How to: Pediatric Endoscopic Transsphenoidal Skull Base Approach and Closure: Technique and Technical Tips

INTRODUCTION

The transsphenoidal corridor is the most common endoscopic endonasal skull base approach, and it involves resection of portions of the anterior wall, posterior wall, and roof of the sphenoid sinus to access the sella, suprasellar, medial cavernous sinus, and clival recess regions. Endoscopic endonasal skull base surgery (EESS) is feasible, safe, and effective for pediatric skull base lesions. Long-term maxillofacial growth does not seem to be impacted by EESS at a young age, but there are some important anatomic considerations in this young population.

The first potential obstacle encountered during pediatric EESS is the relatively narrow nasal aperture in young children. Studies have shown bony piriform aperture width increases slowly in size over time; there is not a single growth spurt after which the aperture increases dramatically. Similarly, the cartilaginous nasal aperture grows slowly with age, with only an average of 2.54 mm diameter increase between the two- and four-year age groups and the 11-13 year age groups. Given these minute changes with age, the nasal aperture is unlikely to be prohibitive to EESS except in very young patients under two years of age or those with other anterior craniofacial dysmorphisms.

Sphenoid sinus pneumatization is also a consideration during pediatric EESS. The process of pneumatization of the sphenoid sinus is variable, but, generally, the sinus does not reach maturity until approximately 10-14 years of age. Pneumatization proceeds in an anterior-to-posterior and caudal-to-cranial direction. Though sphenoid sinuses with a conchal (non-pneumatized) configuration may increase drilling time, studies have shown that sphenoid pneumatization pattern does not affect outcomes in endoscopic skull base surgery in the pediatric population; specifically, it does not impede gross total resection or increase complications.

Perhaps the most important consideration for these cases is the cavernous intercarotid distance. In general, this distance should be at least 1 cm to allow sufficient access to the sella and/or suprasellar spaces. The clival portion of the internal carotid artery tends to have a stable intercarotid distance over time, and, therefore, this distance is generally not of concern in any age group. Patients younger than three or four years may have prohibitively narrow cavernous intercarotid distances; this is the primary reason why EESS is generally reserved for patients four years of age or older.

In this article, we review our pediatric EESS technique in patients with intra-operative high flow cerebrospinal fluid (CSF) leak, with a focus on details that differ from adult transsphenoidal surgery technique.

METHODS

Pre-Operative Evaluation

All patients are referred for CT scan, MRI, ophthalmology, and endocrinology consultations prior to surgery.

Surgical Technique

Following induction of general anesthesia, the endotracheal tube is secured to the left lower face, and the head of the bed is rotated 180 degrees. Cranial fixation pins are applied. The image guidance system is calibrated and accuracy confirmed using bony anatomic landmarks. The patient is then prepped and draped for EESS with the nose, philtrum, and possibly the eyes exposed in the operative field.

The entire approach is performed using a 0-degree endoscope with Endo-Scrub. A 2.7-mm scope may be considered in very young patients if a larger endoscope cannot be accommodated. Lidocaine 0.5%-1.0% with 1:200,000 epinephrine is injected into the head of the middle turbinate, the nasal septum, maxillary line, and into the head of the inferior turbinate bilaterally. A sphenoid injection of local anesthetic is not performed.

Next, a posterior inferior turbinate resection is performed to improve access to the choana bilaterally and provide a reservoir for blood accumulation during dissection. In patients younger than 12 years, there is often adenoid hypertrophy, but we elect not to resect the adenoid during these cases as the adenoid is known to harbor bacteria and biofilms, which could place patients at risk of post-operative infection. Posterior inferior turbinate resection is particularly important on the side where the nasoseptal flap harvest will take place. The inferior turbinates are laterally outfractured first. The microdebrider is used to resect the posterior third of the inferior turbinate. The decision to resect
the turbinate on the contralateral side of the flap harvest is made on a case-by-case basis depending on the size of the working space. Care must be taken to avoid injury to the torus tubarius on either side.

Bilateral endoscopic sphenoidotomies are performed next. The middle turbinates are lateralized using a Freer elevator and preserved throughout the case, even in very young patients. Next, the superior turbinate is identified on each side, and the lower one-third to one-half of it is resected using Tru-Cut instrumentation. The superior portion of the superior turbinate is preserved as this contains some olfactory epithelia. The natural sphenoid ostium is identified just medial to the superior turbinate, and this is expanded medially toward the nasal septum using a 1 Kerrison. In this area, care must be taken to avoid injury to the posterior nasal septal artery, which will serve as the pedicle for the nasoseptal flap. The pedicle runs between the sphenoid ostium and the arch of the choanae.

