28.1 Introduction

Endoscopic endonasal approaches (EEA) to skull base lesions in the pediatric population is a new and emerging field. The first clinical studies on this issue began to be published just around a decade ago. ¹ Because of that, there are no guidelines or solid consensuses in this area, and the principles and techniques of EEA and endoscopic skull base reconstruction (ESBR) in children have been largely imported from the experience already gained with adults. ²

Techniques used for ESBR in children may vary largely, depending mainly on the experience and preferences of the surgical team and on the case itself. Whatever the strategy used, it is essential to completely separate the intracranial content from the nasal cavity and consequently prevent postoperative complications. This is usually achieved after a watertight multilayer closure of the skull base defect, especially for those large openings associated with high-flow cerebrospinal fluid (CSF) leaks. ^{3 ,​ 4}

28.2 Multilayer ESBR in Children: Principles, Materials, and Peculiarities

Multilayer ESBR, rather than a technique itself, should be considered a surgical reasoning or principle—as more layers are correctly selected and placed, the greater are the chances of success. The mnemonic “triple-F” technique reminds surgeons of the most commonly used materials for multilayer ESBR: Fat, Fascia lata, and Flap. ⁴

Fat serves as an autologous graft, which is useful to fill large surgical cavities. Fat grafts can be most commonly harvested from the following sites:

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  Abdominal wall, via an infraumbilical or suprapubic incision: it provides large volumes of fat and resulting scars are minimal and discrete.

  
  
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  Thigh, via a lateral longitudinal incision: it gives good amounts of fat, except in patients with very low body mass indexes. It is the site of choice when fascia lata is also needed, although it may result in unwanted scars.

Fascia lata can also be readily acquired from the lateral aspect of the thigh. It is an excellent autologous graft that is most commonly used as inlay and/or onlay graft to nicely close dural openings. Synthetic dural substitutes (e.g., DuraGen) might be used as alternatives or complements to fascia lata. They are quite useful when fascia lata is not sufficiently available (e.g., in young infants with very large skull base defects) or when skin incisions are undesired.

Harder grafts might also be used to reinforce the skull base closure. Pieces of bone and cartilage harvested from the nasal septum are useful in this context. There is some concern, however, regarding the effects that removal of these grafts might exert on children’s nasal and craniofacial growth. Most recent studies indicate that septoplasty can be safely performed in children ≥ 6 years of age (and possibly in younger infants), without adverse consequences to their nasal and craniofacial development. ⁵ Therefore, such grafts are best used when septoplasty is required prior to ESBR (e.g., when a nasal septum deviation precludes EEA) or when reinforcement of the skull base closure is extremely desirable. ⁶

Since the nasoseptal flap (NSF) was described, it has become the workhorse for ESBR, including the pediatric population. ⁷ It is a versatile flap and should be used whenever possible. ⁸ It is known, however, that septal growth occurs more rapidly between 10 and 13 years of age and nasal septum reaches adult measures only in patients ≥14 years of age. Because of that, NSF may not cover the more anterior skull base or even sellar defects in very young infants. ⁹ In such situations, harvesting other mucosal flaps, like the lateral nasal wall flap, and using free mucosal grafts, taken from nasal floor or from middle turbinates, are very well-accepted alternatives to the classical NSF.

28.3 Decision-Making and Operative Technique

Some factors should guide the decision on how to perform a multilayer ESBR in children. Besides the patient’s age and diagnosis, the following variables must be considered ⁸ :

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  History of prior radiotherapy and/or nasal surgeries.

  
  
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  Location, width, and depth of the skull base defect.

  
  
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  Occurrence of intraoperative dural violation and high-flow CSF leak.

  
  
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  Presence and thickness of bony and dural ledges around the skull base defect.

  
  
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  Availability of grafts, synthetic materials, and regional mucosal flaps.

For small skull base defects (diameter < 1 cm) with low-flow CSF leaks, the use of various layers of grafts and flaps is not usually necessary. However, medium to large defects (diameter ≥ 1–3 cm) located in the anterior cranial fossa or sellar region deserve a bilayer or multilayer reconstruction technique. Examples of how such defects might be reconstructed are depicted in ▶ Fig. 28.1. ^{6 ,​ 10}

The best indication for the multilayer “triple-F” technique is for very large skull base defects, like those resulting from extirpation of clival chordomas, which are usually associated with high-flow CSF leak. ESBR of defects like these are challenging, especially in the pediatric population. For such cases, performing a watertight closure that necessarily includes a vascularized mucosal flap is key. ^{4 ,​ 11}

Reconstruction should begin with the obliteration of any large surgical cavity with fat. Besides preventing the formation of dead spaces, fat grafts also avoid seeping of CSF through the borders of the defect, because of its hydrophobic properties. When large intradural tumors have been removed, fat can also be carefully placed intradurally, without putting neurovascular structures at risk. After that, fascia lata and/or dural substitutes are layered in an inlay or onlay fashion. In some cases, more fat might be layered or used to obliterate normal cavities, which increases the reach of pedicled mucosal flaps. Finally, the NSF is placed on top of the other layers.

There are various other ways in which the multiple layers can be placed. Some examples can be appreciated in ▶ Fig. 28.2 and ▶ Fig. 28.3.