What is a pituitary macroadenoma?

Pituitary Macroadenoma

A pituitary macroadenoma is defined as a pituitary adenoma measuring ≥1 cm in size, which can cause symptoms through mass effect on surrounding structures and/or hormonal dysfunction. 1

Definition and Classification

• Pituitary adenomas are neoplasms (usually non-malignant) arising from the hormone-secreting cells of the anterior pituitary 1
• Classified by size:
  • Microadenomas: <1 cm in diameter 1, 2
  • Macroadenomas: ≥1 cm in diameter 1, 2
  • Giant adenomas: >4 cm in diameter 1, 3
• Macroadenomas account for approximately 48% of all pituitary adenomas 2

Clinical Presentation

Macroadenomas can present with two main types of symptoms:

Mass Effect Symptoms

• Visual field defects (18-78% of patients) due to compression of the optic chiasm 2
• Headaches (17-75% of patients) 2
• Cranial nerve palsies, particularly oculomotor nerve dysfunction in large tumors 1
• Raised intracranial pressure in severe cases 1

Hormonal Dysfunction

• Hypopituitarism (34-89% of patients) due to compression of normal pituitary tissue 2
• Hormone hypersecretion depending on the cell type involved:
  • Prolactin excess (in prolactinomas) 1
  • Growth hormone excess (in somatotropinomas) causing acromegaly or gigantism 2
  • ACTH excess (in corticotropinomas) causing Cushing's disease 2
  • TSH excess (in thyrotropinomas) causing hyperthyroidism 1
• Approximately 30% are non-functioning adenomas that do not produce hormones 2

Diagnostic Approach

• MRI with high-resolution pituitary protocols is the gold standard imaging modality 1
• Contrast enhancement increases the conspicuity of adenomas, which typically appear as hypoenhancing lesions 1
• Complete hormonal evaluation is essential to detect:
  • Hormone hypersecretion 2
  • Hypopituitarism 2
• Visual field testing is mandatory for macroadenomas that approach or compress the optic chiasm 1, 2

Treatment Options

Treatment depends on the type of adenoma and associated symptoms:

Medical Therapy

• First-line treatment for prolactinomas is medical therapy with dopamine agonists (cabergoline or bromocriptine) 2, 4
• Somatostatin analogs may be used for growth hormone and TSH-secreting adenomas 3

Surgical Therapy

• Transsphenoidal surgery is the first-line treatment for most non-prolactin secreting macroadenomas 2, 5
• Indications for surgery in prolactinomas include:
  • Resistance or intolerance to dopamine agonists 4
  • Visual field defects that don't improve with medical therapy 1
  • Tumor growth despite medical therapy 1

Radiation Therapy

• Reserved for cases with incomplete surgical resection or recurrence 3
• May be considered for patients with growing tumors when other treatment modalities have failed 1

Prognosis and Follow-up

• Regular MRI surveillance is necessary to monitor for tumor growth or recurrence 1
• Hormonal evaluation should be performed periodically to assess pituitary function 1
• Visual field testing should be repeated if there are concerns about tumor growth affecting vision 6

Special Considerations

• Macroadenomas are more prevalent in children and young people than in adults, and they tend to be more aggressive in nature 1
• Genetic testing should be considered in young patients with macroadenomas as there is an increased potential for familial or genetic etiology 1
• Pregnancy can cause significant tumor growth in women with macroprolactinomas, requiring close monitoring 4