Journal of Neuro-Oncology

, Volume 89, Issue 2, pp 225–230

99mTc-Tetrofosmin brain SPECT in the assessment of meningiomas—correlation with histological grade and proliferation index

Authors

  • Andreas D. Fotopoulos
    • Department of Nuclear MedicineUniversity of Ioannina School of Medicine
    • Department of NeurosurgeryUniversity of Ioannina School of Medicine
  • Ann Goussia
    • Department of PathologyUniversity of Ioannina School of Medicine
  • Athanasios Papadopoulos
    • Department of Nuclear MedicineUniversity of Ioannina School of Medicine
  • Athanasios P. Kyritsis
    • Department of NeurologyUniversity of Ioannina School of Medicine
  • Konstantinos S. Polyzoidis
    • Department of NeurosurgeryUniversity of Ioannina School of Medicine
  • Spyridon Voulgaris
    • Department of NeurosurgeryUniversity of Ioannina School of Medicine
  • Spyridon Tsiouris
    • Department of Nuclear MedicineUniversity of Ioannina School of Medicine
Clinical-patient studies

DOI: 10.1007/s11060-008-9611-8

Cite this article as:
Fotopoulos, A.D., Alexiou, G.A., Goussia, A. et al. J Neurooncol (2008) 89: 225. doi:10.1007/s11060-008-9611-8

Abstract

Meningiomas account for about 30% of all intracranial tumors. Evaluation of their proliferation rate is useful for assessing their biological behavior. We evaluated prospectively whether 99mTc-Tetrofosmin (99mTc-TF) uptake in meningiomas correlates with cellular proliferative activity and with tumor grade. We prospectively studied 18 meningioma cases. Brain single-photon emission computed tomography (SPECT) by 99mTc-TF was performed within a week prior to surgical excision. In the excised tumor specimens we assessed Ki-67 antigen expression. 14 of 18 patients had benign meningiomas, while the remaining four had anaplastic meningiomas. A significant correlation was found between both 99mTc-TF uptake and tumor grade (r = 0.722, P = 0.001) and between 99mTc-TF uptake and Ki-67 expression (r = 0.930, P < 0.001). There was a significant correlation between the intensity of tracer uptake and tumor recurrence at 1 year postoperative (r = 0.574, P = 0.02). This pilot study implies that 99mTc-TF brain SPECT could prove useful in differentiating benign from anaplastic meningiomas and is a potential indicator of their proliferative activity.

Keywords

Meningioma99mTc-TetrofosminCell proliferationKi-67MIB-1

Introduction

Meningiomas account for nearly 30% of all intracranial tumors, whereas 2–3% of the population in autopsy studies had an incidental asymptomatic meningioma [1]. They are usually diagnosed after the third decade of life and they are twice as frequent in women than in men. According to the World Health Organization (WHO), meningiomas are classified into three grades, benign (grade I), atypical (grade II), and anaplastic (grade III) [2]. Although they usually have a relatively benign clinical course and only a 15% recurrence rate, atypical and malignant ones are associated with high recurrence rates and poor outcome [3, 4].

Tumor prognosis depends on its biological behavior, which is determined by various cellular characteristics. As in all brain tumors, the proliferation potential of meningiomas is essential for their biological characterization and has significant prognostic implications, thus being important for patient management. The nuclear antigen Ki-67 expressed by proliferating cells has become available for routinely processed paraffin section and is considered the most reliable of all other methods, since Ki-67 is expressed in nearly all phases of the cell cycle, with the exception of G0 phase [57]. The MIB-1 antibody reacts to the Ki-67 nuclear antigen in formalin-fixed tissue and was proved sensitive and reliable in determining meningioma grade and biological behavior [811]. Nakaguchi et al. found that an increased MIB-1 staining index was highly correlated with a shorter tumor volume doubling time, while Kasuya et al. showed that for MIB-1 > 3%, the doubling time was below 2 years [12, 13]. However, Ki-67/MIB-1 estimation requires tissue sampling through a biopsy or over the course of a surgical procedure.

