Microcystic meningioma with late-phase accumulation on Thallium-201 single-photon emission computed tomography. Case report

Microcystic meningiomas are rare but benign brain tumors. Previous reports have shown that Thallium-201 single-photon emission computed tomography (²⁰¹Tl SPECT) demonstrated a higher late-phase accumulation of ²⁰¹Tl in malignant or recurrent meningiomas than in nonaggressive meningiomas. No study has reported ²⁰¹Tl SPECT findings in microcystic meningiomas. We here describe a case of a microcystic meningioma with a high ²⁰¹Tl SPECT retention rate in a 62-year-old woman who complained of headache. Computed tomography revealed an intracranial tumor in the right frontal lobe. Moreover, ²⁰¹Tl SPECT revealed a high uptake of ²⁰¹Tl in the tumor, which was particularly prominent in the delayed phase. The uptake index on an early image was 1.46 and that on a delayed image was 1.35. Therefore, the retention index was 0.92. After 2 years of tumor growth, we performed successful radical resection, and histological examination revealed the presence of a microcystic meningioma. Therefore, we concluded that ²⁰¹Tl SPECT may be useful for the preoperative diagnosis of microcystic meningiomas and that late-phase accumulation of ²⁰¹Tl is not a specific finding of malignant brain tumors. Therefore, we need to be careful in the evaluation and judgment of high retention in a delayed image of ²⁰¹Tl SPECT. (author)