Key points
- •
Ventral skull base tumors are rare head and neck tumors that present with nonspecific symptoms.
- •
The principles of endoscopic skull base surgery involve extensive surgical planning and a multidisciplinary approach.
- •
Preoperative assessment is essential to guide surgical approach.
- •
Transnasal endoscopic resection (TER) is a safe and effective surgical option in appropriately selected cases in the presence of an experienced surgical team.
Video content accompanies this article at http://www.oto.theclinics.com .
Introduction
Sinonasal and ventral skull base malignancies represent 3% of all head and neck cancers. Their incidence is 0.83 per 100,000 patients. They usually present with nonspecific symptoms, such as nasal obstruction, epistaxis, and facial pain.
Contemporary management of sinonasal and ventral skull base tumors involves an oncologically sound and multidisciplinary approach. When surgery is indicated, open surgical approaches have long been considered the standard of care. These approaches have been associated, however, with multiple morbidities, including external surgical scarring, wound complications, prolonged brain retraction with all its sequelae, and long postoperative recovery times, resulting in extended hospital length of stays. Postoperative complications with external surgical approaches have been reported as high as 50%, with postoperative mortality at approximately 4% in most published series. This has led to an interest in alternative surgical approaches that would give similar results with less morbidity and in a minimally invasive manner.
Interest in the endonasal approach for management of skull base tumors goes back to the late nineteenth century. In the 1990s, endoscopic-assisted craniofacial resection (CFR) was described. Similar to a traditional CFR, the tumor is approached superiorly through a bicoronal frontal craniotomy, but the sinonasal surgical component is approached inferiorly through a transnasal endoscopic approach. Although somewhat controversial, some investigators have advocated total endoscopic control of tumors (gross tumor removal without microscopic margins), short of a significant dural resection but combined with adjuvant stereotactic radiosurgery.
Over the past 2 decades, the management of chronic sinus disease has shifted from using the open approaches, or transnasal microscopes, to the use of the endoscopes. The wide adaptation of this technique resulted from improved comfort endoscopically navigating the complex anatomy of the parnanasal sinuses, orbit, and skull base. In addition, new technologies, such as intraoperative navigation, have led to the expansion of endoscopic sinus surgery to include the management of neoplasms. Furthermore, improvement in skull base reconstruction techniques, such as using the pedicled nasoseptal flap as well as alloplastic graft techniques, has improved clinical outcomes from endoscopic skull base surgery with a reduction in hospitalization.
The endoscopic approach had been criticized initially for what was perceived as a non–en bloc resection with piecemeal tumor removal that may theoretically result in tumor seeding. Subsequent studies have shown, however, that positive resection margins, and not en bloc resection, is the most significant risk factor for tumor recurrence. It has been shown in different studies that endoscopic transnasal resections carries comparable rates of negative margins to open CFR.
Casiano and colleagues reported the first purely TER of the anterior skull base (ASB) for esthesioneuroblastoma that included resection of the entire anterior ventral skull base (as described in the traditional CFR) with overlying dura. Since then, several studies have compared endoscopic with open approaches in the management of different sinonasal tumors. Although many of these studies are limited due to selection bias in that more advanced and aggressive tumors are more likely to have been treated with an open approach, it shows a growing body of evidence that the TER method is as safe and effective as open approaches in appropriately selected patients and in experienced hands as long as oncologic principles are adhered to. This article presents Dr Casiano’s technique of endoscopic anterior ventral skull base resection and reconstruction.
Introduction
Sinonasal and ventral skull base malignancies represent 3% of all head and neck cancers. Their incidence is 0.83 per 100,000 patients. They usually present with nonspecific symptoms, such as nasal obstruction, epistaxis, and facial pain.
Contemporary management of sinonasal and ventral skull base tumors involves an oncologically sound and multidisciplinary approach. When surgery is indicated, open surgical approaches have long been considered the standard of care. These approaches have been associated, however, with multiple morbidities, including external surgical scarring, wound complications, prolonged brain retraction with all its sequelae, and long postoperative recovery times, resulting in extended hospital length of stays. Postoperative complications with external surgical approaches have been reported as high as 50%, with postoperative mortality at approximately 4% in most published series. This has led to an interest in alternative surgical approaches that would give similar results with less morbidity and in a minimally invasive manner.
Interest in the endonasal approach for management of skull base tumors goes back to the late nineteenth century. In the 1990s, endoscopic-assisted craniofacial resection (CFR) was described. Similar to a traditional CFR, the tumor is approached superiorly through a bicoronal frontal craniotomy, but the sinonasal surgical component is approached inferiorly through a transnasal endoscopic approach. Although somewhat controversial, some investigators have advocated total endoscopic control of tumors (gross tumor removal without microscopic margins), short of a significant dural resection but combined with adjuvant stereotactic radiosurgery.
