Purpose: To evaluate the consistency of fat in the high intensity signals of the normal neurohypophysis and to differentiate the high signal of posterior pituitary from that of dorsum sella. Sagittal SE T1-weighted images with frequency encoding in the horizontal direction were used in order to differentiate the high signal of posterior pituitary and dorsum sella by the vertically-oriented chemical shift artifact.
Material and methods: The sellae of 46 normal volunteers were imaged with a commercially available fat suppression technique and SE sequences with frequency encoding in vertical (25 cases) and horizontal (21 cases) axes.
Results: The high signal intensity was absent in 9% of the normal volunteers with no predilection to any specific age group. None of the cases with posterior pituitary high intensity signals showed suppression of the signal with fat suppression technique. A fat suppression technique was helpful in documenting the hyperintensity in 7% of normal volunteers. Nineteen of the 21 (90%) cases with high signal intensity were detected by routine SE T1-weighted images, whereas 18 of the 19 (95%) cases were detected by imaging with frequency encoding in the horizontal direction.
Conclusion: The high signal does not indicate the presence of fat. Fat suppression technique and a horizontal direction of frequency encoding help in differentiating the high signal of the neurohypophysis from that of dorsum sella.