Pituitary Adenoma Syndromes

Pituitary adenomas are benign neoplasms arising from cells of the anterior pituitary. Their clinical impact depends less on the word benign than on what the lesion produces and what it compresses. A tumour may secrete excess hormone, suppress normal pituitary function by crowding healthy tissue, or expand upward into structures above the sella. Functioning adenomas create a hormone-excess syndrome. A prolactin-secreting adenoma may cause galactorrhoea, menstrual irregularity, infertility, reduced libido, or erectile dysfunction. Excess growth hormone produces acromegalic changes in adults: enlarged hands or feet, coarsened facial features, sweating, headaches, and glucose intolerance. ACTH secretion causes Cushing disease, while rare TSH-secreting lesions cause central hyperthyroidism. Clinically non-functioning adenomas do not produce a recognizable hormone-excess syndrome. They often present later, when their size causes mass effect or hypopituitarism. A lesion expanding upward can compress the optic chiasm. The crossing nasal retinal fibres carry information from the temporal visual fields, so chiasmal compression produces bitemporal hemianopia: loss of peripheral vision on both sides. MRI classifies a lesion smaller than 10 mm as a microadenoma and a lesion 10 mm or larger as...