Since the description of a transnasal approach for treatment of pituitary tumors, transsphenoidal surgery has undergone continuous development. Hirsch developed a lateral endonasal approach before simplifying it to a transseptal approach. Cushing approached pituitary tumors using a transsphenoidal approach but transitioned to the transcranial route. Transsphenoidal surgery was not “rediscovered” until Hardy introduced the surgical microscope. An endoscopic transsphenoidal approach for pituitary tumors has been reported and further advanced. We describe the principles of pituitary surgery including the key elements of surgical decision making and discuss the technical nuances distinguishing the endoscopic from the microscopic approach.
Key points
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The principles of pituitary surgery involve extensive surgical planning and decision making.
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Various technical nuances distinguish the endoscopic from the microscopic transsphenoidal approach.
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Strategies can be used during the nasal, sphenoidal, and sellar stages of surgery to maximize tumor resection, minimize complications, and preserve sinonasal anatomy/function.
Introduction
Evolution of Transsphenoidal Surgery
Since the initial description of a transnasal approach for the treatment of pituitary tumors in 1907, transsphenoidal surgery has undergone continuous evolution marked by close collaboration between neurosurgeons and otolaryngologists. Oskar Hirsch developed a lateral endonasal approach in 1910 that he initially performed as a 5-step procedure over a period of several weeks before simplifying the procedure to a single-step submucosal transseptal approach. Contemporaneously, Harvey Cushing began approaching pituitary tumors using a transsphenoidal approach but transitioned to the transcranial route because of his concern that an endonasal approach provided restricted access and poor illumination, compromising adequate decompression of the optic apparatus. Most neurosurgeons followed Cushing’s lead and transsphenoidal surgery was not “rediscovered” until Jules Hardy introduced the surgical microscope in the 1960s.
The first completely endoscopic transsphenoidal approach for pituitary tumors was reported in 1992 by Jankowski, and further advanced by the collaborative teams of Jho and Carrau in Pittsburgh and Sethi and Pillay in Singapore. Over the last 20 years, the endoscopic technique has been adopted by a multitude of surgeons who have favored the dynamic panoramic view afforded by the endoscope, allowing for improved visualization and better resection of tumors extending into the suprasellar area and cavernous sinuses. In addition, the advent of extended endoscopic endonasal approaches, such as the transplanum and lateral transcavernous approaches, has facilitated resection of large, invasive pituitary tumors that were previously deemed unresectable or requiring transcranial surgery.
Critics of the endoscopic approach have rightfully focused on the loss of stereoscopic vision as a major limitation, with mastery of the procedure demanding a steep learning curve. Prospective studies directly comparing the microscopic and endoscopic approaches for pituitary tumors have not been performed; however, an increasing body of literature has established the safety and noninferiority of endoscopic endonasal techniques, and several studies have demonstrated improvement in the extent of tumor resection. McLaughlin and colleaguesl reported that, after microsurgical resection of pituitary adenomas, endoscopy revealed residual tumor leading to further resection in 36% of cases. Messerer and colleagues found their gross total resection rate increased from 50% using the microscope to 76% on initial conversion to the endoscopic approach. In this review, we describe the principles of pituitary surgery, including the key elements of surgical decision making, and discuss the technical nuances distinguishing the endoscopic from the microscopic approach.
Introduction
Evolution of Transsphenoidal Surgery
Since the initial description of a transnasal approach for the treatment of pituitary tumors in 1907, transsphenoidal surgery has undergone continuous evolution marked by close collaboration between neurosurgeons and otolaryngologists. Oskar Hirsch developed a lateral endonasal approach in 1910 that he initially performed as a 5-step procedure over a period of several weeks before simplifying the procedure to a single-step submucosal transseptal approach. Contemporaneously, Harvey Cushing began approaching pituitary tumors using a transsphenoidal approach but transitioned to the transcranial route because of his concern that an endonasal approach provided restricted access and poor illumination, compromising adequate decompression of the optic apparatus. Most neurosurgeons followed Cushing’s lead and transsphenoidal surgery was not “rediscovered” until Jules Hardy introduced the surgical microscope in the 1960s.
The first completely endoscopic transsphenoidal approach for pituitary tumors was reported in 1992 by Jankowski, and further advanced by the collaborative teams of Jho and Carrau in Pittsburgh and Sethi and Pillay in Singapore. Over the last 20 years, the endoscopic technique has been adopted by a multitude of surgeons who have favored the dynamic panoramic view afforded by the endoscope, allowing for improved visualization and better resection of tumors extending into the suprasellar area and cavernous sinuses. In addition, the advent of extended endoscopic endonasal approaches, such as the transplanum and lateral transcavernous approaches, has facilitated resection of large, invasive pituitary tumors that were previously deemed unresectable or requiring transcranial surgery.
