Quantitative MR evaluation of intracranial epidermoid tumors by fast fluid-attenuated inversion recovery imaging and echo-planar diffusion-weighted imaging

Abstract

Background and purpose: Quantification of MR can provide objective, accurate criteria for evaluation of a given MR sequence. We quantitatively compared conventional MR sequences with fast fluid-attenuated inversion recovery (fast-FLAIR) and echo-planar diffusion-weighted (DW) MR imaging in the examination of intracranial epidermoid tumors.

Methods: Eight patients with surgically confirmed intracranial epidermoid tumors were examined with T1-weighted MR sequences, fast T2- and proton density-weighted dual-echo sequences, fast-FLAIR sequences, and DW echo-planar sequences. We measured the MR signal intensity and apparent diffusion coefficient (ADC) of epidermoid tumors, normal brain tissue, and CSF and calculated the tumor-to-brain and tumor-to-CSF contrast ratios and contrast-to-noise ratios (CNR). Results were compared among the five MR methods.

Results: On fast-FLAIR imaging, the mean signal intensity of epidermoid tumors was significantly higher than that of CSF but significantly lower than that of the brain; the contrast ratio and CNR of tumor-to-CSF were 4.71 and 9.17, respectively, significantly greater than the values with conventional MR imaging. On echo-planar DW imaging, epidermoid tumors showed a remarkably hyperintense signal relative to those of the brain and CSF; the mean contrast ratio and CNR of tumor-to-CSF were 13.25 and 19.34, respectively, significantly greater than those on fast-FLAIR or conventional MR imaging. The mean ADC of epidermoid tumors was 1.197 x 10(-3) mm(2)/s, significantly lower than that of CSF but higher than that of brain tissues.

Conclusion: Fast-FLAIR imaging is superior to conventional MR imaging in depicting intracranial epidermoid tumors. Echo-planar DW imaging provides the best lesion conspicuity among the five MR methods. The hyperintensity of epidermoid tumors on echo-planar DW imaging is not caused by the diffusion restriction but by the T2 shine-through effect.

fig 1.

Inverse correlation between CNR of tumor-to-CSF_ventr on FLAIR images and ADC of epidermoid tumors in the corresponding cases (Pearson correlation coefficient, −.910; P = .0006)

fig 2.

Right CPA epidermoid tumor in a 72-year-old man. A-C, Contrast-enhanced T1-weighted (400/8/2 [TR/TE/excitations]) (A), fast T2-weighted (3000/98/2) (B) and proton density–weighted (3000/14/2) (C) images do not show the epidermoid tumor but only slight expansion of the arachnoid cistern in the right CPA (arrow). D, Fast-FLAIR imaging (10002/148/1, inversion time of 2200) shows the tumor (arrows) as unevenly hyperintense relative to the CSF but hypointense relative to the brain. E, Echo-planar DW imaging (1600/126 [TR/TE] with b value of 1000 s/mm²; field of view, 24 × 24 cm) reveals the tumor as a sharply hyperintense lesion (arrows) relative to the brain and CSF. F, ADC map shows that the intensity of the tumor is similar to that of surrounding brain tissue but much different from that of CSF. Note the uneven diffusion in the lesion (arrows).

fig 3.

Suprasellar region epidermoid tumor in a 47-year-old woman. A, Fast-FLAIR imaging (10002/148/1, inversion time of 2200) shows that epidermoid tumor (black arrows) fills the suprasellar and right ambient cisterns; the hyperintensity in the left ambient and interpeduncular cisterns (white arrows) probably is caused by CSF flow artifacts. B, Echo-planar DW imaging (1600/126 with b value of 1000 s/mm²; field of view, 36 × 24 cm) clearly shows that the tumor (black arrows) is in the suprasellar and right ambient cisterns; the signal in the left ambient and interpeduncular cisterns (white arrow) is greatly attenuated, indicating a fluid nature. Note the susceptibility artifacts (white arrowhead) at the anterior skull base. C, ADC map shows that the ADC of the tumor (black arrows) is similar to that of surrounding brain tissue; the ADCs of left ambient and interpeduncular cisterns are similar to that of the eyes (white arrows).

fig 4.

Right CPA epidermoid tumor in a 48-year-old man. A, On fast-FLAIR imaging (10002/148/1, inversion time of 2200), epidermoid tumor appears to extend over the midline in the prepontine cistern (arrow). B, Echo-planar DW imaging (1600/126 with b value of 1000 s/mm²; field of view, 36 × 24 cm) reveals that the lesion (black arrow) is limited in the right CPA. Note the susceptibility artifacts near the temporal bone (white arrows). C, ADC map shows that the tumor (arrow) has an ADC similar to that of surrounding brain tissue.