Over the past 2 decades, the management of chronic sinus disease has shifted from using the open approaches, or transnasal microscopes, to the use of the endoscopes. The wide adaptation of this technique resulted from improved comfort endoscopically navigating the complex anatomy of the parnanasal sinuses, orbit, and skull base. In addition, new technologies, such as intraoperative navigation, have led to the expansion of endoscopic sinus surgery to include the management of neoplasms. Furthermore, improvement in skull base reconstruction techniques, such as using the pedicled nasoseptal flap as well as alloplastic graft techniques, has improved clinical outcomes from endoscopic skull base surgery with a reduction in hospitalization.
The endoscopic approach had been criticized initially for what was perceived as a non–en bloc resection with piecemeal tumor removal that may theoretically result in tumor seeding. Subsequent studies have shown, however, that positive resection margins, and not en bloc resection, is the most significant risk factor for tumor recurrence. It has been shown in different studies that endoscopic transnasal resections carries comparable rates of negative margins to open CFR.
Casiano and colleagues reported the first purely TER of the anterior skull base (ASB) for esthesioneuroblastoma that included resection of the entire anterior ventral skull base (as described in the traditional CFR) with overlying dura. Since then, several studies have compared endoscopic with open approaches in the management of different sinonasal tumors. Although many of these studies are limited due to selection bias in that more advanced and aggressive tumors are more likely to have been treated with an open approach, it shows a growing body of evidence that the TER method is as safe and effective as open approaches in appropriately selected patients and in experienced hands as long as oncologic principles are adhered to. This article presents Dr Casiano’s technique of endoscopic anterior ventral skull base resection and reconstruction.
Preoperative imaging
Imaging studies should be carefully reviewed with a neuroradiologist, who is an important part of the multidisciplinary team. MR imaging usually helps demonstrates the relationship of the tumor to the surrounding soft tissue and neural structures. CT scan and CT angiogram are used to evaluate bony involvement and vascular relationships, respectively. Intraoperative navigation with CT and MR imaging fusion may be used for more extended ASB resections posteriorly adjacent to the internal carotid artery or optic nerves. Intraoperative navigation is not routinely used, however, by Dr Casiano for ASB resection.
Contraindications and limitations
The key principle in choosing an approach for resection of sinonasal and ventral skull base malignancies is finding the most direct route with the least manipulation of neural and vascular structures. If a crucial neurovascular structure is found ventral or medial to the target structure, a transnasal approach should be reconsidered and the benefits and risks weighed against other approaches.
Some of the contraindications of purely endoscopic procedures are infiltration of nasal bones, massive involvement of the superior or lateral recesses of the frontal sinus, massive involvement of the lacrimal system or orbital structures, or involvement of the lateral recesses or anterior walls of the maxillary sinus. A combined approach (even with more limited external incisions) should be considered when there is extensive tumor infiltration of the dura over the orbital roof or when tumor extends significantly into the brain parenchyma. An external approach may be necessary during the course of TER if surgical margins cannot be cleared due to lack of adequate visualization or access. Therefore, careful preparation is necessary to anticipate all potential intraoperative eventualities. Neurosurgical support must be available in all cases where an open craniotomy may become necessary.
Preoperative surgical considerations
A complete head and neck examination is performed. Any abnormalities that may affect the surgery should be noted. For example, the presence of a septal perforation or tumor involvement, may affect the use of a nasoseptal flap, and alternative reconstruction technique should be planned. The management plan should be discussed carefully with the patient.
Prophylactic antibiotics are administered perioperatively. Acute sinonasal infection may be treated preoperatively with antibiotics. Chronic inflammatory sinus disease can be addressed, however, at the time of the skull base procedure. In a series of 250 cases who had skull base surgery, 20 patients had chronic rhinosinusitis addressed during their ventral skull base surgery. None of the patients in this series had an acute purulent sinusitis. None developed intracranial infections.
Endoscopic surgical procedure
The ASB is formed by the frontal, sphenoid, and ethmoid bones. The posterior table of the frontal sinus forms the anterior limits of the ASB resection. The ethmoid bone, in the midline, gives rise to the cribriform plate, the perpendicular plate of the septum, and the fovea ethmoidalis with ethmoidal septations (anterior and posterior). It articulates anteriorly with the posterior wall of the frontal bone. The olfactory fibers pass from the intracranial cavity to the nasal cavity, forming a pathway that tumors can spread into the nose or intracranially, depending on where they originate. The anterior and posterior ethmoid arteries pass from the orbit to the lateral lamella of the cribriform plate in their corresponding canals. These arteries should be identified and cauterized during surgery.
Traditional oncologic principles should be followed for endoscopic resection of the ASB. The final resection includes bilateral olfactory bulbs, cribriform plates, adjacent dura, and crista galli. The extension of the tumor dictates which additional structures are removed to achieve a negative resection margin.
Endoscopic Technique
- •
The intranasal component of the malignancy is debulked and its origin (epicenter) is identified to plan the extent of resection ( [CR] ). This is done with a microdébrider to expose the nasal septum, lateral nasal wall, and posterior choana. The remaining parts of the procedure are performed mainly with nonbiting forceps to assure adequate mucosal stripping and to yield adequate tissue for final (permanent) pathologic analysis and mapping of involved areas. A suction filter (sock) is used to collect the tissue debris removed by the microdébrider and is labeled carefully for each side of the nose.
