25.1 Introduction

Pediatric sinonasal lesions can arise from a number of congenital, developmental, or neoplastic processes. Fortunately, less than 2% of all paranasal masses diagnosed in children are malignant. Pediatric sinonasal and skull base cancers include a wide range of histologies with various symptoms of presentation, depending on the child’s age, location of the lesion, and disease-specific characteristics. ¹ The diagnosis and management of these lesions can be complex and demand an understanding of sinonasal and skull base embryology, developmental anatomy, location-specific symptoms, and disease-specific behavior. The management of these tumors requires a team approach of medical and surgical services with extensive training and experience, including otorhinolaryngologist, neurosurgeon, radiologist, pathologist, radiation oncologist, and pediatric oncologist. ² In particular, surgical management demands extensive clinical training supplemented by cadaveric dissection to gain the required knowledge of 3D anatomy, specialized instrumentation, and teamwork necessary for optimal outcomes and safety. The resection of malignant tumors via conventional approaches (e.g., craniofacial surgery) harbors difficulties because of the important structures involved and the complexity of the anatomical sites. Needless to say, these external approaches carry considerable risks, which may give rise to many complications, such as intracranial, orbital, neural, cutaneous, and others. ^{3 ,​ 4} Not less important, especially in the pediatric population, is the concern regarding the future skeletal development of the child; this can be significantly impaired in cases of disruption of the craniofacial complex growth centers. ⁵ Better understanding of the skull base anatomy, improved anesthesiological techniques, and the greatly enhanced visualization provided by endoscopes have led to a tremendous evolution of the endonasal approaches. At present, the endoscopic endonasal surgery is well established in the management of inflammatory conditions and benign lesions in the pediatric population, and it is also applied with satisfactory oncological outcomes for sinonasal and skull base malignancies in well-selected cases. ²

25.2 Epidemiology and Pathology

Malignancies of the paranasal sinuses and nasal cavities are rare in the adult population, accounting for approximately 3% of all head and neck cancer. Paranasal sinus malignancies are even more rare in children (0.9%). ⁶ Symptoms may be nonspecific and indolent for months or even years, leading to delay in diagnosis and consequent advanced stage of disease at presentation. Epidemiological studies based on the Surveillance, Epidemiology, and End Results (SEER) database program of the National Cancer Institute (NCI) suggest that rhabdomyosarcoma (RMS) is the most common paranasal sinus malignancy in children, followed by sarcoma, lymphoma, and olfactory neuroblastoma (ONB). ⁶ Other histologic tumor types rarely seen in pediatric age include neuroendocrine carcinoma, yolk sac tumors, spindle cell tumors, adenoid cystic carcinoma, and mucoepidermoid carcinoma. For this reason, of the pediatric skull base are generally divided into RMS and non-RMS malignancies. ¹

RMS is the third most common extracranial solid tumor seen in children and over one-third of RMS in children occur in the head and neck region. ⁶ It is a highly aggressive neoplasm originating from embryonal mesenchyma with potential to differentiate to striated muscle. Incidence of this tumor is most commonly seen in the first decade, with a second peak in adolescence. Histologic subtypes include embryonal (seen more commonly in younger children), alveolar (seen more commonly in adolescence), pleomorphic, and mixed type. The embryonal subtype is associated with the highest 5-year survival rate compared to other subtypes. The therapy of RMS is guided by the extent of the disease. Surgery is generally used for diagnostic issues, since definitive radiochemotherapy usually represents the best treatment option. However, in selected cases of nonresponding tumors and when dealing with persistence of disease, surgical resection with the goal of complete tumor removal is recommended (▶ Fig. 25.1). ²

Sarcomas are malignant mesenchymal tumors of unclear etiology, and are usually low grade and slow growing. Less than 10% are seen in the head and neck, and only 7 to 9% of patients are children. ⁶ Chondrosarcoma represents the most frequent histotype observed in childhood. For high-grade tumors, exclusive radiochemotherapy may be indicated. Surgery is used for biopsy or for persistent lesions. Nonresponding and low-grade lesions may be suitable for surgical resection. ²

Hematolymphoid tumors including B-cell and NK/T-cell lymphomas are rare in the pediatric populations with symptoms that may be nonspecific and indolent for months or even years, leading to delay in diagnosis and consequent advanced stage disease at presentation. ¹ Once the diagnosis is established through a biopsy of the nasal mass under endoscopic assistance, the treatment strategy includes different regimens of chemotherapy, eventually associated with or followed by radiotherapy. ²

