Skull Base Reconstruction Following Resection of Skull Base Chordomas and Chondrosarcomas

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Introduction

Over the past decades, the indications for endoscopic endonasal surgery expanded to include benign and malignant skull base lesions. Many surgical approaches have been described to resect petroclival chordomas and chondrosarcomas; however, expanded endoscopic endonasal approaches (EEA) are the least invasive, have equal or superior resection rates, and fewer complications and adverse sequelae. The progression of EEA for skull base lesions was made possible by advancements in reconstruction of the dura and skull base, and more specifically by the popularization of the nasoseptal flap, use of which has decreased the frequency of postoperative cerebrospinal fluid leak to that of open approaches. In this chapter, we will discuss current options for reconstructing the skull base following resection of petroclival chordomas and chondrosarcomas, whether an open or an endoscopic endonasal approach is used.

Consideration and Goals of Skull Base Reconstruction

Many surgical approaches have been described for resection of petroclival chordomas and chondrosarcomas: anterior transcervical retropharyngeal, transseptal–transsphenoidal, pterional, retromastoid, lateral suboccipital, subfrontal, extended frontal, transbasal, subtemporal–infratemporal, presigmoid–subtemporal, transpetrosal, lateral transcondylar, and transoral–transpalatopharyngeal.

However, over the past two decades, endoscopic endonasal approaches to the skull base have proven to be an effective and safe alternative to open approaches in terms of oncological outcomes, adverse sequelae, complications, and mortality; thus, these techniques have gained wide popularity. Acceptance of endoscopic approaches to expose and resect petroclival chordomas and chondrosarcomas was made possible by the genesis of multidisciplinary teams composed of otolaryngologists and neurosurgeons well trained in endoscopic techniques, and allied specialists (i.e., medical and radiation oncologists, neuroradiologists, neuropathologists, neuroophthalmologists, endocrinologists). Although accumulation of experience with endoscopic endonasal management of benign skull base lesions, acceptance of piecemeal resection of malignant tumors, and technological advances such as surgical navigation and endonasal-powered instrumentation contributed to this evolution, improvements in the success rate for endoscopic repair of cerebrospinal fluid (CSF) leaks secured acceptance of extended endoscopic endonasal resections of chordomas and chondrosarcomas.

Skull base defects can be divided into extradural and intradural. Intradural defects are further subdivided into low- or high-flow leaks. A high-flow CSF leak is defined by the communication of multiple subarachnoid cisterns or a ventricle with the dural defect. Extradural defects are those created by defined by skull base tumor resection that does not out disrupt and cause a CSF leak. Reconstruction following resection of chordomas and chondrosarcomas of the petroclival area is particularly challenging because large defects and high CSF flow rates are often created and because the vector of gravitational force is tangential rather than orthogonal to the interface between closure material and the dura.

Regardless of the approach used to resect the primary tumor, open or endonasal, the goals of reconstruction of skull base defects are the same:

• Water and airtight closure to prevent CSF leak, pneumocephalus, meningitis, and other intracranial infections

• Complete separation of the cranial cavity and brain from the sinonasal tract

• Protection of brain, cranial nerves, and intracranial vessels from desiccation and infection

• Acceleration of the healing process, especially if the patient will undergo postoperative external beam irradiation

• Preservation and rehabilitation of function

• Preservation or restoration of cosmesis

• Avoidance of dead spaces that may contribute to hematomas and infection.

Critical factors to be considered when reconstructing defects following resection of skul base lesions are:

• Size and location of the bony and dural defect:

  Small dural defects are commonly but not universally defined as less than 1 cm in diameter whereas large defects are defined as larger than 3 cm in diameter.

• High- versus low-flow CSF leaks

• Prior radiation therapy or anticipated postoperative radiotherapy

• Previous sinonasal or skull base surgery

• Extent of invasion of sinonasal structures

• Morbid obesity, obstructive sleep apnea (and pressure required for CPAP), and the possibility of increased CSF pressure as suggested by imaging findings (e.g., dilated ventricles, empty sella, expanded optic nerve sheaths)

• Ideally, the route for tumor resection, whether endonasal or open, should be adequate for reconstructing the skull base.

