24 Do’s and Don’ts in Pituitary Surgery

Dharambir S. Sethi and Beng Ti Ang

Introduction

Pituitary surgery has been traditionally performed by neurosurgeons using a sublabial, transseptal, transsphenoidal approach and the operating microscope.¹ The microscope provides excellent magnification, binocular vision, and a good depth of field essential for tumor removal. Transsphenoidal surgery has proven to be a safe and effective first-line therapy for most patients with sellar and suprasellar lesions. It is considered the “gold standard” and is effectively used by many pituitary surgeons around the world. More recently, since the description of endonasal resection of pituitary adenomas in three patients by Jankowski (an otolaryngologist) et al,² there has been a surge of interest in endonasal pituitary surgery. In the past decade, endonasal surgery for pituitary tumors has gained acceptance worldwide.^3–6

Working as a combined rhinology-neurosurgery team, we performed our first endoscopic pituitary surgery in October 1994. This has been a longstanding partnership; close to 500 pituitary tumors have been operated upon using direct endonasal techniques.

Our initial approach was transseptal.⁷ Though the results were encouraging, the transseptal approach had its limitations. One of the main limitations was having to work through a narrow tunnel created by elevating bilateral mucoperichondrial flaps on the nasal septum. Whereas the visualization was not compromised, instrumentation was often difficult, particularly when the situation required two surgeons to be working together while removing the tumor.

To overcome these limitations, we modified our approach to a direct endonasal transsphenoidal approach, avoiding a septoplasty and its inherent complications. This approach enables two surgeons to work through a common transnasal corridor using both hands and at times having four instruments in the operative field.^8,9

This chapter provides some useful clinical pearls and pointers for practitioners venturing into endonasal pituitary surgery.^10–15

Working As a Multidisciplinary Team

Since the introduction of endoscopic sinus surgery almost 25 years ago, otolaryngologists have become trained and experienced in endonasal sinus surgery and endonasal approaches to the sphenoid sinus. This accumulated experience of endoscopic-trained otolaryngologists may be utilized by neurosurgeons in providing endonasal access to the sphenoid sinus and the floor of the sella. The otolaryngologist’s main roles during surgery are to provide relatively bloodless and unimpeded access to the sphenoid sinus through a wide midline sphenoidotomy, and to assist the neurosurgeon in tumor removal.

Although it is possible for a single surgeon to perform this surgery, a team approach is preferred. Once the initial approach is complete, both the neurosurgeon and the otolaryngologist can work together for the remainder of the procedure. In some situations it is important for the two of them to work together, with the otolarynologist holding the endoscope and providing manual manipulation of the endoscope to optimize the visualization, particularly near the end of the procedure when the angled scopes are used and the field of view is constantly changing.

Endoscopic transnasal-transsphenoidal surgery for pituitary tumors is indicated in both endocrine active and nonfunctioning pituitary adenomas. Indications for surgery include all nonsecreting and most secreting pituitary tumors except for prolactinomas, which are usually well controlled by medical therapy with dopamine antagonist.16

Pre- and Perioperative Evaluation

All patients scheduled for pituitary surgery must undergo radiologic evaluation, endocrine assessment, and visual field tests pre- and postoperatively. A preoperative nasal endoscopic examination by the otolaryngologist should also be a part of the routine preoperative assessment. We have, in our institution, developed a “pituitary surgery pathway” for patients undergoing this operation. This is to ensure strict perioperative management compliance by all specialists.

Imaging Studies

Although both computed tomography (CT) and magnetic resonance imaging (MRI) have been used for imaging of the pituitary gland, MRI has become the preferred modality. MRI scanning of the pituitary region involving fine cuts and sagittal and coronal reconstruction is the gold standard imaging method for pituitary disease.¹⁷ Radiologic evaluation should also include CT scans of the nose, paranasal sinuses, and sella turcica. CT scans are useful in studying the bony anatomy; moreover, calcified lesions such as craniopharyngiomas may be more easily identified with CT. CT scans are also a useful alternative to the MRI in patients who are claustrophobic and unable to tolerate an MRI study. The extent of sphenoid pneumatization, sphenoid dominance, internal sinus septa, and their termination on the optic nerve or the internal carotid artery are important anatomical considerations in planning transsphenoidal approach.

