Association of Cerebellar Peduncle Morphometry with Hypertrophic Olivary Degeneration: A Pilot Case-Control Study.

Background and purpose: Hypertrophic olivary degeneration (HOD) is a rare neurological condition resulting from disruption of the dentato-rubro-olivary pathway (DROP). Nearly half the HOD cases, however, lack detectable lesions in the DROP, and fewer than 10% of patients develop the condition following surgical resection of posterior fossa tumors. Based on these observations, we hypothesized that inherent anatomical variations in components of the DROP -specifically the inferior cerebellar peduncle (ICP) and superior cerebellar peduncle (SCP) -may predict susceptibility to HOD.

Materials and methods: This retrospective pilot case-control study included 12 patients who developed unilateral HOD following maximal safe resection of midline posterior fossa tumors and 24 matched controls who underwent tumor resection via the same standardized surgical approach but did not develop HOD. Morphometric measurements of the ICP and SCP were obtained from T2-weighted MRI and recorded as ratios to brainstem width (ICP/medulla, SCP/midbrain). Group comparisons were performed using independent t-tests, and effect sizes were calculated. Receiver operating characteristic analysis assessed the predictive accuracy of these ratios, while logistic regression and bootstrap resampling (10,000 iterations) were used to assess robustness and reproducibility.

Results: The ICP/medulla ratio was significantly lower in HOD cases (0.40 ± 0.04) than in controls (0.47 ± 0.06, p = 0.01), while the SCP/midbrain ratio showed no significant difference (p = 0.78). Effect size analysis indicated a large difference between groups (Cohen's d = -1.14). Receiver operating characteristic analysis demonstrated good predictive accuracy for the ICP/medulla ratio (area under the curve = 0.80, 95% CI, 0.64-0.92). Logistic regression confirmed a significant association between a smaller ICP/medulla ratio and increased HOD risk (p = 0.01). Bootstrap resampling reinforced the reliability of these findings (mean regression coefficient = -30.78, 95% CI: -61.59 to -12.70).

Conclusions: This pilot study suggests that smaller ICP/medulla ratios are associated with a higher likelihood of developing HOD following posterior fossa tumor resection. While preliminary, this novel finding highlights the possible role of these measurements in enhancing preoperative risk assessment.

Abbreviations: DROP = dentato-rubro-olivary pathway; HOD = hypertrophic olivary degeneration; ICP = inferior cerebellar peduncle; ION = inferior olivary nucleus; SCP = superior cerebellar peduncle.