In the pediatric population, malignant tumors of the skull base are rare. Sarcoma (rhabdomyosarcoma, osteosarcoma, chondrosarcoma, Ewing sarcoma), chordoma, lymphoma, olfactory neuroblastoma, and germinoma have all been documented at the skull base in pediatric patients. Comprehensive multidisciplinary evaluation is essential for both diagnosis and management of these patients. Endoscopic endonasal surgery (EES) of the skull base provides access in sagittal and coronal planes and enhances the role of surgical management for these pathologies. Sinonasal malignancies that involve the anterior cranial base require a transfrontal/transcribriform/transplanum approach to the anterior cranial fossa. Reconstruction may be accomplished with a nasoseptal flap or extracranial pericranial flap. Skull base tumors such as chordomas and chondrosarcomas require a transclival approach to the posterior cranial fossa. Reconstruction is multilayer including fascia, fat, and a vascularized flap. Postoperative diversion of cerebrospinal fluid with a lumbar drain decreases the risk of a cerebrospinal fluid leak. Excellent oncologic outcomes can be achieved with acceptable morbidity when EES is incorporated into a multidisciplinary treatment plan.
29 Expanded Endonasal Approaches for Treatment of Malignancy in Children
Endoscopic endonasal surgery (EES) of the skull base includes the entire ventral skull base in sagittal and coronal planes. These approaches are well established as surgical options for adult patients and are increasingly applied to pediatric patients with skull base tumors. Multiple studies have shown that these approaches are safe and effective in the pediatric population. 1 – 6 Open craniofacial surgery in children can potentially disrupt growth centers of the craniofacial skeleton and result in facial asymmetry. It is therefore important to consider endoscopic endonasal approaches when feasible based on patient and tumor characteristics.
In the sagittal plane, endoscopic endonasal approaches extend from the frontal sinus to the craniovertebral junction. 1 Access to the anterior cranial base is provided by transfrontal, transcribriform, and transplanum approaches. 7 , 8 They can be combined to achieve a complete resection of the anterior cranial base for sinonasal malignancy, equivalent to a craniofacial resection. The transsellar approach can be combined with transclival and transodontoid approaches to provide access to the posterior cranial fossa for malignancies of the skull base and nasopharynx. 9 , 10 The main considerations in pediatric EES are the constraints of the developing skull and facial skeleton and small size of patients. As described in this chapter, special considerations are required in the evaluation and treatment of pediatric patients.
EES can be used for both benign and malignant pathology, with the text of this chapter focusing on considerations with malignant tumors. Pediatric skull base malignancies are uncommon and comprise multiple pathologies. 6 , 11 Sarcoma (rhabdomyosarcoma, osteosarcoma, chondrosarcoma, Ewing sarcoma), chordoma, lymphoma, olfactory neuroblastoma, and germinoma have all been documented at the skull base in pediatric patients. Comprehensive multidisciplinary evaluation is essential for both diagnosis and management of these patients. In many cases, surgical resection or surgical debulking is necessary. In some cases, initial treatment with chemotherapy and/or external beam radiation therapy is the best course. A brief description of each tumor type is provided below.
Chordomas originate from the embryonic notochord and present in the midline clival region. They are typically slow-growing tumors that exhibit local invasion, though some tend to grow more aggressively in children. 12 While originating in the clivus, intradural extension is possible. The mainstay of treatment is surgical resection followed by postoperative radiotherapy. While complete resection is best, tumor involvement of vital neurovascular structures may limit resectability. Chordomas of the craniovertebral junction are often more aggressive and gross total resection is more difficult to achieve.
Chondrosarcomas present with similar symptoms as chordomas as they are also typically in the clival region, though they originate and grow in a paramedian position (petroclival synchondrosis). Chondrosarcomas can be subdivided into classic, mesenchymal, and dedifferentiated types, with the mesenchymal and dedifferentiated types showing more aggressive growth. Prognosis is closely related to histologic grade. 13
Rhabdomyosarcoma is the most common sarcoma in the pediatric population and can occur even in the very young. Alveolar and embryonal subtypes are the most common at the skull base. Smaller tumors, lower stage and young age have been shown to have improved prognosis. 14 Parameningeal rhabdomyosarcomas are most commonly treated initially using aggressive chemotherapy with surgery reserved for persistent disease after completion of chemotherapy regimen. 15 If after chemotherapy, the tumor remains unresectable or resection margins are positive, radiation therapy is administered.