In most cases, a left pedicled nasoseptal flap is performed unless there is a significant nasoseptal deviation or a left pterygomaxillary fossa approach is necessary. Using a long-protected needle tip cautery at 13 watts, the inferior incision is made first. The incision is carried along the arch of the choana toward the nasal floor and then anteriorly to the mucocutaneous junction. The incision can be extended along the floor of the nose toward the inferior meatus to widen the flap if necessary, depending on the expected skull base defect. Next, a superior incision is made beginning at the level of the sphenoid ostium. This horizontal incision is carried anteriorly onto the posterior septum, being careful to stay parallel to the floor of the nose to avoid injury to the olfactory mucosa. At the level of the head of the middle turbinate, the incision is carried more superiorly because there is no olfactory mucosa in this area. The superior incision is joined with the anterior mucocutaneous incision. Using a combination of the Cottle and Freer elevators, the nasoseptal flap is elevated in a submucoperichondrial plane anteriorly and submucoperiosteal plane posteriorly to the level of the choanae. Once the nasoseptal flap is completely mobilized, it is rotated into the nasopharynx for storage during the surgical resection. A pledget can be placed over the flap to avoid inadvertent injury.

A posterior septectomy is performed next. Beginning at the head of the left middle turbinate, the Cottle elevator is used to make a vertical incision in the quadrangular cartilage. The posterior cartilage is resected until the osteocartilaginous junction is identified. The posterior superior septal mucosa (olfactory cleft mucosa) is reflected superiorly and preserved throughout the case. The posterior septal bone (vomer) is removed in an anterior-to-posterior direction until the sphenoid rostrum is encountered. A portion of this septal bone, approximately 2 × 2 cm, is removed and set aside for possible use during reconstruction at the end of the case. The sphenoid rostrum is resected using a combination of Kerrison and straight Tru-Cut instrumentation. In older patients, a protected diamond drill can be used if the bone is firm. Once the sphenoid rostrum is removed, there is one large sphenoid cavity. The septations within the sphenoid sinus are removed using Tru-Cut instrumentation, with care taken not to twist the bony septations, as they may be attached to the carotid or optic canals.

The sphenoid cavity is then expanded in all directions to allow unobstructed access to the targeted area. Once a nasoseptal flap is safely harvested, the mucosa overlying the contralateral sphenoid can be resected if necessary to improve access to the sphenoid and skull base. Alternatively, a “rescue flap” can be performed to save this tissue. In this case, the superior portion of a nasoseptal flap incision is made, and the mucosa is reflected inferiorly during the case. At the conclusion, this mucosa is reflected back to its native position.

Just anterior to the face of the sphenoid cavity, there will be posterior ethmoid air cells, which should be resected to improve lateral access. If the access is still narrow, a total ethmoidectomy can be completed to increase lateralization of the middle turbinate.

Once the entire anterior wall of the sphenoid sinus is removed so it is nearly flush with the floor of the sinus, and the planum and opticocarotid recess are clearly visible, the neurosurgical team will perform the intracranial portions of the procedure.

Following surgical resection, a multilayered skull base reconstruction is performed. In general, the closure begins with DuraGen inlay and onlay grafts, followed by septal bone graft reconstruction of the bony sellar/suprasellar defect. Any residual sphenoid septations are curettaged to minimize size and remove any possible residual sinus mucosa. The nasoseptal flap is then rotated into place to cover the entire defect. The mucosal surface of the graft must face intranasally, and there must be direct contact of the flap with bone. To ensure contact, a smooth ring curette is used to press the flap onto the bone, beginning at the pedicle and extending to its distal end. Surgicel is placed around the flap to help keep it in place. Next, tissue glue is laid over the graft and Surgicel. Two pieces of NasoPore are placed, with one overlying the flap and another small piece over the pedicle. Silicone splints coated in mupirocin are placed bilaterally. These are secured in place using a transseptal 3-0 silk suture stitch with the knot tied on the left. An orogastric tube is placed to suction out the stomach contents.

Patients are extubated at the conclusion of the case and admitted to the intensive care unit for neurologic and endocrine monitoring.

RESULTS

From January 1, 2019, to December 31, 2021, 28 pediatric patients had sellar and/or suprasellar lesions and underwent transsphenoidal surgery with resultant high-flow CSF leaks. The mean age was 11.6 years (range 4.2–17.8 years). Each patient underwent surgical resection with nasoseptal flap reconstruction at our institution over the three-year study period. There were no cases of post-operative cerebrospinal fluid leak or nasoseptal flap failure. No cases had to be converted to craniotomy.