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The Pediatric Anterior Base:10.5005/jp-journals-10001-1280 An Otolaryngologist’s Perspective Review Article

The Pediatric Anterior Skull Base: An Otolaryngologist’s Perspective 1Andrew J Chang, 2Ron B Mitchell, 3Gopi B Shah

ABSTRACT encephaloceles predominate in children.2 In addition, juvenile nasopharyngeal angiofibromas (JNAs) originate Anterior skull base tumors have traditionally posed a therapeutic challenge. However, the advancement of skull base and from the sinonasal tract but can extend to involve the skull endoscopic surgery has allowed for more of these lesions to be base. Children pose a therapeutic challenge because of amenable to surgical resection. Though common in the adult their developing skull, , and sinuses2,3,7 and the desire population, surgical approaches in the pediatric population is to avoid any intervention that may lead to developmental not widely described. This chapter discusses the presentation complications. This article will focus on the presentation and treatment for various pediatric anterior skull base lesions. Surgical approaches, complications, and the role of the and treatment of pediatric anterior skull base lesions. otolaryngologist is also discussed. Common surgical approaches, complications, outcomes, and, specifically, the role of the otolaryngologist in the Keywords: Anterior skull base tumors; Children; Pediatric skull base surgery. treatment team will be addressed. How to cite this article: Chang AJ, Mitchell RB, Shah GB. The Pediatric Anterior Skull Base: An Otolaryngologist’s Perspective. ANATOMY Int J Head Neck Surg 2016;7(2):143-148. The anterior cranial is composed of the orbital Nil Source of support: portion of the frontal anteriorly, Conflict of interest: None of the centrally, and the lesser wing and body of the posteriorly.8,9 It is demarcated INTRODUCTION from the middle by the anterior clinoid Skull base tumors have traditionally posed a therapeutic processes and the lesser sphenoid wings, which mark its challenge to the otolaryngologist and neurosurgeon. posterior extent (Fig. 1). Anteriorly, the cribriform plate Prior to the advent of skull base surgery, malignant transmits the olfactory nerves from the superior nasal 10 tumors involving the skull base were considered mucosa, and posteriorly, it articulates with the sphenoid inoperable and almost universally fatal. However, with body, which is the site, from anterior to posterior, of the the advancement of skull base surgery and endoscopic planum sphenoidale, limbus sphenoidale, chiasmatic techniques, previously unresectable lesions can now be sulcus, tuberculum sellae, pituitary fossa, and dorsum managed surgically, and the role of the otolaryngologist sellae. The planum sphenoidale forms the roof of is increasing, especially for those lesions involving the posterior ethmoid sinus and the anterior part of the anterior cranial fossa. Diagnosis and management the sphenoid sinus and borders on the optic canals 11 of skull base tumors are well described in adults, but posterolaterally. only a few reports1-5 exist pertaining to the pediatric When accessing the anterior skull base “from population, primarily because skull base tumors are below,” it is important to note that the floor of the generally uncommon but even rarer in children.1,6 anterior cranial fossa is uneven. The orbital roofs slope In adults, meningiomas and sinonasal malignancies downward medially to join the ethmoid sinuses, and this are the most common anterior skull base lesions, downward slope becomes more exaggerated heading to whereas fibrous dysplasia, esthesioneuroblastomas, and the cribriform area (Fig. 2). Thus, the midline is usually the lowest point of the skull base,10 and an axial plane of dissection, i.e., safe at the area of the ethmoid sinuses 1Chief Resident, 2Professor, 3Assistant Professor may risk injury to the brain if extended medially at the 1-3Department of Otolaryngology—Head and Neck Surgery same level. University of Texas – Southwestern Medical Center, Dallas Texas, USA HISTORY AND PHYSICAL EXAM Corresponding Author: Gopi B Shah, Assistant Professor Department of Otolaryngology—Head and Neck Surgery Clinical findings in pediatric patients with anterior skull University of Texas – Southwestern Medical Center, Dallas base lesions are determined by the location and extent of Texas, USA, e-mail: [email protected] the tumor and do not differ significantly from those seen

International Journal of Head and Neck Surgery, April-June 2016;7(2):143-148 143 Andrew J Chang et al

