**4. Tumors of the cerebellopontine angle, jugular foramen, and craniovertebral junction**

## **4.1 Introduction**

The majority of pediatric brain tumors are located in the posterior fossa, with the most common pathologies being juvenile pilocytic astrocytomas, medulloblastomas, and ependymomas, all of which may require complex approaches when expansive. In this chapter, however, we will discuss primarily extra-axial tumors that specifically involve the skull base. Far lateral or ELITE (extreme lateral infrajugular transcondylar-transtubercular) for ventrolateral pathology, transpetrous approaches for access to the cerebellopontine angle, and anterior approaches can all be used in appropriate situations to maximize exposure to facilitate safe resection and preservation of critical neural structures. As above, we work closely with our otolaryngology partners to assist with transpetrous approaches when indicated and for endoscopic anterior approaches to the clivus and ventral brainstem.

#### **4.2 Regional anatomy**

A comprehensive knowledge of the relevant bony and vascular anatomy is required prior to performing approaches to the posterior fossa. The vertebral artery takes a lateral to medial course after exiting from the transverse foramen of C1 and travels in a groove along the superior edge of the posterior arch of C1 prior to

entering the dura. The artery at this level is sheathed in an organized venous plexus which can bleed briskly but is easily stopped with hemostatic agents. If necessary, the vertebral artery can be mobilized by removing the posterior wall of the transverse foramen which further exposes the occipital condyle. Intradurally, the transverse and sigmoid venous sinuses frame the borders of the posterior fossa. Children less than two years old are more likely to have a persistent occipital sinus, and children with an occipital sinus are more likely to have an absent transverse sinus [28].

The occipital condyles form the connection of C1 to the foramen magnum laterally. The hypoglossal canal runs anterolaterally through the condyle and marks the border of the posterior and middle third of the condyle. Radiographic review of 50 pediatric CT scans demonstrated relative stability in the size and depth of the occipital condyle and hypoglossal canal throughout pediatric development. The jugular tubercle is located superiorly and anteriorly to the hypoglossal canal. Conversely, the jugular tubercle demonstrates significant growth during childhood and only measures 65% of adult size prior to puberty, therefore its removal may not confer as much benefit for lateral skull base approaches in younger children [29].

Laterally, the skull base is defined by the petrous pyramid located between the sphenoid and occipital bones, and houses the facial canal, the petrous carotid artery, and the osseous structures of the inner ear. The superior surface of the petrous bone forms the floor of the middle fossa, and the posterior wall of bone forms the anterior wall of the posterior cranial fossa. The internal auditory meatus houses the meatal segment of the facial nerve and the vestibulocochlear nerve as they exit the cerebellopontine angle and enter the middle of the petrous bone. The cochlea is located just anterior to the fundus and the otic capsule housing the bony labyrinth is located posterior to the internal auditory canal and above the jugular foramen, and can be easily delineated from the surrounding mastoid bone by its yellowish, hard cortical surface.
