Microcystic meningioma diagnosis

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Symptoms depend on tumor location: headaches, seizures, focal deficits, or signs of increased intracranial pressure.

Sometimes found incidentally on imaging.

Extra-axial, well-circumscribed mass.

T2-weighted images: very high signal intensity (bright), more than typical meningiomas, due to the high fluid content of microcysts.

T1-weighted images: usually iso- to hypointense.

After contrast (gadolinium), enhancement can be heterogeneous (not uniform) — different from classic meningiomas which often enhance homogeneously.

May show a “soap-bubble” or reticular appearance.

Sometimes associated with a dural tail.

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.

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, 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 ¹⁾.

A 69-year-old asymptomatic woman underwent magnetic resonance imaging (MRI), revealing a left parietal lobe tumor suspected to be a high-grade glioma (HGG). [18F]Fluciclovine positron emission tomography (PET), which reflects amino acid metabolism, showed moderate uptake [SUVmax 1.4, tumor-to-normal ratio (TNR) 1.9], consistent with HGG, whereas [18F]fluorodeoxyglucose-PET findings demonstrated low uptake (SUVmax 2.5, TNR 0.22), which is atypical for HGG. Surgical and pathologic investigations confirmed the diagnosis of microcystic meningioma, a rare subtype classified as grade 1. Microcystic meningiomas mimic HGG on magnetic resonance imaging and [18F]fluciclovine-PET due to l-amino acid transporter expression, complicating diagnosis ²⁾

This report compellingly illustrates that fluciclovine uptake is not specific for high-grade malignancy in CNS tumors. Clinicians must interpret PET findings in conjunction with clinical history, MRI features, and alternative PET tracers like FDG. Future work should include larger studies evaluating false-positive rates of fluciclovine-PET in brain tumors and the molecular basis of tracer uptake in benign lesions like meningiomas.

Essential for definitive diagnosis.

Microscopic features:

Loose, edematous tissue.

Abundant microcysts filled with fluid.

Round/oval nuclei, sparse mitotic activity.

Positive for EMA (epithelial membrane antigen).

Positive for vimentin.

Low Ki-67 (proliferation index), consistent with low-grade tumor.

Other cystic brain tumors (e.g., hemangioblastoma, pilocytic astrocytoma, metastases).

Imaging and pathology together help distinguish it.