Critics of the endoscopic approach have rightfully focused on the loss of stereoscopic vision as a major limitation, with mastery of the procedure demanding a steep learning curve. Prospective studies directly comparing the microscopic and endoscopic approaches for pituitary tumors have not been performed; however, an increasing body of literature has established the safety and noninferiority of endoscopic endonasal techniques, and several studies have demonstrated improvement in the extent of tumor resection. McLaughlin and colleaguesl reported that, after microsurgical resection of pituitary adenomas, endoscopy revealed residual tumor leading to further resection in 36% of cases. Messerer and colleagues found their gross total resection rate increased from 50% using the microscope to 76% on initial conversion to the endoscopic approach. In this review, we describe the principles of pituitary surgery, including the key elements of surgical decision making, and discuss the technical nuances distinguishing the endoscopic from the microscopic approach.
Principles of surgery
Indications for Surgery
Pituitary adenomas are most frequently categorized as functional or nonfunctional depending on their hormonal secretory pattern. Prolactinomas represent the most common functional adenoma, and the mainstay of treatment is dopamine-agonist medical therapy, with surgical treatment reserved for patients who fail to respond despite dose escalation or are intolerant to the medications. Transsphenoidal surgery remains the primary treatment for adenomas secreting adrenocorticotropic hormone (ACTH, Cushing disease) and growth hormone (acromegaly) with biochemical remission rates significantly correlated with tumor size and invasiveness.
Nonfunctional pituitary adenomas (NFPA) are extremely common. Autopsy and radiographic studies reveal the presence of NFPA in 11% to 27% of the population. Although most NFPAs are microadenomas (<1 cm) and clinically asymptomatic, macroadenomas may present with compressive symptoms including headache, visual impairment, hormonal insufficiency, and cranial nerve palsies caused by cavernous sinus extension. Surgery is generally indicated for patients with macroadenomas causing visual compromise or exhibiting growth on serial imaging studies. Approximately 5% of patients with pituitary adenomas present with apoplexy caused by intratumoral hemorrhage or infarction.
Preoperative Surgical Planning
The main goal in endoscopic pituitary surgery is to maximize tumor resection while avoiding complications such as visual deterioration, cerebrospinal fluid (CSF) leakage, endocrinopathy, vascular injury, and sinonasal morbidity. Although pituitary adenomas are typically benign lesions, recurrences are common after incomplete surgical removal, and thorough preoperative surgical planning is essential to achieve optimal outcomes.
MRI studies reliably delineate the size and extension of pituitary tumors, with the notable exception of some ACTH-secreting microadenomas that may be radiographically occult. Inspection of the preoperative MRI provides an assessment of the likelihood of gross total resection primarily based on cavernous sinus extension as well as a prediction of the surgical challenges that will be encountered, such as intraoperative CSF leakage and a narrow surgical corridor because of reduced distance between the parasellar carotid arteries. Large tumors that extend vertically within the suprasellar area may significantly compromise the diaphragma sellae, or even invade the ventricular system resulting in high-flow CSF leaks requiring more extensive repairs such as nasoseptal flap (NSF) placement, lumbar drainage, or use of autologous tissues (eg, fascia lata or adipose tissue). As discussed in more detail later, preoperative anticipation of the need for an NSF is critical because the flap must be either harvested during the initial nasal stage of the approach or the vascular pedicle to the flap preserved such that a viable flap can be harvested later should it prove necessary. In addition, detection of the position of the normal compressed pituitary gland on the preoperative MRI assists with the preservation of hormonal function as intraoperative distinction of the gland from the tumor based on color and consistency differences is frequently subtle.
