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Histopathological explanation of the MRI target sign in extra-axial schwannomas
Michihito Ishizawa1, Hidetoshi Okabe2, Keiji Matsumoto1
1Department of Orthopaedic Surgery, Shiga University of Medical Science, Otsu, Shiga, Japan.
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-100 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.
Insights
The "target sign" in extremity schwannomas on MRI reveals peripheral mucinous degeneration and a central area of neoplastic cells. This histopathological correlation aids in understanding these specific magnetic resonance imaging findings.
Area of Science:
- Neuropathology
- Radiology
- Oncology
Background:
- Schwannomas are nerve sheath tumors.
- The "target sign" is a specific magnetic resonance imaging (MRI) finding in some schwannomas.
- Understanding the histopathological basis of MRI findings is crucial for diagnosis.
Purpose of the Study:
- To correlate MRI findings, particularly the "target sign," with histopathological features of schwannomas.
- To elucidate the tissue composition of the "target sign" in extremity schwannomas.
Main Methods:
- Correlation of MRI findings with histopathology in 22 extremity schwannoma samples.
- Histopathological analysis included S-100 protein, proliferating cell nuclear antigen (PCNA), and epithelial membrane antigen (EMA) staining.
- Alcian blue staining was also performed.
Main Results:
- Seven of 22 schwannomas showed a "target sign" on T2-weighted MRI (peripheral high signal, central heterogeneous signal).
- Gadolinium-enhanced T1-weighted images showed central heterogeneous enhancement and a peripheral low-signal ring.
- Histopathology revealed S-100 and PCNA positivity in the central neoplastic area and EMA staining in the peripheral degenerative epi/perineurium.
Conclusions:
- The "target sign" in extremity schwannomas on MRI corresponds histopathologically to peripheral mucinous degeneration and a central area of neoplastic cells.
- This study clarifies the nature of the "target sign," aiding in the interpretation of schwannoma imaging.
- The findings support the differentiation between degenerative and neoplastic components within schwannomas exhibiting the "target sign."
