Stereotactic Radiosurgery (SRS) Induced Higher-Grade Transformation of a Benign Meningioma into Atypical Meningioma

Abstract

Background: Stereotactic radiosurgery (SRS) is a widely used treatment modality for the management of meningioma. Whether used as a primary, adjuvant, or salvage procedure, SRS is a safe, less invasive, and effective modality of treatment as microsurgery. The transformation of a meningioma following radiosurgery raises a concern, and our current understanding about it is extremely limited. Only a few case reports have described meningioma dedifferentiation after SRS to a higher grade. Moreover, a relatively small number of cases have been reported in large retrospective studies with little elaboration. Case Description. We report a detailed case description of a 41-year-old man with progressive meningioma enlargement and rapid grade progression after SRS, which was histopathologically confirmed before and after SRS. We discussed the clinical presentation, radiological/histopathological features, and outcome. We also reviewed previous studies that reported the outcome and follow-up of patients diagnosed with grade I meningioma histopathologically or presumed with benign meningioma by radiological features who underwent primary or adjuvant radiosurgery.

Conclusion: The risk of progression after SRS is low, and the risk of higher-grade transformation after SRS is trivial. The early timing for recurrence and field-related radiation may favor a relationship between SRS and higher-grade transformation (causality) although transformation as a part of the natural history of the disease cannot be fully excluded. Tumor progression (treatment failure) after SRS may demonstrate a transformation, and careful, close, and long follow-up is highly recommended. Also, acknowledging that there is a low risk of early and delayed complications and a trivial risk of transformation should not preclude its use as SRS affords a high level of safety and efficiency.

Figure 1

Neuroimaging–MRI ((a–d) with contrast enhancement) shows (a) sphenoid wing meningioma. (b) Frontobasal tumor projecting towards the right side (pre-SRS). (c) Tumor residual occupying the posterior aspect of the sphenoid wing and parasellar region (post-SRS). (d) Tumor occupies all the right middle cranial fossa extending to the cavernous sinuses, sella, and suprasellar regions as well as right prepontine and CP angle. It is also spread to the ipsilateral right superior orbital fissure and a lesser extent optic canal. The second component within the left anterior cranial fossa crossing the midline to the contralateral side and posteriorly to the left sphenoid ridge (post-SRS).

Figure 2

Histopathology. (2011) H&E-stained slide shows meningothelial meningioma, WHO grade I (a). Ki67 index (b). (2015) H&E-stained slide shows recurrent WHO grade I meningioma (c). Ki67 index (d). (2018) H&E-stained slide shows recurrent meningioma with atypical features and increased mitoses, WHO grade II (e). Ki67 index elevated (f).