Favorable Anatomy

For tumors larger than 4 cm in diameter and 80 cm³, gross total resection is feasible using a transcranial approach. ²

Limitations

Transcranial approaches may require significant brain retraction to reach the sella. Tumors that extend into the sphenoid sinus and nasal cavity may be more challenging from this approach.

Favorable Anatomy

A purely endoscopic endonasal approach is favorable for tumors with extracranial extension into the paranasal sinuses and can be used to access the transsphenoidal, transethmoidal, and transpterygoid compartments. When tumors have significant extension into the third and lateral ventricle, adequate visualization can be challenging with just the endoscope. ³ Removal of the tuberculum sellae and planum sphenoidale in an extended transsphenoidal approach allows access to the suprasellar cistern and third ventricle using angled endoscopes. ³

Limitations

Tumors that extend into the lateral ventricle are difficult to access from a purely endoscopic endonasal approach. Lateral extension beyond the internal carotid arteries prohibits gross total resection using a purely endoscopic endonasal approach. ⁴ A craniotomy may be required for tumors with lateral extension beyond the lamina papyracea, especially those requiring an orbital extenteration. ⁵ For very small children, in particular, an endoscopic endonasal approach may be limited by the small intercarotid distance and lack of a pneumatized sella. Pneumatization of the sella begins as early as 2 months of age but may not be complete until about 9 years. ⁶

Favorable Anatomy

Combined approaches allow a more extensive resection while limiting damage to surrounding anatomy. They should be used for extensive tumor growth, either infrasellar or suprasellar. ⁴ For tumors invading the orbital or periorbital regions, optic canal, cavernous sinus, or anterior and middle fossae, a combined approach may expand access into different corridors. If a single approach does not allow safe resection, and the goal is gross total resection, then a planned combined approach may be indicated. Combined approaches may benefit from the advantages while reducing the disadvantages of each approach used separately.

Endoscopic approaches can access skull base lesions from the posterior table of the frontal sinus to the foramen magnum. The transcranial portion of a combined procedure typically adds a subfrontal, a pterional, or an orbitozygomatic craniotomy. ³ An endoscopic endonasal approach can even be combined with a retrosigmoid approach. ⁴ Endoscopic approaches may be limited laterally at the frontal sinus and in the anterior cranial fossa; exposure lateral to the midpupillary line is limited. In the parasellar region, extension of tumors lateral to the internal carotid artery is a relative contraindication to an endoscopic approach. In transpterygoid approaches to the pterygopalatine fossa and infratemporal fossa, extensive tumor involvement of the middle fossa dura or temporal lobe may contraindicate a solely endoscopic approach. A combined approach can be also used after a failed single approach, either in the near term if one approach has been unsuccessful or later, when recurrent growth favors one approach over another. Combined approaches are most often undertaken in attempt to achieve gross total resection.

Tumor Pathology

Certain tumor subtypes may have consistencies more favorable for one approach over another. Combined approaches are particularly useful for malignant skull base tumors such as esthesioneuroblastomas and clival chordomas, and for frontoethmoidal osteomas and giant pituitary adenomas. Combined approaches may be favored for highly vascular lesions, such as intradural juvenile nasopharyngeal angiofibromas (JNA), where an endoscopic-only approach may compromise the surgeon’s ability to control surgical bleeding. ^{1 ,​ 2 ,​ 3 ,​ 4 ,​ 5 ,​ 7} For malignant tumors, in particular, achieving negative tumor margins is crucial for disease control. ⁵ Sinonasal carcinomas widely invading brain may be more safely managed with a combined approach. Combined approaches have also been used for sphenoid wing meningiomas with inferior and lateral invasion of the paranasal sinuses; these tumors can widely involve dura, the transcranial resection can result in a high rate of cerebrospinal fluid (CSF) leakage. ¹ Although most anterior skull meningoencephaloceles can be managed through a purely endoscopic approach, a combined approach may be needed for massive encephaloceles or if sinonasal anatomy has been significantly altered. ⁸