Osteosarcoma is an aggressive malignancy of mesenchymal cell origin. Most cases of pediatric osteosarcoma arise in the limbs, but craniofacial osteosarcomas at the skull base have been reported as well. 16 Prior radiation therapy is a risk factor for development. Most but not all cases of osteosarcoma are associated with elevations in alkaline phosphatase levels. Complete resection is preferred, though chemotherapy is often needed initially to shrink the tumor to a size amenable to resection. Dural involvement, even in the absence of signs on imaging, is common. Radiation-induced sarcomas are particularly difficult to manage and surgery often plays a more prominent role in treatment of these tumors. 15
29.1.4 Ewing Sarcoma
Ewing sarcoma is a primitive tumor of neuro-ectodermal origin and can involve the pediatric skull base. Ewing sarcoma is responsive to aggressive chemotherapy. The role of surgery is limited to resection of residual disease following chemotherapy. Radiotherapy is reserved for those patients with no response to chemotherapy or residual disease following surgery. 17
29.1.5 Olfactory Neuroblastoma
Much less common in children than adults, olfactory neuroblastoma, also known as esthesioneuroblastoma, is a neuroectodermal neoplasm. It arises in the basal layer of the olfactory epithelium and frequently has both intranasal and intracranial components. The most commonly used staging system is the Modified Kadish staging system. 18 Stage A is tumor limited to the nasal cavity, Stage B defines tumor in the nasal cavity and sinuses, Stage C is tumor extending outside the sinonasal cavity, and Stage D includes distant spread of disease. While there is limited data regarding the outcome of pediatric olfactory neuroblastoma, in adult studies, 5-year disease-specific survival rates following treatment range from 92% in low-grade tumors (limited to nasal cavity and sinuses) to 50% in high-grade tumors (intracranial and metastatic disease). 19 In general, surgical resection with negative margins is the primary treatment of choice. In larger tumors and those with adverse histologic features, adjuvant radiation therapy is recommended. In cases where the tumor has extended into brain parenchyma or into the orbit, neoadjuvant chemotherapy followed by surgery or radiation therapy may be considered to improve outcome and decrease morbidity. In young pediatric patients, olfactory neuroblastomas are aggressive tumors but respond well to chemotherapy. 20 , 21
Germinomas are rare tumors affecting children and young adults. They arise from intracranial midline germ cells (totipotential cells), commonly in intrasellar and suprasellar locations. Dissemination of primary intracranial germinomas through the cerebrospinal fluid (CSF) is common, spreading through both the ventricular system and the subarachnoid space. 22 It is essential to image the entire brain and spine to evaluate for additional disease. Germinomas are chemo- and radio-sensitive; therefore, total resection is not essential. 22 Histologic diagnosis is necessary and can often be achieved through an endoscopic endonasal approach.
Primary lymphoma at the skull base is very rare. In pediatric patients, both Burkitt’s lymphoma and non-Hodgkin’s lymphoma have been reported in the skull base. 23 – 25 In most of these case reports, the presenting symptom was related to cavernous sinus involvement. Tissue is necessary for diagnosis but treatment is primarily chemotherapy.
29.2 Preoperative Evaluation
A full head and neck exam and neurologic exam are prudent in all patients. In young children this can be challenging due to the inability to follow commands to test neurologic function. However, with diligent examination, it can often be accomplished. For example, eye movements can be assessed by visual tracking of a toy or interesting object. Careful attention to reactions to touch sensation can help determine sensory nerve function. Facial movement is evident if the patient is crying. If the tumor is in proximity to the orbit or optic nerve, an ophthalmology evaluation is prudent. Nasal endoscopy can provide useful information and a limited examination is well tolerated by most patients, even infants. Biopsy of a nasal mass is generally not attempted in an office setting due to discomfort and risk of bleeding.
Both computed tomography (CT) and magnetic resonance imaging (MRI) are essential in the evaluation of children with skull base malignancy. Sedation is often needed to obtain high-quality images, particularly for MRI. Consideration of these needs (including discussions with the pediatric radiologist and anesthesiologist) will enable good images to be obtained the first time. Both CT and MRI should be configured to work with an intraoperative image guidance system. If treatment will involve primary chemotherapy and/or radiation, it is still important to obtain high-quality imaging prior to treatment to have knowledge of pre-treatment tumor boundaries. If a tumor appears highly vascular, angiography with possible embolization just prior to surgery may reduce intraoperative blood loss and improve visualization. In tumors encasing the internal carotid artery, preoperative balloon occlusion testing should be considered.
Treatment planning includes careful review of preoperative imaging. Development and pneumatization of the sinuses is dependent on the age of the patient. 26 – 28 The frontal sinuses are the last to develop and are often aplastic on one side. Incomplete pneumatization of the sphenoid sinus (conchal or pre-sellar pattern) obscures key anatomical landmarks (optic nerves and carotid arteries) and necessitates careful drilling with increased reliance on image-based navigation. If any adjunctive transmaxillary approach is being considered, carefully note the position of permanent tooth buds; the surgical corridor is limited and there is risk of injury to permanent dentition.
In cases of malignant tumors, patients and their guardians should have a full discussion of treatment options not only with the surgical team but also with a pediatric hematologist-oncologist for consideration of all medical implications and treatments of the cancer diagnosis. It is highly advised that cases are discussed in a multidisciplinary tumor board format with providers knowledgeable in medical, surgical, interventional treatment as well as rehabilitation specific to pediatric patients.
29.3 Perioperative Management
All patients should be at least typed and screened. For infants and small children, blood should be readily available, due to their smaller total blood volume and limited reserve with hemorrhage. Similarly, good intravenous access is necessary. If only small bore intravenous lines are possible due to patient size, multiple lines should be placed. Expected blood loss and resuscitation needs should be discussed with the anesthesia team prior to surgery and throughout the case.