Reconstruction of the Skull Base

The authors favor reconstruction of skull base defects using pedicled vascular flaps, multilayer reconstruction techniques, and the aforementioned principles, especially for central skull base defects. However, multiple options available to reconstruct the skull base bone and dura can be divided as discussed below.

Use of Synthetic and Heterologous Materials

Heterologous materials are commonly used to reconstruct the dural and skull base defects. They can either be used as a single layer or as part of a multilayer closure. Germani et al. described the reconstruction of large skull base defects (>2 cm) using a single layer of acellular dermal graft placed in inlay or onlay fashion with a 97% success rate. We favor the use of collagen matrix (e.g., DuraGen, Integra Life Sciences, Plainsboro, NJ, USA) ( Fig. 22.1 ). The texture and pliability of collagen matrix permit its safe placement around critical neurovascular structures. It is used to obliterate intradural dead space or as the subdural inlay of a multilayer closure ( Fig. 22.1 ). The most commonly used synthetic heterologous materials in skull base surgery are summarized in Table 22.1 .

Table 22.1

Synthetic Grafts

Generic Name	Ultra Pure Collagen	Acellular Dermal Allograft	Small Intestinal Submucosa (SIS)
Brand Name	DuraGen Plus	AlloDerm	Cook Biodesign
Composition	Ultra Pure Collagen (Type I) sourced from bovine Achilles tendon	Acellular dermal matrix processed from banked human cadaver skin	Nonporous, absorbable, multilayer sheet of extracellular collagen matrix derived from porcine small intestinal submucosa
Thickness	3–4.5 mm	Thin: 0.23–0.51 mm
		Medium: 0.53–1.02 mm
		Thick: 1.04–2.28 mm
		Extra Thick: 2.30–3.30 mm
Advantages	Expandable with fluids preventing CSF pockets formation and dead spaces	Can be used as a sole graft material for large dural defects (>2 cm)

Vascularized Flaps

Vascularized flaps for reconstructing the ventral skull base are divided into intranasal or local and extranasal or regional.

The intranasal/local flaps include:

• Posterior pedicled nasoseptal or Hadad–Bassagaisteguy flap

• Bilateral nasoseptal flap (“Janus flap”)

• Reverse nasoseptal flap (Caicedo flap)

• Posterior pedicle inferior turbinate flap

• Posterior pedicle middle turbinate flap

• Lateral nasal wall flaps—anterior pedicled or Hadad–Bassagaisteguy flap 2 (HBF2) and posterior pedicled or Carrau–Hadad flap (CHF)

The extranasal/regional flaps include:

• Temporoparietal fascia flap

• Pericranial and galeopericranial flap

• Occipital galeopericranial flap

• Temporalis muscle flap

• Palatal flap (Oliver pedicled palatal flap)

• Pedicled facial buccinator and facial artery musculomucosal flap

• Salpingopharyngeus flap (Dicle flap)

The main intranasal flaps suitable for reconstruction of petroclival defects include the nasoseptal flap, the posteriorly based lateral nasal wall flap, and the inferior turbinate flap. The main extranasal flaps are the temporoparietal fascia and the pericranial flaps. We will discuss all the available vascularized flaps with a special focus on the main ones.

Nasoseptal or Hadad–Bassagaisteguy Flap

Many prefer mucoperichondrial/mucoperiosteal nasoseptal flap (NSF) ( Figs. 22.2 and 22.3 ; Case 1 ; Case 2 ) for reconstructing skull base defects following an endoscopic endonasal tumor resection. It is a vascular pedicle flap based on the posterior nasoseptal artery, a branch of the posterior septal artery, and a terminal branch of the sphenopalatine artery. The NSF can reconstruct large skull base defects. Overall rates of postoperative CSF leaks dropped to less than 5% after adopting this flap for endoscopic reconstruction of the ventral skull base defects. Postoperative CSF leaks rates for high-flow leaks remain slightly higher, ranging from 5% to 7%.

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