A major objective is therefore the development of radiolabeled tracers for the noninvasive scintigraphic evaluation of tumor proliferation in vivo. 18F-2-fluoro-2-deoxy-d-glucose (18F-FDG), 11C-thymidine, and 18F-3′-deoxy-3′-fluorothymidine (18F-FLT) are positron emission tomography (PET) tracers that have been evaluated toward this scope [14, 15]. As regards conventional (non-PET) functional imaging by single-photon emission tomography (SPECT), technetium-99m pentavalent dimercapto-succinic acid [99mTc-(V)DMSA] is a tumor-seeking compound that has been shown to depict cellular proliferation both in vivo and in vitro [15, 16]. The SPECT tracer technetium-99m Tetrofosmin (99mTc-TF) has been found to depict brain tumors, while it can also reliably distinguish high- from low-grade gliomas [17, 18]. To our knowledge, no study has directly correlated 99mTc-TF uptake by meningioma with their malignant potential.

The present work evaluated prospectively whether 99mTc-TF uptake in meningiomas correlates with their cellular proliferative activity (as immunohistologically assessed by the Ki-67 index), as well as with their grade.

Materials and methods

Eighteen consecutive cases of meningioma (four males, 14 females; mean age 64.1 years) diagnosed over a 26-month period between January 2005 and March 2007, were prospectively enrolled in the study. They all had been preoperatively evaluated by anatomic brain imaging [computed tomography (CT) and magnetic resonance imaging (MRI)] and shortly after were submitted to functional imaging by 99mTc-TF SPECT. Surgical excision was performed within a week after scintigraphy. The degree of tumor removal was scored according to the Simpson grading system [19]. Surgical specimens were graded following the WHO criteria [2] and the Ki-67 index was evaluated. The mean follow-up period following surgery was 19.4 months (range: 6–34). The study was approved by the institutional review board and informed consent was received from all patients.

99mTc-Tetrofosmin SPECT and image analysis

Brain SPECT was obtained 30 min after intravenous injection of 925 MBq (25 mCi) 99mTc-TF activity dose. The radiopharmaceutical was prepared using a powder kit (Myoview, General Electric Healthcare Ltd, Buckinghamshire, UK), that was reconstituted with technetium-99m pertechnetate (99mTcO4) sterile solution in the Nuclear Medicine Department. All studies were implemented in a dual-head γ-camera (Millennium VG3, General Electric Medical Systems—Europe, Buc Cedex, France), equipped with a pair of high-resolution, parallel-hole collimators. The matrix was set at 128 × 128 pixels; the photopeak was centred at 140 keV, with a symmetrical 10% window. The tomographic imaging parameters consisted of a 360°-rotation angle, a 3°-step-and-shoot technique, and an acquisition time of 30 s per frame. Raw imaging data were reconstructed using the Butterworth-filtered back-projection algorithm, generating tomographic views of the brain in the three planes (transverse, coronal, and sagittal).

Radiotracer accumulation in meningiomas was first assessed visually. Then a semiquantitative method of image analysis was applied, with calculation of the lesion-to-normal (L/N) uptake ratio: a region-of-interest (ROI) was manually defined around the lesion on the transverse slice with the highest tumoral tracer uptake—in close reference to the corresponding CT/MRI slice—and a second identical mirror region was drawn on the contralateral normal side of the brain. The L/N ratio was calculated by dividing the average counts in the tumor region, with the average counts in the normal region. The ROIs were evaluated for eligibility by two independent experienced Nuclear Medicine physicians; any possible disagreements were solved by consensus or discussion with a third physician.

Histopathology and Ki-67 immunohistochemical assay

Meningiomas were graded according to the WHO histopathologic classification [2]. An immunohistochemical method (avidin-biotin-peroxidase complex) was performed on 4-μm-thick, paraffin-embedded tumor sections for the demonstration of the Ki-67 protein expression; the monoclonal murine antibody MIB-1 (Dako S.A., Glostrup, Denmark) was applied at a 1:20 dilution.