Although a conventional MRI scan of the pituitary fossa provides information about the location, size, and boundaries of the lesion and its relationship to adjoining structures, the prediction of the consistency of macroadenomas is controversial.^18–20 Prediction of the consistency of pituitary tumors on diffusion-weighted (DW) MRI has recently been reported.²¹

Visual Field Testing

Progressive deterioration of visual fields is often the principal neurologic criterion on which surgical management decisions are based. Humphrey and Goldmann visual field evaluations are useful even if there appears to be no contact between the optic pathway and the pituitary mass, because field defects may reflect previous impingement, potential vascular shunting, or displacement of the chiasm following decompression.

Endocrine Evaluation

The perioperative endocrine management of a patient undergoing pituitary surgery may vary depending on the size of the pituitary lesion, the type of the lesion, the surgical approach (transsphenoidal, craniotomy), and the preoperative endocrine function.

Otolaryngology Assessment

A preoperative nasal endoscopic examination to exclude any active rhinosinusitis is undertaken by the otolaryngologist. Preoperative nasal endoscopy also provides useful information about the nasal anatomy, such as turbinate hypertrophy, concha bullosa, or a gross septal deviation that may necessitate a septoplasty for access to the sphenoid sinus. Preoperative treatment of nasal and paranasal sinus infections until there is complete return to normal is essential. Perioperative prophylactic antibiotics are routinely used.

Having the Right Setup

One of the most important prerequisites for endonasal pituitary surgery is having a good videocamera system, sinus surgery and neurosurgical instruments, a dedicated neuroanesthesiologist, and assisting nursing staff members who have been specially trained for this type of surgery. Intraoperative neuronavigation and intraoperative MRI (iMRI) are not an absolute necessity but are employed in various institutions as adjuncts to maximize resection and also in expanded endonasal approaches.

Operative Setup

The Digital Endoscopic Video Camera System (Karl Storz Endoscopy, Flanders, NJ) is placed at the cephalic end of the table to enable both surgeons to view the surgery on the video monitor. The neuroanesthetist is at the caudal end of the table. The scrub nurse and the instrument trolley are at the left cephalic end. Imaging studies are displayed for intraoperative reference. The otolaryngologist stands on the right side of the operating table and the neurosurgeon on the left side.

About 1 cm of the posterior part of the vomer is removed with a reverse-cutting forceps to facilitate the introduction of instruments from both nostrils. This step permits a panoramic view of the sphenoid sinus and enables the two surgeons to use both hands to introduce up to four separate instruments, two through each nostril. The access to the sphenoid sinus is complete. For a very wide access, necessary in some patients with large tumors requiring an extended approach, the entire posterior bony nasal septum may be removed to facilitate instrumentation.

The sphenoid sinus is next examined with 0-, 30-, and 70- degree, 4-mm endoscopes, and important anatomical land-marks within noted (Fig. 24.1). Of particular importance are the structures on the lateral wall. The carotid prominence, optic prominence, and opticocarotid recess can be well identified when the sphenoid sinus is well pneumatized. On the lateral recess of a well-pneumatized sphenoid sinus, the second branch of the trigeminal nerve (V2) and the vidian canal may be identified superolaterally and inferomedially, respectively.

On the posterior wall, the tuberculum sella, the anterior wall of the sella, and the clivus are identified. The location of the intersinus septa, if any, is noted. If these septa have to be removed, extreme caution is exercised, as they often terminate on the carotid canal or the optic canal. It is safer to use Tru-Cut instruments to remove these septa. Injudicious avulsion of the septa with non–Tru-Cut instruments may cause fracture of the thin bone overlying the cavernous sinus or the optic nerve with resultant hematoma, intractable bleeding, or even blindness. Caution is also exercised in not stripping the sphenoid mucosa, as this may result in considerable bleeding.