Pituitary Adenoma

What is it?

Tumor caused by neoplasia of the anterior pituitary gland
Young and middle-aged women are most affected
Visual loss is usually slow, but may be acute from tumor hemorrhage (“pituitary apoplexy”)
Most tumors that affect vision are endocrinologically silent
Brain MRI is often diagnostic, but…
Trap: other masses can mimic pituitary adenoma on MRI
Transsphenoidal surgery usually provides dramatic visual improvement, but…
Large extrasellar extension may pose extra surgical risk
Marked pre-operative vision impairment adversely affects visual outcome

Core clinical features
- Subacute or chronic visual loss, often monocular
- Sudden visual loss usually means tumor hemorrhage in “pituitary apoplexy”
- Nerve fiber bundle and/or hemianopic defect
- Afferent pupil defect
- Optic discs appear normal or pale
Possible accompanying clinical features
- Chronic or new headache
- Hormonally-silent tumors are typically larger and more vision-impairing at presentation than the following hormonally-active tumors
  - Prolactin-secreting: galactorrhea, amenorrhea, decreased libido, impotence
  - Growth hormone-secreting: acromegaly, gigantism
  - Corticotrophin-secreting: cushingoid features, diabetes, myopathy
  - Thyrotropin-secreting: hyperthyroidism, goiter
  - Gonadotropin-secreting: precocious puberty, decreased libido
Imaging features
- Avidly and heterogeneously enhancing mass originating in the pituitary gland with extension into the suprasellar space
- Belt-like constriction between the sellar and suprasellar components of the tumor because of a tight diaphragma sellae

Order brain MRI
Trap: watch out for the following masses that mimic pituitary adenoma on MRI: pituitary hyperplasia, craniopharyngioma, metastasis, germ cell tumor, aneurysm, lymphocytic hypophysitis
Order serum prolactin: >200ng/ml signals a prolactinoma, which is usually treated first with a dopamine agonist (cabergoline)
Tip: non-prolactinoma sellar masses often elevate prolactin (“stalk effect”), but never above 200ng/ml
Refer non-prolactinomas to a neurosurgeon

Prolactinomas often shrink rapidly with dramatic visual improvement following dopamine agonist (cabergoline) therapy, making surgery unnecessary, but…
Trap: dopamine agonist therapy is not always effective or tolerated and must be maintained indefinitely
Non-prolactinomas are effectively managed by transsphenoidal or wide endonasal surgery with visual improvement or stabilization in >90%
If the tumor must be approached transcranially, visual improvement is less likely and visual damage is more likely
Tip: pituitary apoplexy must be managed with prompt hormonal replacement and fluids, but surgery can probably be briefly delayed without adverse consequences to allow for metabolic stabilization
Regrowth of tumor is uncommon but may occur many years after initial treatment, so you must maintain imaging and clinical surveillance
Radiation therapy is reserved for non-candidates for surgery, large post-operative residual tumors, or tumor regrowth