Differentiation of spinal myxopapillary ependymomas from schwannomas by contrast-enhanced MRI.

BACKGROUND: Spinal myxopapillary ependymomas (MPEs) and schwannomas (SCHs) are both frequently located at the conus and caudal regions. The differentiation between MPEs and SCHs before surgery is crucial. Signal patterns of MPEs and SCHs on T2-weighted (T2W) magnetic resonance imaging (MRI) are diverse. Gadolinium (Gd+)-enhanced areas in MRI scans areas are areas where tumor cells are abundant. Therefore, investigating these enhanced areas should facilitate the differentiation. This study aimed to evaluate Gd+ areas in MRI scans in spinal MPEs and SCHs. Furthermore, the relation between MRI pattern and pathological features was investigated.

METHODS: In total, 41 patients with spinal MPEs (n = 7) or SCHs (n = 34) around the conus medullaris were included. SCHs were classified per the Gd+ area of the tumor on T1-weighted (T1W) contrast images, into Gd+ areas with T2W hyperintensity (Gd+/T2high) (n = 4, 11.8%) or Gd+ areas with T2W isointensity (Gd+/T2iso) (n = 30, 88.2%). Four patients with Gd+/T2iso were selected randomly for comparison. In three patient groups, T2 values at the Gd+ area and tumor cell density as measured by HE stains (cell density) were compared.

RESULTS: T2 values at the Gd+ area was higher in patients with MPE than in those with SCH with Gd+/T2high, and significantly higher than that in patients with SCH with Gd+/T2iso. Cell density was significantly lower in patients with MPEs than for those with SCHs with Gd+/T2high, and those with SCHs with Gd+/T2iso.

CONCLUSION: The evaluation of the Gd+ area proved useful because it excludes cysts or necrotic portions. If the Gd+ area is hyperintense on T2WI, MPEs can be suspected. If the Gd+ area is isointense on T2WI, SCHs can be suspected. There were several exceptional cases of SCH with a Gd+ area that was hyperintense on T2WI. This could be explained by pathological findings showing low cell density, as is typical for MPEs.