201Tl-SPECT, 1H-MRS, and MIB-1 Labeling Index of Central Neurocytomas: Three Case Reports

Summary. Summary.   Background: The proliferative activity and metabolic features of three central neurocytomas were investigated using the findings of thallium-201 single photon emission computed tomography (²⁰¹Tl-SPECT) and proton magnetic resonance spectroscopy (¹H-MRS), and the MIB-1 labeling index (MIB-1 LI).   Method: The early and delayed ²⁰¹Tl indixes were calculated as the ratio of tumour to normal brain tissue uptake by ²⁰¹Tl-SPECT. In vivo single-voxel ¹H-MRS was performed with echo time of 272 msec to evaluate the metabolites including choline (Cho), N-acetyl aspartate (NAA) and creatine/phosphocreatine (Cre). An external standard reference was used to semiquantitate each metabolite. MIB-1 LI was determined in the surgical specimens.   Findings: The MIB-1 LI was 0.5%, 1.2%, and 7.5% in an atypical central neurocytoma without intraventricular extension. Significant ²⁰¹Tl uptake was observed on delayed images in all three central neurocytomas. ¹H-MRS showed the high Cho peaks relative to the NAA and Cre peak. The signal at 3.55 ppm, which may be due to inositol or glycine, was observed in one central neurocytoma.   Interpretation . Both ²⁰¹Tl-SPECT and ¹H-MRS did not reflect the proliferative potential of central neurocytomas.     

201Tl-SPECT and 1H-MRS study of benign lateral ventricle tumors: differential diagnosis of subependymoma

The introduction of computed tomography (CT) and magnetic resonance (MR) imaging has resulted in the detection of increasing numbers of asymptomatic intraventricular tumors. Establishing the correct preoperative diagnosis is important to prevent unnecessary surgical intervention. Our study includes nine cases of benign lateral ventricle tumors including two cases of central neurocytoma, two of subependymal giant cell astrocytoma, two of pilocytic astrocytoma and three of subependymoma treated surgically between 1996 and 2003. MR imaging, proton MR spectroscopy (¹H-MRS) and thallium-201 single photon emission computed tomography (²⁰¹Tl-SPECT) were performed in all patients. All three types of tumor demonstrated heterogeneous enhancement on MR imaging with gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA) and increased choline (Cho) peak and decreased N-acetyl aspartate (NAA) and creatine (Cre) peaks on ¹H-MRS. ²⁰¹Tl-SPECT showed high uptake of ²⁰¹Tl without wash out in all cases of central neurocytoma, subependymal giant cell astrocytoma and pilocytic astrocytoma, but no uptake in cases of subependymoma. Absence of ²⁰¹Tl uptake in contrast with enhancement on MR imaging and the ¹H-MRS features of modest elevation of the Cho/Cre ratio, reduction of the NAA peak and presence of lactate/lipid peaks are characteristic features of subependymomas and useful to establish a preoperative diagnosis.     

Magnetic resonance spectroscopy detects brain injury and predicts cognitive functioning in children with brain injuries

Proton magnetic resonance spectroscopy (1H-MRS) and neuropsychological assessment were utilized in a longitudinal investigation of traumatic brain injury (TBI) in children. A spectroscopic imaging protocol was implemented, and neurometabolite ratios of NAA/Cre and Cho/Cre were calculated for anterior and posterior halves of a supraventricular slab of brain tissue. NAA/Cre was reduced and Cho/Cre increased in TBI patients as compared to controls, for both brain regions. Each ratio predicted aspects of neuropsychological performance, though the specific relationships varied somewhat by region and function. Anterior NAA/Cre increased and anterior Cho/Cre decreased from 3 to 21 weeks post-injury, suggesting neurometabolic recovery.     

