Last Updated: February 18, 2020
Diagnosis, Indications for Surgery and Preoperative Considerations
For a detailed discussion of the diagnostic indications for surgery and preoperative considerations in patients with suspected pituitary adenoma, please refer to the chapter on Pituitary Adenoma: Diagnosis and Operative Considerations.
PTERIONAL CRANIOTOMY FOR RESECTION OF PITUITARY ADENOMAS
Use of the pterional approach for pituitary adenoma resection is exceedingly rarely indicated. In less than 3% of patients, I use the transcranial, and more specifically, the pterional approach for reaching residual tumors unattainable through transsphenoidal surgery.
The major indications for the transcranial approach include significant intracranial tumor expansion well beyond the parasellar boundaries and a dumbbell-shaped tumor with a very narrow diaphragmatic neck. The presence of ectatic carotid arteries projecting along the midline is another contraindication to the transsphenoidal route, justifying the use of transcranial corridor.
The major limitations of the transcranial approach are the need for brain manipulation and difficulty in accessing the intrasellar component of the tumor, which is conveniently accessed transsphenoidally. The use of an endoscope has expanded the reach of the transsphenoidal route, obviating the need to use a transcranial corridor in almost all cases.
The remainder of this section focuses on nuances of technique for using the pterional route for reaching and resecting pituitary adenomas. For additional technical guidance for performing the pterional approach, please refer to the chapter on Pterional Craniotomy.
After completion of the craniotomy and dural opening, the anterior Sylvian fissure is split and the frontal lobe gently mobilized using dynamic retraction. The regional arachnoid membranes are dissected open and the parachiasmatic area is widely exposed. The tumor is typically covered by the ipsilateral optic nerve and the diaphragm encases the superior tumor capsule. The ipsilateral optic nerve can be relieved by large-scale decompression via operative trajectories medial and lateral to the nerve.
The lateral trajectory requires dissection between the carotid artery and the optic nerve. The internal carotid artery perforating vessels on the inferior and posterior surface of the optic chiasm and their associated arachnoid layers should be carefully protected. Preservation of these perforators decreases the risk of hemorrhage and ischemic infarction of the surrounding vital tissues; these complications are a significant source of morbidity from this operation.
An adherent tumor capsule poses a significant surgical challenge. If the capsule is attached to the perforating vessels of the carotid artery, posterior communicating artery, or middle cerebral artery, subtotal resection is prudent. The conservative approach involves removing only the core of the macroadenoma and leaving the capsule behind to preserve the tethered critical structures.
Adherent tumor capsule often engulfs the small and medium-size arteries at the skull base and therefore is refractory to total excision. The extra risk imposed by an attempted radical capsule removal is not justified. In this setting, the surgeon should focus on decompression of the nerves/chiasm and permissible adenoma resection, not endangering other structures. Radiotherapy is a reasonable option after partial resection.
TRANSNASAL TRANSPHENOIDAL RESECTION OF PITUITARY MACROADENOMAS
This procedure begins with standard preparation for transsphenoidal surgery with a noncaustic antiseptic agent used to cleanse the patient’s nasal compartment, gingival surface, and lower face. Placement of intranasal absorbable cotton soaked with a dilute cocaine solution is optionally used to induce vasospasm within the mucosa. This promotes hemostasis during the initial submucosal dissection.
I previously discussed the technical nuances for the microscope-guided approach in the chapter on Microscope-Guided Endonasal Transsphenoidal Approach of the Cranial Approaches volume. Moreover, the endoscopic-guided route is discussed in the Endoscopic Expanded Transnasal Approach. Please refer to these chapters for information regarding the initial and final stages of the operation, including exposure and closure.
The techniques of macroadenoma resection during microscope- and endoscope-guided surgeries are very similar and will be discussed herein. The endoscopic method offers significantly enhanced direct visualization of the operative space and greater working angles, thereby minimizing the risk of an inadvertent injury to the surrounding structures.
Specifically, macroadenoma resection is more efficient under endoscopic guidance because of the importance of wide visualization that increases the operator’s confidence in more aggressive maneuvers and resection. In other words, the improved view of the lateral blind spots via angled endoscopes promotes maneuvers that would have been considered risky under microscopic guidance.
The following section describes resection of macroadenoma through both microscope and endoscope-assisted methods. For a more detailed discussion of the advantages and disadvantages of microscope-assisted versus endoscope-guided adenoma resection, see Pituitary Adenoma: Diagnosis and Operative Considerations. I routinely employ the endoscopic route for resection of pituitary adenomas and I believe it provides remarkable advantages for maximizing safe tumor removal.
Persistent bleeding from the resection cavity indicates residual tumor. The most appropriate technique for achieving hemostasis is gross total tumor removal. Upon removal of the last pieces of the tumor, bleeding immediately ceases spontaneously. Minimal packing of Gelfoam may be needed to stop venous bleeding.
After gross total resection of the tumor, the diaphragm will prolapse and essentially fill the entire sella. This prolapse can hide tumor fragments along the corners of the sella. To inspect these corners further, I place a small cottonoid patty on the diaphragm and gently mobilize the diaphragm superiorly using the suction device. This maneuver allows easy inspection of the gutters that frequently house additional pieces of tumor. Similarly, the collapsed folds of the diaphragm, often evident around giant tumors, conceal tumor and these hidden spots should be inspected carefully to avoid surprise findings on postoperative imaging.
The intact pituitary gland is more firm and vascular and should not be aggressively manipulated.
Formation of scar within the recurrent tumors prevents them from descending into the sella. More aggressive and nontraditional maneuvers including sharp dissection within the sella under careful endoscopic vision are often necessary to mobilize the tumor within septations and achieve reasonable resection. The risk of CSF leakage is high but this risk should not prevent radical subtotal removal. Intraoperative MRI has a role for advancing surgery of the recurrent tumors.
Growth hormone and adrenocorticotropin-secreting macroadenomas present special challenges in their resection because their invasion of the cavernous sinus and surrounding dural membranes precludes their gross total resection in some cases. Patients harboring such tumors should undergo meticulous microsurgical resection to establish a cure. I pursue intracavernous removal of these tumors under endoscopic guidance. Transdiaphragmatic protrusion of these tumors requires sharp dissection of the diaphragm and their gross total removal.
For a more detailed description of postoperative considerations, remission parameters for secreting tumors, and complications related to macroadenoma resection, see the chapter on Pituitary Adenoma: Diagnosis and Operative Considerations.
Pearls and Pitfalls
- Tumor resection along the medial aspects of the cavernous sinus may lead to venous bleeding. Cauterization in this region is not advised, but use of thrombin-soaked Gelfoam powder to pack the bleeding site is reasonable.
- Inadequate bone removal along the floor of the sella (frequently laterally or anteriorly) is the most common cause of inadequate tumor resection.
- Subtotal tumor removal and apoplexy of the residual tumor is typically the cause of symptomatic postoperative hematoma.
Contributor: Benjamin K. Hendricks, MD
For additional illustrations of using endoscopes during skull base surgery, please refer to the Jackler Atlas by clicking on the image below:
*Redrawn with permission from Tew JM, van Loveren HR, Keller JT. Atlas of Operative Microneurosurgery, WB Saunders, 2001. © Mayfield Clinic
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