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Introduction/Purpose Prior work by our group has shown Pituitary-to-Sella Ratio (PSR) to reliably reflect treatment response following successful CSF shunting or venous sinus stenting (VSS) for Idiopathic Intracranial Hypertension (IIH). We sought to directly compare PSR to ventricular volume (VV) as noninvasive measures of intracranial pathophysiology in surgically managed IIH patients.Materials and Methods We performed retrospective chart review of all adult patients treated for IIH with successful CSF shunting or VSS at our institution from 2018-2025. We then assessed how PSR and VV change from pre-operative imaging to post-operative imaging (≥21 days post-op) following surgical intervention. PSR was manually segmented in Sectra PACS. VV was determined as the sum of the bilateral lateral ventricles as automatically calculated using SynthSeg 2.0 in FreeSurfer 8.1.0. Any SynthSeg segmentations with DICE scores ≤0.65 for CSF, white or gray matter segmentations were manually reviewed and corrected as necessary. We also calculated Ventricle-to-Intracranial Volume Ratio (VIR) as VV/(Total Intracranial Volume). Signed-rank tests were utilized to assess for significant differences between pre- and post-operative values for each of PSR, VV, and VIR.Results We identified 32 patients (19 shunted and 13 VSS) meeting inclusion criteria with the appropriate pre- and post-operative imaging available. Median [IQR] pre-operative PSR, VV and VIR were 0.50 [0.43,0.60], 9890 [7518,15487] mm 3, and 7.13E-3 [5.82E-3,11.34E-3] respectively. Median [IQR] post-operative PSR, VV and VIR were 0.62 [0.52,0.74], 9654 [6317,14322] mm3, and 7.02E-3 [5.50E-3,10.33E-3] respectively. PSR was significantly increased with a median change of +0.109 (p=2.9E-4) from pre- to post-operative imaging with a Hedges’ g [95% CI] of 0.68 [0.33—1.06]. A multivariate linear regression model (PSR Percent Change ~ 1 + Pre-Operative PSR * Surgery Type) revealed no significant effect of pre-operative PSR (OR [95% CI] of 0.74 [0.50—1.10], p=0.15), surgery type (shunt versus VSS, OR [95% CI] of 1.14 [0.83—1.56], p=0.42), or the interaction of these two variables (OR [95% CI] of 0.69 [0.38—1.23], p=0.22) on percent change in PSR from pre- to remote post-operative imaging. Neither VV nor VIR were significantly different between pre- and post-operative imaging (p=0.78 and p=0.85, respectively). Furthermore, this lack of significant difference held when considering only shunted patients (N=19) for VV (p=0.053) and VIR (p=0.099).Conclusion PSR, and not lateral ventricular volume, is a sensitive measure of treatment response following surgical management of IIH. Importantly, PSR demonstrates significant increases regardless of surgical modality whereas VV and VIR do not reliably change even when considering only shunted IIH patients.Disclosures M. Cotroneo: None. A. Finkelstein: None. S. Mendoza-Ayus: None. G. Kohli: None. D. Schartz: None. M. Bender: None.