Pituitary surgery: Knowing when boldness is suitable
Experience, fortitude and due caution are vital to discerning which tumors are operable and which are better candidates for Gamma Knife radiotherapy.
Well, about 10 percent of us are walking around with a pituitary tumor, according to autopsy studies of “natural causes” deaths. Most such growths are benign and need only occasional MRI monitoring. A smaller group of tumors, though, erode physical health markedly. These patients are grateful for prospects of a complete cure, via aggressive surgery, and for the potential to reclaim years of their lives.
Two types of pituitary tumors emerge: Non-secreting growths that can present with “mass effect” – headaches, facial pain or numbness, or visual field deficits – from compressed nerves.
“Sometimes patients have had a couple of fender-benders and they don’t know why,” said Dr. Manuel Ferreira, director of the pituitary program at UW Medicine’s Neurosciences Institute at Harborview Medical Center.
It is the other subset of pituitary tumors – hormone-secreting – that Ferreira sees more frequently. Hormone overproduction can cause conditions such as acromegaly and Cushing’s disease, both of which provoke diabetes and hypertension and lower life expectancy by 20 years or more. Almost uniformly, these patients succumb to heart failure or heart attack, Ferreira said.
“These patients are aware of their pituitary conditions and being managed medically. They come to me with very poorly controlled sugars, sometimes on hundreds of units of insulin a day and/or multiple blood pressure meds that barely control their hypertension.”
Rationale for surgery in such cases is straightforward: About 95 percent of the time, total resection of secreting tumors cures the endocrinopathy and the resulting diabetes and hypertension.
Two factors demand caution, though:
Weighing benefit and risk
- Anything less than 100 percent removal of a secreting tumor “does the patient no good,” Ferreira said.
- Many tumors spread into the cavernous sinuses – passageways for the cranial nerves and carotid arteries. Surgery’s risk of injury to these structures, not to mention the brain and the pituitary itself, is historically high.
The calculus tends to lead surgeons to perform less-aggressive surgery and recommend radiotherapy/radiosurgery to treat the tumor’s remainder. Ferreira, credentialed to perform both skull-base surgery and Gamma Knife radiosurgery, has unique vision on which growths are operable. He built his skills at Massachusetts General, one of the nation’s busiest pituitary centers.
“Regions of the cavernous sinus were traditionally accessed blindly,” Ferreira said. “Now we have angled endoscopes that give a panoramic view, nicely lit. The obvious application is to go into the cavernous sinus to resect a secreting tumor, rather than performing a sub-total resection, giving the patient radiation and hoping you cure them.”
Ferreira described approaching these growths through a nostril, carefully punching through a thin sheath of bone and into the sella turcica, where the pituitary gland resides. He can drill the bone around the cavernous sinus and mobilize the carotid artery to safely explore and remove tumor tissue.
Patients who may be surgical candidates for pituitary tumors, secreting or not, have an unparalleled resource in the region, he said: the collective wisdom of UW Medicine specialists in neurosurgery, neuropathology, neuro-radiology, neuro-ophthalmology, radiation oncology, endocrinology and interventional radiology.
The skull base tumor board meets weekly to discuss every patient case, weighing risks and benefits of varied approaches to generate a consensus recommendation. Some patients are not candidates for surgery because the tumor adheres to, or invades, an artery or nerve or because they have complicated pre-existing conditions.
That's where radiation comes in.
192 precisely targeted beams
Gamma Knife treatments have two goals, said Dr. Jason Rockhill: “Stop tumor growth – and for a non-secreting tumor we have a greater than 80 percent chance of achieving that. For tumors that over-secrete hormones, the goal is to reduce the secretion, and our success rate is 40-60 percent.”
Rockhill, a UW associate professor of radiation oncology and neurological surgery, is an expert in Gamma Knife, the colander-shaped instrument that surrounds a patient’s head to deliver radiation beams from up to 192 angles.
“You can cause neurological loss like blindness. You have to keep the dose down to normal tissues but high enough to kill the tumor.”
Sometimes a tumor is too close to normal tissue to risk delivering a larger, single-session dose. The latest Gamma Knife, Perfexion with Extend, allows smaller and safer “fractionated” doses over a span of days. To accommodate this, however, the patient typically needs to have a stereotactic frame screwed into his skull at each visit in order to keep the head still and to exactly replicate the beams’ delivery angles.
Rockhill gets patients around this onerous task by making a customized bite block, the other end of which is fastened to the Gamma Knife, aligning the patient quickly and perfectly. In three to five sessions, Rockhill can maximize tumor control and minimize risk to normal tissues.
To refer a patient or learn more, contact the UW Medicine Transfer Center at 888.731.4791.
Why does it matter that UW Medicine neurosurgeons can remove certain pituitary tumors with a procedure performed at maybe a half-dozen sites in the nation?
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