Normal Anterior Pituitary Size on CT and MRI
The anterior pituitary (adenohypophysis) is the glandular lobe of the pituitary gland housed within the sella turcica, responsible for secreting key hormones including GH, TSH, ACTH, FSH, LH, and prolactin. Accurate measurement of its anteroposterior (AP) diameter is essential for distinguishing physiologic enlargement from pathologic processes such as macroadenoma or hyperplasia. Both CT and MRI are used to assess pituitary size, with MRI offering superior soft-tissue contrast for detailed evaluation.
Normal Reference Values
| Orientation | Location | Measurement |
|---|---|---|
| Anteroposterior | <12 Years Old | <6 mm |
| Anteroposterior | Puberty | <10 mm |
| Anteroposterior | Pregnancy | <12 mm |
| Anteroposterior | Adult Male | <8 mm |
| Anteroposterior | Adult Female | <9 mm |
Clinical Significance
Pituitary size is physiologically dynamic. The gland normally enlarges during puberty and pregnancy due to lactotroph and gonadotroph hyperplasia; failing to account for these states can lead to false-positive diagnoses of pathologic enlargement. In children under 12 years, an AP diameter exceeding 6 mm warrants further evaluation. In adult males, the threshold is 8 mm, and in adult females 9 mm, reflecting known sexual dimorphism.
A pituitary mass exceeding normal limits may indicate a microadenoma (≤10 mm) or macroadenoma (>10 mm), with the latter more likely to cause mass effect on the optic chiasm, cavernous sinus invasion, or hypothalamic compression. Diffuse symmetric enlargement without a discrete nodule more commonly reflects hyperplasia. A key pitfall is misidentifying a normally convex superior margin in adolescent girls or pregnant women as pathologic.
- Pituitary adenoma (macro- or microadenoma)
- Pituitary hyperplasia (physiologic or secondary, e.g., hypothyroidism)
- Craniopharyngioma
- Rathke cleft cyst
- Metastatic disease to the pituitary stalk/gland
Reference: M.D. DM, Grossman RI. Neuroradiology, The Requisites. Elsevier Health Sciences. (2010)
Imaging Notes
On MRI, the AP diameter is best measured on a sagittal T1-weighted image at the midline, from the anterior to posterior margin of the pituitary parenchyma within the sella. Post-gadolinium coronal sequences are critical for detecting focal hypointense adenomas against the homogeneously enhancing normal gland. The pituitary stalk should be central; deviation may indicate a mass effect.
On CT, the gland is assessed in coronal and sagittal reconstructions using thin-slice (≤1.5 mm) technique, ideally with contrast. CT is inferior to MRI for soft-tissue characterization but remains useful when MRI is contraindicated. Bony sella dimensions and erosion patterns can provide complementary diagnostic information on CT.