Fig. 1: Skull base from cadaver. Anterior cranial fossa: Fig. 2: Noncontrast computed tomography sinus, coronal image (blue arrow), cribriform plate (triangle), lesser wing of sphenoid (star), shows the skull base. The depth of the olfactory fossa (white star) or optic (wide blue arrow), anterior clinoid process (blue circle). the height of the skull base is determined by the distance between : sella (oval) (red arrow), fora- the lateral lamella (white arrow) and the cribriform plate (red arrow) men ovale (green arrow), (yellow arrow), foramen lacerum (navy arrow). : internal auditory canal (gray arrow), (white arrow), (black imaging can help differentiate between neoplastic or arrow), (“X”) inflammatory tissue and assists in confirming certain diagnoses, such as meningoceles, nasal gliomas, and in the adult population.2 In a retrospective chart review retained secretions.9 Computed tomography or MR of children undergoing resection of skull base lesions, angiography may be considered for lesions extending to Hanbali et al4 found that the most common complaints the middle cranial fossa involving the internal carotid were visual, nasal, and facial deformity. Blindness artery (ICA), vertebrobasilar system, or cavernous sinus. or diplopia may predict orbital involvement, while Conventional angiography may be considered in certain anosmia can be seen in advanced tumors involving the situations: evaluation of the circle of Willis, extent of cribriform plate. Other clinical manifestations noted in tumor involvement on the ICA, or distinguishing tumor 10 the literature include recurrent sinus infection, headache, from aneurysm. and heaviness of the head.4,5 DIFFERENTIAL DIAGNOSIS Physical exam includes a thorough cranial nerve exam as a well as an endoscopic exam. Hanbali et al4 Pediatric skull base tumors are rare, usually benign, and found that the most common clinical findings in have a male predominance.1,3 Although tumor types children with skull base lesions requiring resection vary tremendously, most tumors are of mesenchymal included decreased facial sensation, restricted ocular origin.4 Whereas the most common anterior skull base motility, decreased visual acuity, and proptosis. tumors in adults are nasal or sinonasal malignancies Examination with a 2.7 mm flexible scope or a rigid and meningiomas, these are rare in children, who are telescope—0°, 30°, and 70°—is feasible with appropriate more likely to have encephaloceles, fibrous dysplasia, topical anesthesia and parental cooperation with esthesioneuroblastomas,2 and nerve sheath tumors.3 nurse assistance. If an adequate exam cannot be Encephaloceles are extensions of intracranial struc- performed, general anesthesia may be necessary for tures outside the skull and have an incidence of about nasal endoscopy. 0.2 per 1,000 live births and fetal deaths.12 Interestingly, Imaging via computed tomography (CT) and mag- in North America, these usually occur occipitally, but in netic resonance imaging (MRI) is essential and should South America, they are usually found in the anterior be performed with contrast in axial, coronal, and sagit- cranial fossa.2 tal planes.8 Fine-cut CT (submillimeter slices) provides Fibrous dysplasia is an anomaly of the precursors critical anatomic information important for surgery, of bone, in which the transformation of woven bone to including the presence and extent of erosion of the lamellar bone does not occur, leading to an overgrowth of skull base or orbital wall, position of vessels and nerves, well-vascularized fibrous stroma surrounding distorted and presence of intersinus septa. Magnetic resonance osseous trabeculae. When it involves the sphenoid wing, it 144 ijhns

