Microcystic meningioma diagnosis [Neurosurgery Wiki]

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====== Microcystic meningioma diagnosis ======

{{rss>https://pubmed.ncbi.nlm.nih.gov/rss/search/1lClT3-kMn79C0SkNq4Uw6cZ6ftVXEUfgBBHCeS3ROYv-eegNp/?limit=15&utm_campaign=pubmed-2&fc=20250426054637}}
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===== 1. Clinical evaluation =====

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

Sometimes found incidentally on imaging.

===== 2. Imaging =====

==== MRI Characteristics ====

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.
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==== SPECT ====

Microcystic [[meningioma]]s 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 ((Matano F, Adachi K, Murai Y, Kitamura T, Ohashi R, Teramoto A, Morita A.
Microcystic Meningioma with Late-phase Accumulation on Thallium-201 single-photon
emission computed tomography: Case Report. Neurol Med Chir (Tokyo). 2014 Jan 10. 
[Epub ahead of print] PubMed PMID: 24418788.)).

==== Fluciclovine Positron Emission Tomography ====

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 meningioma]]s mimic HGG on magnetic resonance imaging and [18F]fluciclovine-PET due to l-amino acid transporter expression, complicating diagnosis
((Takenaka J, Hirata K, Watanabe S, Ishi Y, Kudo K. Fluciclovine-PET Uptake in Microcystic Meningioma Mimicking High-grade Glioma: A Case Report. Clin Nucl Med. 2025 Apr 24. doi: 10.1097/RLU.0000000000005924. Epub ahead of print. PMID: 40279665.))
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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 tumor]]s and the molecular basis of tracer uptake in benign lesions like meningiomas.


==== 3. Histopathology ====

Essential for definitive diagnosis.

Microscopic features:

Loose, edematous tissue.

Abundant microcysts filled with fluid.

Round/oval nuclei, sparse mitotic activity.

==== Immunohistochemistry ====

Positive for EMA (epithelial membrane antigen).

Positive for vimentin.

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

==== 4. Differential diagnosis ====

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

Imaging and pathology together help distinguish it.