颈髓急性损伤后的磁共振波谱评价

目的:探讨颈髓急性损伤后磁共振波谱(1H-MRS)的诊断价值。方法:对19例急性颈髓损伤患者根据神经功能分为完全性损伤及不全性损伤两组,选取创区与创区头侧远端颈髓行1H-MRS,半定量分析氮-乙酰门冬氨酸(NAA)、胆碱(Cho)、肌酸(Cr)和乳酸(Lac)含量的比值。结果:颈髓完全性损伤组中NAA/Cho、NAA/Cr显著减低,Lac/Cho显著增高,其创区头侧远端Lac/Cho含量也增高(P<0.05);不完全损伤组中仅Lac/Cho含量增加,头侧远端乳酸含量亦增高(P<0.05)。颈髓损伤不同程度组间NAA/Cho、NAA/Cr有显著性差异(P<0.05)。结论:1H-MRS所测NAA/Cho、NAA/Cr从代谢水平反映颈髓损伤的不同程度,创区头侧远端Lac/Cho比值增高提示颈髓隐匿损伤的存在。     

The use of magnetic resonance spectroscopy in the subacute evaluation of athletes recovering from single and multiple mild traumatic brain injury

Abstract Advanced neuroimaging techniques have shown promise in highlighting the subtle changes and nuances in mild traumatic brain injury (MTBI) even though clinical assessment has shown a return to pre-injury levels. Here we use (1)H-magnetic resonance spectroscopy ((1)H-MRS) to evaluate the brain metabolites N-acetyl aspartate (NAA), choline (Cho), and creatine (Cr) in the corpus callosum in MTBI. Specifically, we looked at the NAA/Cho, NAA/Cr, and Cho/Cr ratios in the genu and splenium. We recruited 20 normal volunteers (NV) and 28 student athletes recovering from the subacute phase of MTBI. The MTBI group was categorized based upon the number of MTBIs and time from injury to (1)H-MRS evaluation. Significant reductions in NAA/Cho and NAA/Cr ratios were seen in the genu of the corpus callosum, but not in the splenium, for MTBI subjects, regardless of the number of MTBIs. MTBI subjects recovering from their first MTBI showed the greatest alteration in NAA/Cho and NAA/Cr ratios. Time since injury to (1)H-MRS acquisition was based upon symptom resolution and did not turn out to be a significant factor. We observed that as the number of MTBIs increased, so did the length of time for symptom resolution. Unexpected findings from this study are that MTBI subjects showed a trend of increasing NAA/Cho and NAA/Cr ratios that coincided with increasing number of MTBIs.     

Metabolic and cognitive response to human traumatic brain injury: a quantitative proton magnetic resonance study

Proton magnetic resonance spectroscopy (1H-MRS) offers a unique insight into brain cellular metabolism following traumatic brain injury (TBI). The aim of the present study was to assess change in neurometabolite markers of brain injury during the recovery period following TBI. We studied 19 TBI patients at 1.5, 3, and 6 months postinjury and 28 controls. We used 1H-MRS to quantify N-acetylaspartate (NAA), creatine (Cre), choline (Cho), and myoinositol (mIns) in occipitoparietal gray matter (GM) and white matter (WM) remote from the primary injury focus. Neuropsychological testing quantified cognitive impairment and recovery. At 1.5 months, we found cognitive impairment (mean z score = -1.36 vs. 0.18,p < 0.01), lower NAA (GM: 12.42 mM vs. 13.03, p = 0.01; WM: 11.75 vs. 12.81, p < 0.01), and elevated Cho (GM: 1.51 vs. 1.25, p < 0.01; WM: 1.98 vs. 1.79, p < 0.01) in TBI patients compared with controls. GM NAA at 1.5 months predicted cognitive function at outcome (6 months postinjury; r = 0.63, p = 0.04). GM NAA continued to fall by 0.46 mM between 1.5 and 3 months (p = 0.02) indicating continuing neuronal loss, metabolic dysfunction, or both. Between 3 and 6 months, WM NAA increased by 0.55 mM (p = 0.06) suggesting metabolic recovery. Patients with poorer outcomes had elevated mean GM Cho at 3 months postinjury, suggesting active inflammation, as compared to patients with better outcomes (p = 0.002). 1H-MRS offers a noninvasive approach to assessing neuronal injury and inflammation following TBI, and may provide unique data for patient management and assessment of therapeutic efficacy.     

