Chapter 106 - Transsphenoidal surgery

Summary

Transsphenoidal surgery is the surgical approach of choice in treatment of sellar and parasellar tumors. The pathologies include pituitary adenomas, craniopharyngiomas, meningiomas, Rathke's cysts, chordomas, or, rarely, infectious etiologies and autoimmune disorders. The most common indication for transsphenoidal surgery is a pituitary adenoma that originates from the anterior lobe of a pituitary gland. The anterior lobe secretes prolactin (PRL), adrenocorticotropic hormone (ACTH), growth hormone (GH), thyroid-stimulating hormone (thyrotropin) (TSH), luteinizing hormone (LH), and follicle-stimulating hormone (FSH). Pituitary adenomas can be divided by size into microadenomas (< 1 cm) and macroadenomas (> 1 cm). Pituitary adenomas are also classified as clinically functioning (hyper-secreting, endocrine active) or as non-functioning (no hormone secretion, inactive). Patients can present with symptoms due to mass effect: headaches, visual deficits, cranial nerve neuropathies, and hydrocephalus or endocrine disturbance from hormone hypersecretion or hypopituitarism. The hypersecretory symptoms include amenorrhea-galactorrhea and infertility (hyperprolactinemia); Cushing's disease and hypercortisolism (ACTH); gigantism or acromegaly (GH); and thyrotoxicosis (TSH). Less common presentations of pituitary adenomas occur in association with certain endocrine syndromes (e.g., multiple endocrine neoplasia). In addition to recording the patient history and conducting a physical exam, the diagnostic evaluation for the majority of patients should include obtaining endocrine laboratory and MRI results (especially dynamic pituitary sequences). The main indication for treatment of these tumors is to reestablish normal hormonal secretion and to address the mass effect. The current treatment modalities include transsphenoidal surgical resection, medical management, and radiotherapy.

As our understanding of the physiology and pathophysiology of the hypothalamic-pituitary-end organs (e.g., thyroid, adrenal, gonads) has evolved, medical options have emerged for treatment alternatives for some of the functioning pituitary adenomas, the most common of which are prolactinomas. Currently, prolactinomas are primarily managed medically. The hypothalamic release of dopamine inhibits hypophyseal prolactin secretion, so dopaminergic-agonists have been developed (i.e., bromocriptine, cabergoline) to suppress prolactin secretion. Approximately 80% of patients with prolactinomas are controlled by medical therapy alone with a resultant normalization of prolactin and significant tumor shrinkage. The treatment is lifelong as agents are tumorstatic; withdrawal of the therapy will lead to tumor re-growth. Another drawback of the dopamine agonist treatment is that it causes tumor scarring and fibrosis, which can make any possible surgery much more difficult. Tumor fibrosis usually occurs in about one year after initiating treatment; therefore, early surgical intervention is preferred if the patient elects to proceed with surgery because of personal preference, management failure, or drug side-effects (headache, dizziness, nausea, postural hypotension).