30 Open Approaches to the Anterior Skull Base in Children

Oshri Wasserzug, Ari DeRowe, Barak Ringel, Dan M. Fliss

Summary

The wide variety, nature, and extent of pediatric skull base lesions along with its rarity entail customization of the appropriate surgical approach for its extirpation. Also, the anatomical differences, anticipated craniofacial growth, and the significant overall psychosocial effect compared to adults pose a much more difficult therapeutic challenge.

This chapter will review the different open approaches to the anterior skull base while discussing their advantages and disadvantages.

Pediatric, skull base surgery, craniofacial surgery, open approaches

30 Open Approaches to the Anterior Skull Base in Children

30.1 Introduction

Skull base lesions in children and adolescents are rare, and comprise only 6.4% of all skull base surgery. ¹ It includes a wide range of pathological conditions originating from neural, mesenchymal, notochordal, and epithelial origin. ² Anterior skull base lesions dominate, averaging slightly more than 50% of the cases. ³

There are several differences between cranial base lesions and tumors in adults and in children. First, the types of tumors, their biological behavior, and oncologic management vary between adults and children. ⁴ Second, anatomic differences in children may influence the choice of surgical approach. ³ ^, ⁵ ^, ⁶ Third, in addition to the different anatomy, the surgeon should also consider the growth centers in children, trying to avoid damage to these important structures. ⁷

In sharp contradiction to the adult population, the most common lesions of the anterior skull base in the pediatric population are congenital lesions: encephaloceles and fibrous dysplasias. Nevertheless, malignant tumors, of which sarcomas are the most frequent, are not uncommon in children.

Although endoscopic skull base surgery in children is gaining popularity in developed countries, in many cases open surgery is still required. In addition, in developing countries, which accounts for more than 80% of the world’s population, limited access to expensive equipment precludes the use of endoscopic surgery.

The open approaches that are used most frequently for surgical resection of anterior skull base tumors are the transfacial/transmaxillary, subcranial, and subfrontal. Reconstruction of anterior skull base defects is discussed in a separate chapter in this book.

With this large armamentarium of surgical approaches, tailoring the most suitable approach to a specific lesion in regard to its nature, location, and extent is of utmost importance.

In this chapter we review the literature on the current role of open approaches to the anterior skull base in children.

The following approaches are currently applied for surgical extirpation of anterior skull base tumors in children: (1) subfrontal, (2) subcranial, (3) transfacial/transmaxillary, (4) combined subcranial–transfacial approach, (5) combined subcranial–midfacial degloving, and (6) combined subcranial–transorbital. ¹ ^, ³ ^, ⁴ ^, ⁸ ^– ¹⁵

The approaches that are used most widely for surgical resection of anterior skull base tumors are the transfacial/transmaxillary, subcranial, and subfrontal approaches. ³ ^– ⁵

30.2 Bilateral/Unilateral Subfrontal Approach

This approach is primarily used for tumors of the anterior skull base with intracranial involvement. It has the advantage of minimizing brain retraction due to wider exposure of the floor of the anterior cranial fossa.

30.2.1 Surgical Technique

The patient is placed supine with his head held in a Mayfield headholder.
The skin is cut posterior to the frontal hairline from one zygoma to the other (▶ Fig. 30.1), and the scalp flap and the pericranial flap are reflected anteriorly (▶ Fig. 30.2).
Craniotomy is performed involving both the anterior and posterior tables of the frontal sinuses ¹⁶ (▶ Fig. 30.3). If an obliteration of the frontal sinus is performed, the pericranial flap is used after meticulous removal of all visible mucosa.
In cases in which cranialization is carried out, the posterior wall of the frontal sinus is drilled out and the anterior wall osteotomized segment is repositioned in its original location. When the tumor extends more inferiorly into the orbits and the cribriform area, nasal osteotomies are performed along the mid-portion of the nasal bones and along the naso-lacrimal suture line.
The dura is dissected off the bone and then orbital osteotomies are done, i.e., the roof and lateral wall of each orbit are removed. By that stage, the tumor is widely exposed and extirpated.

**Fig. 30.1** The bicoronal incision line. The skin is cut posterior to the frontal hairline from one zygoma to the other.

**Fig. 30.2** The scalp flap is raised and separated from the pericranium. The pericranium is dissected as a pedicled flap in continuity with the periorbit.

**Fig. 30.3** Craniotomy is performed involving both the anterior and posterior tables of the frontal sinuses.

30.3 The Subcranial Approach

The subcranial approach is the most widely used approach to the anterior skull base in our institution.

The main advantage of the subcranial approach is wide exposure of the anterior skull base from below, providing superb access to the sphenoethmoidal, clival, nasal, and orbital regions. Another advantage is minimal manipulation of the frontal lobe and the avoidance of facial scars.

30.3.1 Surgical Technique

A skin incision is made 2 cm behind the hairline with its lateral border being the supra-auricular area and a bicoronal flap is raised in a supraperiostal plane.
The flap is raised anteriorly beyond the glabella and the supraorbital ridges (▶ Fig. 30.4). The periosteum is elevated from the nasal bones, exposing the nasal tip medially and the lacrimal crests laterally (▶ Fig. 30.5).

**Fig. 30.4** The flap is raised anteriorly beyond the glabella and the supraorbital ridges.

**Fig. 30.5** The periosteum is elevated from the nasal bones, exposing the nasal tip medially and the lacrimal crests laterally.

The dissection is then continued superficial to the temporalis fascia laterally, and the supraorbital nerve, vein, and artery are dissected from the supraorbital notch.

Exposure of the roofs and the medial and lateral walls of both orbits is done and the anterior ethmoidal arteries are clipped. The periosteum overlying the nasal bones is dissected. The bicoronal flap is then reflected forward over the face and held in position with fishhooks. ¹⁶
The next step is osteotomy of the anterior or the anterior and posterior walls of the frontal sinus, the proximal segment of the nasal bone, and part of the medial wall of the orbit (▶ Fig. 30.6). Miniplates are applied to enable precise repositioning of the bony fragments at the end of the surgery. A type A (▶ Fig. 30.6) osteotomy signifies osteotomy of the anterior frontal sinus wall and nasal bone that are removed en-bloc. A type B osteotomy signifies drilling burr holes (▶ Fig. 30.7), after which the posterior frontal sinus wall is resected.
The fronto-naso-orbital segment is then extracted (▶ Fig. 30.8) and stored in saline. Bilateral sphenoidotomy and bilateral ethmoidectomy ensues, and by that time the tumor is fully exposed and oncological resection can be undertaken.
Reconstruction begins with the dura, which can be repaired primarily with sutures or using fascia. The fascia is placed in two layers—the first layer is tucked under the dura, and the second layer is aligned to cover the lower surface of the ethmoidal roof and the sphenoidal area (▶ Fig. 30.9).
In order to reduce telecanthus, two threads are guided through the medial canthal ligament and driven underneath the fronto-naso-orbital segment to the contralateral anterior frontal sinus wall and fixed to the plates.
The bony fronto-naso-orbital segment is then repositioned and fixed with titanium miniplates in its original anatomical place (▶ Fig. 30.10).
▶ Fig. 30.11 depicts the subcranial cavity post-subcranial excision of a pediatric sarcoma. The naso-fronto-orbital segment has been elevated. On the right, the superior, medial, and inferior walls of the orbit have been reconstructed with 3D titanium mesh.