The Pediatric Anterior Skull Base: An Otolaryngologist’s Perspective can encroach upon the optic nerve, leading to progressive Other anterior skull base lesions described in visual loss.2 Although there is a 25% risk of recurrence children include ossifying fibromas, sarcomas, plexiform with partial removal of the lesion, radiation is not neurofibromas, adenocarcinomas, adenoid cystic recommended in cases of incomplete resection as there is carcinomas, and neuroblastomas.1,3 When malignant, risk of malignant transformation.13 Unfortunately, there sarcomas are the most common skull base malignancy are also reports of spontaneous malignant transformation in children, sixfold more common than nonsarcoma in the absence of radiation exposure.14 malignancies, and predominate at the anterior, compared Esthesioneuroblastomas, or olfactory neuroblastomas, with the middle or posterior, skull base in a two-to-one ratio.4 are tumors of neuroectodermal origin believed to arise Some sarcomas, including osteosarcoma, malignant fibrous from the mitotically active basal layer of the olfactory histiocytoma, fibrosarcoma, and spindle cell sarcoma, have epithelium.15 Surgery alone is advocated in cases of been reported in children who had previously undergone low-grade tumors if complete resection with margins radiation, most commonly for retinoblastoma.1 can be achieved, with the addition of radiation for close margins or residual or recurrent disease. Chemotherapy MANAGEMENT is recommended for high-grade tumors.2 Though rare, sinonasal pathology, such as a JNA, can The management of anterior skull base tumors in children extend to involve the skull base. These benign, vascular, is similar to that in adults and depends on the tumor type locally aggressive tumors are predominantly found in and location, surgical resectability, and the availability and adolescent males and are thought to originate from a effectiveness of adjuvant therapies. However, management persistent vascular plexus after involution of the first strategies must take into account the patient’s age and branchial arch16 at the . It can developmental stage, as many therapies are known to have 4 grow toward the pterygomaxillary fossa, infratemporal detrimental effects on growth and function. fossa, and the inferior orbital with extension into the anterior and middle cranial fossae (Fig. 3). There are Medical many classification systems including Fisch, Chandler, Chemotherapy has not been useful for solid tumors of Andrews, and most recently Radkowski, which help the skull base in children, other than for rhabdomyo- define the tumor based on extent and skull base erosion. sarcoma.5 The tumors are preoperatively embolized, and surgical Cranial radiotherapy, be it external beam or resection may involve an open or, more commonly, brachytherapy, is frequently used as adjuvant therapy an endoscopic technique. The presence of sinonasal in adults with solid tumors of the skull base. However, it pathology with potential skull base extension highlights has a more limited role in children because of concerns for the importance that otolaryngologists, especially the generalized growth retardation, pituitary insufficiency rhinologist or pediatric otolaryngologist who manages and its associated hormonal disturbances, and irreversible these patients, have a strong understanding of skull visual consequences due to proximity of the .4In base pathology and anatomy. regard to stereotactic radiosurgery, long-term effects in children have not been adequately assessed, and its role in the treatment of benign skull base tumors in children is unclear.17 Thus, for pediatric patients harboring benign tumors or low-grade malignant lesions, achieving complete resection is more critical than it is in adults, because supplementation with adjunctive radiotherapy is not desirable. In fact, even subtotally resected tumors are generally observed, with radiation being reserved only for progressive, multifocal, or unresectable disease.4

Surgical Prior to proceeding with surgery, the operability of the lesion must first be assessed. Invasion of the brain stem, internal carotid arteries, cavernous sinuses, spinal cord, Fig. 3: Coronal T1-weighted MRI with contrast shows a juvenile or any portion of the brain that, if removed, will give a nasopharyngeal angiofibroma extending from the nasopharynx to 8,10 middle cranial fossa. The arrow highlights the proximity to internal poor quality of life are all contraindications to surgery. carotid artery Invasion of the optic chiasm is a relative contraindication, International Journal of Head and Neck Surgery, April-June 2016;7(2):143-148 145 Andrew J Chang et al because blindness is not an acceptable outcome of carotid or cavernous sinus extension, or any instance surgery.8 Additionally, evidence of distant metastases where it will not be possible to remove all tumor safely or poor physical state of the child would also serve as with a margin of healthy tissue.8 contraindications.8,10 There are various endoscopic endonasal approaches There are various craniofacial approaches to skull that can be used, and the decision depends on the location, base tumors, and the decision primarily depends on nature, and malignancy of the lesion or tumor. These the extent of the lesion. In young children, the anterior approaches can be classified as transnasal, transethmoid, cranial fossa is relatively shallow and the frontal sinuses and transseptal. Extended transnasal approaches are not well developed, making access to this area easier include transplanum, transsphenoidal, transpterygoid, 2 than in adults. The most commonly used approaches transclival, and transpharyngeal. A combination of combine frontal craniotomy with some form of transfacial these approaches18 may be needed if the lesion extends exposure, including transoral or transpalatal approach, posteriorly to the middle cranial fossa. The transethmoid lateral rhinotomy, Le Fort I osteotomy, and midfacial approach is appropriate for lesions involving the ethmoid 10 degloving. Although these approaches are commonly sinus, medial orbital wall, and sphenoid sinus. The utilized in adults, they must frequently be modified in transseptal and transnasal approaches are ideal for children to avoid complications specific to this population. lesions involving the central skull base, clivus, sella, and In 1910, an endonasal transseptal, transsphenoidal parasellar regions, such as pituitary adenomas, and avoid approach was first described to remove pituitary the lateral wall of the sphenoid sinus, carotid artery, and 18 tumors. The development of endoscopic technique optic nerve9,18 (Fig. 5). and image-guided computer-assisted surgery has Skull base defects were initially closed with full- revolutionized the surgical management of skull thickness skin grafts when this surgery was pioneered in base tumors, and endonasal surgery has become the the 1950s and 1960s.19,20 The 1970s brought a shift to using 5,10 procedure of choice, primarily for midline lesions. galeal and pericranial flaps and now more commonly the With improved technology, angled scopes, image nasoseptal flap is used as a pedicled vascularized flap in guidance systems, and high-speed drills, it is now the closure of the defects21 (Figs 6 and 7). possible to access the midline skull base from the frontal Robotic endoscopic skull base surgery and transoral sinus to the second cervical vertebra and from the sella robotic surgery theoretically provide the advantage of to the jugular foramen endoscopically5,10,18 (Fig. 4). The improved visualization, access, and precision, but more endoscope can also be used as an adjunct with open clinical investigation is needed before these techniques approaches to eliminate the need for certain facial are widely accepted.10 incisions as well as to look in areas hidden from the field of view of a microscope.10 The endoscopic approach COMPLICATIONS should not be used if there is involvement of the orbit, far lateral extent of the maxillary sinus, involvement of dura Potential complications of skull base surgery include lateral to the maximum convexity of the orbit, internal cerebrospinal fluid leak and the increased risk of

