Objective : Pituitary apoplexy is life-threatening clinical syndrome caused by the rapid enlargement of a pituitary tumor due to hemorrhage and/or infarction. The pathogenesis of pituitary apoplexy is not completely understood. We analyzed the magnetic resonance imaging (MRI) of pituitary tumors and subsequently correlated the radiological findings with the clinical presentation. Additionally, immunohistochemistry was also performed to determine whether certain biomarkers are related to radiological apoplexy. Methods : Thirty-four cases of pituitary adenoma were enrolled for retrospective analysis. In this study, the radiological apoplexy was defined as cases where hemorrhage, infarction or cysts were identified on MRI. Acute clinical presentation was defined as the presence of any of the following symptoms: severe sudden onset headache, decreased visual acuity and/or visual field deficit, and acute mental status changes. Angiogenesis was quantified by immunohistochemical expression of fetal liver kinase 1 (Flk-1), neuropilin (NRP) and vascular endothelial growth factor (VEGF) expression, while microvascular density (MVD) was assessed using Endoglin and CD31. Results : Clinically, fourteen patients presented with acute symptoms and 20 for mild or none clinical symptoms. Radiologically, fifteen patients met the criteria for radiological apoplexy. Of the fifteen patients with radiologic apoplexy, 9 patients presented acute symptoms whereas of the 19 patient without radiologic apoplexy, 5 patients presented acute symptoms. Of the five biomarkers tracked, only VEGF was found to be positively correlated with both radiological and nonradiological apoplexy. Conclusion : While pituitary apoplexy is currently defined in cases where clinical symptoms can be histologically confirmed, we contend that cases of radiologically identified pituitary hemorrhages that present with mild or no symptoms should be designated subacute or subclinical apoplexy. VEGF is believed to have a positive correlation with pituitary hemorrhage. Considering the high rate of symptomatic or asymptomatic pituitary tumor hemorrhage, additional studies are needed to detect predictors of the pituitary hemorrhage.