Value of MIB-1 labelling index (LI) in gliomas and its correlation with other prognostic factors. A clinicopathologic study

BACKGROUND: In recent years, the monoclonal antibody MIB-1 has become the main factor to measure the proliferative potential of glial tumors. This antibody is equivalent to Ki-67, which is used in frozen sections, and reacts with a nuclear protein that is expressed through the cell cycle. We have investigated the value of MIB-1 Labelling Index (LI) as an independent prognostic factor in gliomas and its relationship with clinical and pathological parameters. METHODS: MIB-1 LI was determined in 139 gliomas by using the Streptavidin-Biotin Complex (SBC) immunohistochemical method. MIB-1 LI immunoreactivity was measured with an automatic cell counting system. Survival was studied by using the Kaplan-Meier bivariant analysis and Cox multivariant regression. RESULTS: In bivariant analysis MIB-1 LI increased with age, histological grade and a supratentorial lateral location. Only size and tumor grade were significant in Cox regression. CONCLUSIONS: Perhaps this proliferation marker is influenced by many factors which reduce its value as an isolated prognostic parameter.     

1H-MRS检测正常中老年人纹状体和黑质代谢功能

目的探讨中老年人纹状体和黑质1 H-MRS各参数值正常参考范围。方法纳入健康中老年志愿者32名,采用单体素PRESS序列对纹状体、多体素PRESS序列对黑质进行1 H-MRS扫描,分析N-乙酰天门冬氨酸(NAA)、胆碱(Cho)和肌酸(Cr)含量及各参数比值。结果左右侧纹状体和黑质NAA/Cr、Cho/Cr、NAA/Cho、NAA/(Cho+Cr)差异均无统计学意义(P均0.05)。综合两侧结果,纹状体NAA/Cr、Cho/Cr、NAA/Cho、NAA/(Cho+Cr)均值及95%CI分别为1.39(1.33~1.45)、0.90(0.86~0.94)、1.58(1.50~1.66)、0.73(0.70~0.76);黑质上述比值均值及95%CI分别为2.36(1.85~2.87)、1.38(1.12~1.65)、1.70(1.59~1.81)、0.93(0.86~1.00);纹状体及黑质中NAA/(Cho+Cr)比值均最稳定。结论正常中老年人黑质和纹状体1 H-MRS各参数中,NAA/(Cho+Cr)比值最稳定,可为研究累及黑质和纹状体区域的疾病提供正常参照。     

Genetic differences between neurocytoma and dysembryoplastic neuroepithelial tumor and oligodendroglial tumors

OBJECT: Because of their histological similarities, it is occasionally difficult to differentiate neurocytoma and dysembryoplastic neuroepithelial tumor (DNT) from oligodendroglial tumors. This study was conducted to investigate genetic differences among these tumor types in terms of loss of heterozygosity on chromosomes 1p and 19q, and p53 gene mutation. METHODS: A total of 24 tumors were analyzed, consisting of eight central neurocytomas, three DNTs, seven oligodendrogliomas, four oligoastrocytomas, and two undetermined extraventricular tumors with neurocytoma features (ETNFs). Allelic loss was determined using microsatellite markers that cover the common deletions on chromosomes 1p and 19q in oligodendrogliomas. A p53 gene mutation was identified using polymerase chain reaction-single-strand conformation polymorphism analysis and subsequent direct sequencing. Immunohistochemical studies with synaptophysin and electron microscopy investigations were also conducted. Allelic loss on 1p and 19q was detected in six oligodendrogliomas (86%) and in three oligoastrocytomas (75%), but in none of the central neurocytomas or DNTs. A p53 missense mutation was detected at codon 161 (GCC-->ACC, Ala-->Thr) in only one oligoastrocytoma without allelic loss. Synaptophysin was expressed in all central neurocytomas and DNTs, in three oligodendrogliomas (43%), and in three oligoastrocytomas (75%). Of the ETNFs, one demonstrated synaptophysin expression and neural ultrastructures but lacked genetic alterations, whereas the other showed allelic loss on 1p and 19q but was negative immunohistochemically and ultrastructurally. The former was diagnosed as a potential intraparenchymal neurocytoma and the latter as an oligodendroglioma. CONCLUSIONS: Despite histological similarities, central neurocytomas and DNTs are genetically distinct from oligodendroglial tumors. Examination for allelic loss on 1p and 19q and for p53 mutation can be useful for making this distinction.     

