Pituitary adenoma

Classification and key characteristics

• Size: microadenomas are less than 10 mm in diameter and macroadenomas are 10 mm or larger.
• Function: functioning (hormone-secreting) adenomas produce excess pituitary hormones; nonfunctioning adenomas do not secrete clinically relevant amounts.
• Local behaviour: most are non-invasive, some are invasive (extending into dura, cavernous sinus, or bone), and pituitary carcinomas with distant spread are very rare.
• Cell type: classified by the hormone produced or by lineage (e.g., lactotroph, somatotroph, corticotroph, gonadotroph, thyrotroph) identified with hormone assays and immunohistochemistry.

Clinical presentation and diagnosis

Symptoms reflect two main mechanisms: hormone excess and mass effect. Hormone-related syndromes include hyperprolactinemia (galactorrhea, menstrual disturbance, infertility), growth hormone excess (acromegaly), and corticotropin excess (Cushing disease). Mass effects can produce headaches and visual field defects, classically bitemporal hemianopsia due to optic chiasm compression. Nonfunctioning microadenomas are often discovered incidentally on imaging performed for unrelated reasons and are commonly termed "pituitary incidentalomas." Diagnostic evaluation combines biochemical endocrine testing with high-resolution magnetic resonance imaging (MRI) to image the pituitary and surrounding structures; the pituitary gland is often discussed in general terms at background resources.

When invasive behavior is suspected, imaging assesses extension into the cavernous sinus, bone, or dura. Invasion of adjacent bones such as the sphenoid bone is a recognized pattern; references to the local skull base anatomy and sphenoid sinus may be found at anatomy resources.

Treatment options and follow-up

Treatment is individualized according to tumor type, size, symptoms, and patient factors. Management approaches include:

1. Observation with periodic biochemical testing and MRI for small, nonfunctioning lesions without symptoms.
2. Medical therapy — for example, dopamine agonists (cabergoline, bromocriptine) are highly effective for prolactin-secreting adenomas; somatostatin analogues and other agents may be used for growth hormone–secreting tumors.
3. Surgery — transsphenoidal resection is the most common surgical approach to remove or decompress symptomatic adenomas, particularly macroadenomas compressing the optic apparatus.
4. Radiotherapy — conventional or stereotactic radiotherapy can be used for residual, recurrent, or medically resistant tumors.

Long-term follow-up frequently involves both endocrine surveillance and periodic imaging because hormone deficiencies or recurrences can appear years after initial therapy.

Epidemiology, prognosis, and notable points
Pituitary adenomas are among the more common intracranial neoplasms encountered in clinical practice. Many remain clinically silent and are found incidentally on imaging or at autopsy. Functioning adenomas most commonly secrete prolactin, followed by growth hormone and ACTH; nonfunctioning adenomas often present later because symptoms arise mainly from size. While the majority behave in a benign fashion and respond to treatment, invasive adenomas and the very rare pituitary carcinomas require more complex management. Advances in imaging, endocrinology, and surgical techniques over the last century have improved detection and outcomes, but individualized care remains essential to address the tumor's hormonal effects and local consequences.