ONB, also termed esthesioneuroblastoma, is very rare in children, with an estimated incidence of less than 0.1 per 100,000 children younger than 15 years. ⁶ It is a malignant neoplasm that arises from the olfactory epithelium, most frequently located at the cribriform plate, the upper surface of the superior turbinates, and the upper third of the nasal septum. Because of its rarity and indolence in children, it has been difficult to develop standard treatment protocols. However, multimodal therapy including surgery followed by radiation therapy has been indicated, especially in patients with advanced disease (▶ Fig. 25.2). In patients with Hyams grade IV disease (poorly differentiated ONB), combined therapy including induction chemotherapy, surgery, and radiation therapy had better outcomes. ²

Primitive neuroectodermal tumors (PNETs) of the sinuses are rare in children, but must be considered in the differential diagnosis of a paranasal sinus mass. Histologic features of undifferentiated small round cells elicit a differential diagnosis including Ewing’s sarcoma, ONB, and RMS. Treatment may include surgery and chemoradiation. ² Prognosis for PNET is extremely poor, with a high incidence of both local recurrences and distant metastases.

25.3 Pretreatment Workup

The role of the endoscopic skull base surgeons in these cases is variable and tailored to the histology of the disease. Endoscopic endonasal surgery can be used as a diagnostic tool for biopsy to guide chemotherapy and radiation; for resection or debulking of the tumor in order to downstage the lesion in preparation for chemotherapy or radiation therapy or both; surgery may be performed in several cases to relieve symptoms; and rarely, total resection can be planned for some non-rhabdosarcoma cases of appropriate size and location. However, it is mandatory to define the goals of treatment before surgery in every case. ²

Imaging workup includes CT scan and contrast-enhanced MRI for all patients. Total body staging can be performed with contrast-enhanced CT scan, while PET was reserved for patients with aggressive histotypes. ⁷

Remarkably, before surgery, the parents of the patient must be fully informed about the surgical proposal and of the possibility of shifting to a conventional external approach (if deemed necessary), and they must give their written consent to the treatment plan. In this respect, the patients are prepared in the operating theater for both the endoscopic and a possible external approach. Dedicated instrumentations are used. A magnetic navigation system is advisable intraoperatively and an ultrasound Doppler probe can be helpful in selected cases to identify major vessels.

25.4 Surgical Technique

Endoscopic endonasal approaches to the skull base can be used safely to manage sinonasal and skull base lesions in pediatric patients. Understanding the age-dependent pneumatization patterns of the paranasal sinuses, particularly the sphenoid and frontal sinuses, is critical for planning a safe endonasal approach in such patients. According to the site of origin, extent, and tumor histology, the endoscopic resection can be performed unilaterally (resection extended anteroposteriorly from the posterior wall of the frontal sinus to the planum sphenoidale and laterolaterally from the nasal septum to the lamina papyracea) or bilaterally (extending the resection from one lamina papyracea to the opposite one). ⁷ The traditional concept of oncologic surgery on en bloc resection to avoid the risk of tumor spilling is now debated, gradually being replaced by the concept of disassembling the lesion, having under view the limits between normal and diseased mucosa. The step-by-step technique of the endoscopic endonasal resection (EER) is summarized as follows (▶ Fig. 25.3):

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  Tumor origin identification. The lesion is gradually debulked starting from the core, in order to identify its site of origin. In this phase, it is crucial to preserve the surrounding anatomic structures, because these are useful landmarks for orientating the subsequent surgical steps.

  
  
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  Exposure of the surgical field. In the case of bilateral resection, removal of the posterior two-thirds of the nasal septum is performed to gain better exposure of the surgical field and to optimize the endonasal maneuverability of dedicated instruments, using the two-nostril, four-hand technique. In this step, a wide sphenoidotomy (with removal of intersinus septum and sphenoid rostrum in bilateral cases) is crucial to expose the posteroinferior margin of the dissection. The frontal sinus is approached by Draf type IIb sinusotomy in the case of unilateral EER, whereas Draf type III sinusotomy is performed if the EER involves both sides. The frontal sinusotomy represents the anterosuperior margin of the dissection, allowing precise identification of the beginning of the anterior cranial fossa.

