The Pediatric Anterior Skull Base: An Otolaryngologist’s

The Pediatric Anterior Skull Base: An Otolaryngologist’s Perspective

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

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The Pediatric Anterior Skull Base: An Otolaryngologist’s Perspective1Andrew J Chang, 2Ron B Mitchell, 3Gopi B Shah

ABSTRACT

Anterior skull base tumors have traditionally posed a therapeutic challenge. However, the advancement of skull base and endoscopic surgery has allowed for more of these lesions to be amenable to surgical resection. Though common in the adult population, surgical approaches in the pediatric population is not widely described. This chapter discusses the presentation and treatment for various pediatric anterior skull base lesions. Surgical approaches, complications, and the role of the otolaryngologist is also discussed.

Keywords: Anterior skull base tumors; Children; Pediatric skull base surgery.

How to cite this article: Chang AJ, Mitchell RB, Shah GB. The Pediatric Anterior Skull Base: An Otolaryngologist’s Perspective. Int J Head Neck Surg 2016;7(2):143-148.

Source of support: Nil

Conflict of interest: None

INTRODUCTION

Skull base tumors have traditionally posed a therapeutic challenge to the otolaryngologist and neurosurgeon. Prior to the advent of skull base surgery, malignant tumors involving the skull base were considered inoperable and almost universally fatal. However, with the advancement of skull base surgery and endoscopic techniques, previously unresectable lesions can now be managed surgically, and the role of the otolaryngologist is increasing, especially for those lesions involving the anterior cranial fossa. Diagnosis and management of skull base tumors are well described in adults, but only a few reports1-5 exist pertaining to the pediatric population, primarily because skull base tumors are generally uncommon but even rarer in children.1,6 In adults, meningiomas and sinonasal malignancies are the most common anterior skull base lesions, whereas fibrous dysplasia, esthesioneuroblastomas, and

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RevIew ARtIcle

1Chief Resident, 2Professor, 3Assistant Professor1-3Department of Otolaryngology—Head and Neck Surgery University of Texas – Southwestern Medical Center, Dallas Texas, USA

Corresponding Author: Gopi B Shah, Assistant Professor Department of Otolaryngology—Head and Neck Surgery University of Texas – Southwestern Medical Center, Dallas Texas, USA, e-mail: [email protected]

10.5005/jp-journals-10001-1280

encephaloceles predominate in children.2 In addition, juvenile nasopharyngeal angiofibromas (JNAs) originate from the sinonasal tract but can extend to involve the skull base. Children pose a therapeutic challenge because of their developing skull, face, and sinuses2,3,7 and the desire to avoid any intervention that may lead to developmental complications. This article will focus on the presentation and treatment of pediatric anterior skull base lesions. Common surgical approaches, complications, outcomes, and, specifically, the role of the otolaryngologist in the treatment team will be addressed.

ANATOMY

The anterior cranial fossa is composed of the orbital portion of the frontal bone anteriorly, cribriform plate of the ethmoid bone centrally, and the lesser wing and body of the sphenoid bone posteriorly.8,9 It is demarcated from the middle cranial fossa by the anterior clinoid processes and the lesser sphenoid wings, which mark its posterior extent (Fig. 1). Anteriorly, the cribriform plate transmits the olfactory nerves from the superior nasal mucosa,10 and posteriorly, it articulates with the sphenoid body, which is the site, from anterior to posterior, of the planum sphenoidale, limbus sphenoidale, chiasmatic sulcus, tuberculum sellae, pituitary fossa, and dorsum sellae. The planum sphenoidale forms the roof of the posterior ethmoid sinus and the anterior part of the sphenoid sinus and borders on the optic canals posterolaterally.11

When accessing the anterior skull base “from below,” it is important to note that the floor of the anterior cranial fossa is uneven. The orbital roofs slope downward medially to join the ethmoid sinuses, and this downward slope becomes more exaggerated heading to 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 may risk injury to the brain if extended medially at the same level.

