Pituitary Microadenoma

KEY FACTS

Terminology

• Microadenoma: ≤ 10 mm in diameter

Imaging

• Intrasellar mass is typical location

  • Rare: Ectopic origin outside pituitary fossa

• Best technique = dynamic contrast-enhanced thin-section T1-weighted MR

  • Generally enhance more slowly than adjacent normal pituitary

  • Beware: 10-30% can be seen only on dynamic contrast-enhanced scans

  • Occasionally, adenoma may be cystic or hemorrhagic

• Intrapituitary “filling defect” may be benign nonneoplastic cyst, as well as incidental microadenoma

Top Differential Diagnoses

• Rathke cleft cyst

• Craniopharyngioma

• Pituitary hyperplasia

• Other nonneoplastic cyst (e.g., pars intermedia cyst)

Pathology

• Adenomas are almost always WHO grade I

  • Pituitary carcinoma exceedingly rare (diagnosed when metastatic disease identified)

• Can occur as part of multiple endocrine neoplasia type 1, Carney complex, or McCune-Albright syndrome

Clinical Issues

• Symptoms of secreting tumors vary according to type

  • Prolactinoma is most common functional adenoma

  • Asymptomatic/nonfunctioning adenoma most common

• ~ 20-25% incidental finding at autopsy

• Medical therapy (bromocriptine, cabergoline) reduces prolactin secretion to normal in 80%

• Surgical (transsphenoidal) curative in 60-90%

TERMINOLOGY

IMAGING