  
  
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  Centripetal removal. Once the posteroinferior and anterosuperior margins of the resection are exposed, a subperiosteal dissection of the nasoethmoidal–sphenoidal complex is performed unilaterally or bilaterally (according to the extension of disease), to expose the lateral margins. The lamina papyracea is included in the dissection when the tumor is in close proximity to or frankly involved in it. Sphenopalatine arteries must be cauterized and divided in this phase. Techniques to minimize and control intraoperative blood loss are critical in pediatric patients owing to their overall lower blood volume compared with adult patients. When required by the extension of the disease, an endoscopic medial maxillectomy can be performed, to achieve good control of the whole maxillary sinus. This surgical step has to be associated with nasolacrimal duct exposure and resection, just below the lacrimal sac. ⁸ Superiorly, the dissection is continued in the anteroposterior direction, by resecting the olfactory fibers and the basal lamella of the ethmoidal turbinates. The entire nasoethmoidal–sphenoidal complex is then isolated and pushed toward the central part of the nasal fossa (centripetal technique) to extract it transorally or through the nasal vestibule. The surgical margins are checked by frozen section and, if necessary, the dissection is continued until free margins are obtained.

  
  
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  Skull base removal. According to the extension of the disease, the EER can be extended to include the anterior skull base (ASB) as well (endoscopic resection with transnasal craniectomy). The ethmoidal roof is exposed using a drill with a diamond burr. The anterior and posterior ethmoidal arteries are identified, cauterized, and divided. The crista galli is carefully detached from the dura and removed with blunt instruments, preserving the integrity of the dural layer.

  
  
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  Intracranial work. The key point for subsequently performing an optimal skull base reconstruction is to properly dissect the epidural space over the orbital roofs laterally, the planum sphenoidale posteriorly, and the posterior wall of the frontal sinus anteriorly before starting the resection of the dura. The dura is then incised and circumferentially cut with scissors, far away from the suspected area of tumor spread. The falx cerebri is clipped in the anterior portion before its resection to avoid sagittal sinus bleeding, then its posterior portion at the level of the sphenoethmoidal planum is resected. The arachnoidal plane over the intracranial portion of the tumor is then dissected and separated from the brain parenchyma. The specimen, including the residual tumor, the ASB, and the overlying dura, together with one or both of the olfactory bulbs, is removed transnasally. The dural margins are sent for frozen sections.

  
  
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  Skull base reconstruction. The resulting skull base defect is reconstructed by the endoscopic endonasal multilayer technique, performed preferably using autologous materials. Advances in skull base reconstruction after endoscopic surgery have allowed surgeons to perform more extensive resections while maintaining acceptable rates of post-reconstruction cerebrospinal fluid (CSF) leak or other potential complications. Regarding the materials used, the fascia lata and/or the iliotibial tract possess the best characteristics in terms of thickness, pliability, and strength. ⁷ For the first intradural layer of duraplasty, the graft has to be at least 30% larger than the dural defect and split anteriorly on the midline to adjust to the falx cerebri in case of bilateral resection. The second layer, intracranial and extradural, needs to be precisely sized and tacked between the previously undermined dura and the residual ASB bone. Pieces of fatty tissue are placed to eliminate the dead space between the second and third layers and to flatten the residual denuded ASB. The third extracranial layer has to cover all the exposed ASB but must not overlap the frontal sinusotomies in order to avoid a postoperative mucocele. The borders of the second and third layers are properly fixed with fibrin glue. In case of a tumor not involving nasal tissues (e.g. septum, contralateral turbinates) and without multifocal localizations, the third layer of the skull base reconstruction can be performed using local flaps. Sinonasal flaps include the nasoseptal flap, the septal flip-flap, the inferior turbinate, and the middle turbinate flaps. ^{9 ,​ 10} Their use facilitates rapid healing of the surgical cavity, especially in patients who require adjuvant irradiation. The potential size of every kind of flap is smaller in pediatric patients, and careful preoperative and intraoperative planning helps ensure the appropriateness of their use for skull base reconstruction. Reconstructions are then covered with hemostatic materials such as Surgicel (Johnson & Johnson Medical, Arlington, TX) and fibrin glues such as Tisseel (Baxter, Deerfield, IL) or DuraSeal (Covidien, Dublin, Ireland). Nasal packing with absorbable or nonabsorbable materials is kept for about 48 hours. Lumbar drains are not routinely used postoperatively. but early revision surgery is preferred in case of skull base reconstruction failure (▶ Fig. 25.4).

  

  

For lesions filling the frontal sinus or encroaching on the ASB with intradural extension over the orbital roof or with brain parenchyma infiltration, the EER has to be combined with an external transcranial approach. ¹¹ The procedure is performed by two surgical teams (neurosurgeons and otorhinolaryngologists) working simultaneously through a transnasal and transcranial corridor, respectively.