Far Lateral Approach and Principles of Vertebral Artery Mobilization

28 Far Lateral Approach and Principles of Vertebral Artery Mobilization

João Paulo Almeida, Mateus Reghin Neto, and Evandro de Oliveira

28.1 Introduction

The far lateral approach is a lateral approach, which provides access to the postero-lateral aspect of the posterior cranial fossa. It is suitable to treat intra- and extra-axial lesions located at the antero-lateral aspect of the craniocervical junction.

One of the most technically demanding steps of the approach is the mobilization of the vertebral artery, to optimize the surgical exposure.

28.2 Indications

• Lesions located at the anterior and lateral aspect of the craniocervical junction:

◦ Vertebral artery (VA), vertebro-basilar junction and posterior inferior cerebellar artery (PICA) aneurysms.

◦ Tumors located at the anterior part of the foramen magnum and upper cervical spine.

◦ Tumors located at the lower third portion of the clivus and posterior aspect of the foramen jugular.

28.3 Patient Positioning

• Semi-sitting position (See Chapter 24)

◦ Initially in the supine position, the patient’s head is fixed to the Mayfield or Sugita head holder with three or four pins placed bilaterally over the superior temporal lines.

◦ The patient’s body is gradually brought to a semi-sitting position such that the knees are level with the heart. The head holder adaptor is attached to the table between the hips and the knees and arched back as necessary to accommodate patient’s body habitus, connecting to the Mayfield head holder.

◦ From a neutral position, the head is carefully flexed toward the chest. This maneuver improves the exposure of the craniovertebral junction at the atlas (C1)-occipital condyle articulation and facilitates the dissection of muscles of the suboccipital region.

◦ During flexion of the head the distance between the chin and chest should not be smaller than 2 cm, in order to avoid obstruction of the venous return by the internal jugular veins.

28.4 Skin Incision

• Horseshoe cutaneous incision (Fig. 28.1)

◦ Starting point: The incision begins in the midline, approximately 3 cm below the inion.

◦ Course: Incision runs straight upward until 2 cm above the external occipital protuberance, then it turns laterally, above the superior nuchal line, toward the asterion. Finally, it turns downward and laterally over the posterior border of the sternocleidomastoid muscle. Abundant irrigation of operative field with physiological solution is imperative at all times during the procedure in order to avoid gaseous embolization.

◦ Ending point: It ends approximately 5 cm below the mastoid apex, where the transverse process of the atlas can be palpated through the skin.

Fig. 28.1 Skin incision

28.4.1 Critical Structures

• Occipital artery.

• Greater and lesser occipital nerves.

28.5 Soft Tissues Dissection

• Muscles dissection

◦ After inferomedial retraction of the scalp flap toward the midline, the most superficial layer of muscles, formed by the sternocleidomastoid and splenius capitis muscles (laterally), and trapezius and semispinalis capitis muscles (medially) are exposed (Fig. 28.2).

◦ The sternocleidomastoid muscle is divided below its insertion, with preservation of its upper attachment for closure. Lateral retraction of that muscle exposes the superior portion of the splenius capitis muscle.

◦ The trapezius and splenius capitis muscles are detached, while preserving an upper cuff of their attachment for closure. After medial and inferior reflection of these muscles, the longissimus capitis, semispinalis and levator scapulae muscles are exposed (Fig. 28.3).

Fig. 28.2 Exposure of the superficial muscle layer.
Abbreviations: E = ear; OA = occipital artery; SC = splenius capitis; SF = skin flap; SM = sternocleidomastoid muscle; T = trapezius

Fig. 28.3 Muscular exposure after reflection of the sternocleidomastoid and trapezius muscles.
Abbreviations: E = ear; LC = longissimus capitis muscle; LS = levator scapulae muscle; OA = occipital artery; SM = sternocleidomastoid muscle; SMC = semispinalis capitis muscle; SO = superior oblique muscle.

◦ The longissimus capitis is reflected downward exposing the semispinalis capitis, superior and inferior oblique muscles, and the transverse process of the atlas.

◦ Medial reflection of the semispinalis capitis muscles is done in order to expose the suboccipital triangle (Fig. 28.4).

◦ The suboccipital triangle is defined above and medially by the rectus capitis posterior major, above and laterally by the superior oblique muscle and below and laterally by the inferior oblique muscle (Fig. 28.4). These muscles are reflected medially to expose the contents of the suboccipital triangle.

◦ In summary, with exception of the sternocleidomastoid, medial retraction of the muscles rather than lateral and inferior reflection is recommended. This maneuver avoids the presence of a muscular bulk between the surgeon and the dura mater, reducing the depth of the exposure.

• Exposure of the vertebral artery (Fig. 28. 5)

◦ The vertebral artery (VA), venous plexus of the vertebral artery and first cervical (C1) nerve root run in the suboccipital triangle.

◦ Adequate exposure of the VA at the suboccipital triangle demands partial obliteration and dissection of the vertebral artery venous plexus.

◦ The artery is usually found after dissection of the superior border of the posterior arch of atlas. C1 nerve usually runs on the lower surface of the artery, between the VA and the posterior arch of C1.

◦ Careful dissection of the venous plexus until exposure of entrance of the VA into the intradural space is recommended.

• Mobilization of the vertebral artery

◦ After dissection of the suboccipital triangle and exposure of the extradural extra-foraminal segment of the VA (V3 segment) mobilization of this vessel may be performed.

◦ Removal of half of the posterior arch of C1 and the posterior root of its transverse foramen allows for downward and medial mobilization of the VA, which improves the exposure of the occipital condyle (Fig. 28.6).

◦ Opening of the dura surrounding the VA at the entrance of the intradural space and cut of the first dentate ligament allow further mobilization of the VA.