Shear Stiffness of 4 Common Intracranial Tumors Measured Using MR Elastography: Comparison with Intraoperative Consistency Grading

Abstract

Background and purpose: The stiffness of intracranial tumors affects the outcome of tumor removal. We evaluated the stiffness of 4 common intracranial tumors by using MR elastography and tested whether MR elastography had the potential to discriminate firm tumors preoperatively.

Materials and methods: Thirty-four patients with meningiomas, pituitary adenomas, vestibular schwannomas, and gliomas scheduled for resection were recruited for MR elastography. On the elastogram, the mean and the maximum shear stiffnesses were measured by placing an ROI on the tumor. Blinded to the MR elastography findings, surgeons conducted qualitative intraoperative assessment of tumor consistency by using a 5-point scale. Histopathologic diagnosis was confirmed by using the resected specimens. The mean and maximum shear stiffnesses were compared with histopathologic subtypes, and the intraoperative tumor consistency was graded by the surgeons.

Results: The mean and maximum shear stiffnesses were the following: 1.9 ± 0.8 kPa and 3.4 ± 1.5 kPa for meningiomas, 1.2 ± 0.3 kPa and 1.8 ± 0.5 kPa for pituitary adenomas, 2.0 ± 0.4 kPa and 2.7 ± 0.8 kPa for vestibular schwannomas, and 1.5 ± 0.2 kPa and 2.7 ± 0.8 kPa for gliomas. The mean and maximum shear stiffnesses for meningiomas were higher than those of pituitary adenomas (P < .05). The mean and maximum shear stiffnesses were significantly correlated with the surgeon's qualitative assessment of tumor consistency (P < .05). The maximum shear stiffness for 5 firm tumors was higher than that of nonfirm tumors (P < .05).

Conclusions: MR elastography could evaluate intracranial tumors on the basis of their physical property of shear stiffness. MR elastography may be useful in discriminating firm tumors preoperatively.

Fig 1.

A passive pneumatic driver (MR Touch; GE Healthcare) was placed in a 12-channel phased array Neurovascular Array Coil (A). Shear waves were introduced in the brain by using this system (B).

Fig 2.

Comparison of the _meanSS and _maxSS determined by using MRE among histopathologically variable intracranial tumors: 13 cases of meningiomas (_meanSS = 1.9 ± 0.8 kPa, _maxSS = 3.4 ± 1.5 kPa), 11 cases of pituitary adenomas (_meanSS = 1.2 ± 0.3 kPa, _maxSS = 1.8 ± 0.5 kPa), 6 cases of vestibular schwannomas (_meanSS = 2.0 ± 0.4 kPa, _maxSS = 2.7 ± 0.8 kPa), and 4 cases of gliomas (_meanSS = 1.5 ± 0.2 kPa, _maxSS = 2.7 ± 0.8 kPa). The _meanSS and _maxSS of meningiomas were higher than those of the pituitary adenomas (P < .05). Box-and-whisker plots show the _meanSS (A) and _maxSS (B). The lower and upper hinges of the boxes denote the 25th and 75th percentiles, respectively. The median (50th percentile) of each distribution is indicated by the line. The whiskers on each side denote the 10th and 90th percentiles.

Fig 3.

Scatterplot of the _meanSS and _maxSS (kPa) determined by using MRE and a 5-point scale of intraoperative qualitative assessment of tumor consistency in 13 patients with meningiomas. Although the _meanSS did not significantly correlate with the grading (A), significant correlations between the _maxSS and the grading were obtained (B) (P < .05) (Spearman rank order test).

Fig 4.

Scatterplot of the _meanSS and _maxSS (kPa) determined by using MRE and a 5-point scale of intraoperative qualitative assessment of tumor consistency in 34 patients with 4 common intracranial tumors. Both the _meanSS and _maxSS were significantly correlated with the surgeon's grading (P < .05) (Spearman rank order test).

Fig 5.