HISTORY AND PHYSICAL EXAM

Clinical findings in pediatric patients with anterior skull base lesions are determined by the location and extent of the tumor and do not differ significantly from those seen

Andrew J Chang et al

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in the adult population.2 In a retrospective chart review of children undergoing resection of skull base lesions, Hanbali et al4 found that the most common complaints were visual, nasal, and facial deformity. Blindness or diplopia may predict orbital involvement, while anosmia can be seen in advanced tumors involving the cribriform plate. Other clinical manifestations noted in the literature include recurrent sinus infection, headache, and heaviness of the head.4,5

Physical exam includes a thorough cranial nerve exam as a well as an endoscopic exam. Hanbali et al4 found that the most common clinical findings in children with skull base lesions requiring resection included decreased facial sensation, restricted ocular motility, decreased visual acuity, and proptosis. Examination with a 2.7 mm flexible scope or a rigid telescope—0°, 30°, and 70°—is feasible with appropriate topical anesthesia and parental cooperation with nurse assistance. If an adequate exam cannot be performed, general anesthesia may be necessary for nasal endoscopy.

Imaging via computed tomography (CT) and mag-netic resonance imaging (MRI) is essential and should be performed with contrast in axial, coronal, and sagit-tal planes.8 Fine-cut CT (submillimeter slices) provides critical anatomic information important for surgery, including the presence and extent of erosion of the skull base or orbital wall, position of vessels and nerves, and presence of intersinus septa. Magnetic resonance

imaging can help differentiate between neoplastic or inflammatory tissue and assists in confirming certain diagnoses, such as meningoceles, nasal gliomas, and retained secretions.9 Computed tomography or MR angiography may be considered for lesions extending to the middle cranial fossa involving the internal carotid artery (ICA), vertebrobasilar system, or cavernous sinus. Conventional angiography may be considered in certain situations: evaluation of the circle of Willis, extent of tumor involvement on the ICA, or distinguishing tumor from aneurysm.10

DIFFERENTIAL DIAGNOSIS

Pediatric skull base tumors are rare, usually benign, and have a male predominance.1,3 Although tumor types vary tremendously, most tumors are of mesenchymal origin.4 Whereas the most common anterior skull base tumors in adults are nasal or sinonasal malignancies and meningiomas, these are rare in children, who are more likely to have encephaloceles, fibrous dysplasia, esthesioneuroblastomas,2 and nerve sheath tumors.3

Encephaloceles are extensions of intracranial struc-tures outside the skull and have an incidence of about 0.2 per 1,000 live births and fetal deaths.12 Interestingly, in North America, these usually occur occipitally, but in South America, they are usually found in the anterior cranial fossa.2

Fibrous dysplasia is an anomaly of the precursors of bone, in which the transformation of woven bone to lamellar bone does not occur, leading to an overgrowth of well-vascularized fibrous stroma surrounding distorted osseous trabeculae. When it involves the sphenoid wing, it

Fig. 2: Noncontrast computed tomography sinus, coronal image shows the skull base. The depth of the olfactory fossa (white star) or the height of the skull base is determined by the distance between the lateral lamella (white arrow) and the cribriform plate (red arrow)

Fig. 1: Skull base from cadaver. Anterior cranial fossa: crista galli (blue arrow), cribriform plate (triangle), lesser wing of sphenoid (star), optic canal (wide blue arrow), anterior clinoid process (blue circle). Middle cranial fossa: sella (oval) foramen rotundum (red arrow), fora-men ovale (green arrow), foramen spinosum (yellow arrow), foramen lacerum (navy arrow). Posterior cranial fossa: internal auditory canal (gray arrow), jugular foramen (white arrow), hypoglossal canal (black arrow), foramen magnum (“X”)



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can encroach upon the optic nerve, leading to progressive visual loss.2 Although there is a 25% risk of recurrence with partial removal of the lesion, radiation is not recommended in cases of incomplete resection as there is risk of malignant transformation.13 Unfortunately, there are also reports of spontaneous malignant transformation in the absence of radiation exposure.14

Esthesioneuroblastomas, or olfactory neuroblastomas, are tumors of neuroectodermal origin believed to arise from the mitotically active basal layer of the olfactory epithelium.15 Surgery alone is advocated in cases of low-grade tumors if complete resection with margins can be achieved, with the addition of radiation for close margins or residual or recurrent disease. Chemotherapy is recommended for high-grade tumors.2

Though rare, sinonasal pathology, such as a JNA, can extend to involve the skull base. These benign, vascular, locally aggressive tumors are predominantly found in adolescent males and are thought to originate from a persistent vascular plexus after involution of the first branchial arch16 at the sphenopalatine foramen. It can grow toward the pterygomaxillary fossa, infratemporal fossa, and the inferior orbital fissure with extension into the anterior and middle cranial fossae (Fig. 3). There are many classification systems including Fisch, Chandler, Andrews, and most recently Radkowski, which help define the tumor based on extent and skull base erosion. The tumors are preoperatively embolized, and surgical resection may involve an open or, more commonly, an endoscopic technique. The presence of sinonasal pathology with potential skull base extension highlights the importance that otolaryngologists, especially the rhinologist or pediatric otolaryngologist who manages these patients, have a strong understanding of skull base pathology and anatomy.

