branch with no problem, but a lateral medullary infarct followed, probably due to occlusion of the perforating vessels. The same anatomical variation was incidentally discovered in the second patient. To the authors' knowledge, neither this anatomical variation of the PICA nor the aneurysm's topography has been previously described angiographically. This highlights the role of angiography in pretreatment evaluation of aneurysms especially when perforating vessels or small accessory branches that are poorly visualized on angiographic studies are concerned, as in the territory of the PICA. Anatomy is sometimes unpredictable, and the surgeon must be very careful when confronted with these variations because they are potentially dangerous for endovascular treatment 6).