**2.3 Regional pathology**

The most common tumors involving the anterior skull base and parasellar space in children include meningiomas, fibrous dysplasia, craniopharyngiomas, pituitary adenomas, juvenile nasopharyngeal angiofibromas (JNA), dermoid and epidermoid tumors, and gliomas.

Meningiomas can arise from the dura of the olfactory groove, planum/tuberculum sphenoidale or anterior clinoid process [11, 12]. Pediatric meningiomas are rarer in children than adults and typically associated with NF-2 or prior radiation treatment. Some studies suggest that meningiomas in children are more aggressive than meningiomas in adults, but these findings have yet to be validated in large studies.

Adamantinomatous craniopharyngiomas are the most common craniopharyngiomas found in children [13]. The diversity of their clinical presentation reflects their relationship to the surrounding pituitary, infundibulum, hypothalamus, and optic apparatus (**Figure 1**). A majority of craniopharyngiomas have a suprasellar component, and approximately one third extend into the anterior or middle cranial fossa [13]. Extension into the third ventricle can contribute to hydrocephalus, which can produce nonspecific symptoms such as headaches, nausea, and vomiting. Visual field or acuity defects are commonly present, as are symptoms of endocrine dysfunction, of which growth hormone (GH) appears to be the most commonly affected. Some may have large cystic components (**Figure 2**). Adenomas can present similarly, but typically have a more benign clinical course than craniopharyngiomas with respect to cranial neuropathy and hydrocephalus. The specific clinical presentation depends on the secreting subtype of tumor, with prolactinomas occurring most commonly.

#### **Figure 1.**

*A 13-year-old male presented with short stature and worsening peripheral vision, with a large papillary craniopharyngioma. MRI with contrast (A) coronal, (B) axial, (C) sagittal. Post operative MRI after resection through an endonasal transsphenoidal approach is shown in the bottom row (D-F). A small amount of fat graft can be seen in filling the cranial defect (E).*

#### **Figure 2.**

*This is a 4-year-old male who presented with vomiting and progressive vision loss with a suprasellar cystic papillary craniopharyngioma (A). An endoscopic trans-nasal, trans-cribriform approach was taken for resection. Fat graft is seen filling the craniotomy in the immediate post operative (B) and is partially resorbed with return of normal anatomic structure three months post-operatively (C).*

JNAs classically occurs in adolescent boys and present with painless nasal obstruction and intermittent epistaxis [14]. They can originate in any part of the nasal cavity, but have a predilection for the posterolateral wall of the nasal cavity, adjacent to the sphenopalatine foramen. From here they can spread to the nasal cavity, nasopharynx, orbit, paranasal sinuses and intracranial compartment. The tumor often has a rich blood supply from the internal maxillary artery, which can serve as a target for pre-operative liquid particle embolization.

Dermoid and epidermoid cysts are indolent lesions that present with vague symptomatology related to intracranial hypertension and aseptic meningitis. Occasionally, they produce cranial nerve deficits, seizures, and behavioral changes. Dermoid cysts occur in the midline and epidermoid cysts occur in the parasellar spaces. Dermoid cysts are typically associated with a sinus tract, which are most commonly found at the glabella. Epidermoid cysts are classically associated with high intensity on diffusion-weighted images (DWI) [15].

Optic pathway gliomas (OPG) are prevalent in neurofibromatosis type 1 (NF1) and virtually all cases occur before 10 years of age. Sporadic OPGs have a more aggressive clinical course than NF1-associated OPGs, especially hypothalamic OPGs, which are less frequent in NF-1. Considered indolent, OPGs rarely progress after adolescence and optimal treatment remains controversial. When possible, visual function should be spared as long as possible before attempting resection [16].

#### **2.4 Surgical approaches**

The endonasal corridor can be used to access lesions in the anterior skull base via the classic trans-sellar/parasellar approach, the trans-tuberculum and trans-planum approach, and at its rostral extent the trans-cribriform approach. Each of these anatomic modules are delimited by critical neurovascular structures in the coronal plane.

All the endonasal approaches are performed with bi-nostril access and with a bimanual four-hand neurosurgery-otolaryngology team. Pre-operative evaluation of the paranasal sinuses with high resolution CT is essential, and care is taken to note deviated septum or bony spurs that may limit visualization or movement in the endonasal corridor. We do not routinely give peri-operative steroids, unless hypocortisolism is seen on preoperative workup. A microscope is always kept in the room and balanced with the observer scope on the left side of the primary surgeon.

A septal flap is raised before the sellar phase of the surgery only in cases where a high-flow CSF leak is expected. The posterior septum is resected before entering the sphenoid phase to facilitate visualization of the entire sella. The sella is expanded laterally to the lamina papyracea and anteriorly to the planum. Pneumatization of

the sphenoid sinus aids in this phase of the exposure and identification of critical neurovascular structures surrounding the sella [17, 18]. Doppler ultrasonography can help identify the carotid artery where tumors may distort or encase vascular anatomy. The dura of the sella is then exposed between the cavernous sinuses. The medial optico-carotid recesses and tuberculum sphenoidale may also be resected for more lateral and rostral exposure, respectively, than is typically afforded by a trans-sellar approach.

Extension of this exposure rostrally can provide access to the posterior wall of the frontal sinus, between the medial orbital walls limited by the laminae papyracea. In this case, the nasal corridor described above is expanded with uncinetectomy, maxillary antrostomy, and ethmoidectomy. Care should be taken to avoid avulsing the ethmoidal arteries during ethmoidectomy, or coagulating the stumps of the ethmoidal arteries into the orbital wall, resulting in retrobulbar hematomas and orbital compartment syndrome. The lamina papyracea can be removed itself to provide access to the medial orbital wall [19].