磁共振氢质子波谱鉴别软组织肿瘤良恶性的价值

目的探讨1H-MRS在软组织肿瘤定性诊断中的应用价值。方法收集经手术及病理证实的12例良性和10例恶性软组织肿瘤患者,分析其1H-MRS各代谢物浓度比值（Cho/Cr、Cho/NAA、Cr/NAA）及其相关性。结果①恶性和良性软组织肿瘤Cho/Cr比值分别为3.72±2.76、0.88±0.53,差异有统计学意义（P〈0.05）,Cho/NAA和Cr/NAA差异均无统计学意义（P均〉0.05）。②良性软组织肿瘤Cr浓度与Cho及NAA浓度均呈正相关（r=0.884、0.822,P均〈0.01）,其余代谢物浓度间均无相关性（P均〉0.05）。③恶性软组织肿瘤Cr浓度与NAA浓度呈正相关（r=0.952,P〈0.001）,其余代谢物浓度间均无相关性（P均〉0.05）。结论 Cho/Cr比值可作为良、恶性软组织肿瘤鉴别诊断的重要依据。Cho/Cr比值升高提示软组织肿瘤为恶性可能性大;Cho/Cr比值降低提示软组织肿瘤为良性可能性大。     

Craniopharyngioma with rapid regrowth--role of MIB-1 labeling index

The treatment of craniopharyngioma becomes quite difficult when it extends into the third ventricle. In a 4-year-old boy, we encountered a large cystic craniopharyngioma which grew into the third ventricle. Initially, the tumor was successfully removed via a right transcallosal transchoroidal approach. A residual part seemed to have remained in the right perioptic region. Even though the patient had an episode of SIADH, his postoperative course was uneventful. He developed visual disturbance 4 months after the initial operation. CT and MRI revealed a large suprasellar mass. The tumor was totally resected via a right pterional approach. Careful follow-up disclosed again a small recurrent lesion in the anterior commisure. Gamma knife therapy was used to successfully reduce the volume of the tumor. The MIB-1 labeling index (LI) of the specimen taken at the time of the first operation was at 9.2% and that of the second operation at 21.2%. Recently, the importance of MIB-1 LI for assessing proliferative activity of this tumor was reported. In patients whose MIB-1 LI is higher, they have more significant rate of recurrence. Our results also indicate that in cases where MIB-1 LI indicates a high value, careful follow-up is necessary. Through fact of the necessity of two operations and additional gamma knife therapy, we would like to stress the importance of MIB-1 LI in indicating the proliferative activity of this tumor. These surgical procedures are presented here, and the role of MIB-1 LI in determining the proliferative activity of craniopharyngioma is also discussed.     

Characterizing 'mild' in traumatic brain injury with proton MR spectroscopy in the thalamus: Initial findings

OBJECTIVE: Although most mild traumatic brain injury (mTBI) patients suffer any of several post-concussion symptoms suggestive of thalamic involvement, they rarely present with any MRI-visible pathology. The aim here, therefore, is to characterize their thalamic metabolite levels with proton MR spectroscopy (1H-MRS) compared with healthy controls. METHODS: T1-weighted MRI and multi-voxel 1H-MRS were acquired at 3 Tesla from 20 mTBI (Glasgow Coma Scale score of 15-13) patients, 19-59 years old, 0-7 years post-injury; and from 17 age and gender matched healthy controls. Mixed model regression was used to compare patients and controls with respect to the mean absolute N-acetylaspartate (NAA), choline (Cho) and creatine (Cr) levels within each thalamus. RESULTS: The mTBI-induced thalamic metabolite concentration changes were under +/- 13.0% for NAA, +/- 13.5% for Cr and +/- 18.8% for Cho relative to their corresponding concentrations in the controls: NAA: 10.08 +/- 0.30 (mean +/- standard error), Cr: 5.62 +/- 0.18 and Cho: 2.08 +/- 0.09 mM. These limits represent the minimal detectable differences between the two cohorts. CONCLUSION: The change in metabolic levels in the thalamus of patients who sustained clinically defined mTBI could be an instrumental characteristic of 'mildness'. 1H-MRS could, therefore, serve as an objective laboratory indicator for differentiating 'mild' from more severe categories of head-trauma, regardless of the presence or lack of current clinical symptoms.     

