Dr. Sarah Olson, Neurosurgeon, Greenslopes Private Hospital, Brisbane
As a surgeon there are several ways we can approach pituitary tumours. Unless surgery is an emergency (usually threatened vision) time should be spent working with the patient to determine the best way of treating their condition.
Meeting the patient
It is important to find out what problem the patient has. This can be determined often from imaging and from the blood tests usually arranged by an endocrinologist.
A patient who has a prolactinoma (generally speaking an elevated prolactin more than 10 times the upper limit of normal) will not come to surgery as a first option but be treated medically.
The general indications for surgery are: neurological dysfunction (usually an abnormality on visual field testing), a growing pituitary lesion, acromegaly and cushing’s disease.
There are many patients with incidental pituitary tumours or lesions in the pituitary gland that will never cause them a problem in their lifetime and it is not necessary to operate on everyone. 15% of people are found to have a pituitary tumour at autopsy when they have died of other causes and pituitary abnormalities seen in 22% of patients having an MRI of their brain for another reason.
It is important to find out the patients general health and whether they are fit to undergo major surgery.
It is important to look at the size of a patient’s nose and whether or not the nostril is big enough for a retractor. If not then we must decide to operate either under the upper lip or to use an endoscope to remove the tumour. Small nostrils can still make surgery with an endoscope more difficult as the angles of instruments in relation to each other is reduced.
We must obtain a nasal history from the patient. Nasal trauma, recurrent sinusitis, multiple nasal operations can make surgery via the nose more hazardous. A patient who has current sinusitis or and upper respiratory infection should delay their operation until it is cleared unless surgery is being performed as an emergency.
The use of anticoagulants must be revealed to a surgeon. Warfarin, clexane, aspirin, plavix are all hazardous drugs and can cause significant bleeding. In the natural medicines anticoagulants like ginko or fishoil must also be revealed.
Reviewing the Imaging
Both an MRI and CT can be helpful. A CT gives surgeons an idea of the bone surrounding the skull base. Some patients have poorly aerated sphenoid sinuses which makes access more difficult via the nose and these patients need to be well planned for.
Others may have a disease such as McCune Albright Syndrome where the bone is exceptionally thick in association with a pituitary tumour.
As a surgeon we need to be certain ourselves that the patient has a tumour rather than an aneurysm of the carotid artery. The MRI will help us determine that looking at flow voids in the lesion. Operating on an aneurysm via a nasal approach would be life threatening to the patient.
We need to look at the position of the carotid arteries. If they are too close together surgery is hazardous via any route. Sometimes the carotid arteries touch in the middle of the tumour. Aberrant arteries running through the sella also need to be looked for.
A tumour which is dumbbell shaped is more difficult to operate on via the nose but not impossible.
A tumour extending laterally outside the carotids into the cavernous sinus will not easily be removed via either a nasal or a cranial approach.
A tumour which has a large extension into the cranial cavity particularly into the middle anterior and posterior fossas may not be able to be completely removed via the nose and the extension may require a craniotomy. Some patients require both operations.
Meningiomas of the sella and parasella area are much firmer tumours and harder to remove. They have traditionally in the past been done via a cranial approach however some are now being operated on via a nasal approach as technology has improved. Similarly some pituitary tumours are very hard and if they have not been able to be removed via a transsphenoidal approach a surgeon may recommend a cranial approach.
Rathke’s cleft cysts and craniopharyngiomas are congenital lesions (the patient is born with them). As such they are quite integral and stuck to normal structures. Peeling their capsules off normal structures can result in significant deficits for a patient. Usually a surgeon will operate nasally but for patients who have recurrent difficulties a cranial approach may be advocated. Some surgeons advocate leaving a sella open without packing to allow the cysts of these problems to continually drain into the nose. Alternatively they may leave a small amount of tubing in the sella to allow drainage into the nasal cavity.
Types of operation:
Transseptal transnasal approach
This is the traditional operation via the nose for a pituitary tumour. The nasal septal mucosa is elevated back to the sphenoid sinus. The sinus is then entered and from there the pituitary fossa entered.
Transeptal transnasal approach to pituitary tumours
The surgeon detaches the back of the nasal septum from the anterior aspect of sphenoid sinus and then enters the sphenoid sinus. From there then the pituitary fossa is entered.
Both these operations utilize a microscope and a retractor in the nose
Endonasal approach to pituitary tumours
Endoscopic endonasal approach
Utilises an endoscope in the nose rather than a microscope and retractor. It is effectively the same operation as an endonasal approach. Because the light is closer to the object of interest however illumination is brighter and the procedure does not require any retraction in the nose. It will allow better panoramic views if an angled endoscope is used.
It does require however two surgeons and the use of endoscope in the nose can make the passage of other instruments more difficult.
Endoscopic Endonasal Approach to Pituitary tumours
ref: Illustration by Craig Luce
Expanded endonasal approach
Is an endonasal approach but more bone of the skull base may be removed to access tumours in parasella areas or the anterior cranial fossa.
Expanded Endonasal Approach to Pituitary Tumours
ref: Neurosurg Focus 2005 American Association of Neurological Surgeons
Craniotomy for pituitary tumours
Is generally done for cases where the tumour cannot be accessed easily via the nose or where the tumour is thought to be too difficult in its consistency to remove via the nose. It is also done where a transsphenoidal operation has not worked for a patient and an alternative plan is required.
A transfrontal approach enables the surgeon to see both sides of the pituitary fossa easily but is a longer approach and usually requires a large incision.
A pterional approach is a unilateral approach and is shorter but does not afford the same visibility of the opposite side.
Minimally invasive incisions can be made in select patents who are suitable often via an eyebrow incision.
Transfrontal Approach to Pituitary Tumours
ref: Mayfield Clinic for Brain and Spine
In conclusion there are several ways to operate on pituitary tumours. A surgeon must choose what they believe is best for a patient and the type of operation which in they feel for them yields the best results with the least morbidity for a patient.