Normal Pituitary Gland Size
The normal pituitary gland height in adults averages 5.4 ± 0.9 mm, with an upper limit of normal being 9 mm in women and slightly less in men, as measured on MRI imaging. 1
Normal Dimensions by Age and Sex
Adults
- Average height: 5.4 ± 0.9 mm 1
- Women: Up to 9 mm can be normal 2
- Superior margin may normally bulge in younger women
- Both larger size and convex contour are associated with younger age
- Men: Generally smaller than women
Children and Adolescents
- Pituitary gland volumes gradually increase with age in both sexes 3
- Growth spurt during early puberty, more prominent in girls 3
- Girls generally have larger pituitary volumes than boys except at ages 1-2 years and 8-9 years 3
Posterior Pituitary Bright Spot
- Should always be visible on T1-weighted MRI 4
- Normal dimensions:
- Long axis: 4.8 mm (normal range: 1.2-8.5 mm)
- Short axis: 2.4 mm (normal range: 0.4-4.4 mm)
- Size decreases with patient age 4
Clinical Significance of Pituitary Size
Microadenomas vs. Macroadenomas
- Traditionally, pituitary adenomas are classified as:
- Microadenomas: <10 mm
- Macroadenomas: ≥10 mm
- Giant adenomas: ≥40 mm
However, recent research suggests that a 20 mm threshold may be more clinically relevant, as this is when the likelihood of requiring surgery increases significantly 5.
Empty Sella Syndrome
- Associated with smaller pituitary gland size (mean 3.63 mm vs. 5.05 mm in controls) 6
- Up to 40% of patients may have at least one hormone deficiency 6
- Requires comprehensive hormonal evaluation
Imaging Considerations
- MRI is the gold standard for pituitary imaging 7
- High-resolution pituitary protocols should be used for optimal visualization 7
- CT can identify large pituitary abnormalities but is less sensitive than MRI 7
- Both low and high-density areas may be seen within the normal gland on CT 2
Important Clinical Pearls
- A normal pituitary gland can have a convex superior margin, especially in younger women 2
- Serum prolactin levels do not appear to correlate with CT appearances of the normal gland 2
- When evaluating pituitary size, both age and sex should be considered as important variables
- Abnormal pituitary size may indicate functional or non-functional adenomas, empty sella syndrome, or other pathologies
When interpreting pituitary imaging, it's essential to consider these normal variations to avoid misdiagnosing normal anatomical variants as pathological conditions.