Benign Transformation of Atypical Meningioma: A Rare Histopathological Phenomenon at Recurrence.

Meningiomas are one of the most frequent primary central nervous system (CNS) tumors. According to the World Health Organization (WHO) classification of brain tumors, meningiomas are categorized into Grade 1 (benign meningioma; 80%), Grade 2 (atypical meningioma; 4%-15%), and Grade 3 (anaplastic meningiomas; 1%-3%). Grade 2 meningioma has a higher recurrence rate, ranging from 29%-52%. However, the transformation from atypical meningioma into benign meningioma is poorly understood. The present article describes a patient with Grade 2 meningioma that transformed into a benign subtype. A 51-year-old female with a history of seizures, presented with left-sided progressive weakness. Radiological imaging revealed a large extra-axial parasagittal lesion measuring 5 cm × 5 cm × 4.8 cm, suggestive of meningioma. The patient underwent subtotal resection of the lesion. Histologically, the tumor was in favor of Grade 2 meningioma. Radiological follow-up 8 years postoperatively revealed a recurrent meningioma. The patient underwent right-sided craniotomy and resection of the parasagittal meningioma. The histopathological features were suggestive of a Grade 1 meningioma. The transformation from atypical to benign meningiomas is rarely reported and the mechanism remains unclear. The present case provides insights into the natural history of this entity, describes possible etiologies, and lists the surgical management with an emphasis on preoperative radiological imaging and histopathological investigations.