40 Far-Lateral Approach and Its Variants
Abstract
Lesions at the craniocervical junction that demand surgical treatment are not rare. Choosing the adequate approach is mandatory to achieve optimal treatment with minimal morbidity. In this chapter, we will describe the far-lateral approach to the craniocervical junction and its variations, reviewing the regional anatomy and technical nuances.
Keywords: far lateral, transcondylar, foramen magnum, skull base, posterolateral approach
40.1 Background
The craniocervical junction is a frequent site of neoplastic, vascular, and degenerative diseases that often require surgical management. Their locations and extension along the base of the skull and cervical spine are key factors when deciding the adequate surgical approach.1 , 2 , 3 , 4
Essentially, three approaches with some degree of variations have been used to reach lesions in this area: transoral, retrosigmoid suboccipital, and far-lateral. Midline approaches are rarely used, and used mainly for select large tumors, allowing extensive debulking for further dissection of the adjacent neurovascular structures.5
The transoral approach, although offering a direct route to the clivus and craniocervical junction, is rarely employed due the limited access to tumors with lateral extension and increased risk of cerebrospinal fluid (CSF) leak and meningitis, especially when dealing with intradural lesions.5 , 6 , 7
The far-lateral approach consists of a lateral suboccipital craniotomy associated with the removal of the lateral edge of the foramen magnum all the way to the condyle and lateral mass of C1.4 It offers a wide and sterile exposure of craniocervical junction, allowing the surgeon to work parallel to the skull base, minimizing the need for retraction. Mobilization of the vertebral artery (VA) and occipital condyle drilling can be done in select cases for maximal exposure ( Fig. 40.1, Fig. 40.2, Fig. 40.3, Fig. 40.4, and Fig. 40.5).
Several variants of the far-lateral approach have been proposed. Those variants are mainly related with the removal or not of the occipital condyle and its extension, and their anatomical aspects are extensively described in the study by Wen et al.7
40.2 Indications
The far-lateral approach can be used to reach lesions of the inferior third of the clivus, with or without inferior extension to the craniovertebral junction or upper cervical vertebrae.2 , 5 , 7 , 8 Its limits are the nasopharynx anteriorly, the spinomedullary junction posteriorly, and the jugular bulb and XII nerve superiorly. The inferior limit is tailored to each patient, as the skin incision can be as low as necessary2 (Fig. 40.6, Fig. 40.7, Fig. 40.8). The main advantages of this approach are the safe exposure of the space anterior to the neuroaxis and the ability to attack the lesion in a parallel plane. Besides, the surgical corridor is short, wide, and sterile, and stabilization, if needed, can be performed via the same exposure.1
40.3 Surgical Technique
40.3.1 Patient Positioning
The patient is placed in lateral position, with the head fixed parallel to the floor with a three-pin headrest device. The ipsilateral shoulder is slightly mobilized anteriorly and inferiorly. The thigh and abdominal regions should be prepared for possible fascia lata and fat harvest, respectively (Fig. 40.9).
Fig. 40.9Positioning and skin incision. (a–d) Patient is placed in a true lateral position with the head parallel to the floor. Ipsilateral shoulder is slightly displaced anterior and inferiorly and the contralateral arm is well supported. (e, f) Demonstration of the C-shaped skin incision about 3 cm posteriorly around the pinna and centered in the mastoid tip.
40.3.2 Skin Incision
The skin incision begins at the level of the pinna, running posteriorly 2 cm behind the mastoid tip, extending inferior and anteriorly to the level of C4, reaching the anterior border of the sternocleidomastoid muscle. The skin flap is elevated anteriorly, exposing the external jugular vein, the greater auricular nerve, and the sternocleidomastoid muscle (Fig. 40.9).
40.3.3 Intradural versus Extradural Approach
We perform different muscular dissections for extradural and intradural lesions.
For extradural lesions, the sternocleidomastoid, splenius capitis, and longissimus capitis muscles are detached from the skull base in one layer and mobilized inferiorly and posteriorly.
When the goal is to approach an intradural lesion, the sternocleidomastoid muscle is dissected and mobilized anteriorly, whereas the splenius capitis is dissected and mobilized posteriorly (Fig. 40.10 and Fig. 40.11).
The remaining soft tissue work is the same in both situations, as described below.
