Since its description by Ketcham et al. in the 1960s, oncologic surgery of the anterior skull base tumors has included an anterior craniofacial resection. Initially, the surgical approach comprised transfacial and transcranial components that were performed in tandem. Subsequently, skull base surgeons adopted the subcranial approach, as first described by Tessier and Derome, to decrease the need for retraction of the brain, thus replacing the transcranial route. A subcranial approach consists of a bifrontal craniotomy and supraorbital and/or facial osteotomies (in one or more segments) via scalp (e.g., coronal) and facial incisions (e.g., Weber-Ferguson, lateral rhinotomy, or midface degloving incisions). Despite the improved exposure and decreased cerebral morbidity, the subcranial approach still involves some retraction and manipulation of the frontal lobes. This may result in frontal lobe contusion, edema, and ultimately encephalomalacia and cognitive dysfunction. In addition, facial and scalp incisions, while necessary, are associated with postoperative pain and visible scars. A craniofacial resection usually generates a convalescence that lasts weeks. Furthermore, wound infections and inadequate healing may lead to malunion of the bone grafts, loss of cranio-orbital bone grafts, potential deformities, and the need for further interventions and protracted complications.

Paranasal sinus surgery evolved similarly, as endoscopic sinus surgery replaced open sinus surgery, providing superior visualization, precise dissection, and less inherent trauma. Initially, however, the skull base was considered off-limits during endoscopic endonasal surgery. Experience eventually propelled an expansion of its indications to include skull base lesions such as meningoencephaloceles and cerebrospinal fluid (CSF) fistulas. These eventually progressed to the surgical management of benign tumors and, subsequently, malignancies.

Expanded endonasal approaches (EEA), evolved following advances in rod lens endoscopy, improved digital camera/monitor definition, customization of surgical instruments, and refinements in electrophysiologic monitoring, jointly with image-guided surgery equipment. Endoscopic endonasal approaches take advantage of the natural sinonasal corridor to reach tumors of the anterior cranial base in a caudocephalic angle (subbasal route). This path eliminates completely the need for retraction of the frontal lobes; however, some manipulation may still be necessary due to extension of tumor. Facial incisions and osteotomies are unnecessary, thus decreasing postoperative pain and eliminating wound complications and conspicuous scars.

Fundamental oncologic principles and goals of tumor resection should not be breached regardless of the surgical approach. A complete resection, confirmed by intraoperative histologic analysis (when available), is paramount. Therefore, a comparison of skull base defects produced by an endonasal resection with those of open craniofacial resection should not yield a significant difference (Fig. 28.1). Typically, both types of surgical ablation result in a transdural defect extending from the posterior wall of the frontal sinus to the planum sphenoidale (anteroposteriorly), and from the periorbita on one side to the contralateral periorbita (laterolaterally). Intradurally, the olfactory bulbs and tracts are also resected (brain can also be resected as needed although the indication for surgery under these circumstances is controversial). Novel reconstructive flaps have greatly improved outcomes regarding postoperative CSF leaks, previously a common source of morbidity. Similarly, the goals of preservation (or improvement) of function, cosmesis, and quality of life are critical considerations.
These, however, are deeply influenced by the intrinsic morbidity associated with the individual approaches; thus, in adequately selected patients, the endoscopic endonasal approach offers tremendous advantages.

The preoperative evaluation of patients who are being considered for an endoscopic endonasal resection does not differ from that of other surgical techniques. We rely on imaging including computed tomographic scan (CT) and magnetic resonance imaging (MRI) to evaluate the bony and soft tissue extensions of the tumor, including orbital and intracranial extensions, and perineural and vascular invasion and to judge the degree of tumor vascularity. We use a CT angiography in patients with tumors that are intimately associated to critical neurovascular structures.

It is critical to confirm the tumor histology before the definitive surgery. However, some exceptions exist, such as tumors with pathognomonic imaging characteristics, patient comorbidities that increase the surgical risk of a second surgery, and institutional logistics. These deserve special consideration to using intraoperative histologic analysis followed by a definitive resection. Otherwise, large tumors that are easily visualized in the anterior nasal cavity may be biopsied in the office setting. Other tumors are better biopsied in the operating room to obtain an adequate volume of tissue, and where bleeding can be managed more efficiently. In addition, this provides an opportunity to better map the origin and extent of the tumor.

A fused PET and CT scan is best to identify metastasis in patients presenting with advanced disease, and those who present with tumors that are known to spread hematogenously. Sarcomas and other high-grade malignancies presenting with dural transgression also warrant a cytologic examination of the CSF and an MRI of the spine to rule out “drop metastasis.”

Our current technique for an endoscopic anterior skull base resection follows the basic principles of EEA including the interdisciplinary teamwork by an otolaryngologist and a neurosurgeon (operating simultaneously throughout most of the surgery), the use of a posterior septectomy to merge the paired nasal cavities, and wide expansion of the sinonasal corridor to fully expose the tumor and to afford the possibility of bimanual dissection.

Under general endotracheal anesthesia, the patient is positioned supine with the head of the table elevated 15 to 30 degrees and the head of the patient slightly rotated to the right and tilted to the left and fixed by a 3-pin head holder. Safety belts and/or tape further secure the patient to allow lateral rotation of the operating table during the surgery. We typically use an optical tracking image guidance system (Stryker Navigation, Kalamazoo, MI) that is registered immediately after positioning the patient. This is followed by the placement of electrophysiologic monitoring electrodes. We use monitoring of the cortical responses to simultaneous stimulation of the upper and lower extremities, via median and tibial nerves, respectively (i.e., somatosensory evoked potentials or SSEPs). Changes in cortical responses, caused by cerebral ischemia or edema, can be detected earlier than changes in other physiologic parameters. SSEPs provide an early alert to a developing complication such as ischemia, intracranial hemorrhage, or parenchymal edema. Electromyography helps to identify specific cranial nerves by direct stimulation (i.e., CNs II, IV, VI in the cavernous sinus or superior orbital fissure) and to alert against injury.

Preparation of the nasal cavity includes the application of oxymetazoline solution (0.05%) by spray or saturated pledgets and injection of the middle meatus and anterior septum with lidocaine 1% and epinephrine 1/100,000. Broad-spectrum perioperative prophylactic antibiotics with CSF penetration and corticosteroids are administered before initiating the surgery.

First, the nasal cavity is carefully examined with 0- and 45-degree endoscopes to map the extent of the tumor and delineate the anatomy. This is followed by debulking of the tumor and middle turbinectomies (to provide an adequate working space and visualization). Exenteration of the ethmoid sinuses is dictated by the bulk and origin of the tumor. Similarly, the extent and origin of the tumor also determines the need for a unilateral or bilateral exposure and resection.

Following a middle turbinectomy and uncinectomy, a wide medial maxillary antrostomy serves to identify medial and inferior orbital walls. We prefer to identify the frontal recess at this point, using a prebullar technique. Exenteration of the ethmoid sinuses and/or debulking of the tumor proceed from anterior to posterior

Stay updated, free articles. Join our Telegram channel

Join