Histopathological explanation of the MRI target sign in extra-axial schwannomas

Background: To better understand the nature of magnetic resonance imaging (MRI) findings in schwannomas, especially in the target sign of these findings, the histopathological investigation was performed. Methods: The MRI findings were correlated with histopathological features in 22 samples of schwannomas, which were mostly resected from the extremities. The histopathological analyses included alcian blue staining and immunohistochemical staining for S-10 0 protein, proliferating cell nuclear antigen (PCNA) and epithelial membrane antigen (EMA). Results: Seven of the 22 samples of schwannomas of the extremities exhibited target signs including a peripheral zone of homogeneously high signal intensity and a central zone of heterogeneous signal intensity in T2-weighted images. Gadolinium-enhanced T1-weighted images demonstrated a central heterogeneous enhancement and a peripheral ring of homogeneously low signal intensity. Histopathologically, S-100 and PCNA were positive only in the central heterogeneous signal area. In contrast, EMA was only stained on the degenerative epi/perineurium in the peripheral zone. Conclusion: In schwannomas of the extremities showing target sign in T2-weighted images, histopathologically, the peripheral areas were suggested to be mucinous degeneration of the epineurium or perineurium, while the central areas were composed of truly neoplastic cells. (c) 2020 Published by Elsevier B.V. on behalf of The Japanese Orthopaedic Association.

Automated summary

In schwannomas of the extremities showing target sign in T2-weighted images, histopathologically, the peripheral areas were suggested to be mucinous degeneration of the epineurium or perineurium, while the central areas were composed of truly neoplastic cells.