Objective: To investigate the predictability of MRI and the possible biological markers of cavernous sinus invasion of pituitary adenomas associated with four phenomenas: angiogenesis, cell proliferation, apoptosis and matrix metalloproteinase. Methods: We evaluated 45 patients with pituitary adenoma according to the MRI, surgical findings and the immunohistochemistry staining of tumor tissues. Results: The results have shown that the sensitivity of MRI for predicting cavernous sinus invasion in this prospective study was 60%, its specificity 85%, its positive predictive value 83.33%, negative predictive value 62.96%. 45 specimens of pituitary adenomas were analyzed for expression of F8, VEGF, Ki-67, c-myc, Bcl-2, nm23 and MMP-9 immunoreactivity using immunoperoxidase staining. MVD was assessed using F8-related antigen. The results have shown that MVD of invasive pituitary adenomas was significantly higher than that of noninvasive (P<0.001). There was an association between the invasion of pituitary adenomas and Ki-67 LI (P=0.039) or the expression of VEGF (P<0.001) and MMP-9 (P<0.001). But c-myc LI and Bcl-2 expression have no association with invasiveness of pituitary adenomas (P=0.061 versus P=0.201). On the other hand, there is an inverse relationship between nm23 expression and tumor invasion (P<0.001). Conclusion: Parasellar extension of pituitary adenomas through the medial wall of the cavernous sinus is diagnosed at surgery, and with sensitive gadolinium-enhanced MRI, its extent can be partly determined by radiology. Although our study has shown that MVD and the expression of VEGF, Ki-67, nm23 and MMP-9 have associations with invasiveness of pituitary adenomas, they are lack of specificity. These markers can only provide some useful information.