**4.2 Pituitary dysfunction**

Pituitary dysfunction is generally caused by the adenoma compression over normal secretory glandular tissue or the pituitary stalk. Usually, significant tumor growth (size >1 cm) and pituitary compression is needed to cause pituitary dysfunction. GH is the first hormone to be affected, followed by LH and FSH, then TSH and lastly ACTH. Single hormonal dysfunction due to pituitary compression is extremely rare. Pituitary stalk compression may result in hyperprolactinemia due to the loss of inhibitory control from hypothalamus which manifest as a moderate elevation in prolactin level (usually <150 μg/l).

### **4.3 Mass effect**

Pituitary macroadenomas may extend to the suprasellar region causing compression to the optic nerves and chiasm. Visual impairment is seen in about 40–60% of patients upon presentation and the classical presentation is bitemporal hemianopsia. In addition, suprasellar mass growth may result in hypothalamic compression with subsequent disturbances in eating, emotion or sleep pattern. Rarely, 3rd ventricle extension may result in obstructive hydrocephalus. Parasellar extension into cavernous sinus is usually asymptomatic, however, oculomotor, abducens and trigeminal nerves compressive symptoms may occur. Additional parasellar extension may compress the mesial temporal lobe which can result in seizures.

#### **4.4 Pituitary apoplexy**

Pituitary apoplexy is defined as sudden onset of intense headache associated with visual field defects, ophthalmoplegia, and/or altered mental status [6]. Pituitary apoplexy is clinically observed in 1–7% of pituitary adenomas [6, 7]. The accepted pathophysiology is tumor outgrowth of the vascular blood supply

*Pituitary Adenomas: Classification, Clinical Evaluation and Management DOI: http://dx.doi.org/10.5772/intechopen.103778*

resulting in hemorrhagic infarction of the tumor mass [8]. Headache is the most common symptom which is usually felt over frontal or retro-orbital areas. However, visual field defects, cranial nerves palsy, and meningeal irritation signs and symptoms are not uncommon. Approximately 80% of patients have anterior pituitary hormonal dysfunction with ACTH deficiency being the most critical one.

There is evidence suggesting that the risk of pituitary apoplexy is higher in functional pituitary adenomas (e.g. GH-secreting adenomas and prolactinomas). However, there is contradicting data demonstrating a higher risk in non-functional ones [7]. Multiple risk factors for pituitary apoplexy have been identified including; sudden changes in blood pressure, (e.g. major surgeries), coagulative disorders and anticoagulation usage, radiotherapy, estrogen-based oral contraceptive pills, and head trauma [6, 7, 9].
