Advanced MRI to differentiate schwannomas and metastases in the cerebellopontine angle/internal auditory canal

Abstract

Background and purpose: Differentiating schwannomas and metastases in the cerebellopontine angles (CPA)/internal auditory canals (IAC) can be challenging. This study aimed to assess the role of diffusion-weighted imaging (DWI) and dynamic contrast-enhanced MRI (DCE-MRI) to differentiate schwannomas and metastases in the CPA/IAC.

Methods: We retrospectively reviewed 368 patients who were diagnosed with schwannomas or metastases in the CPA/IAC between April 2017 and February 2022 in a single academic center. Forty-three patients had pretreatment DWI and DCE-MRI along with conventional MRI. Normalized mean apparent diffusion coefficient ratio (nADCmean) and DCE-MRI parameters of fractional plasma volume (Vp), flux rate constant (Kep), and forward volume transfer constant were compared along with patients' demographics and conventional imaging features between schwannomas and metastases as appropriate. The diagnostic performances and multivariate logistic regression analysis were performed using the significantly different values.

Results: Between 23 schwannomas (15 males; median 48 years) and 20 metastases (9 males; median 61 years), nADCmean (median: 1.69 vs. 1.43; p = .002), Vp (median: 0.05 vs. 0.20; p < .001), and Kep (median: 0.41 vs. 0.81 minute^-1 ; p < .001) were significantly different. The diagnostic performances of nADCmean, Vp, and Kep were 0.77, 0.90, and 0.83 area under the curves, with cutoff values of 1.68, 0.12, and 0.53, respectively. Vp was identified as the most significant parameter for the tumor differentiation in the multivariate logistic regression analysis (p < .001).

Conclusions: DWI and DCE-MRI can help differentiate CPA/IAC schwannomas and metastases, and Vp is the most significant parameter.

Keywords: CPA; DCE-MRI; DWI; metastasis; schwannoma.

FIGURE 1

A 67‐year‐old female with a schwannoma in the left internal auditory canal (IAC). (A) Postcontrast T1‐weighted image shows a homogeneously enhancing lesion in the left IAC. (B) A region of interest (ROI) was placed on the solid component of the tumor on the apparent diffusion coefficient (ADC) map and normalized mean ADC was calculated. (C) As well, an ROI was also placed on the permeability map, and (D) Vp (blood plasma volume), (E) Kep (flux rate constant), and (F) Ktrans (forward volume transfer constant) maps were created. The corresponding values of Vp, Kep, and Ktrans (arrows) were 0.04, 0.53, and 0.5, respectively. Colors of parameters: black, low value; green, intermediate value; red, high value

FIGURE 2

A 32‐year‐old female with a metastatic lesion from melanoma in the left cerebellopontine angle (CPA). (A) Postcontrast T1‐weighted image shows a heterogeneously enhancing lesion in the left CPA. (B) T2‐weighted image shows a cystic component within the mass and edematous changes in the adjacent left cerebellum. (C) A region of interest (ROI) was placed on the solid component of the mass. Normalized mean apparent diffusion coefficient was 1.09. (D, E, F) An ROI was placed on the permeability map, and Vp (blood plasma volume), Kep (flux rate constant), and Ktrans (forward volume transfer constant) were calculated (arrows). Vp, Kep, and Ktrans were 0.19, 0.67, and 0.13, respectively. Colors of parameters: black, low value; green, intermediate value; red, high value

FIGURE 3

A 32‐year‐old female with a metastatic lesion from breast cancer in the left internal auditory canal (IAC). (A) Postcontrast T1‐weighted image shows a homogeneously enhancing lesion in the left IAC. (B) On apparent diffusion coefficient (ADC) map, normalized ADC mean is 1.07. (C, D, E) A region of interest was placed on the solid component on the permeability map. Blood plasma volume, flux rate constant, and forward volume transfer constant (arrows) were 0.21, 1.08, and 0.29, respectively. Colors of parameters: black, low value; green, intermediate value; red, high value

FIGURE 4

Receiver operating characteristics curves of statistically significant parameters between metastases and schwannomas in diffusion‐weighted imaging and dynamic contrast‐enhanced MRI analyses. Vp, blood plasma volume; Kep, flux rate constant; nADCmean, normalized mean apparent diffusion coefficient; AUC, area under the curves