Radiotherapy and radiosurgery play important roles in the treatment of brain tumors. However, radiation is closely related to several long-term complications, including leukoencephalopathy, vascular injury, arteritis, neuritis, hypothalamic-pituitary axis insufficiency, and radiation-induced neoplasia [1,2]. Among radiation-induced neoplasias, meningioma is the second most common tumor that can occur after cranial radiotherapy [3]. Radiosurgery is also not an exception to radiation-induced tumors [4,5].

Various cases of radiation-induced meningioma (RIM) have been reported since the first report of RIM in the radiotherapy field after radiotherapy for optic nerve glioma was reported in 1953. Additionally, RIM is known to have different histological characteristics and a poorer prognosis than sporadic meningiomas [6,7]. In this paper, we report a case of RIM with different pathologies that occurred consecutively after radiotherapy.

A 23-year-old woman presented with a growing mass in the right frontal dura. The patient had a medical record of medulloblastoma at 2 years of age. She had received a chemotherapy regimen consisting of vincristine, dactinomycin, cyclophosphamide, and doxorubicin after surgical resection, as well as whole-brain radiotherapy, with a total dose of 5,520 cGy. On follow-up magnetic resonance imaging (MRI) performed at 13 years of age, 11 years after combined treatment, medulloblastoma had not recurred (Fig. 1A). However, a left sphenoid ridge meningioma was observed (Fig. 1B). The meningioma presented as a large enhancing calcified mass invading the cavernous sinus and foramen ovale. The sphenoid meningioma was surgically removed. The pathological diagnosis was transitional meningioma, and 2-3% of tumor cells expressed Ki-67 (Fig. 2A, B). Gamma Knife surgery (GKS) was performed for the cavernous sinus remnant tumor (Fig. 3; marginal dose of 14 Gy at 50% isodose level).

On follow-up MRI performed at 21 years of age, another RIM with a size of 22 mm was found in the right temporal dura. For temporal meningiomas, only GKS was performed (Fig. 4; marginal dose of 14 Gy at the 50% isodose level).

On follow-up MRI performed 1 year after GKS, the treated right temporal dura meningioma was stable, but a newly developed meningioma was observed in the right frontal dura (Fig. 5). Since the growth rate of the right frontal meningioma was very high in the follow-up MRI performed 3 months later, surgery was performed instead of GKS. The right temporal meningioma was stable with GKS, but it was decided to be removed because it was very close to the right frontal meningioma and could therefore be removed at the same time. Tumors were extensively removed with the origin dura (Fig. 6; Simpson grade 1). The pathological diagnosis of a right frontal tumor was atypical meningothelial meningioma. Histopathological examination revealed frequent mitoses (6-8/10 high-power fields [HPFs]), and immunohistochemical analysis revealed Ki-67 expression in 15-20% of tumor cells (Fig. 2C, D). The pathological diagnosis of a right temporal tumor was a meningothelial meningioma. Histopathological examination revealed frequent mitoses (1/10 HPFs), and immunohistochemical analysis revealed Ki-67 expression in 1-2% of tumor cells (Fig. 2E, F). The postoperative clinical course was uneventful, and the patient showed no neurological deterioration. Approximately 3 months after the first surgery, a follow-up MRI showed that the right temporal and frontal meningiomas were well removed.

The history of the patient’s disease, treatment, and outcomes are summarized in Table 1. The histopathological analyses of the removed RIM are summarized in Table 2.

The etiology of RIM cannot be clearly distinguished with sporadic meningioma, Cahan’s criteria may help define RIM. Cahan’s criteria were suggested in 1948, which were used to define a radiation-induced sarcoma [8,9]. And the modified Cahan’s standard used as the standard for RIM demonstration is as follows. (1) The lesion must be located an irradiated field. (2) A reasonable time interval, preferably longer than 4 years, must have elapsed between the initial irradiation and the new lesion. (3) The lesion must be histologically different from the previously original neoplasm. (4) The patient does not have a genetic predisposition for tumorigenesis. The patient should not have a genetic predisposition for tumor formation.

In this case, there were no medical record on the original radiation field of meningioma since the patient received radiation therapy 21 years ago. However, we believe that meningiomas could be included in the radiation field for medulloblastoma because the medulloblastoma of the patient was located in the high infratentorial area and the meningiomas were located in the low supratentorial area. Therefore, the authors judged that the meningiomas in this patient satisfies all four conditions required for RIM.

Since Mann et al. [10] first reported RIM in 1953, a large number of RIMs have been reported. According to reports, RIM has characteristics different from sporadic meningioma.

As shown in this case, RIM can develop several decades after exposure to radiation, and various grades of meningiomas can occur at various sites. Therefore, patients who have undergone radiotherapy need follow-up for RIM for a long time, and appropriate treatment for the expected grade should be applied.