Other anterior skull base lesions described in children include ossifying fibromas, sarcomas, plexiform neurofibromas, adenocarcinomas, adenoid cystic carcinomas, and neuroblastomas.1,3 When malignant, sarcomas are the most common skull base malignancy in children, sixfold more common than nonsarcoma malignancies, and predominate at the anterior, compared with the middle or posterior, skull base in a two-to-one ratio.4 Some sarcomas, including osteosarcoma, malignant fibrous histiocytoma, fibrosarcoma, and spindle cell sarcoma, have been reported in children who had previously undergone radiation, most commonly for retinoblastoma.1

MANAGEMENT

The management of anterior skull base tumors in children is similar to that in adults and depends on the tumor type and location, surgical resectability, and the availability and effectiveness of adjuvant therapies. However, management strategies must take into account the patient’s age and developmental stage, as many therapies are known to have detrimental effects on growth and function.4

Medical

Chemotherapy has not been useful for solid tumors of the skull base in children, other than for rhabdomyo-sarcoma.5

Cranial radiotherapy, be it external beam or brachytherapy, is frequently used as adjuvant therapy in adults with solid tumors of the skull base. However, it has a more limited role in children because of concerns for generalized growth retardation, pituitary insufficiency and its associated hormonal disturbances, and irreversible visual consequences due to proximity of the orbit.4In 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, or any portion of the brain that, if removed, will give a poor quality of life are all contraindications to surgery.8,10 Invasion of the optic chiasm is a relative contraindication,

Fig. 3: Coronal T1-weighted MRI with contrast shows a juvenile nasopharyngeal angiofibroma extending from the nasopharynx to middle cranial fossa. The arrow highlights the proximity to internal carotid artery


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because blindness is not an acceptable outcome of surgery.8 Additionally, evidence of distant metastases or poor physical state of the child would also serve as contraindications.8,10

There are various craniofacial approaches to skull base tumors, and the decision primarily depends on the extent of the lesion. In young children, the anterior cranial fossa is relatively shallow and the frontal sinuses are not well developed, making access to this area easier than in adults.2 The most commonly used approaches combine frontal craniotomy with some form of transfacial exposure, including transoral or transpalatal approach, lateral rhinotomy, Le Fort I osteotomy, and midfacial degloving.10 Although these approaches are commonly utilized in adults, they must frequently be modified in children to avoid complications specific to this population.

In 1910, an endonasal transseptal, transsphenoidal approach was first described to remove pituitary tumors.18 The development of endoscopic technique and image-guided computer-assisted surgery has revolutionized the surgical management of skull base tumors, and endonasal surgery has become the procedure of choice, primarily for midline lesions.5,10 With improved technology, angled scopes, image guidance systems, and high-speed drills, it is now possible to access the midline skull base from the frontal sinus to the second cervical vertebra and from the sella to the jugular foramen endoscopically5,10,18 (Fig. 4). The endoscope can also be used as an adjunct with open approaches to eliminate the need for certain facial incisions as well as to look in areas hidden from the field of view of a microscope.10 The endoscopic approach should not be used if there is involvement of the orbit, far lateral extent of the maxillary sinus, involvement of dura lateral to the maximum convexity of the orbit, internal

carotid or cavernous sinus extension, or any instance where it will not be possible to remove all tumor safely with a margin of healthy tissue.8

There are various endoscopic endonasal approaches that can be used, and the decision depends on the location, nature, and malignancy of the lesion or tumor. These approaches can be classified as transnasal, transethmoid, and transseptal. Extended transnasal approaches include transplanum, transsphenoidal, transpterygoid, transclival, and transpharyngeal. A combination of these approaches18 may be needed if the lesion extends posteriorly to the middle cranial fossa. The transethmoid approach is appropriate for lesions involving the ethmoid sinus, medial orbital wall, and sphenoid sinus. The transseptal and transnasal approaches are ideal for lesions involving the central skull base, clivus, sella, and parasellar regions, such as pituitary adenomas, and avoid the lateral wall of the sphenoid sinus, carotid artery, and optic nerve9,18 (Fig. 5).

