Endocrine Abstracts

Background: Over 90% of the blood supply to the adenohypophysis arises from hypothalamic portal vessels, in contrast to the systemic blood supply to the posterior lobe. A pre-existing, or tumour stimulated direct (non-portal) blood supply has been suggested as a possible pathogenic mechanism for prolactinoma development.

Methods: 6 patients (3 microprolactinomas (mic), and 3 macroprolactinomas (mac)), and one control subject were imaged using a 3T magnet and intravenous gadolinium contrast. Sagittal imaging was performed, using a 2D inversion recovery turbo flash sequence, matrix 128x128, slice thickness of 6 mm, repeated every 30ms. Blood flow to each quadrant of the sagitally imaged pituitary (anterior (A), upper (U), lower (L) and posterior (P)), was assessed by comparing half-life (Tc) to contrast enhancement plateau.

Results: Tc/ms (mean, [1SD]) was significantly shorter for the posterior lobe, and the quadrants enhanced consistently in the order P (136 [58-319]), U (158 [52-480]), A (354 [149-842]), L (529 [222-1260]), p=3 x 10-9. Comparing mac and mic, there was no difference between Tc of the posterior lobe (Tc=232 and 110, p=0.08), but the anterior lobe of mac enhanced significantly more slowly than mic (Tc=1088 and 221, p=0.004).

Conclusion: In all patients enhancement of the posterior lobe occurs more rapidly than the anterior, consistent with a systemic supply to the posterior lobe. The pattern of pituitary vascular perfusion does not alter between tumour types; however, a slower enhancement of the anterior lobe in macroprolactinomas does not support the hypothesis of a direct systemic blood supply to macroadenomas.