Comparison of the _meanSS and _maxSS was determined by using MRE among tumors with an intraoperative consistency scale of 1–3 that were nonfirm and those with a scale of 4 and 5 that were firm; there were 29 cases that were nonfirm (_meanSS = 1.6 ± 2.6 kPa; _maxSS = 2.4 ± 1.2 kPa) and 5 cases that were firm (_meanSS = 3.0 ± 2.6 kPa; _maxSS = 4.2 ± 1.9 kPa). The _maxSS values in firm tumors were higher than those in nonfirm tumors (P < .05; Mann-Whitney U test). Box-and-whisker plots show the _meanSS (A) and _maxSS (B). The lower and upper hinges of the boxes denote the 25th and 75th percentiles, respectively. The median (50th percentile) of each distribution is indicated by the line. Whiskers on each side denote the 10th and 90th percentiles.

Fig 6.

Upper: Left parasagittal meningioma in a 44-year-old woman. A, Axial postcontrast T1-weighted MR imaging shows a strongly enhanced tumor (arrow). B, Axial T2-weighted MR imaging shows a hyperintense tumor (arrow). C, Wave MRE image (arrow). D, Elastogram shows tumor shear stiffness (arrow) (_meanSS = 2.1 kPa; _maxSS = 4.7 kPa). The intraoperative tumor consistency was intermediate (scale 3). E, Histopathologic examination of the resected tumor indicates meningothelial meningioma (hematoxylin-eosin stain; scale bar, 200 μm). Upper middle: follicle-stimulating hormone–producing adenoma in a 41-year-old woman. F, Axial postcontrast T1-weighted MR imaging shows a weakly enhanced tumor (arrow). G, Axial T2-weighted MR imaging shows an isointense tumor (arrow). H, Wave MRE image (arrow). I, Elastogram shows tumor shear stiffness (arrow) (_meanSS = 0.9 kPa; _maxSS = 1.1 kPa). The intraoperative tumor consistency was soft (scale 1).J, Histopathologic examination of the resected tumor indicates diffuse adenoma (hematoxylin-eosin stain; scale bar, 200 μm). Lower middle: Left vestibular schwannoma in a 50-year-old woman. K, Axial postcontrast T1-weighted MR imaging shows a strongly enhanced tumor (arrow). L, Axial T2-weighted MR imaging shows a mixed intensity tumor (arrow). M, Wave MRE image (arrow). N, Elastogram shows tumor shear stiffness (arrow) (_meanSS = 2.5 kPa; _maxSS = 3.3 kPa). The intraoperative tumor consistency was moderate (scale 3). O, Histopathologic examination of the resected tumor indicates a schwannoma with a dominant Antoni A-type region (hematoxylin-eosin stain; scale bar, 200 μm). Lower: Right insular glioma in a 55-year-old woman. P, Axial postcontrast T1WI MR imaging shows a ring-enhanced tumor (arrow). Q, Axial T2-weighted MR imaging shows a mixed intensity tumor (arrow). R, Wave MRE image (arrow). S, Elastogram shows tumor shear stiffness (arrow) (_meanSS = 1.5 kPa; _maxSS = 2.2 kPa). The intraoperative tumor consistency was moderate (scale 3). T, Histopathologic examination of the resected tumor indicates glioblastoma (hematoxylin-eosin stain; scale bar, 200 μm).

Fig 7.

Intraoperative tumors with a firm consistency. Upper: Left cerebellopontine angle meningioma in a 51-year-old man. A, Axial postcontrast T1-weighted MR imaging shows a strongly enhanced tumor (arrow). B, Axial T2-weighted MR imaging shows an isointense tumor (arrow). C, Wave MRE image (arrow). D, Elastogram shows tumor shear stiffness (arrow) (_meanSS = 4.4 kPa; _maxSS = 7.2 kPa). The intraoperative tumor consistency was mostly firm, requiring ultrasonic aspiration at a high setting (scale 4). E, Histopathologic examination of the resected tumor indicates fibrous meningioma (hematoxylin-eosin stain; scale bar, 200 μm). Lower: Nonfunctioning recurrent pituitary adenoma in a 63-year-old woman. F, Axial postcontrast T1-weighted MR imaging shows a strongly enhanced tumor (arrow). G, Axial T2-weighted MR imaging shows an isointense tumor (arrow). H, Wave MRE image (arrow). I, Elastogram shows tumor shear stiffness (arrow) (_meanSS = 1.6 kPa; _maxSS = 2.1 kPa). The intraoperative tumor consistency was mostly firm, requiring ultrasonic aspiration at a high setting (scale 4). J, Histopathologic examination of the resected tumor indicates diffuse adenoma with fibrosis (hematoxylin-eosin stain; scale bar, 200 μm).