Skull base defects were initially closed with full-thickness skin grafts when this surgery was pioneered in the 1950s and 1960s.19,20 The 1970s brought a shift to using galeal and pericranial flaps and now more commonly the nasoseptal flap is used as a pedicled vascularized flap in the closure of the defects21 (Figs 6 and 7).

Robotic endoscopic skull base surgery and transoral robotic surgery theoretically provide the advantage of improved visualization, access, and precision, but more clinical investigation is needed before these techniques are widely accepted.10

COMPLICATIONS

Potential complications of skull base surgery include cerebrospinal fluid leak and the increased risk of

Fig. 4: With the use of angled endoscopes, the skull base is reached endoscopically from the ethmoid roof, planum sphenoidale, sella, clivus, and dens of second vertebral body

Fig. 5: Skull base view from sinuses showing planum sphenoidale (circle), tuberculum sellae (green arrow), sella turcica (star), carotid arteries (triangles), optic nerves (“x”), opticocarotid recess (blue arrows), clivus (red arrow)



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meningitis associated with it, visual disturbances, intracranial complications from direct injury to the brain, carotid artery, cranial nerves, venous sinuses, and metabolic complications involving the pituitary gland such as diabetes insipidus. Cerebrospinal fluid leak is the most common complication, usually manifesting as rhinorrhea, and can occur in up to 20% of resections.5,10,18 Some can be managed conservatively, usually with a lumbar drain, but postoperative leaks often require surgical closure. Most orbital complications are due to direct injury to the optic nerve or extraocular muscles or from bleeding into the orbit, causing diplopia, decreased visual acuity, or even blindness.9 Pneumocephalus can occur suddenly in the postoperative period if a patient attempts to blow his or her nose, and tension pneumocephalus can manifest as confusion, obtundation, and neurologic deterioration due to the intracranial mass effect.10 Though bleeding is a risk in any procedure, there are a relatively large number of important vessels susceptible to injury during skull base surgery including the anterior and posterior ethmoid arteries, sphenopalatine artery, maxillary artery, and ICA and its branches.9

In a relatively large series of 26 pediatric patients who underwent skull base approaches for tumor resection, Teo et al3 found an overall complication rate of 57%. Most were due to worsening of preexisting cranial nerve palsies with 37% having permanent sequelae. Another study1 found a 30% minor complication rate without any major complications or deaths. One complication that is surprisingly absent from reports is retardation of growth as a result of craniofacial resection.3,22 This is thought to be because osteotomies do not normally pass through the growth centers of the facial skeleton.2 In their report on 26 pediatric patients, Teo et al3 found no long-term disturbances of

facial growth patterns after surgical disruption of the skull base.

OUTCOMES

A higher percentage of initial complete resections of anterior skull base tumors has been noted in pediatric patients when compared with their adult counterparts, and is thought to be in part due to better defined tissue planes in children.3 The higher rate of complete resection, in combination with the high incidence of benign tumors, explains why children have better prognosis with skull base lesions (81–83% 3-year survival compared with 45–80% in adults).1,3 Castelnuovo et al23 found that radical endoscopic endonasal resection led to either complete or partial recovery of quality of life within the first year of surgery. McCoul et al24 also noted improvement in quality of life in a prospective study.

CONCLUSION

Tumors of the skull base are rare in the pediatric popu-lation. Resection is the optimal treatment of skull base benign lesions and for most low-grade malignancies. The surgical approach needs to be individualized based on the age of the patient, tumor location, and its pathological features. As an otolaryngologist who sees many of these highly complex skull base children, it is imperative to have a strong foundation in skull base anatomy, under-stand surgical options, be facile with the endoscope, and communicate well with the neurosurgeon, ophthalmolo-gist, radiologist, and oncologist.

REFERENCES

1. Gross ND, Ganly I, Patel SG, Blisky MH, Shah JP, Kraus DH. Results of anterior skull base surgery in pediatric and young adult patients. Skull Base 2010 Mar;20(2):75-81.

Fig. 6: Nasoseptal flap harvested off the septum and pedicled to posterior septal artery (white arrow)

Fig. 7: Nasoseptal flap is tucked against the skull base defect in onlay fashion (red arrow). Also shown is an inlay dural substitute that can be needed (black arrow)


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2. Tsai EC, Santoreneos S, Rutka JT. Tumors of the skull base in children: review of tumor types and management strategies. Neurosurg Focus 2002 May 15;12(5):e1.

