Steps of the Expanded Extreme Lateral Approach: A Systematic and Consequential Anatomical Description

Introduction: Variations of the extreme lateral approach vary from minimally aggressive to the most aggressive. Considering different pathologies, no single source systematically unifies all the specific steps for the most aggressive surgical variation. This study systematically and qualitatively analyzed an expanded extreme lateral approach (EELA) to assess its surgical and anatomical boundaries. Consequential steps of the EELA are detailed, maximal safe surgical borders are elucidated and optimal visualized anatomy is standardized.

Methods: EELA was completed in five cadaveric specimens with maximal exposure of anatomical boundaries. All dissection steps were systematically completed and recorded, ensuring homogeneity in approach. Dissection steps and important anatomical landmarks were described.

Results: Cutaneous and muscles dissection: inverted U-shaped incision was performed. Muscular dissection was completed lateral to medial, except along the sternocleidomastoid muscle being reflected laterally. This prevents visual obstruction of the surgical corridor by muscle layers and improves surgical view.

Nerve identification in the carotid sheath: cranial nerves can be identified in the carotid sheath. CN XI is the first nerve identified as it courses toward the sternocleidomastoid muscle and can be traced backward into the carotid sheath. Identification of CN XII in the carotid sheath is clarified by visualization of the C1 nerve root where it runs along the carotid sheath giving a common branch to CN XII. CN IX is the most deeply seated nerve and courses closest to the carotid artery along its posterior surface. CN X can be identified by following CN XI in the distal to proximal direction which runs adjacent to it.

Craniotomy, craniectomy and C1 drilling: craniotomy can be performed safely by identifying the posterior condylar vein and posterior point on the digastric groove. A line interconnecting these two points represents a landmark for a safe zone, where drilling posterior to this will not cause injury to the sigmoid sinus.

Following identification of the facial nerve exiting the skull base, drilling the tip of the mastoid process facilitates optimal surgical visualization. Safe resection of the condyle and C1 vertebra can be performed after the vertebral artery is freed from the C1 foramen and mobilized medially. Extradural drilling of the jugular tubercle aids in accessing the front of the medulla and inferior pons. Resection of the C1 lateral mass exposes the odontoid process and the lower clivus. It is imperative to understand the borders of the clival drilling while staying uniplanar with the drilling level. Following resection of the bony structures, a surgical corridor is created providing maximal access to the dorsolateral medulla and, to a lesser extent, the ventral medulla and inferior pons.

Conclusion: This stepwise, systematic, and consequential anatomic study combines and unifies details of one of the most aggressive (expanded) versions of the extreme lateral approach, the EELA, but also produces maximal surgical visualization and operative maneuverability. EELA should be considered when dealing with large destructive intra- and extracranial lesions at the craniovertebral junction and jugular foramen. Craniocervical fixation is an integral consideration when proposing the use of this radical but effective skull base approach

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Publication History

Article published online:
12 February 2021