Central neurocytoma: 9 case series and review

BACKGROUND: Reviewing the literature on central neurocytoma revealed that functional outcomes traditionally have been assessed by KPS. However, KPS is not sufficiently sensitive to assess functional outcomes compared with the Barthel Index and the Functional Independence Measure (the FIM instrument). Discussion of other functional assessments and various aspects of central neurocytomas has never been documented clearly. METHODS: Nine case series of primary central neurocytomas received total or STR at our hospital. The clinical features, neuroradiologic findings, histopathologic features, and functional outcomes were listed and analyzed. Moreover, the functional outcomes were assessed using KPS, Barthel Index, and FIM instrument. The follow-up period ranged from 8 to 33 months after surgery. RESULTS: Patients with increased GFAP positivity or MIB-1 index greater than 3% did not have the worst scores in functional assessments. The functional outcomes of the cases presented here, including KPS, Barthel Index, and FIM instrument, were listed in Table 4. Most patients achieved good functional outcomes. The average KPS, Barthel Index, and FIM instrument were 86.25 +/- 14.08 (range, 60-100), 86.88 +/- 17.31 (range, 50-100), and 111 +/- 17.02 (range, 78-126), respectively. CONCLUSION: Most of the patients in this investigation achieved good ability to independently perform daily activity. Whether the high score of functional outcome was correlated with benign tumor course or 5-year survival rate remains uncertain. We recommend regular follow-up for detecting tumor growth or recurrence, although central neurocytomas are always benign.     

Metabolic changes in the ischemic penumbra after carotid endarterectomy in stroke patients by localized in vivo proton magnetic resonance spectroscopy (1H-MRS).

Carotid endarterectomy (CEA) is known to be effective in reducing recurrent ischemic attacks, sometimes accompanied with the functional improvement, for patients with internal carotid artery (ICA) flow lesions by increase in perfusion and/or removal of embolic sources. However, the exact mechanism of how the CEA affects the cerebral metabolism in relations to the perfusion increase in noninfarcted hypoperfused peripheral areas to the center of the lesion (e.g., ischemic penumbra or border zone) is not yet clearly known. The existence of the ischemic penumbra and its long-term viability has also been argued. We designed a prospective study to investigate the metabolic changes in the ischemic penumbra for patients with ICA flow lesions and cerebral infarct (or ischemia) before and after CEA using localized in vivo proton magnetic resonance spectroscopy ((1)H-MRS). The results of (1)H-MRS showed significantly decreased choline (Cho)/creatine (Cr) and increased N-acetylaspartate (NAA)/Cho ratios in the periphery of the lesion for the patients after CEA as compared to those who underwent only medical treatments. The more significant changes in the cerebral metabolite levels were observed in the patients who showed the improved cerebral perfusion by single photon emission computed tomography after CEA than in those who did not. In conclusion, our data suggest the existence of the ischemic penumbra, which were viable for a longer period than previously thought; CEA seems to improve the cerebral metabolism that may result from the improved perfusion at the ischemic penumbra.     

Proliferation rate of intracranial meningiomas as defined by the monoclonal antibody MIB-1

Paraffin-embedded surgical specimens from 55 meningiomas were immunostained after microwave processing using the streptavidin/peroxidase method and the monoclonal antibody (moAb) MIB-1 to the Ki-67 antigen. The authors assessed proliferative labelling index (LI) from a series of surgically removed meningiomas using immunohistochemical methods and MIB-1, and they correlated this index with clinical, radiological, and histological factors. No relationship was found between LI, sex, age, resection and histological grades, or volume. Symptoms, location, and peritumoural oedema did have a significant relationship to the MIB-1 LI. The symptomatic patients, i.e. those with tumours at the base of the skull and with GR3 peritumoural oedema (grade 3), had a greater chance of higher MIB-1 LI. It was proven that the increase of one unit in peritumoural oedema classification gave an increased risk of 3.312 and an LI greater than 3%. The authors also discuss the different methods of evaluating LIs in meningiomas, based on the available literature.     

