Pituitary adenoma

A tumour of less than 10 mm in diameter is called a microadenoma and is usually confined within the sella turcica (Fig.1) (see microadenoma pituitary).

A macroadenoma is a tumour of more than 10 mm in diameter and usually extends beyond the confines of the sella turcica, upward toward the chiasm and hypothalamus, downward toward the sphenoid sinus and laterally toward the cavernous sinuses (see macroadenoma pituitary)

Pituitary adenomas are usually benign tumours, and pituitary carcinomas are very rare. Metastases from pulmonary or breast tumours may grow within the pituitary gland. With regard to the hormone secreted, prolactinomas and ACTH-secreting tumours are usually microadenomas, located most commonly in a lateral position within the pituitary gland. GH-secreting adenomas and nonsecreting tumours (null cell adenomas, oncocytomas) are usually macroadenomas. Other secreting tumours like TSH-, FSH- or LH-secreting adenomas are very rare.

Neuroradiological diagnosis is based mainly on MRI findings, since this modality is the most accurate and most informative.

The study should be performed with coronal and sagittal thin slice T1-weighted images, without and with contrast enhancement. Microadenomas are usually iso-hypointense and are particularly well seen after gadolinium injection when the pituitary gland enhances homogeneously. The direction of growth of macroadenoma is well appreciated and involvement of chiasm and cavernous sinus may be detected.

CT is less accurate in demonstrating microadenomas and the relationship with the surrounding structures.

Plain film are no longer used routinely since the sella floor changes may be absent or may not reflect the true size and position of the tumour.

GS