Skip to content

Pituitary Microadenoma

Summary

fleuron

  • Small (<10 mm) benign tumour arising from the anterior pituitary gland
  • May be functional (hormone-secreting) or non-functional
  • Often incidentally discovered on imaging; can cause endocrine dysfunction or mass effect1

Pathophysiology

  • Monoclonal neoplasm arising from adenohypophyseal cells
  • Classified based on hormone secretion:
    • Prolactinomas (most common)
    • Growth hormone-secreting
    • ACTH-secreting (Cushing's disease)
    • TSH-secreting
    • Gonadotropin-secreting
    • Non-functioning
  • Exact etiology unknown; genetic factors and hormonal stimulation may play a role

Demographics

  • Prevalence: 10-20% in general population (based on autopsy studies)
  • More common in women
  • Peak incidence: 30-50 years of age
  • Functional adenomas more common in younger patients

Diagnosis

  • Clinical presentation:
    • Asymptomatic (incidental finding)
    • Endocrine dysfunction (depending on hormone secretion)
    • Headache, visual disturbances (rare in microadenomas)
  • Laboratory tests:
    • Hormone levels (prolactin, IGF-1, ACTH, cortisol, TSH, free T4)
    • Dynamic endocrine testing (e.g., dexamethasone suppression test)

Imaging

  • MRI:
    • Modality of choice for diagnosis and follow-up
    • T1-weighted sequences:
    • Hypointense compared to normal pituitary tissue
    • Best visualised on post-contrast images
    • T2-weighted sequences:
    • Variable signal intensity
    • Dynamic contrast-enhanced imaging:
    • Delayed enhancement compared to normal pituitary tissue
  • CT:
    • Less sensitive than MRI
    • May show focal hypodense lesion
    • Useful for detecting calcifications or bony changes

panels-1

  • 50-year-old patient with headaches, joint pain and carpal tunnel syndrome was found to have elevated serum growth factor.
  • MRI showed a 4 mm hypoenhancing lesion in the right side of the gland.
  • The lesion was only subtly apparent on T2-weighted imaging.

Treatment

  • Depends on hormone status: dopamine agonists for prolactinomas, transsphenoidal surgery for Cushing's/acromegaly; non-functioning lesions are observed
  • Dynamic contrast MRI shows the microadenoma as a focus of delayed enhancement relative to the avidly enhancing normal gland

Differential diagnosis

Differential Diagnosis Differentiating Feature
Rathke's cleft cyst Typically midline; no enhancement (rather than hypo-enhancement); T1 and T2 hyperintense signal; intracystic nodule

  1. Melmed et al. Clinical Biology of the Pituitary Adenoma. 2022. Endocrine reviews - Open in new tab. ↩