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Objective: The purpose of this study was to determine whether the preoperative MRI findings of enhanced diffusivity, macrocyst content, and internal hemorrhage in pituitary macroadenomas are predictive of successful transsphenoidal hypophysectomy., Materials and Methods: We retrospectively reviewed the preoperative and postoperative sella protocol MR images of 28 patients who underwent transsphenoidal hypophysectomy for chiasm-compressing macroadenoma. Chiasmatic decompression defined surgical success. Two neuroradiologists differentiated nonsolid (macrocystic and macrohemorrhagic) from solid tumors, computed apparent diffusion coefficient (ADC) and T2-weighted signal intensity normalized to pons in solid tumors, and measured change in tumor height. A neuropathologist graded reticulin content in tumor specimens. Categorical and dichotomous variables were examined with the chi-square or Fisher's exact test; continuous-scale data were analyzed with the Student's t test, analysis of variance, or linear regression., Results: Transsphenoidal hypophysectomy succeeded in the management of 10 of 11 nonsolid tumors and nine of 17 solid tumors (p = 0.049). The ratios of tumor to brainstem ADC in the nine successfully resected solid tumors were higher than in the eight cases of failed treatment (p = 0.008) with no significant difference in ratio of tumor to brainstem T2-weighted signal intensity (p = 0.76). All six solid tumors with enhanced diffusivity (ratio of tumor to brainstem ADC > 1.1) were successfully managed with transsphenoidal hypophysectomy, compared with three of 11 with an ADC ratio less than 1.1 (p = 0.009). There was a significant main effect of ADC ratio groupings on change in tumor height (p = 0.02), and a linear relation was found between ADC ratio and change in tumor height (p = 0.04). Taken together, tumors with nonsolid features or an ADC ratio greater than 1.1 were highly resectable (p < 0.001; sensitivity, 0.84; specificity, 0.89). ADC ratios in reticulin-poor solid tumors were higher than those in reticulin-rich tumors (p = 0.024)., Conclusion: Macrocystic and macrohemorrhagic adenomas and solid tumors with enhanced diffusivity are more likely to be successfully managed with transsphenoidal hypophysectomy. Transsphenoidal hypophysectomy of solid, enhancing tumors with restricted diffusion is more likely to fail, possibly because of the greater reticulin content of the tumor; initial transcranial surgery may be appropriate in these cases.