Summary
Pediatric skull base and craniofacial surgery presents a unique challenge since the potential benefits of therapy must be balanced against the cumulative impact of treatment on craniofacial growth and the potential for serious psychosocial issues.
The unique demands and physiologic consequences of skull base surgery in pediatrics merit special attention and the distinctive anatomical features of the pediatric skull base must be well understood and anticipated for the prevention of distinct surgical complications.
2 The Distinctive Anatomical Features of the Pediatric Skull Base
2.1 Introduction
Compared to adults, the size of the cranial base and maxillofacial complex in children is smaller, the cranial bone is thinner, and the floor of the frontal and middle cranial fossa may be flatter. 1 Anatomic landmarks that are found in the fully developed cranium of adults can be absent or different in babies. Examples of those are a more anteriorly located pterion, an absent superior orbital fissure, and undeveloped mastoid process. In addition, neurovascular elements in children are thinner and more fragile than in adults, 2 whereas the brain itself is denser and less amendable to physical manipulation.
2.2 Cranial Fossae
The human skull grows rapidly during the first four years of life (▶ Fig. 2.1). The maximal growth rate at birth slopes down to a minimum in pre-puberty, and returns to a smaller second spike at puberty. The growth of the skull base is slower than that of the calvaria, with the anterior, middle, and posterior fossae each developing at different rates. The anterior fossa undergoes ossification starting at birth, when it is still cartilaginous, until the third year of life when it nearly attains adult structure. During the second year of life the mastoid starts to project inferiorly from the squamous and petrous parts of the temporal bone and undergoes pneumatization up until adolescence, with the middle fossa reaching its final size approximately at the age of 10. The posterior fossa is the last to attain mature form. It is comprised mainly of the occipital bone with a lesser contribution of the sphenoid anteriorly and the temporal bone laterally. There are four synchondroses which begin to fuse during the second year of life but do not fuse completely until the age of 4 at the posterior junction (exo-occipital and squamous segment) and age of 8 at the anterior junction (basi-occipital and exo-occipital). At the age of 10 the posterior fossa nearly achieves adult proportions. The spheno-occipital synchondrosis, which is the main axis of skull base growth, fuses at the ages 12 to 15 and ossifies only at early adulthood.
2.3 Anterior Skull Base
All the adult structures are present at the small nasal cavity of the newborn, resulting in a relatively narrow and delicate airway passage. The nasal turbinates are voluminous such that the middle meatus is hardly functional. Some of the children are born with a supreme turbinate that usually involutes with growth. The cavum in the newborn lies low and the choana is round with a 6 mm diameter. Its size grows and its shape changes until the age of 12 years, when the sphenoid sinus is usually well developed. The opening of the Eustachian tube is first located behind the inferior turbinate at the level of the hard palate. At the age of 4 years it reaches its final location behind the posterior end of the middle turbinate. 3
2.4 Paranasal Sinus Development
The paranasal sinus development is a complex and extremely variable process (Table 2.1). It begins with evaginations from the lateral nasal wall (except from the sphenoid sinus). During the seventh week of gestation several projections develop into the nasal capsule; the maxilloturbinals form the inferior turbinate; the ethmoturbinals form the middle, superior, and supreme (26%) turbinates. The furrows between those projections form the nasal meatus and the infundibulum. The nasoturbinal develops into the agger nasi; and the uncinate process develops on the superior–posterior border of the agger nasi. The attachments of these structures to the lateral nasal wall form the lamellae. During the first pneumatization, the furrows continue to grow and contribute to the pneumatization of the ethmoid bone, maxillary bone, frontal bone, and agger nasi. The second pneumatization occurs postnatally, mostly completed by the age of 12 to 14 years. 4
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