The tumor sections were reviewed by two independent experienced neuropathologists and a quantitative estimation based on the percentage of positive cells was performed: all cells with nuclear staining were considered positive, irrespectively of intensity; the Ki-67 index was defined as the percentage of the positive cells in the total cells counted. Any discrepancy between the two physicians was solved by consensus.

Data analysis

To investigate whether the tumor grade, proliferation status and recurrence status play significant role in 99mTc-TF uptake by meningiomas, Spearman rank univariate correlation analysis was performed between the degree of tracer uptake (as expressed by the L/N ratio) and the three variables of interest (i.e., Ki-67 expression, grade, and recurrence). A two-sided P-value <0.05 was considered statistically significant.

Results

Table 1 summarizes the patient’s gender, histopathology, scintigraphic tumor characteristics, resection grade, follow-up and recurrence at 1-year post-surgery. In 17 of 18 patients a Simpson grade I tumor removal was achieved. Histology of the surgically resected tumors provided the diagnosis of meningioma. Fourteen lesions were benign and four anaplastic. The intensity of tumoral tracer uptake on visual image assessment ranged from faint to profound. Malignant meningiomas tended to exhibit a higher tracer uptake (Fig. 1), as compared to lesions of low histological grade and/or low Ki-67 expression (Fig. 2).
https://static-content.springer.com/image/art%3A10.1007%2Fs11060-008-9611-8/MediaObjects/11060_2008_9611_Fig1_HTML.jpg
Fig. 1

Patient #11: (a) Gadolinium-enchanced gradient echo T1-weighed MRI slice in a 49-year-old female patient with a benign meningioma; (b), Low tracer uptake in the corresponding reconstructed transverse SPECT slice (arrow); (c), Ki-67 expression ~1.5% (immunohistochemical stain MIB-1)

https://static-content.springer.com/image/art%3A10.1007%2Fs11060-008-9611-8/MediaObjects/11060_2008_9611_Fig2_HTML.jpg
Fig. 2

Patient #4: (a). Gadolinium-enchanced gradient echo T1-weighed MRI slice in a 76-year-old male with; (b) Profound focal 99mTc-Tetrofosmin uptake in the reconstructed transverse SPECT slice (arrow); (c) Ki-67 expression ~20% (immunohistochemical stain MIB-1)

Table 1

Detailed data of the 18 patients diagnosed with meningioma

 

Age/Sex

Tumor histopathology

Grade

Ki-67 (%)

(L/N)

Resection grade

Follow-up (months)

Recurrence at 1-Year post-surgery

1

72/M

Angiomatous

I

0.5

3.5

I

12

No

2

51/M

Meningothelial

I

0.5

5.7

III

20

No

3

74/M

Anaplastic

III

15

9.9

I

22

Yes

4

76/M

Anaplastic

III

20

9.8

I

6

No†

5

70/F

Anaplastic

III

3

10.2

I

28

Yes

6

59/F

Anaplastic

III

5

9.6

I

8

No†

7

71/F

Meningothelial

I

0.1

1.8

I

34

No

8

67/F

Psammomatous

I

0.1

2.3

I

31

No

9

75/F

Meningothelial

I

2

8.9

I

31

No

10

58/F

Angiomatous

I

0.1

1.2

I

26

No

11

49/F

Meningothelial

I

1.5

4.9

I

16

No

12

57/F

Angiomatous

I

0.1

2.2

I

12

No

13

60/F

Psammomatous

I

0.5

4.0

I

13

No

14

75/F

Meningothelial

I

1

4.5

I

26

No

15

59/F

Transitional

I

0.5

3.5

I

28

No

16

75/F

Meningothelial

I

1

4.6

I

15

No

17

50/F

Meningothelial

I

1

5.2

I

12

No

18

56/F

Transitional

I

0.5

1.1

I

11

No

Abbreviations: M = male, F = female, L/N = lesion to normal ratio of 99mTc-Tetrofosmin uptake, † = deceased

