pituitary adenoma

Classification

• microadenomas (< 1 cm)
• macroadenomas (> 1 cm)

Etiology

• sporadic
• familial
  • multiple endocrine neoplasia-1 (MEN1)
  • familial acromegaly
  • McCune-Albright syndrome
  • Carney syndrome

Epidemiology

• 10% of primary brain tumors
• incidentally discovered pituitary neoplasms are common

Pathology

(classification)

• functional neoplasm
  • prolactin (PRL)-secreting tumors are the most common
  • tumors may also be derived from cells secreting:
    • growth hormone (GH)
    • ACTH
    • TSH
    • gonadotropins (LH, FSH)
  • plurihormonal hormones secreting combinations of PRL, GH, TSH, ACTH & glycoprotein hormone alpha subunit
  • autonomous hormone secretion (diminished response to feedback inhibition)
• non-functional neoplasm (1/3)

Genetics

• nearly all are monoclonal in origin
• loss of heterozygosity in 20% of sporadic pituitary adenomas
  • chromosome 9
  • chromosome 11q13
  • chromosome 13
• defects in AIP are associated with
  • predisposition to pituitary adenoma
  • familial isolated pituitary adenoma

Clinical manifestations

• depends upon size & function (pituitary hormone secretions)
• galactorrhea, amenorrhea, impotence (prolactinoma)
• increased hand & foot size, increased spacing of teeth (acromegaly)
• hyperthyroidism (TSH-secreting adenoma)
• proximal muscle weakness, facing rounding, centripedal obesity, violaceous striae, diabetes mellitus, hypertension (Cushing's disease, ACTH secretion)
• headaches, visual field loss*, cranial nerve palsy, diabetes insipidus, hypopituitarism (pituitary mass effect, pituitary apoplexy)

* often bitemporal quadrant visual field defect

• onset of visual field defect is generally gradual

Laboratory

• 8 AM serum cortisol*
  • serum ACTH: elevated with Cushing's syndrome
  • dexamethasone suppression test for Cushing's syndrome
    • 1 mg of dexamethasone fails to suppress serum ACTH
    • 8 mg of dexamethasone suppresses urinary free cortisol
• serum TSH, serum T4, free T4*
• serum prolactin*
  • elevated with prolactinoma; > 200 ng/mL confirms diagnosis
  • if < 200 ng/mL, also consider hypothyroidism
• serum IGF-1*: elevated with acromegaly
• growth hormone suppression test
  • failure of oral glucose to suppress serum GH is consistent with acromegaly
• ADH (serum sodium, serum osmolality, urine sodium, urine osmolality)
• serum LH serum FSH, 8 AM serum testosterone (male) serum estradiol (female)
• AIP gene mutation (familial pituitary adenoma)

* initial testing for pituitary incidentaloma

Radiology

• MRI of the sella turcica if pituitary mass effect suspected
  • first test after hydrocortisone administration (see pituitary apoplexy)
  • if bitemporal hemianopia, MRI neuroimaging with gadolinium contrast when renal function CKD3 or better
• repeat MRI at 6 months for incidentally discovered asymptomatic non-functioning pituitary adenoma to rule-out rapidly-growing neoplasm
• incidentally found pituitary macroadenomas are associated with 25% risk of enlargement over time, thus serial imaging is indicated

Complications

• mass effect of compression on normal pituitary
  • a large pituitary adenoma can cause panhypopituitarism
• pituitary apoplexy
• complications of hypophysectomy

Differential diagnosis

• see specific type of pituitary adenoma & pituitary hormone that it secretes
• pituitary gland is diffusely enlarged in untreated hypothyroidism & in normal pregnancy

Management

• most functional pituitary adenomas require treatment
  • exception is microprolactinoma in women with normal menses
• non-functional tumors require treatment only with well-defined sequellae of tumor growth
  • asymptomatic pituitary microadenomas do not require treatment
• neurosurgery is first line treatment for macro-adenomas & hypersecretory adenomas
  • the exception is prolactinoma for which treatment with a dopamine agonist is preferred [1]l
  • referral for visual impairment related to adenoma or pituitary apoplexy, mass abuts or compresses the chiasm or optic nerves on MRI
• radiation therapy
  • residual disease after 1st line therapy
  • patients who cannot undergo surgery
• treat hormone deficiencies
  • stress dose hydrocortisone if undiagnosed complication prior to MRI

More general terms

• pituitary neoplasm
• adenoma

More specific terms

• pituitary adenoma/ACTH secreting
• pituitary adenoma/ADH secreting
• pituitary adenoma/FSH secreting
• pituitary adenoma/GH secreting (somatotrophinoma)
• pituitary adenoma/LH secreting
• pituitary adenoma/non-secreting
• pituitary adenoma/prolactin secreting (prolactinoma)
• pituitary adenoma/TSH secreting
• pituitary incidentaloma

Additional terms

• acromegaly
• Carney complex
• McCune-Albright syndrome
• multiple endocrine neoplasia type-1 (MEN-1); multiple endocrine adenomatosis; Wermer Syndrome

Patient information

pituitary adenoma patient information

Database

• OMIM: https://mirror.omim.org/entry/102200