The Far Lateral Approach

Preoperative Considerations

• The far lateral provides wide access to the dorsolateral compartment yet allowing exposure to the lateral aspect of the ventromedial compartment of the posterior fossa (270° visualization of the circumference around the medulla).

• Variants of the far lateral approach:

  • Transcondylar

  • Supracondylar

  • Paracondylar

• CT angiography (CTA) or angio-MRI (MRA) may be useful to study the anatomy of the vertebral arteries (VA), posterior spinal and the posterior inferior cerebellar arteries (PICA).

Indications

• Posterior fossa tumors that have their epicenter in the dorsolateral compartment.

• Intra-axial tumors with anterior extension affecting the cerebellar hemisphere, tonsil, foramen of Magendie and the anterolateral and posterior surfaces of the medulla oblongata and lower pons.

• Cerebrovascular lesions affecting the posterior circulation (vertebral artery and PICA artery aneurysms).

• The far lateral approach provides a wider caudal exposure of the posterior fossa compared to the retrosigmoid approach (more suitable for lesions involving foramen magnum, the occipital condyle and the inferior petroclival junction, the posterior aspect of the jugular foramen and hypoglossal nerve).

Contraindications/Alternatives

• Limited access to the ventromedial compartment, including the petroclival region and the lateral aspect of the middle and lower thirds of the clivus.

• The far lateral approach provides limited access to the superior aspect of the internal acoustic meatus, facial and trigeminal nerves, anterior inferior cerebellar artery (AICA) and tentorium (better accessed through the retrosigmoid approach).

• The endoscopic endonasal transclival and far medial approaches are emerging strategies to approach more anterior lesions with important involvement of the ventromedial compartment of the posterior fossa (anterior to the medulla and pons). The endonasal route provides limited access to the posterolateral compartment.

• For complex lesions with large invasion of the posterior fossa, a combined far lateral–far medial approach could provide the most efficient and safest surgical option.

• Lesions with infra- and supratentorial components might benefit from a combined far lateral and temporal bone craniotomy, middle fossa approach and variable mastoid drilling.

Bone Anatomy ( Figure 22.1 )

• The external occipital protuberance — inion — serves as a reliable landmark to infer the position of the torcula — the confluence of the superior sagittal, straight and transverse sinuses.

• The superior nuchal line is an important landmark for the muscular incision during the far lateral approach. It is shaped by the tendinous insertion of the nuchal muscles (sternocleidomastoid, trapezius, splenius capitis and semispinalis capitis).

• The asterion (a confluence of the lambdoid, squamosal and occipitomastoid sutures) is a reliable landmark for the position of the transverse sinus, as it becomes the sigmoid sinus.

• The inferior nuchal line (between the superior nuchal line and the foramen magnum) corresponds to the insertion of the suboccipital muscles.

• The digastric groove may serve as a landmark to identify the mastoid and the sigmoid sinus in the supracondylar variant and as a landmark of the facial nerve in the paracondylar variant of the far lateral craniectomy.

• The condylar part of the occipital bone is formed by:

  • Occipital condyle: Articulates with the atlas to form the atlanto-occipital joint. Just above the occipital condyle is the hypoglossal canal, which crosses the occipital bone at a 45° angulated anterolateral trajectory. The hypoglossal canal — and nerve — divides the condylar part of the occipital bone into the condylar compartment, below the hypoglossal canal, and the jugular tubercle compartment, above the hypoglossal canal.

  • Condylar fossa: Often contains the posterior condylar emissary vein. Its bleeding can be brisk and it may be confused with bleeding from the hypoglossal venous plexus, which could misguide the next surgical steps.

  • Jugular tubercle: Serves as the roof of the hypoglossal canal and the floor of the jugular foramen.

• The jugular foramen has three different compartments:

  • Sigmoid (posterior): Contains the sigmoid sinus, the jugular bulb and the meningeal branches of the ascending pharyngeal and occipital arteries.

  • Neural (medial): Accessory (IX), vagus (X) and glossopharyngeal (XI) nerves.

  • Petrosal (anterior): Inferior petrosal sinus.

• The transverse foramen of the atlas (C1) anchors the vertebral artery before it loops medially above the posterior arch of C1 and runs together with the C1 nerve. The VA and C1 nerve are embedded into the vertebral venous plexus and connective tissue, which puts them at risk of inadvertent lesion VA dissection.

Surgical Procedure