Special Considerations

Most combined approaches are performed collaboratively by neurosurgeons and otolaryngologists. Preoperatively, a balloon-occlusion test can be used to assess the safety of sacrifice of the internal carotid artery. Preoperative tumor embolization can reduce blood loss during resection of some JNA and meningiomas. ⁹

More extensive tumor resection can increase the risk of CSF leak. ⁴ A multilayer closure including a vascularized nasoseptal flap is extremely important in preventing CSF leakage. In cases of extensive resection, collaboration with plastic surgery may improve reconstruction of the orbit and skull base. As combined approaches performed in tandem can be lengthy, some surgeons prefer to stage them.

Clinical Presentation

The patient is a 10-year-old boy who presented with a several year history of intermittent headaches but was otherwise neurologically intact. He later began to have vomiting and lethargy, prompting his physicians to obtain a head CT, which demonstrated a skull base lesion that was faintly calcified with approximately 4 mm of midline shift. An MRI better characterized the lesion as a 4.7 × 6.9 × 7.6 cm multiloculated cystic skull base originating from the sella turcica (▶ Fig. 8.1). Notably, the lesion obliterated the sphenoid and posterior ethmoid sinus and invaded bilateral cavernous sinuses. In addition, the lesion extended superiorly, displacing the optic chiasm superiorly and compressing the frontal lobe. The patient did not have any visual field deficits or gross endocrine abnormalities but had no have short stature and obesity, which are classic features of a child with a craniopharyngioma. Although diabetes insipidus can occur with craniopharyngiomas and even more so with germ cell tumors, the patient did have symptoms of DI. To confirm the diagnosis of craniopharyngioma, and rule out other lesions such as a sarcoma, the child underwent an endoscopic transnasal biopsy.

Surgical Approach

A combined approach from above and below was planned because of the superior to inferior extent of the lesion and goal for an aggressive resection of the benign pathology. The tumor was initially debulked from above through a bifrontal craniotomy. At the end of the resection, an endoscope was inserted endonasally to ensure that there was no residual tumor.

At the beginning of the procedure, the patient was given preoperative steroids and antibiotics. A lumbar drain was placed for brain relaxation and postoperative diversion of CSF to prevent CSF leak. The patient was placed supine and the head was fixed in three-pin Mayfield head holder in a neutral position. Even a little head extension is preferred to flexion. Neuronavigation was used for the procedure to help identify proximity to critical structures. The patient was prepped for a bicoronal incision with the nose covered with a sterile towel. A large pericranial flap was dissected and left attached posteriorly to keep it vascularized. Subgaleal dissection was performed down to the level of both orbital rims with special care not to injure the supraorbital nerve artery and vein. The supraorbital foramen was opened with a small chisel to free the nerve and subperiosteal dissection was carried out bilaterally into the orbit and in the midline to the level of the nasofrontal suture. The orbitofrontal craniotomy consisted of a bifrontal bone flap and resection of the orbital rim with an orbital bandeau bilaterally. Small burr holes were placed on either side of the sagittal sinus and at the keyholes laterally in the pterion underneath the temporalis muscle. The bifrontal craniotomy was then performed using a craniotome. The frontal lobe dura was freed from the orbital roof and partially freed from the crista galli anteriorly. The supraorbital osteotomies were then performed from an intracranial approach using the reciprocating saw and small chisels and a mallet. The removal of the supraorbital bar was critical to extend the subfrontal access, which opens up the anterior corridor to allow the surgeon to look up with minimal to no retraction on the frontal lobe. The dura was then opened, and the sagittal sinus was isolated and ligated with two 2–0 silk sutures and transected along with the falx. CSF was drained off through the lumbar drain for better frontal lobe relaxation. Greenberg 3/8 inch retractors were used to gently elevate the frontal lobe over wet Telfa to keep the brain moist. Using neuronavigation, we localized the intracranial portion of the tumor and its frontal extent. The olfactory nerve and olfactory bulbs were identified and transected, as planned, on the right side. The gyrus rectus on the right side was also partially resected subpially to avoid further retraction on the frontal lobe while exposing the large multilobulated cystic tumor. The operative microscope was then brought in for closer microdissection.

