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This study evaluates the temporal evolution of the spatial relationship between the pituitary adenoma transsphenoidal surgical cavity and the adjacent optic chiasm and discusses implications on timing and choice of radiotherapy modality. This retrospective observational review analyzed factors that might influence the postoperative relationship between the surgical cavity and the optic chiasm, including tumor type, craniocaudal tumor and resection cavity dimensions, the preoperative distance between tumor and the optic chiasm, the presence of cavernous sinus invasion, and the choice of intraoperative packing material. Changes observed on magnetic resonance imaging in the preoperative, immediate (within 72 h), and delayed (≥3 months) postoperative periods were compared. Sixty-five patient histories were analyzed. Preoperatively, the pituitary adenoma was apposed to the optic chiasm in 43 patients (66%). Postoperatively, 34 patients (52%) in the immediate postoperative period and 54 patients (83%) in the delayed postoperative period had a distance ≥2 mm between the resection cavity and the optic chiasm. This distance provides a greater margin of safety with adjuvant radiosurgery. Preoperative tumor size showed a strong association with postoperative descent of the optic chiasm. Preoperative tumor size and degree of mass effect on the optic chiasm predict postoperative changes. In this study, the distance between the resection cavity and the optic chiasm was greater at ≥3 months postoperatively than in the immediate postoperative period, regardless of preoperative mass effect, indicating radiotherapy planning should be deferred to ≥3 months postoperatively when not precluded by aggressive histological characteristics that necessitate more immediate treatment. To investigate the temporal relationship between the postoperative sellar surgical cavity and the adjacent optic apparatus after transsphenoidal resection of pituitary adenomas and the implications for radiotherapy. • MRIs were evaluated in 65 patients after transsphenoidal pituitary adenoma surgery. • A subset of these patients may require adjuvant radiotherapy. • Radiosurgery is safest when the optic chiasm is >2 mm from the resection cavity. • The surgical cavity involutes predictably, increasing distance from the optic chiasm over time. [ABSTRACT FROM AUTHOR]