10.1 Introduction

The development of minimally invasive transcranial and endonasal keyhole approaches to the skull base has progressed significantly over the past few decades. These developments have made the approaches to the parasellar region safer and less invasive. Two approaches, specifically, have risen with the popularity of minimally invasive techniques. The approaches are the endonasal transsphenoidal approach and the subfrontal approach through an eyebrow incision. Here, we dissect the factors that help decide which approach is appropriate for varying pathologies in the pediatric population.

10.2 Specific Pediatric Considerations

The three factors that deserve special attention in the pediatric population are the concerns with the growing skull, the pyriform aperture width, and the development of the paranasal sinuses. Any cranial opening that bridges a skull suture has the potential to alter growth patterns. Done properly, the eyebrow craniotomy should not transgress any calvarial suture and, therefore, should not alter any of the normal growth patterns of the pediatric skull.

Many of the instruments designed for extended endonasal surgery are either larger or the same diameter as the endoscope and when the surgery requires more than one instrument, cluttering will occur and may impede the natural fluidity of surgery. One has to imagine a scenario where the carotid artery is injured and several suction instruments and endoscopes are urgently needed through two extremely small apertures. If the size of the pyriform aperture is limiting the rapid and unimpeded passage of instruments to the skull base, the result could be disastrous. Consequently, our recommendation is that the endonasal approach to the parasellar region should be reserved for children with pyriform apertures greater than 6 mm in diameter.

The sphenoid sinus normally reaches half of its adult size by the age of 7 years, reaching its maximal size at the end of the adolescent growth spurt (▶ Fig. 10.1). ¹ It goes without saying that the pneumatization of the sphenoid sinus provides an ideal, though not absolutely necessary, operative corridor to perform a routine transsphenoidal approach to the sellar region. Many times, however, the sellar region can still be approached through a variant of the presellar or conchal sphenoid sinus. In direct correlation with the sphenoid sinus pneumatization is the development of the bony impressions of the internal carotid artery and the optic nerves in the sphenoid bone. These protuberances provide helpful landmarks for the surgeon and are useful in the anatomical orientation necessary to avoid neurovascular injuries. When absent in an underdeveloped sphenoid sinus, there is added risk of disorientation and subsequent injury. Other anatomical, perhaps more reliable, landmarks such as the Vidian canal, orbital apex, medial orbital wall, sphenoid roof, and paraclival carotid may mitigate this risk. As the sphenoid sinus grows, it also expands the intercarotid distance—the horizontal distance between each of the internal carotid arteries. An average adult’s intercarotid distance is between 12 and 18 mm (▶ Fig. 10.2). ² It has been studied that an intercarotid distance less than 10 mm would make transsphenoidal surgery more difficult, which is approximately the size of a normal 3- to 4-year-old child’s intercarotid distance. ^{2 ,​ 3} A narrow intercarotid corridor is not unique to the pediatric population but certainly encountered more often in the diminutive pediatric skull base. For pathology that extends above the diaphragma sellae, an intercarotid distance greater than 15 mm is mandatory for facile and safe instrument manipulation.

When one combines all these pediatric requirements, a suitable candidate for the endonasal approach to the parasellar region is a patient older than 7 years of age. This will vary by the size of the child and the size of the nose, but as a general rule, any complex parasellar pathology in a child younger than 7 years should be approached transcranially.

10.3 The Two-Point Rule

As a general rule, most tumors have a long axis. In other words, tumors are rarely perfectly round and more often than not are oval or even cylindrical. If you mark both extreme ends of the tumor and draw a line between the points and then carry that line to the surface, it will give some indication as to the best approach. In ▶ Fig. 10.3, the long axis of the tumor projects to the coronal suture. The best trajectory for this craniopharyngioma is a transcallosal, transforaminal approach. Conversely, the long axis of the tumor in ▶ Fig. 10.4, as seen best on the axial images, when carried to the surface, projects to the eyebrow. Finally, the long axis of the tumor in ▶ Fig. 10.5 projects to the tip of the nose and hence should be removed by an endonasal approach. When a tumor has several axes, the endoscope is invaluable in assisting the surgeon to look around corners and remove those parts of the tumor that are hidden from the limited line of view afforded by the microscope (▶ Fig. 10.3c, d).

10.4 The Optic Chiasm

A high-resolution midsagittal MRI image may show the position of the optic chiasm. When the chiasm is prefixed, it diminishes the prechiasmatic space and thereby limits the corridors by which one reaches a suprasellar lesion transcranially. ▶ Fig. 10.6 shows a tumor that would be ideal for an endonasal approach. The chiasm is prefixed, the sphenoid sinus is well aerated, and the long axis of the tumor projects to the tip of the nose. Conversely, the tumor in ▶ Fig. 10.7 would be ideally approached through an eyebrow incision and a subfrontal trajectory because the optic chiasm is in the normal position, the sphenoid sinus is poorly aerated, and the long axis of the tumor is in the anteroposterior plane.