Quantitative assessment of brainstem distortion in vestibular schwannoma and its implication in occurrence of hydrocephalus

Purpose: Anatomical distortion directly affects the clinical status of patients with vestibular schwannomas (VSs). It may vary for a given tumor size due to variability in posterior fossa anatomy. We aimed to quantitatively assess brainstem distortion (BSD) and review its role in occurrence of hydrocephalus associated with VSs.

Methods: Sixty-six patients with small (<3 cm, n= 8; 12.1%); large (3-4 cm; n= 26; 39.4%) and giant (>4 cm; n= 32; 48.5%) VSs were included. Cystic VSs were excluded. Tumor size, tumor-extent, linear displacement (LD; distance between line bisecting pons (line 1) and posterior fossa midline (line 2)) and angular distortion (AD; angle subtended between lines 1 and 2) in axial-T2-MRI section through pons, and their effect on hydrocephalus were assessed.

Results: Significant BSD occurred in a younger age (p value = .004/.003), larger-sized tumor (p value = .001/.002), hydrocephalus (p value = .001/.001), trigeminal (V) nerve palsy (p value = .004/.003) and long tract signs (p value = .001/.034). Tumors crossing midline had significant association with hydrocephalus (p value = .003). LD increased progressively even for 4-5 cm-sized tumors while AD stabilized. Receiver operating characteristic (ROC) curve revealed that diagnostic accuracy of LD (area under the ROC curve (AUROC): 78.9% (95% CI: 67.2%, 90.5%, p < .001)), AD (AUROC:77.6% (95% CI:65.8%, 89.5%, p < .001)) and LD × AD (AUROC:80.3% (95% CI: 69.2%, 91.2%, p < .001)) for predicting occurrence of hydrocephalus was better than tumor size (AUROC: 66.7% (95% CI: 53.5%, 79.9%, p < .05). Cut-off values of LD and AD for predicting occurrence of hydrocephalus were 6.25 mm and 14.6°, respectively. Hydrocephalus was significantly more when both LD was greater than 6.25 mm and AD was greater than 14.5° (p value = .034). The role of LD and AD in influencing hydrocephalus was greater than categorization based on tumor size (Spearman's correlation coefficient: 0.535 and 0.248, respectively). Hydrocephalus occurred at a lesser cut-off value of LD and AD when compared to long tract signs.

Conclusions: LD and AD values in VSs have a significantly greater influence in the development of hydrocephalus compared to tumor size, and may aid, more reliably, in the prediction of hydrocephalus.