Direct Microscopic Transsphenoidal Surgery with Hybrid Use of Endoscopy

5 Direct Microscopic Transsphenoidal Surgery with Hybrid Use of Endoscopy

Abstract

The merits of direct endonasal microscopic transsphenoidal surgery (TSS) with the hybrid use of endoscopy are well recognized in contemporary neurosurgical practice for central skull base lesions. These include: easy and safe direct access to the lesion with no intervening brain tissue, preservation of the integrity of oral and nasal cavity, mitigation of inherent complications of craniotomy, and efficient tumor resection, facilitated by the panoramic view of the endoscope. Variations in TSS approach mirror its temporal evolution over the past 100 years and are credited to several avant-garde pioneers.1,2,3,4,5 The resurgence of neuroendoscopy^6,7,8 for solo or hybrid use and the introduction of endonasal extended direct TSS approach enhanced the list of indications for this route to encompass giant pituitary adenomas with extensions into the suprasellar region, medial cavernous sinus, or the clivus, and to include other lesions in this region such as craniopharyngiomas, Rathke’s cyst, dermoid cyst, and select cases of meningiomas or chordomas. This chapter describes the four stages of direct endonasal microscopic TSS approach and refers to the technical aspects of hybrid use of endoscope. The author highlights the important anatomical landmarks for guidance and includes pearls, challenges, and recommendations related to each stage of the intervention.

Keywords: Keywords: transsphenoidal, microscope, endoscope, pituitary, sellar, approach, tumor

5.1 Introduction

Transsphenoidal surgery (TSS) represents the first keyhole approach to central skull base pathologies and is the gold standard for resection of pituitary adenomas. Advancement in neuroimaging and navigation, refinement of surgical microscopes, and recent resurgence of endoscopy facilitated the admission of the direct endonasal TSS approach to the realm of minimally invasive interventions with excellent surgical outcomes. In fact, this approach has become the preferable route to treat a wide range of sellar lesions with or without extensions into the suprasellar region, cavernous sinus, sphenoid sinus, or the clivus; these include: giant pituitary adenomas, craniopharyngeomas, Rathke’s or dermoid cysts, and some select cases of meningiomas and chordomas.

The direct endonasal microscopic TSS was first reported as technical note by Griffith and Veerapen in 1987.⁹ The merits of this approach are well recognized, namely its direct and safe access to the pathology with no intervening neural tissue, integrity of the oral and nasal cavities, enhanced bimanual dexterity to perform microsurgical dissection, three-dimensional visualization and depth control with unobstructed surgical site for the instruments, mitigation of inherent complications of craniotomy, and more recently the panoramic view with extended visual arm offered by the hybrid use of the endoscope to achieve a more efficient resection of the pathology. The selection of the best TSS option is governed by the nature and extent of the lesion, the surgeon’s preference, bias inherent in neurosurgical training, experience, and practice trends. However, each approach has its indications, merits, and limitations, and the neurosurgeon should be acquainted with the different variants to select the proper match and achieve the best outcome.

5.2 Direct Endonasal Microscopic TSS with Hybrid Use of Endoscopy

5.2.1 Patient Preparation

The clinical pathway should include thorough clinical examination, detailed visual field and acuity tests, complete biochemical data and recent hormonal profile, and detailed MRI and magnetic resonance angiography (MRA) studies with good review of the sphenoid sinus anatomy or a CT scan as an alternative test for the latter. Oral endotracheal intubation is performed with packing of the oropharynx to avoid blood collection into the stomach. We prefer to fix the head in a three-point fixation clamp to prevent sudden inadvertent movement and to use neuronavigation at different stages of the procedure. This negates the need for fluoroscopy, correlates external skull base anatomy with intracranial (IC) structures, and guides tumor resection and tools position in the surgical field, in addition to its greatest value in repeated surgery for recurrent tumors. Eventually the skin of the nasolabial triangle, nasal vestibules, and the site for potential fat graft harvest at the abdomen or lateral thigh are prepped and draped in the usual manner.

5.2.2 Endonasal Stage I

The surgical microscope is introduced early at this stage and a low-profile medium-size nasal speculum is placed through the right nostril between the middle turbinate and the nasal septum guided by the navigation system. A medial posterior sphenoseptal mucosal flap is elevated after submucosal infiltration with 0.25% lidocaine and 1:200,000 adrenalin, using a 22-gauge, 3-inch spinal needle that facilitates mucosal dissection. Attention is paid not to injure the sphenopalatine artery that courses posterolaterally, which may lead to epistaxis. The nasal septum is then fractured and displaced to the contralateral side, leaving a small residual bony septum attached to the sphenoid crest. The nasal speculum is exchanged for a longer bivalve sphenoid retractor placed along both sides of the posterior residual bony septum to retract the mucosal flap laterally and ensure wide exposure of the sphenoid rostrum. The small posterior portion of the bony septum is then removed using a small rongeur and reserved for reconstruction of the sellar floor. A Killian nasal speculum is an alternative option for children and some patients with small nares. The sphenoid crest represents an important landmark of the sphenoid midline. Eventually the ostia of the sphenoid sinus are negotiated on both sides of the rostrum, located just medial to the posterior insertion of the superior turbinate and about 7 mm from the sphenoidal crest.^10,11

5.2.3 Sphenoid Sinus Stage II

A high-speed drill with curved tapered attachment to a 3 mm diamond burr is used to elevate the sphenoid rostrum (face-lift) between the two ostia supported by 1 to 2 mm Kerrison rongeur. A meticulous preoperative study of the sinus anatomy and pneumatization is very important.10,11,12,13,14 The septi within the sphenoid sinus are identified in correlation with the preoperative MRI/CT images and eventually removed using a rongeur or diamond drill with special care not to injure the underlying cavernous carotid or optic chiasma. Removal of the sphenoid mucosa reduces the incidence of postoperative mucocele formation. The sellar floor, the carotid bulge on both sides, and the chiasmal impression are identified using the navigation system. Now, proceed with a wide opening of the sellar floor and exposure of the dura using the diamond drill and Kerrison. Extending exposure laterally over the carotid recesses and cavernous sinuses and anteriorly to the circular sinus is recommended in the case of macroadenomas or as part of an extended approach. Bleeding is controlled with hemostatic agents, using Hemo patch or Floseal (Fusion Medical Technologies, Baxter Healthcare Corporation, Freemont, CA) and tamponade with cottonoids.

5.2.4 Intrasellar Stage III

The widely exposed dura is opened in a cruciate shape, and it is preferable to start near the central part of the dura and then extend the opening in four directions. This will prevent potential tearing of the arachnoid membrane superiorly or the medial wall of the cavernous sinus laterally. It is advisable to use the ball dissector to enucleate the microadenoma with its pseudocapsule and preserve the normal gland—better named as selective resection. For larger intrasellar tumors we should aim to achieve gross resection and use the endoscope as described later to remove residual tumor hidden behind the stalk, medial cavernous sinus, or in sub-diaphragm area. Care should be taken to maintain the integrity of the herniated arachnoid membrane—to prevent cerebrospinal fluid (CSF) leakage—and the intracavernous carotid artery using the Doppler sonography (Fig. 5.1 and Fig. 5.2). Bleeding from the cavernous sinus can be controlled by inserting small pieces of Surgicel and thrombin into the cavernous sinus and using Floseal.