A firm capsule of the tumor was dissected from the surrounding frontal lobe white matter. After the dissection along the lateral margin of the tumor, the dissection was carried out along the inferior and medial aspects of the tumor. Birefringent calcium specks could be visualized inside of the capsule, which is classic for craniopharyngioma. The takeoff of the R A1 off the supraclinoid carotid and optic nerve was dissected free of the tumor capsule and we then followed the A1 medially to the anterior communicating (ACom) complex. We dissected the tumor capsule on either side of the A2 segments as well as optic nerves between both carotid arteries. It was also important to open up the Sylvian fissure to identify the M1 perforators, which were adherent to the tumor capsule. This dissection is much higher risk at the time of reoperation or post radiation since the adventitia around the vessel wall is often violated. A CT angiogram can be helpful prior to reoperation to rule out a pseudoaneurysm or vasculopathy due to the craniopharyngioma in particular. After a significant portion of the tumor was debulked, the tumor capsule was gently pulled down and dissected from the overlying frontal lobe white matter and hypothalamus. A tumor capsule that is markedly adherent to the hypothalamus and basal ganglia might be better left due to the high risk for hypothalamic dysfunction. The tumor extended into the sellar region, although the pituitary could not clearly be identified as separate from the tumor. In the end, approximately 90% of the intracranial tumor mass was debulked from above. Our otolaryngology colleagues then began their portion of the operation endonasally. This second surgery could be staged if needed in a very young child or if there was any frontal lobe swelling or coagulopathy.

The enlarged sella was further opened with an ethmoidectomy, allowing access to the anteromedial and posterior aspect of the skull base. The eroded bone structures within the sphenoid and ethmoid sinuses were identified and a remnant of a midline bony septum was removed. We then performed a radical resection of the remaining intracranial tumor mass and tumor capsule guided by neuronavigation. Along the soft palate, the tumor capsule was very adherent to the mucosa as well as the basilar artery.

For closure, the pericranial flap was divided and first used to line the subcranial resection cavity as a free graft. The endoscope was introduced through the right nostril and the resection cavity was inspected, with any visible residual tumor resected. The endoscope was also introduced through the widened sella from above to inspect all angles of the tumor resection. Gross total removal, apart from the adherent capsule as mentioned earlier along the A2s, was confirmed using the endoscope. Two Merocel nasal packings were introduced through both nostrils to support the cranial base reconstruction from below. The vascularized pericranial flap was then used to line the anterior cranial fossa. To reconstruct the bony defect, a split bone graft from the calvarium was obtained in the right frontal area. The calvarium was split using the oscillating saw and chisels. A 2 × 1.5 cm piece of calvarium was now placed in the bony defect of the skull base. Tissue glue was put on top of the pericranial flap to hold it in place. The dura was then closed primarily except in the areas where the dura was detached from the crista galli where a dural matrix graft was used with Tisseel. Tack-off sutures were performed in the frontal craniotomy area. The orbitofrontal bone flap including the frontal bone and orbital bandeau was now reconstructed using resorbable fixation. We left the lumbar drain in place but clamped until a postoperative scan was obtained and we had a postoperative examination to follow. The lumbar drain was then opened at a drain rate of 10 mL/h. Special attention was paid in the pediatric intensive care unit (ICU) to the occurrence of syndrome of inappropriate antidiuretic hormone (SIADH) and diabetes insipidus (DI) with frequent serum sodium checks. Final diagnosis was a craniopharyngioma and the patient has not had any recurrence of his tumor over a the 10-year follow-up (▶ Fig. 8.2).