3. Teo C, Dornhoffer J, Hanna E, Bower C. Application of skull base techniques to pediatric neurosurgery. Childs Nerv Syst 1999 Mar;152(2-3):103-109.

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5. Venkataramana NK, Anantheswar YN. Pediatric anterior skull base tumors: our experience and review of literature. J Pediatr Neurosci 2010 Jan;5(1):1-11.

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7. Shah RK, Dhingra JK, Carter BL, Rebeiz EE. Paranasal sinus development: a radiographic study. Laryngoscope 2003 Feb;113(2):205-209.

8. Donald, P.; Brodie, H. Skull base surgery. Lee KJ., editor. Essential otolaryngology: head & neck surgery. 10th ed. New York, NY: McGraw-Hill; 2012. p. 162-191.

9. Stamm, AC.; Pignatari, SS.; Balsalobre, L. Transnasal endoscopic-assisted surgery of the anterior skull base. Flint, PW.; Haughey, BH.; Lund, VJ.; Niparko, JK.; Richardson, JA.; Robbins, T.; Thomas, JR., editors. Cummings otolaryngology. 6th ed. Philadelphia, PA: Saunders;2015. p. 2671-2700.

10. Walvekar, RR.; Culicchia, F.; Nuss, DW. Surgery of the anterior and middle cranial base. In: Flint, PW.; Haughey, BH.; Lund, VJ.; Niparko, JK.; Richardson, JA.; Robbins, T.; Thomas, JR., editors. Cummings otolaryngology. 6th ed. Philadelphia, PA: Saunders; 2015. p. 2671-2700.

11. Hitotsumatsu T, Matsushima T, Rhoton AL. Surgical anatomy of the midface and the midline skull base. Oper Tech Neurosurg 1999 Dec;2(4):160-180.

12. Stevenson RE, Allen WP, Pai GS, Best R, Seaver LH, Dean J, Thompson S. Decline in prevalence of neural tube defects in a high-risk region of the United States. Pediatrics 2000 Oct;106(4):677-683.

13. Mortensen A, Bojsen-Møller M, Rasmussen P. Fibrous dysplasia of the skull with acromegaly and sarcomatous transformation. Two cases with a review of the literature. J Neurooncol 1989 May;7(1):25-29.

14. Taconis WK. Osteosarcoma in fibrous dysplasia. Skeletal Radiol 1988;17(3):163-170.

15. Barnes L, Kapadia SB. The biology and pathology of selected skull base tumors. J Neurooncol 1994;20(3):213-240.

16. Kumar AR, Nayak JV, Janisiewicz AM, Li G, Oghalai JS. The combined subtemporal-transfacial approach for the resection of juvenile nasopharyngeal angiofibromas with intracranial extension. Otol Neurotol 2015 Jan;36(1):151-155.

17. Eder HG, Leber KA, Eustacchio S, Pendl G. The role of gamma knife radiosurgery in children. Childs Nerv Syst 2001 May;17(6):341-346.

18. Stamm AM. Transnasal endoscopy-assisted skull base surgery. Ann Otol Rhinol Laryngol Suppl 2006 Sep;196:45-53.

19. Ketcham AS, Wilkins RH, Van Buren JM, Smith RR. A combined intracranial facial approach to the paranasal sinuses. Am J Surg 1963 Nov;106:698-703.

20. Smith RR, Klopp CT, Williams JM. Surgical treatment of cancer of the frontal sinus and adjacent areas. Cancer 1954 Sep;7(5):991-994.

21. Newman J, O’Malley BW Jr, Chalian A, Brown MT. Microvascular reconstruction of cranial base defects: an evaluation of complication and survival rates to justify the use of this repair. Arch Otolaryngol Head Neck Surg 2006 Apr;132(4):381-384.

22. Lang DA, Neil-Dwyer G, Evans BT, Honeybul S. Craniofacial access in children. Acta Neurochir (Wien) 1998;140(1):33-40.

23. Castelnuovo P, Lepera D, Turri-Zanoni M, Battaglia P, Bolzoni Villaret A, Bignami M, Nicolai P, Dallan I. Quality of life following endoscopic endonasal resection of anterior skull base cancers. J Neurosurg 2013 Dec;119(6):1401-1409.

24. McCoul ED, Anand VK, Schwartz TH. Improvements in site-specific quality of life 6 months after endoscopic anterior skull base surgery: a prospective study. J Neurosurg 2012 Sep;117(3):498-506.

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The Pediatric Anterior Skull Base: An Otolaryngologist’s