Preoperative antibiotics should be administered prior to the start of the surgical procedure. If intradural resection is planned, the use of antibiotics with good CSF penetration is recommended. Children have thinner skin and are at higher risk of pressure ulceration; therefore, all pressure points should be carefully padded. Children, particularly infants, are highly susceptible to hypothermia and adequate warming should be maintained.
The patient is placed in the supine position and the head is fixated with a pediatric Mayfield head clamp with additional support for the head using a padded horse-shoe attachment. Fixation of the head facilitates extension and rotation of the head to a more ergonomic surgical position and prevents any movement during critical parts of the surgical dissection.
Neuromonitoring should be used when tumor is in proximity to neurovascular structures and/or cranial nerves. 29 Somatosensory-evoked potentials monitor cortical brain function and provide a measure of global ischemia. Electromyography of motor cranial nerves can be performed to aid in identification and prevention of injury. 29 In these cases, paralysis should be avoided. If significant intradural dissection is anticipated, CSF diversion through a lumbar drain should be discussed. Spinal drains are usually placed at completion of the surgery.
29.4 Surgical Technique
29.4.1 Anterior Cranial Fossa: Transfrontal/Transcribriform/Transplanum Approach
Sinonasal malignancies often involve the bone of the anterior cranial base and may extend to the dura. The goal of surgery is to remove all bone surrounding the tumor and remove the layers of the cranial base that are involved by tumor (▶ Fig. 29.1). For a prototypical skull base malignancy such as an olfactory neuroblastoma, this usually includes resection of the bone, dura, and olfactory bulbs and tracts on one or both sides.
If the tumor is large, debulking of the tumor is performed to establish the extent of the tumor and provide visualization of surrounding landmarks. Bipolar electrocautery of the tumor surface provides hemostasis.
Bilateral complete ethmoidectomies and sphenoidotomies are performed and mucosa is stripped from the skull base to expose the bony margins. The middle turbinates are resected to the plane of the skull base without violation of the dura.
On the side of the tumor, the lamina papyracea is removed to the plane of the skull base to establish a lateral margin (▶ Fig. 29.2). If there is tumor invasion of the bone, the periorbital may be resected for an additional margin.
The anterior and posterior ethmoidal arteries are identified on the orbital side of the bone, cauterized with bipolar electrocautery, and transected. The orbital periosteum is elevated from the orbital roof to provide additional exposure if there is lateral extension of the tumor along the skull base or dura (▶ Fig. 29.3).
On the side opposite the tumor, the lateral margin of resection is the roof of the ethmoid sinus unless the tumor crosses the midline.
The nasal septum is transected inferior to the tumor from the nasion to the posterior edge of the septum. If there is no invasion of the nasal septum, a nasoseptal flap can be elevated on the side contralateral to the tumor. A frozen section of the septal mucosa margin on the side of the tumor is performed.
A Draf 3 frontal sinusotomy is performed with drilling of the crista galli in the midline to expose the posteri- or table of the frontal sinus (▶ Fig. 29.4).
The optic canals are identified posteriorly and the bone of the planum sphenoidale is thinned with a drill (4 mm coarse diamond bit) anterior to the optic canals.
The roof of the ethmoids is thinned with the drill to expose the dura beyond the margins of resection (▶ Fig. 29.2 and ▶ Fig. 29.5). This may include the orbital roof on the side of the tumor.
Periosteum is elevated from the crista galli which is drilled in an anterior to posterior direction. It is not necessary to remove the entire crista galli. The bone of the posterior table of the frontal sinus is drilled to establish a margin anterior to the tumor and the cribriform plate.
All bone is elevated from the skull base to expose the dura (▶ Fig. 29.6). The cribriform plates can be fractured at the midline.
Epidural dissection of the dura from the bone is performed circumferentially to facilitate resection of dural margins later in the procedure.
The dura is incised laterally (roof of ethmoid or orbit), and the incisions are extended with microscissors, taking care not to injure underlying cortical vessels (▶ Fig. 29.7).
Anteriorly, the falx is cauterized and transected with microscissors in an anterior-to-posterior direction to the free edge of the falx (▶ Fig. 29.8). This releases the specimen anteriorly.
The olfactory bulbs and tracts are dissected free from the frontal lobes and remain attached to the dural specimen. If tumor is adherent, a subpial dissection of tumor from the surface of the brain is performed (▶ Fig. 29.9).
The posterior dural cut at the planum sphenoidale includes the dura and olfactory tracts.
The entire dural specimen is removed en bloc and oriented for pathology.
Circumferential dural margins are excised for frozen section analysis (▶ Fig. 29.10). If necessary, additional bone can be removed from the orbital roof to extend the lateral margin. Additional margins are taken from the olfactory tracts (▶ Fig. 29.11).
The dural defect (▶ Fig. 29.12) is reconstructed with an inlay fascial graft, onlay fascial graft tucked in an epidural plane, and a vascularized flap (nasoseptal flap or extracranial pericranial flap) that covers all exposed dura and bone surrounding the dural defect (▶ Fig. 29.13). Fascial grafts may be cadaveric or autologous fascia lata.