Semiquantitative data analysis confirmed that the intensity of tracer uptake displayed a strong linear positive correlation with MIB-1 expression (r = 0.930, P < 0.001). Significant correlation was also found between 99mTc-TF uptake and meningioma grade (r = 0.722, P = 0.001). Two patients (cases 3 and 5) with anaplastic meningiomas showed clinical and radiomorphologic evidence of recurrence in the follow-up period 6 and 9 months after surgery, respectively, while another two deceased due to other co-morbidities. There was a significant correlation between the intensity of tracer uptake and tumor recurrence at 1 year postoperative (r = 0.574, P = 0.02). The remaining patients are alive and free of recurrence on follow-up.

Discussion

Although considered generally benign, the growth potential of meningiomas varies. Some remain unchanged in size for a long period, while others tend to grow rapidly [13]. Surgical resection remains the treatment mainstay. In benign meningiomas this is associated with a high cure rate, provided that the entirety of the tumor is excised. However, there is always considerable risk of recurrence (estimated between 9% and 32%) even after apparently complete resection with excision of the surrounding dura and involved bone, suggesting that biological heterogeneity exists among benign lesions [20, 21]. On the contrary, recurrence is very common in high-grade lesions, even after total resection [4, 22]. All these suggest that assessment of tumor’s biological behavior could serve as an important prognostic factor.

Quantitative assessment of the proliferation status in meningiomas is proved useful for the assessment of their biological behavior and for patient prognosis. A number of techniques assessing cell kinetics have been developed to understand the biological behavior of tumors, such as mitotic index, proliferating cell nuclear antigen (PCNA) labelling index, autoradiographic measurement of tritiated thymidine uptake, bromodeoxyuridine uptake, p53 protein, flow cytometry, assessment of argyrophilic nucleolar region indices, and Ki-67 labelling index [2228]. Ki-67 antigen, which is expressed in the G1, S, G2, and M phases of cell cycle, being absent only in the G0 phase has been reported to correlate better with tumor aggressiveness [24]. MIB-1 is a murine monoclonal antibody that binds Ki-67 antigen. Several studies have reported a significant correlation between meningioma grade and MIB-1 index [21, 29]. Roser et al. in a series of 600 meningioma patients, reported that typical meningiomas exhibited a 3.28% mean MIB-1 index, grade II meningiomas a 9.95% MIB-1 index, and grade III meningiomas had a 12.18% mean MIB-1 index [29]. Additionally, Ki-67/MIB-1 is a more sensitive and reliable method in determining tumor grade since it has been proven useful in predicting their behavior and tendency to recur [9, 11]. Matchuno et al. recently reported that meningiomas with MIB-1 staining index ≥3% had a significantly higher tendency of recurrence, whereas Kakinuma et al. found MIB-1 index between 0.8% and 58.8% in recurrent meningiomas group versus 0.09–19.9% in non-recurrent group [30, 31]. The study of Sasaki et al. supports these findings [32]. Nevertheless, immunostaining methods require direct tissue sampling and for that reason a non-invasive metabolic imaging technique that could reliably assess the proliferation potential of meningiomas would be very useful.

Several imaging modalities have been used for that purpose. Neuromorphological workup provided by CT and MRI are not conclusive since they can only identify blood–brain barrier breakdown and edema. Brain PET has been introduced as a method of intracranial lesion metabolic imaging. PET imaging with the use of the glucose analog 18F-FDG was first used. Lippitz et al. reported in a series of 62 meningiomas that 18F-FDG is suitable to serve as non-invasive predictor of tumor growth characteristics [33]. However, the uptake kinetics of 18F-FDG reflect glucose metabolism (i.e., both glucose transport and phosphorylation), whose modifications are only indirectly related to the proliferation status of a tumor. 11C-thymidine and 18F-FLT are positron-emitting tracers developed to image tumor proliferation through the estimation of the rate of DNA synthesis. Carbon-11 short half-life and 11C-thymidine’s rapid in vivo degradation preclude its wide clinical use; 18F-FLT is proving promising, but is still under evaluation. 11C-methionine has been proven useful in a pilot study for predicting meningioma proliferative potential [34]. Nevertheless, PET remains relatively expensive and not widely available.

