Indications
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The transnasal transsphenoidal approach is employed for various pathologies involving the sella, suprasellar space, and sphenoid bone, including pituitary adenomas, Rathke pouch cyst, and craniopharyngiomas. Other indications include clival chordomas, meningiomas, metastatic lesions, and medial temporal lobe lesions such as encephaloceles.
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This approach is minimally traumatic to the brain, avoids brain retraction, does not create visible scars, provides excellent visualization of the pituitary, and is thought to cause less surgically related morbidity than transcranial approaches.
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This approach can be augmented with the use of an operative microscope and an endoscope. The operative microscope affords magnification, illumination, and three-dimensional viewing, and the endoscope expands the surgeon’s field of view. Both tools can be used simultaneously to complement each other.
Contraindications
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A classic transnasal approach is relatively contraindicated in cases of sphenoid sinusitis or ecstatic midline carotid arteries. Other relative contraindications include relatively small sellae, tumors with firm consistency, lesions with extensive intracranial invasion into the anterior cranial fossa or lateral or posterior extension, and asymmetric sellae. For these types of lesions, an expanded endonasal approach must be considered to maximize the visualization of lesions and to minimize potential vascular or neural complications.
Planning and positioning
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The sella can be approached by three transsphenoidal approaches: direct transnasal, submucosal tunnel via an anterior mucosal incision, or sublabial. The direct transnasal approach provides adequate visualization of the sella with minimal tissue dissection.
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Magnetic resonance imaging (MRI) provides the most useful preoperative imaging. T1-weighted images with and without gadolinium are useful for defining sellar anatomy and the relationship of sellar lesions to surrounding structures, including the optic chiasm, cavernous sinus, and internal carotid artery. T2-weighted images are useful for identifying cystic structures. Computed tomography (CT) scans are also helpful for defining sellar bony anatomy and identifying different subtypes of sphenoid sinus (i.e., conchae) that would be encountered intraoperatively.
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Special care should be taken in cases in which there is a suspicion of a vascular lesion with aneurysms in the cavernous carotid and cases in which surrounding vascular structures can be similar on imaging to pituitary lesions.
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Intraoperatively, surgical navigation with MRI or CT as an adjunct can be used in cases in which the anatomy is distorted by either the tumor or prior surgeries. Some authors have also reported the use of intraoperative real-time MRI, which can be considered if available for complex cases.
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Preoperative endocrine evaluation by an endocrinologist helps identify conditions of hormone excess or deficiency. This evaluation is especially critical for patients with hypoadrenalism or hypothyroidism, which pose surgical and anesthetic risks if not corrected before surgery. In addition, patients with prolactinomas may be sufficiently treated with dopamine agonist therapy, obviating the need for surgery. An evaluation by a neuroophthalmologist helps identify and define a patient’s preoperative visual acuity and visual field ability.
Figure 9-1:
Preoperative T1-weighted contrast MRI defines sellar anatomy and the relationship of sellar lesions to surrounding structures.
Figure 9-2:
The patient is positioned supine with the head elevated above the right atrium. The head is placed in a three-pin fixation device, with the neck flexed and turned toward the right shoulder so that a midline axis of approach is aligned with the surgeon’s field of view. The fluoroscope is positioned to give a coplanar view of the sella, and navigational devices are positioned for ease of view. An orogastric tube should be used to prevent drainage of blood products into the esophagus, which can result in immediate postoperative emesis or aspiration pneumonia. Some surgeons place a role of Kerlex gauze into the oropharynx as an alternative.
Figure 9-3:
The patient’s nose and facial structures are prepared with povidone-iodine (Betadine) solution, and the nasal mucosa is prepared with cotton-tip applicators soaked with Betadine solution. After preparation, the nose is packed with pledgets soaked with oxymetazoline (Afrin). Most patients are given ceftriaxone before beginning the surgery, and patients with Cushing syndrome are given preoperative stress dose steroids. The right lower abdominal quadrant, above the waste line, or the right thigh is prepared for harvesting of a fat or fascia lata graft. Also, a lumbar drain can be placed preoperatively if the tumor has suprasellar extension; a drain is optional if the lesion abuts the sellar diaphragm.Related posts:
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