Fig. 4: With the use of angled endoscopes, the skull base is reached Fig. 5: Skull base view from sinuses showing planum sphenoidale endoscopically from the ethmoid roof, planum sphenoidale, sella, (circle), tuberculum sellae (green arrow), sella turcica (star), carotid clivus, and dens of second vertebral body arteries (triangles), optic nerves (“x”), opticocarotid recess (blue arrows), clivus (red arrow) 146 ijhns

The Pediatric Anterior Skull Base: An Otolaryngologist’s Perspective

Fig. 6: Nasoseptal flap harvested off the septum and pedicled Fig. 7: Nasoseptal flap is tucked against the skull base defect in to posterior septal artery (white arrow) onlay fashion (red arrow). Also shown is an inlay dural substitute that can be needed (black arrow) meningitis associated with it, visual disturbances, facial growth patterns after surgical disruption of the intracranial complications from direct injury to the skull base. brain, carotid artery, cranial nerves, venous sinuses, and metabolic complications involving the pituitary gland such OUTCOMES as diabetes insipidus. Cerebrospinal fluid leak is the most A higher percentage of initial complete resections of common complication, usually manifesting as rhinorrhea, anterior skull base tumors has been noted in pediatric 5,10,18 and can occur in up to 20% of resections. Some can be patients when compared with their adult counterparts, managed conservatively, usually with a lumbar drain, but and is thought to be in part due to better defined tissue postoperative leaks often require surgical closure. Most planes in children.3 The higher rate of complete resection, orbital complications are due to direct injury to the optic in combination with the high incidence of benign tumors, nerve or extraocular muscles or from bleeding into the explains why children have better prognosis with skull orbit, causing diplopia, decreased visual acuity, or even base lesions (81–83% 3-year survival compared with 9 blindness. Pneumocephalus can occur suddenly in the 45–80% in adults).1,3 Castelnuovo et al23 found that radical postoperative period if a patient attempts to blow his or endoscopic endonasal resection led to either complete or her nose, and tension pneumocephalus can manifest as partial recovery of quality of life within the first year of confusion, obtundation, and neurologic deterioration due surgery. McCoul et al24 also noted improvement in quality to the intracranial mass effect.10 Though bleeding is a risk of life in a prospective study. in any procedure, there are a relatively large number of important vessels susceptible to injury during skull base CONCLUSION surgery including the anterior and posterior ethmoid Tumors of the skull base are rare in the pediatric popu- arteries, sphenopalatine artery, maxillary artery, and ICA lation. Resection is the optimal treatment of skull base 9 and its branches. benign lesions and for most low-grade malignancies. The In a relatively large series of 26 pediatric patients surgical approach needs to be individualized based on who underwent skull base approaches for tumor the age of the patient, tumor location, and its pathological 3 resection, Teo et al found an overall complication rate of features. As an otolaryngologist who sees many of these 57%. Most were due to worsening of preexisting cranial highly complex skull base children, it is imperative to nerve palsies with 37% having permanent sequelae. have a strong foundation in skull base anatomy, under- 1 Another study found a 30% minor complication stand surgical options, be facile with the endoscope, and rate without any major complications or deaths. One communicate well with the neurosurgeon, ophthalmolo- complication that is surprisingly absent from reports gist, radiologist, and oncologist. is retardation of growth as a result of craniofacial resection.3,22 This is thought to be because osteotomies REFERENCES do not normally pass through the growth centers of 1. Gross ND, Ganly I, Patel SG, Blisky MH, Shah JP, Kraus DH. 2 the facial skeleton. In their report on 26 pediatric Results of anterior skull base surgery in pediatric and young patients, Teo et al3 found no long-term disturbances of adult patients. Skull Base 2010 Mar;20(2):75-81. International Journal of Head and Neck Surgery, April-June 2016;7(2):143-148 147 Andrew J Chang et al

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