Overview
This lecture covers the anatomy, classification, and behavior of pituitary gland tumors, focusing on adenomas, their types, and recent WHO classification updates.
Pituitary Adenoma Classification
- Pituitary adenomas are mostly benign tumors arising from pituitary tissue.
- Adenomas are classified as non-secretory (null cell or gonadotroph adenomas) and secretory types.
- Non-secretory adenomas do not produce hormone-related symptoms.
- Gonadotroph adenomas stain for gonadotropin hormones but do not actively secrete them, thus considered non-secretory.
- Secretory adenomas include prolactinomas (prolactin), growth hormone adenomas (cause acromegaly/gigantism), and ACTH adenomas (cause Cushing's Disease).
Tumor Behavior and Rarity
- About half of pituitary adenomas are non-secretory, and the other half are secretory.
- Most adenomas (95-99%) are benign; a small number are atypical or aggressive.
- Pituitary carcinomas are extremely rare and may metastasize.
Updated WHO Classification
- The new WHO classification is based on tumor cell lineage and transcription factor expression.
- Three main transcription factors: TPIT, PIT1, and SF1, direct tumor lineage.
- TPIT lineage: corticotroph adenomas (ACTH tumors).
- PIT1 lineage: somatotroph (growth hormone), lactotroph (prolactin), mixed or plurihormonal tumors, and rare thyrotroph (TSH) adenomas.
- SF1 lineage: gonadotroph adenomas, typically most benign.
- Silent corticotroph adenomas are invasive but non-secretory, not causing Cushing's.
- PIT1 lineage tumors are currently identified as the most invasive, especially towards the cavernous sinus.
Key Terms & Definitions
- Pituitary Adenoma — Benign tumor of the pituitary gland.
- Non-secretory Adenoma — Tumor that does not produce excess hormones.
- Secretory Adenoma — Tumor that secretes excess hormones, causing clinical syndromes.
- Prolactinoma — Tumor that overproduces prolactin.
- Acromegaly/Gigantism — Conditions from excess growth hormone.
- Cushing's Disease — Condition from excess ACTH.
- Transcription Factor — Protein that regulates cell lineage in tumor classification (e.g., TPIT, PIT1, SF1).
- Silent Corticotroph Adenoma — Invasive ACTH cell tumor with no hormone excess.
- Gonadotroph Adenoma — Tumor from SF1 lineage, usually benign and non-secretory.
Action Items / Next Steps
- Review the updated WHO pituitary tumor classification and associated transcription factors.
- Familiarize yourself with the typical clinical presentations of secretory versus non-secretory adenomas.