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Foramen magnum and inferior clivus


Core Procedures

  • Far-lateral approach and transcondylar extension

  • Endoscopic endonasal approach to the inferior clivus and foramen magnum

Surgical surface anatomy

The C1 transverse process can often be palpated adjacent to the mastoid process; it acts as a reliable landmark for C1 and the location of the vertebral artery during muscular dissection.

Clinical anatomy

Multiple approaches are directed at the foramen magnum (FM) and inferior clivus from both ventral and dorsal directions. An appreciation of locoregional osseous, muscular and neurovascular anatomy is instrumental in performing these approaches safely. Among posteriorly directed approaches, a simple midline posterior suboccipital approach to the foramen magnum has been well described and is commonly used for FM decompression, e.g. for Chiari malformation. The surgically relevant anatomy for performing a far lateral craniotomy and its transcondylar extension, as well as the anatomical principles surrounding a ventral endoscopic endonasal approach to the anterior FM, are discussed here. Other approaches to this region are outside the scope of this chapter.

Surgical approaches and considerations

Far-lateral approach: basic and transcondylar extension

Indications

In its basic form, the far-lateral approach includes a suboccipital craniotomy and C1 hemi- or complete laminectomy without removal of parts of the occipital condyle, thereby providing access to lesions located along the posterior aspect of the FM, e.g. a meningioma. This approach can then be tailored to perform either a transcondylar exposure, in which removal of the posterior part of the occipital condyle improves access to the lower clivus and the area anterior to the medulla oblongata, or a supracondylar transtubercular exposure, involving drilling of the hypoglossal canal followed by the jugular tubercle. The latter exposure provides improved access to the anterior aspect of the brainstem and visualization of the origin of the poster­ior inferior cerebellar artery (PICA) from the vertebral artery (e.g. as may be necessary for clipping a PICA aneurysm). A third variation is a paracondylar exposure (without drilling of the occipital condyle), which provides access to the posterior part of the jugular foramen and can be combined with a transmastoid approach.

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