Computed tomography (CT) studies provide complementary information helpful in surgical planning. Coronal and sagittal reconstructions reveal bony changes, such as erosion of the sellar floor and dorsum, and can be used intraoperatively for image guidance, especially in patients with altered sinonasal anatomy related to previous surgery. Similarly, we have found preoperative nasal endoscopy helpful to optimize our surgical plan and avoid complications related to paranasal sinus disease or anatomic variability. Typically, chronic rhinosinusitis does not represent an absolute contraindication to transsphenoidal surgery; however, patients with acute rhinosinusitis, especially those with fungal disease, should be treated appropriately before elective surgery Preoperative otolaryngologic evaluation is critical in patients with acromegaly who frequently present challenges for airway management during surgery because of soft tissue hypertrophy and bony abnormalities
Surgical Approach: Nasal Stage
The endoscopic surgical approach for pituitary tumors can be divided into the nasal, sphenoidal, and sellar stages. Since the inception of our endoscopic skull base program at Thomas Jefferson University in 2005, we have advocated for a team approach between otolaryngology and neurosurgery. The complementary skill of experienced sinus and pituitary surgeons has enabled us to optimize oncologic outcomes and minimize complications, both minor and major. Our approach to pituitary surgery has evolved and we have adopted a tailored approach to these tumors based on their size, invasiveness, and secretory pattern, allowing us to minimize sinonasal disruption without compromising tumor resection.
Patients are positioned supine with the head on a gel headrest. Neuronavigation is used routinely to help guide the surgical approach and assess the adequacy of tumor resection with co-registration of the preoperative CT and MRI using facemask fiducials. Although neuronavigation is valuable, over-reliance on this adjunct and a failure to correlate with anatomic landmarks can lead the surgeon off course. The head is slightly elevated to reduce mucosal congestion and bleeding during the approach. We do not routinely prepare the skin of the face or nasal cavity with antiseptic solution, but graft sites such as the lateral thigh for fascia lata or adipose tissue should be prepared in a sterile standard fashion.
The turbinates are gently lateralized with a blunt instrument. Although routine resection of the middle turbinates is favored by some surgeons to increase the nasal working corridor, we have found that turbinate lateralization combined with a limited posterior septectomy provides more than sufficient access to the sella for pituitary tumor resection and minimizes postoperative patient sinonasal morbidity. A binarial approach is typically performed allowing 2 surgeons to work simultaneously with up to 4 instruments in the field, including the endoscope. In our experience, a pedicled NSF is rarely necessary for cranial base repair during standard transsellar pituitary adenoma resection; however, in certain cases the need for an NSF is unanticipated or may become necessary during future surgeries. As such, we advocate at least unilateral preservation of the NSF whenever possible and have described a variety of tailored approaches to the sphenoid sinus that enable NSF preservation applicable to endoscopic pituitary surgery. Our standard approach, termed the “1.5 approach,” involves an ipsilateral wide sphenoidotomy (“1”) on the working instrument side with a limited contralateral sphenoidotomy (“0.5”) on the endoscope side ( Fig. 1 A). The limited sphenoidotomy is performed by extending the natural sphenoid os superiorly with Kerrison rongeurs, thus preserving the more inferiorly located sphenopalatine artery supply to the nasal septal mucoperiosteum and mucoperichondrium. Addition of a limited posterior septectomy (typically 1 cm) allows communication of the binarial sphenoid exposures and provides ample working room and maneuverability (unpublished data). In patients with nasal obstruction caused by septal deviation or large spurs, a “tunnel approach” is performed involving a septoplasty and submucosal “tunnel” with a wide contralateral sphenoidotomy ( Fig. 1 B). The approach begins with a standard hemi-transfixion incision used for septoplasty, and the septal mucoperichondrium is raised and extended posteriorly over the vomer and laterally along the sphenoid rostrum. A septoplasty or spur removal is then performed, with the resultant unilateral “tunnel” analogous to the standard microscopic transseptal approach with preservation of the NSF ipsilaterally. On the contralateral side, a wide sphenoidotomy is performed. If NSF harvest proves necessary, the superior and inferior incisions for the flap can be performed and elevation completed on the “tunnel” side. The NSF harvest and replacement (“raise and return”) approach involves a standard harvest of the NSF combined with a wide contralateral sphenoidotomy. We typically reserve this approach for cases in which there is a high likelihood of NSF use, such as tumors with very significant vertical suprasellar extension or that extend anteriorly over the planum where, depending on tumor consistency, an extended endonasal approach may become necessary for complete tumor resection. This approach is also used for cases with potential for a high-flow CSF leak. If cranial base repair with the NSF proves unnecessary, the flap can be returned to its native position along the septum. These “raised and returned” flaps tend to heal quite well with minimal crusting and postoperative discomfort. We do not advocate routine harvest of the NSF, however, as this technique is associated with increased sinonasal morbidity including the possibility of olfactory dysfunction, septal perforation, and sensory loss because of superior alveolar nerve injury. A variety of investigators have described “rescue flap” modifications where the NSF is partially raised during the nasal stage such that the vascular pedicle is preserved, although these modifications have been associated in some cases with increased risk of olfactory loss.
