The paramedian suboccipital approach (PMSOA) is used to treat lesions that affect one cerebellum hemisphere, in cases where it is not necessary to expose the midline or the cerebellopontine angle. The usual pathologies treated by this approach are tumors (metastasis, hemangioblastomas, etc.), ischaemic or haemorrhagic lesions, or vascular malformations (VMFs, cavernomas) [1], [2], [3] (Fig. 1 C-D). Different incisions can be used in order to expose the occipital bone and perform the craniotomy, usually done on an inion-mastoid line, varying its particular location in between the middle 1 ⁄ 3 of said line, depending on the lesion’s exact position. The craniotomy and incison’s size are determined according to the pathology. In some cases, a small incision and a craniotomy centered on the occipital bone is enough, whether when it comes to bigger lesions it is necessary to carry out a larger incision with a wider craniotomy that extends to the foramen magnum [2], [3]. In those cases, as a muscular dissection plane is not possible, the approach requires a transmuscular pathway which does not have constant anatomical landmarks and can therefore, with the dissection of the craniocervical junction (CCJ), eventually compromise the V3 segment of the vertebral artery (V3s-VA) (Fig. 1 A-B).

This scenario greatly differs from other approaches to the suboccipital region because of its lack of constant bony landmarks, such as the mastoid process or the inferior nuchal line on the retrosigmoid approach [4], or those with larger incisions as the extreme lateral inferior transcondylar-transtubercular exposure (ELITE) or the far lateral approach, where a bigger exposure of the region can identify different repairs to protect the V3s-VA (the C1 transverse process, the atlantomastoid line, the fat pad of the suboccipital triangle, the artery of Salmon, and the suboccipital venous plexus of Zolani) [5], [6], [7], [8], [9], [10], [11], [12], [13].

Though rare, the iatrogenic lesion of V3s-VA is potentially fatal with an incidence of 0.2% within the craniocervical surgery [14], [15]. In cases where the lesion of this segment is generated with monopolar electrosurgery, the repair may not be successful, even when performed by experienced vascular neurosurgeons [14], [15]. This injury happens most frequently during instrumented cervical spine surgery, followed in incidence by posterior fossa approaches such as the far lateral or retrosigmoid approach [14], [15], [16], [17]. Although there have been described certain anatomical structures for an approximation to the V3s-VA in this particular approaches [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], to date, there are still no studies that propose neither direct nor indirect landmarks to locate this segment on the paramedian suboccipital approach. Therefore, we consider the implementation of a reference system to identify the V3s-VA on the PMSOA necessary in order to prevent its injury.

The aim of our study is to present, with the use of specific measurements on anatomical dissections, angiotomography and neuronavigation, a system of practical implementation on the operating room, by the use of anatomical and topographical landmarks, to locate the V3s-VA on the PMSOA with the help of minimal or basic tools.