Indications
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Indications for the transsphenoidal approach have significantly increased with the addition of the endoscope. Using a team approach with a skilled endoscopic rhinologist has rendered the endoscopic transsphenoidal approach a valid minimal access method for exposing various midline skull base pathologies involving the planum sphenoidale, tuberculum sellae, medial cavernous sinus, pterygoid bone, and infrasellar clivus.
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The most common indication for the endoscopic transsphenoidal approach is a sellar mass. These lesions include pituitary adenomas, Rathke cleft cysts, and craniopharyngiomas. Although microadenomas and small macroadenomas do not require extended approaches, lesions with suprasellar, cavernous sinus and clival extension can be resected with the extended endoscopic transsphenoidal approaches.
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Extradural and intradural chordomas can be resected using an endoscopic transsphenoidal approach with transclival extension.
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Meningiomas of the planum sphenoidale, meningiomas of the tuberculum sellae, and some small olfactory groove meningiomas are amenable to endoscopic, endonasal resection.
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Juvenile nasal angiofibromas arising from the pterygopalatine fossa can be removed through an endoscopic endonasal approach, even with extension into the infratemporal fossa and Meckel cave.
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Malignant tumors such as esthesioneuroblastoma, squamous cell carcinoma, and adenocarcinoma can be resected through an endoscopic transsphenoidal approach if the surgeon is confident that negative margins can be achieved.
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Encephaloceles, meningoencephaloceles, and other midline skull base defects prone to cerebrospinal fluid (CSF) leakage can be repaired through endonasal endoscopic approaches, avoiding a craniotomy.
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Large tumors that cannot be completely removed with an endoscope are not always contraindications to this approach. Depending on the age of the patient and the surgical goals, an endoscopic approach may augment a secondary cranial approach with internal decompression or a staged resection.
Contraindications
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Careful case selection is crucial to the success of this minimal access approach. Pathology extending laterally over the orbits or lateral and posterior to the carotid arteries is difficult to access, even when using extended endonasal approaches.
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Lesions extending into or posterior to the frontal sinus can be difficult to reach even with angled scopes. Additionally, the nasoseptal flap may not reach this far anteriorly, and skull base closure may be challenging.
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Invasion of the cavernous sinus is not an absolute contraindication but requires careful preoperative evaluation of surgical goals. The risk to surrounding neurovascular contents should be carefully assessed in the event the surgeon elects to enter the cavernous sinus to resect the tumor through a medial approach. Alternatively, an intentional subtotal resection or biopsy may be performed and augmented with planned postoperative stereotactic radiotherapy. Availability of an interventional neuroradiologist is crucial in preparation for endoscopic surgery around the carotid artery.
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The differential diagnosis of large sellar and suprasellar masses includes hypothalamic hamartomas, large intracranial aneurysms, and germ cell tumors. These lesions require a very different work-up and approach, and meticulous evaluation should be undertaken in appropriate patients to rule out such diagnoses preoperatively.
Planning and positioning
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Appropriate instrumentation for the endoscopic transsphenoidal approach differs from the instrumentation used for standard transcranial microsurgical approaches. Long, straight instruments with pistol grips are best for endoscopic approaches; specially designed bayoneted instruments can also be used. Monopolar cautery is favored for mucosal bleeding; bipolar coagulation is used with dural and intracranial structures. A tissue shaver or microdébrider is useful for resection of intranasal pathology; intracranial lesions require gentle bimanual suction, an ultrasonic aspirator, or a radiofrequency device. A micro-Doppler probe can be useful for identifying vascular structures. It is important to ensure that all endoscopic visualization equipment is working before starting the surgery. A range of endoscopes including 18-cm and 30-cm scopes with 0-degree, 30-degree, and 45-degree lenses should be available. High-definition cameras and widescreen displays allow the surgeon to visualize normal and abnormal structures. A sheath around the scope can be used to irrigate and clean the lens during the operation to minimize the need for repeated removal and introduction of the scope. Finally, a scope holder is often useful to maintain a fixed, steady field of view during aspects of the case in which mobile visualization is not required.
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After induction of general anesthesia, intravenous antibiotics (2 g of cefazolin or 1 g of vancomycin) and steroids (except in the setting of Cushing disease) are given. For large extended cases, we administer triple antibiotics. Injection of intrathecal fluorescein is an optional procedure that can help to identify CSF leaks during the surgery. After pretreating with antihistamines, 10 mL of CSF is removed via lumbar puncture, mixed with 0.2 mL of 10% fluorescein, and reinjected into the thecal sac. Alternatively, a lumbar drain may be placed for postoperative drainage if the risk of CSF leak is high. The head is placed in three-point pin fixation, elevated above the heart, and extended 10 to 15 degrees. If a fixed position is unnecessary, a horseshoe head holder may be used.
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Neuronavigation is not required but is highly recommended in endoscopic endonasal surgery. Navigation provides real-time information about the angle of approach and localization. Additionally, navigation allows the surgeon to tailor the approach for maximal visualization of pathology with minimal exposure and manipulation of vital neurovascular structures.
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The abdomen should be prepared for harvesting of a fat graft in case of CSF leak after resection of an intrasellar lesion. For extended approaches in which a large skull base defect is anticipated, the thigh should be prepared for harvesting fascia lata. A nasoseptal flap may also be harvested for large skull base defects.
Figure 46-1:
Operating room organization. Ergonomic placement of equipment is essential because endoscopic procedures require nondirect tools for visualization (i.e., viewing screens, neuronavigation). The patient’s head is positioned in the center of the operating room, angled slightly away from the anesthesia team. Two projection screens are used to allow easy visualization for the main operator and the assistant. A primary surgeon who is right-handed should stand on the patient’s right side.
Figure 46-2:
After positioning of the patient, the nose should be prepared and draped in a triangular fashion, exposing both nares. Cottonoids saturated with 4 mL of 4% cocaine are placed in the nares to vasoconstrict the nasal mucosa. Additional preparation and draping of the abdomen and lateral thigh should be done as necessary for harvest of fat and fascia lata.
