Simple identification of the third segment of the extracranial vertebral artery by extreme lateral inferior transcondylar-transtubercular exposure (ELITE).

PURPOSE: The exposure of the third segment of the extracranial vertebral artery (V3) is an important step in the extreme lateral inferior transcondylar-transtubercular exposure (ELITE) approach. The muscular suboccipital triangle provides one of the landmarks to identify the V3 segment; however, identification of this triangle and dissection of the V3 segment is not always straightforward in the actual surgery. Blind dissection below the level of the foramen magnum can lead to vertebral artery injury. While the surgeon may be able to readily define the V3 segment of the vertebral artery by feeling its pulse, it is important to have a safe systematic approach to finding the V3 segment when the vessel is illusive. We propose a simple method to identify the V3 segment avoiding accidental injury of the vertebral artery.

METHODS: Sixteen cadaver heads (using both sides) were prepared by injecting red- or blue-coloured silicone into their arteries and veins, respectively. We performed an ELITE bilaterally on each cadaver head following four key bony landmarks. A postauricular lazy S-shaped skin incision was made centered just behind the mastoid tip. The posterior neck muscles were cut along the line of the skin incision behind the attachment of the sternocleidomastoid muscle to expose the occipital bone. All the incised muscles were reflected anteriorly as the ELITE is a dorsolateral approach. A suboccipital craniotomy was made exposing the posterior half of the sigmoid sinus up to the inferior retrosigmoid point (point A). The foramen magnum was opened after the craniotomy was completed. The dura on the foramen magnum was followed posteriorly in order to identify the occipital midline dural point (point B) that is identified by the bony ridge at the junction of the posterior fossa dura on the foramen magnum and the posterior most aspect of the spinal dura. The posterior tubercle of C1 (point C) was identified directly inferior to Point B. The posterior arch of C1 was followed anteriorly from the tubercle to find the "J-groove", which cradles the vertebral artery (point D). The V3 segment lies above this groove, covering the paravertebral venous plexus. We measured the distances between the landmarks introduced above after completion of the exposure.

RESULTS: The distance between points A and B was 30.5 +/- 5.6 mm, points B-C was 10.4 +/- 2.3 mm, points C-D was 19.1 +/- 3.8 mm. The V3 segment was identified using the anatomical relationships described above in all heads. In no cadaver specimen was the artery injured.

CONCLUSIONS: Identification of the V3 segment of the vertebral artery by systematically detecting the four anatomical points defined above is simple and much safer than a direct dissection below the foramen magnum.