Pituitary Adenoma and Hormone Excess States

Pituitary adenomas are benign tumours of the anterior pituitary that may secrete hormones autonomously, producing characteristic excess syndromes such as prolactinoma, acromegaly (growth hormone excess), and Cushing's disease (adrenocorticotropic hormone excess), or may be hormonally silent and cause symptoms through local mass effect. They are among the most common intracranial tumours and a central concern of pituitary endocrinology.

Definition

A pituitary adenoma is a benign neoplasm arising from anterior pituitary cells; a hormone-excess state is the clinical syndrome produced when such an adenoma autonomously oversecretes a pituitary hormone (for example prolactin, growth hormone, or adrenocorticotropic hormone).

Scope

This topic covers the classification of pituitary adenomas by the hormone they secrete (or by their non-functioning status), the clinical syndromes of hormone excess, and the mass effects of pituitary tumours. It is a reference overview of these entities and does not provide diagnostic thresholds, imaging protocols, or treatment regimens.

Core questions

• Which pituitary cell types give rise to functioning adenomas and what excess syndromes result?
• How do hormone-secreting and non-functioning adenomas differ in presentation?
• How does tumour mass effect produce symptoms independent of hormone secretion?

Key concepts

• Functioning versus non-functioning adenoma
• Prolactinoma
• Acromegaly (growth hormone excess)
• Cushing's disease (ACTH excess)
• Microadenoma versus macroadenoma
• Mass effect and visual field compromise

Mechanisms

Pituitary adenomas arise from clonal expansion of a single anterior pituitary cell type, and the secretory phenotype of the cell of origin determines the clinical syndrome: lactotroph tumours cause hyperprolactinaemia, somatotroph tumours cause growth hormone excess and acromegaly, and corticotroph tumours cause adrenocorticotropic hormone-driven Cushing's disease (Melmed, 2020). In acromegaly, sustained growth hormone excess raises insulin-like growth factor 1 and drives soft-tissue and skeletal overgrowth (Katznelson et al., 2014). In Cushing's disease, excess adrenocorticotropic hormone stimulates adrenal cortisol overproduction (Nieman et al., 2008). Non-functioning adenomas instead cause symptoms by compressing adjacent structures, including the optic chiasm and the normal pituitary, leading to visual loss and hormone deficiency.

Clinical relevance

Hormone-excess syndromes from pituitary adenomas have systemic consequences and are recognised by the constellations of features each produces, while non-functioning tumours are recognised by mass effect and hypopituitarism. This topic describes how these entities are conceptualised and classified; it is a reference, not a source of management or dosing advice.

Epidemiology

Pituitary adenomas are very common as incidental findings at autopsy and on imaging, but clinically relevant tumours are considerably less frequent. Prolactinomas are the most common functioning subtype, followed by growth hormone- and adrenocorticotropic hormone-secreting tumours; non-functioning adenomas make up a large share of clinically apparent macroadenomas (Melmed, 2020).

History

The link between pituitary tumours and clinical syndromes was established in the early twentieth century, when acromegaly and what became known as Cushing's disease were tied to pituitary pathology. The later identification of distinct hormone-secreting cell types and the development of specific hormone assays allowed adenomas to be classified by their secretory product, the framework reflected in current endocrine guidelines (Katznelson et al., 2014; Nieman et al., 2008).

Key figures

• Shlomo Melmed
• Laurence Katznelson
• Lynnette Nieman

Seminal works

• melmed-2020-nejm
• katznelson-2014
• nieman-2008

Frequently asked questions

Are pituitary adenomas cancerous?

The overwhelming majority are benign and do not spread; truly malignant pituitary carcinomas are rare. Even benign adenomas can cause significant problems through hormone excess or pressure on nearby structures.

What is the difference between a functioning and a non-functioning adenoma?

A functioning adenoma autonomously secretes a pituitary hormone and produces an excess syndrome such as acromegaly or Cushing's disease, whereas a non-functioning adenoma does not oversecrete a recognised hormone and usually presents through mass effect or pituitary hormone deficiency.