As regards conventional (non-PET) functional brain imaging, SPECT with various single-photon emitting tracers has been previously evaluated. Thallium-201 (201Tl) was one of the first radiotracers that have been used. Gungor et al. reported that 201Tl uptake can predict the proliferative activity of glioma [35]. Recently, Tedeschi et al. reported that 201Tl concentration could differentiate preoperatively intracranial meningiomas with different biological behavior, while Jinnouchi et al. managed to predict malignant potential of meningiomas by 201Tl retention [36, 37].

Technetium-99m-labeled compounds have also been studied. These were proved advantageous over 201Tl, due to 140 keV γ-ray energy, high photon flux, higher spatial resolution, less radiation burden to the patient, and excellent availability. To our knowledge, no study thus far has assessed the value of 99mTc-TF in differentiating benign from malignant meningiomas and its use as a potential indicator of their proliferative activity.

99mTc-TF is a lipophilic cationic diphosphine routinely used for myocardial perfusion imaging [38]. Its whole uptake mechanism bears similarities to 99mTc-Sestamibi, as it depends mainly on regional blood flow and cell membrane integrity: it enters cells mainly via passive transport driven by the negative potential of the intact cell membrane and mostly localizes within the cytosol and only a fraction passes into the mitochondria [39]. In the healthy brain, uptake of 99mTc-TF is seen in the choroid plexuses, pituitary gland, and scalp, but not in the normal brain parenchyma, since it does not cross the intact BBB [18]. 99mTc-TF has been reported to depict various tumors including lung cancer, thyroid carcinoma, and breast cancer [4042]. Studies on human glioma cell lines substantiated a plausible clinical superiority of 99mTc-TF over 99mTc- Sestamibi for brain tumor evaluation [43, 44]. Thus, far little has been reported on the in vivo 99mTc-TF capability for brain tumor imaging [18]. We recently reported that 99mTc-TF SPECT could distinguish radiation necrosis from tumor recurrence, neoplastic from non-neoplastic intracerebral hemorrhage and correlates with glioma aggressiveness as assessed by MIB-1 immunohistochemistry [4548]. These previous observations are upheld by the results of the present study that displayed a significant correlation of 99mTc-TF uptake with Ki-67 expression tumor grade. Anaplastic meningiomas tended to exhibit a higher radiotracer uptake as compared to typical tumors. Likewise, meningiomas with higher proliferation index tended to exhibit increased 99mTc-TF uptake. Furthermore, there was no overlap of the 99mTc-TF uptake between typical and anaplastic meningiomas. In our study we also found a significant correlation of 99mTc-TF uptake with risk of recurrence at 1 year postoperative. Nevertheless, a limitation of this study pertains to the absence of grade II meningiomas in the study population. Therefore, further studies, using larger number of patients with each histological meningioma type, should be focused on whether 99mTc-TF brain SPECT could prove useful in distinguishing grade I from grade II meningiomas or grade II from grade III meningiomas.

Conclusively, we suggest that 99mTc-TF uptake in meningiomas is likely to be an indicator of their proliferative activity, closely paralleling Ki-67 expression. A criticism to this suggestion could mainly derive from the limited number of the cases studied. Furthermore precise ROI depiction around the lesion in low-grade tumors is more elaborate, even under CT/MRI guidance, due to the lesser intensity of tracer uptake. The regional histological heterogeneity observer in meningiomas comprises another possible methodological drawback, since the tumor block selected for staining might not always enfold the highest proliferative areas of the neoplasm [49, 50]. Even so, we believe that since the correlation between 99mTc-TF uptake and cell proliferation was found unambiguously solid permits us to consider this initial evidence as strong enough to substantiate further research regarding the clinical utility of this imaging modality in affecting management decisions.

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© Springer Science+Business Media, LLC. 2008