Fig. 40.3Stepwise dissection and mobilization of vertebral artery. (a, b) Following reflection of muscles of suboccipital triangle, vertebral artery is exposed surrounded by a venous plexus. It travels through foramen transversarium of C1 and runs around atlantooccipital joint to pierce dura. (c, d) Opening of foramen transversarium of C1 and mobilization of vertebral artery medially and inferiorly. Atlantooccipital joint is better exposed. (e) Global view of the area dissected. Atlant. Cond., atlantal condyle; C1 Transv. Proc., C1 transverse process; C2 Gangl., C2 ganglion; For. Transv., foramen transversarium; Great. Occip. N., greater occipital nerve; Occip. Cond., occipital condyle; VA, vertebral artery; VA Musc. Br., vertebral artery muscular branch; Ven. Plex. (Suboccip. Cav. Sin.), venous plexus (suboccipital cavernous sinus).
Fig. 40.10Stepwise muscular dissection. (a) Following skin reflection, sternocleidomastoid muscle and temporalis fascia as well as greater auricular nerve are exposed. (b) Sternocleidomastoid muscle is mobilized anteriorly. (c) Splenius capitis is displaced posteriorly. (d) Longissimus capitis muscle is reflected inferiorly. Suboccipital triangle, containing vertebral artery inside, is exposed. Great. Aur. N., greater auricular nerve; Inf. Obliq., inferior oblique muscle; Long. Cap., longissimus capitis muscle; Splen. Cap., splenius capitis muscle; Sternocleid. Musc., sternocleidomastoid muscle; Sup. Obliq., superior oblique muscle; Temp. Musc. Fascia, temporalis muscle fascia; VA, vertebral artery.
Fig. 40.11Stepwise muscular dissection. (a) Exposure of sternocleidomastoid muscle and temporalis muscle fascia as well as greater auricular nerve, following skin reflection. (b) Anterior displacement of sternocleidomastoid muscle exposing the underlying splenius capitis muscle. (c) Posterior mobilization of splenius capitis muscle exposing longissimus capitis muscle. (d) Inferior displacement of longissimus capitis exposing the underlying suboccipital triangle. (e) Close view of suboccipital triangle containing the vertebral artery inside. (f) Anterior mobilization of superior oblique muscle. (g) Posterior displacement of inferior oblique muscle. (h) Posterior mobilization of rectus capitis posterior muscles. (i) Partial removal of posterior arch of C1, in inset image, and after that the performance of suboccipital craniotomy. (j) Partial removal of posterior aspect of occipital condyle. C1 Transv. Proc., C1 transverse process; Great. Aur. N., greater auricular nerve; Inf. Obliq., inferior oblique muscle; Long. Cap., longissimus capitis muscle; Occip. Cond., occipital condyle; Rec. Cap. Post., rectus capitis posterior major/minor; Splen. Cap., splenius capitis muscle; Sternocleid. Musc., sternocleidomastoid muscle; Sup Obliq., superior oblique muscle; Temp. Musc. Fascia, temporalis muscle fascia; VA, vertebral artery.
Fig. 40.4Stepwise dissection of a far lateral approach by lateral route using a C-shaped skin incision around the pinna. (a) Skin reflection depicting the underlying sternocleidomastoid muscle and greater auricular nerve. (b) Sternocleidomastoid muscle is mobilized anteriorly and splenius capitis muscle posteriorly, depicting underlying longissimus capitis muscle. (c) Longissimus capitis muscle is mobilized, demonstrating the underlying suboccipital triangle. (d) Better view of suboccipital triangle. (e) Following muscles reflection, the vertebral artery, surrounded by a dense venous plexus, is exposed. During surgery the plexus is not dissected and it is kept attached around the vessel to avoid excessive bleeding. (f, g) Better view of vertebral artery travelling through foramen transversarium of C1 and running around atlantooccipital joint. (h, i) Opening of foramen transversarium and mobilization of vertebral artery medially and inferiorly. C1 arch represents an obstacle for further mobilization. (j) Removal of C1 arch. It is important to mention that during surgery first the vertebral artery is freed from the foramen transversarium and then C1 arch is removed; after that, the suboccipital craniotomy is performed. Atlant. Cond., atlantal condyle; C1 Lat. Mass, C1 lateral mass; C1 N. Dors. Ram., C1 nerve dorsal ramus; C1 Transv. Proc., C1 transverse process; For. Transv., foramen transversarium; Great. Aur. N., greater auricular nerve; Inf. Obliq., inferior oblique muscle; Long. Cap., longissimus capitis; Musc. Br., muscular branch; Occip. A., occipital artery; Occip. Cond., occipital condyle; Rec. Cap. Post. Maj., rectus capitis posterior major; Sig. Sin., sigmoid sinus; Splen. Cap., splenius capitis muscle; Sternocleid. Musc., sternocleidomastoid muscle; Sup. Obliq., superior oblique muscle; VA, vertebral artery; Ven. Plex. (Suboccip. Cav. Sin.), venous plexus (suboccipital cavernous sinus).
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