磁共振波谱成像观察多发性硬化与视神经脊髓炎患者丘脑代谢产物

目的利用1H-MRS探讨多发性硬化（MS）及视神经脊髓炎（NMO）患者丘脑代谢产物的变化。方法对32例MS患者（MS组）、28例NMO患者（NMO组）和35名健康志愿者（正常对照组）行丘脑1H-MRS扫描,计算并比较各组丘脑代谢产物比值[N-乙酰天门冬氨酸（NAA/Cr）、胆碱/肌酸（Cho/Cr）、肌醇/肌酸（mI/Cr）]。结果三组间NAA/Cr差异有统计学意义（P〈0.05）。与正常对照组比较,MS组丘脑NAA/Cr明显减低（t=-3.45,P〈0.05）,而Cho/Cr及mI/Cr差异无统计学意义（t=0.086、0.661,P均〉0.05）。与正常对照组比较,NMO组丘脑NAA/Cr、Cho/Cr及mI/Cr差异均无统计学意义（t=-0.792、1.408、1.735,P均〉0.05）。结论 1H-MRS显示MS患者丘脑NAA/Cr减低,提示此区域存在轴索损伤,而NMO患者丘脑受损不明显,反映出MS与NMO存在不同的病理变化,有助于二者的鉴别诊断。     

Proliferation rate of intracranial meningiomas as defined by the monoclonal antibody MIB-1: correlation with peritumoural oedema and other clinicoradiological and histological characteristics

Paraffin-embedded surgical specimens from 55 meningiomas were immunostained after microwave processing using the streptavidin/peroxidase method and the monoclonal antibody (moAb) MIB-1 to the Ki-67 antigen. The authors assessed proliferative labelling index (LI) from a series of surgically removed meningiomas using immunohistochemical methods and MIB-1, and they correlated this index with clinical, radiological, and histological factors. No relationship was found between LI, sex, age, resection and histological grades, or volume. Symptoms, location, and peritumoural oedema did have a significant relationship to the MIB-1 LI. The symptomatic patients, i.e. those with tumours at the base of the skull and with GR3 peritumoural oedema (grade 3), had a greater chance of higher MIB-1 LI. It was proven that the increase of one unit in peritumoural oedema classification gave an increased risk of 3.312 and an LI greater than 3%. The authors also discuss the different methods of evaluating LIs in meningiomas, based on the available literature.     

Diagnosis of brain tumor with proton MR spectroscopy--the quantification of gliomas compared with normal brain

We conducted quantification of proton MR spectroscopy (MRS) using water signal as an internal standard, in order to quantify the concentrations of metabolites in normal adult brains and in gliomas in vivo. Single-voxel spectra were acquired using a point-resolved spectroscopic (PRESS) pulse sequence as part of the Probe. P spectroscopy package on a GE Signa Horizon Hispeed LX1.5T scanner (TR/TE/Ave = 3000 msec/30 msec/64). The volume of interest (VOI) varied from 15.0 x 15.0 x 15.0 mm3 to 20.0 x 20.0 x 20.0 mm3 for the brain. The present study included 26 healthy volunteers and 12 patients with gliomas, whose diagnoses were verified by histologic examination. The calculated concentrations of N-acetyl-aspartate (NAA), creatine (Cre) and choline (Cho) in normal hemispheric white matter were 23.66 +/- 1.94 mM (mean +/- SD), 12.97 +/- 1.44 mM, and 4.38 +/- 0.60 mM, respectively. We found they were not necessarily uniform in different parts of the brain, for example, in the pons and basal ganglia. The concentrations of NAA and Cre decreased in all gliomas (p < 0.001). Cho concentration also decreased in the glioma (p < 0.005). The NAA/Cre, NAA/Cho, and Cre/Cho ratios can distinguish normal brain from gliomas, and NAA/Cho ratio can distinguish low-grade astrocytoma from the high-grade group. The results indicate that this noninvasive method offers reasonable estimation of metabolite concentrations in the brain in vivo and therefore is useful in diagnoses of gliomas.     

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.