- •
Sinuses are opened and landmarks identified. This include a Draf III (Lothrop) procedure and an extended sphenoid sinusotomy, removing the sphenoid rostrum and intersinus septum along with the mucosa. The optic nerves and carotid arteries are identified. An endoscopic medial maxillectomy is performed if the tumor appears to involve the ethmoid sinus and extends to the medial maxilla (middle meatal wall or inferior turbinate). This involves the systematic removal of the ipsilateral inferior and middle turbinate, medial maxillary wall with nasolacrimal duct, a total ethmoidectomy without mucosal preservation, and removal of the lamina papyracea, throughout the length of the ethmoid cavity. A total ethmoidectomy, without mucosal preservation, and a middle meatal antrostomy are performed also on the contralateral side, mainly if the tumor appears to extend beyond the confines of the olfactory cleft to the contralateral side, if the biologic nature of the neoplasm warrants bilateral ASB resection or if there is any radiologic evidence of disease on the contralateral side. In select neoplasms where contralateral extension is not evident, a unilateral hemi-ASB resection may be a viable option. In these cases, the contralateral mucoperichondrium of the nasal septum and falx cerebri (with olfactory bulb) is preserved. The long-term olfactory function with this procedure, however, is unknown.
- •
The nasal septum is resected inferior to the area of tumor involvement from posterior wall of the frontal sinus to the rostrum of the sphenoid bone. Margins from the nasal septal mucosa are sent for frozen section analysis bilaterally.
- •
If the septal mucosa is not involved by the tumor, a septal flap can be harvested for reconstruction prior to the septectomy.
- •
The posterior table of the frontal sinus and the planum sphenoidale are identified in the course of performing the Draf III (extended) frontal and extended sphenoid sinusotomy (discussed previously). These structures form the anterosuperior and posteroinferior limits of the resection.
- •
The sphenopalatine foramen is identified and cauterized bilaterally if a nasoseptal flap is not used. Otherwise, it is preserved on the ipsilateral side of the flap. The crista galli is removed between the 2 leaves of falx cerebri (dura), by first drilling with a diamond bur and then dissecting it free with a small dural elevator. The fovea ethmoidalis and sphenoid rostrum anterior to the optic chiasm are thinned with a large cutting and/or diamond bur or ultrasonic bone emulsifier to an eggshell thickness ( Fig. 1 ), and the bone is removed piecemeal with a Kerrison bone rongeur, to expose the underlying dura circumferentially around the remaining perpendicular plate of the nasal septum, the middle and superior turbinate remnants, and the olfactory cleft bilaterally. The anterior and posterior ethmoidal arteries are cauterized with a bipolar or monopolar cautery. This creates a floating ASB, which pulsates and is easily moved with a suction tip.
Fig. 1
Artistic depiction of the anterior ventral skull base after initial exposure prior to endoscopic craniotomy.
( From Casiano RR, editor. Endoscopic sinonasal dissection guide. New York: Thieme Medical Publishers; 2011; with permission.)
- •
The dura is elevated off the orbital roof in a lateral direction to facilitate further resection and sampling of dural margins as well as placement of the graft during reconstruction. A wide margin of dura is resected, extending from the posterior wall of the frontal sinus to the anterior planum sphenoidale. Fine skull base microscissors may be use to cut the dura. Dr Casiano, however, prefers a small Thru-Cut Forceps to make the cuts as well as sample dural margins simultaneously. Laterally, the dural margin initially is resected a few millimeters medial to the junction of the orbital wall and the ethmoid roof. The dura, bilateral cribriform plate with olfactory bulbs, middle and superior turbinate remnants, and superior perpendicular plate remnant of the septum are removed en bloc through the nose as a final specimen.
- •
Adjacent brain parenchyma is inspected for the presence of neoplasm and frozen sections are sent circumferentially from the dural margins, olfactory nerve endings, septum, and nasopharynx. Additional margins are sent as needed. Brain parenchyma involvement can be systematically removed through a gentle suction traction technique, cauterizing any feeding vessels with bipolar cautery ( Fig. 2 ).
Fig. 2
Artistic depiction of the undersurface of the brain after endoscopic craniotomy and resection of the anterior ventral skull base.
( From Casiano RR, editor. Endoscopic sinonasal dissection guide. New York: Thieme Medical Publishers; 2011; with permission.)
- •
In cases of no ventral skull base erosion or thinning, the dura generally is kept intact after thorough bone removal, unless tumor histology dictates dural removal as well. The bone is left undisturbed if the tumor does not extend to the skull base with a clear aerated space between the tumor and the ethmoid roof.
- •
Endoscopic marsupialization of the lacrimal duct remnant and inferior lacrimal sac is performed with a cutting forceps or powered instruments to minimize the chance of subsequent stenosis and secondary epiphora.
Fig. 3 shows the preoperative and postoperative CT scans of a patient with a left-sided esthesioneuroblastoma who underwent a typical endoscopic anterior ventral skull base resection.
