Invasive Pituitary Adenomas

Preoperative Considerations

• Pituitary adenomas are benign epithelial neoplasms derived from the pituitary glands. In the absence of a macroscopic capsule, those lesions can infiltrate adjacent structures such as the cavernous and sphenoid sinuses, dura and brain parenchyma. These tumors are considered invasive pituitary adenomas.

• They are characterized by their mass effect on bordering structures such as the optic nerves and chiasm, as well as for their capacity to disturb hormonal homeostasis.

• Visual symptomatology is the most common presentation, bitemporal hemianopsia being the classic symptom. Other symptoms include headaches, diplopia and occasional cerebrospinal fluid rhinorrhea.

• Hormonal disturbances can cause different syndromes; the most common are Cushing's disease, acromegaly and hyperprolactinemia.

• Treatment options include surgery, medication and radiotherapy. The treatment selection will depend on several factors:

  • Size and pneumatization of sphenoid sinus.

  • Tortuosity and position of carotid arteries.

  • Intracranial tumor extensions.

  • Suspicion about the pathology of the tumor.

  • Therapeutic history of the patient.

Indications

• Medical therapy is often required when surgery is delayed, contraindicated, or unsuccessful.

  • Drug therapy is especially useful in cases of prolactinomas, where the use of dopamine agonists is highly effective to achieve hormonal control and reduction of the tumoral mass.

  • Patients with acromegaly may benefit from the adjuvant use of somatostatin analogues postoperatively in order to achieve control of the disease.

  • Radiation therapy may be considered in patients whose disease is not controlled by surgical or medical therapy.

• Indications for surgery:

  • Visual deficits secondary to compression of the optic apparatus.

  • Cranial nerve deficits secondary to cavernous sinus invasion.

  • Apoplexy.

  • Macroprolactinomas that do not respond to medical treatment.

  • GH- or ACTH-secreting adenomas.

• The goals of the surgery are:

  • Resection of the tumor.

  • Decompression of the visual apparatus.

  • Improvement of the endocrinological symptoms.

  • Pathology diagnosis of the lesion.

  • Complete resection is challenging to achieve in large invasive pituitary tumors that present marked cavernous sinus invasion, regardless of the approach.

• Transcranial approaches are especially useful in the treatment of invasive pituitary adenomas, which present:

  • Significant extension into the anterior, middle or posterior cranial fossa; as well as those tumors that have lateral extension beyond the middle cerebral artery and/or those tumors encasing the anterior cerebral artery.

  • Suspicion of an important fibrous component of the tumor.

  • Small or underpneumatized sphenoidal sinus.

  • Uncertainty about the actual pathology of the tumor (i.e. a possible meningioma).

  • If transsphenoidal surgery has already failed.

• Some examples of feasible approaches for invasive pituitary tumors are:

  • Transsphenoidal (and transsphenoidal staged).

  • Subfrontal , bifrontal or extended-bifrontal, transbasal — used in suprasellar tumors with significant superior, inferior or lateral extension.

  • Supraorbital — for adenomas confined to the sellar region with minimal parasellar extension lateralized to one side.

  • Pterional — in cases of pre-fixed chiasm with limited extension.

  • Orbitozygomatic — in cases with marked suprasellar or parasellar extension or invasion of the cavernous sinus or interpeduncular cistern.

• Extended endoscopic approaches have been recommended as useful alternatives for resection of giant invasive adenomas by experienced surgeons. (For endoscopic management, please refer to Section 5: Endoscopic Approaches to Skull Base Tumors). This may be especially useful in:

  • Patients unable to tolerate transcranial surgery.

  • Longstanding damage of the chiasm (may not tolerate additional trauma like mobilization required through the transcranial route).

  • Palliative debulking.

• Another valid option for extensive cases is a combined approach (staged or not) or endoscope assisted-microneurosurgery.

• Close collaboration between surgeons, endocrinologists and radio-oncologists is essential in the management of invasive pituitary adenomas since combined therapies may be key for tumor control.

• Preoperative evaluation

  • Neuroimaging: MRI sequences to describe the size, location and relation with CNS structures of the tumor. CT scans are useful when additional description of the osseous anatomy is required, particularly when the patient has been exposed to previous cranial surgeries.

  • Endocrine assessment for hormonal overload and/or deficiency. Special attention is given to thyroxine and cortisol levels.

  • Neuro-ophthalmological evaluation.

Surgical Procedure

The goal of this chapter is to describe the most common alternatives to the transsphenoidal approach for those invasive pituitary adenomas with marked extension to the suprasellar or parasellar regions or after a partial removal via the transsphenoidal approach: pterional, orbitozygomatic and bifrontal approaches. For endoscopic management, please refer to Chapter 23, Chapter 24, Chapter 25 .