Positron emission tomographic imaging of acoustic neuromas

[18F]fluorothymidine and [18F]fluorodeoxyglucose PET Imaging Demonstrates Uptake and Differentiates Growth in Neurofibromatosis 2 Related Vestibular Schwannoma

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Objective:

To investigate whether [¹⁸F]fluorothymidine (FLT) and/or [¹⁸F]fluorodeoxyglucose (FDG) positron emission tomography (PET) can differentiate growth in neurofibromatosis 2 (NF2) related vestibular schwannomas (VS) and to evaluate the importance of PET scanner spatial resolution on measured tumor uptake.

Methods:

Six NF2 patients with 11 VS (4 rapidly growing, 7 indolent), were scanned with FLT and FDG using a high-resolution research tomograph (HRRT, Siemens) and a Siemens Biograph TrueV PET-CT, with and without resolution modeling image reconstruction. Mean, maximum, and peak standardised uptake values (SUV) for each tumor were derived and the intertumor correlation between FDG and FLT uptake was compared. The ability of FDG and FLT SUV values to discriminate between rapidly growing and slow growing (indolent) tumors was assessed using receiver operator characteristic (ROC) analysis.

Results:

Tumor uptake was seen with both tracers, using both scanners, with and without resolution modeling. FDG and FLT uptake was correlated (R² = 0.67–0.86, p < 0.01) and rapidly growing tumors displayed significantly higher uptake (SUV_mean and SUV_peak) of both tracers (p < 0.05, one tailed t test). All of the PET analyses performed demonstrated better discriminatory power (AUC_ROC range = 0.71–0.86) than tumor size alone (AUC_ROC = 0.61). The use of standard resolution scanner with standard reconstruction did not result in a notable deterioration of discrimination accuracy.

Conclusion:

NF2 related VS demonstrate uptake of both FLT and FDG, which is significantly increased in rapidly growing tumors. A short static FDG PET scan with standard clinical resolution and reconstruction can provide relevant information on tumor growth to aid clinical decision making.

Inflammation and vascular permeability correlate with growth in sporadic vestibular schwannoma

BACKGROUND

Inflammation is hypothesized to be a key event in the growth of sporadic vestibular schwannoma (VS). In this study we sought to investigate the relationship between inflammation and tumor growth in vivo using the PET tracer 11C-(R)-PK11195 and dynamic contrast enhanced (DCE) MRI derived vascular biomarkers.

METHODS

Nineteen patients with sporadic VS (8 static, 7 growing, and 4 shrinking tumors) underwent prospective imaging with dynamic 11C-(R)-PK11195 PET and a comprehensive MR protocol, including high temporal resolution DCE-MRI in 15 patients. An intertumor comparison of 11C-(R)-PK11195 binding potential (BPND) and DCE-MRI derived vascular biomarkers (Ktrans, vp, ve) across the 3 different tumor growth cohorts was undertaken. Tissue of 8 tumors was examined with immunohistochemistry markers for inflammation (Iba1), neoplastic cells (S-100 protein), vessels (CD31), the PK11195 target translocator protein (TSPO), fibrinogen for vascular permeability, and proliferation (Ki-67). Results were correlated with PET and DCE-MRI data.

RESULTS

Compared with static tumors, growing VS displayed significantly higher mean 11C-(R)-PK11195 BPND (-0.07 vs 0.47, P = 0.020), and higher mean tumor Ktrans (0.06 vs 0.14, P = 0.004). Immunohistochemistry confirmed the imaging findings and demonstrated that TSPO is predominantly expressed in macrophages. Within growing VS, macrophages rather than tumor cells accounted for the majority of proliferating cells.

CONCLUSION

We present the first in vivo imaging evidence of increased inflammation within growing sporadic VS. Our results demonstrate that 11C-(R)-PK11195 specific binding and DCE-MRI derived parameters can be used as imaging biomarkers of inflammation and vascular permeability in this tumor group.

Case Report and Review of the Literature of Schwannomas that Originate from the Falx Cerebri

BACKGROUND

Schwannomas not related to cranial nerves are very rare. Here, we present a case of a schwannoma that originated from the falx cerebri and review reported cases in the literature.

CASE DESCRIPTION

A 36-year-old male experienced generalized seizures following right hemiparesis predominantly in his lower extremity. Magnetic resonance imaging revealed a round tumor attached to the falx cerebri on the left side. Radiologically, the tumor appeared to be a falx meningioma. We performed gross total removal of the tumor. Pathology showed a schwannoma that originated from the falx cerebri. Right hemiparesis disappeared soon after surgery.

CONCLUSION

Although distinguishing a schwannoma of the falx cerebri from a falx meningioma and metastasis is difficult preoperatively, inclusion of schwannoma of the falx cerebri in the differential diagnosis is important, especially when the patient is relatively young and/or the tumor lacks dural tail sign.

Current molecular imaging of spinal tumors in clinical practice

Energy metabolism measurements in spinal cord tumors, as well as in osseous spinal tumors/metastasis in vivo, are rarely performed only with molecular imaging (MI) by positron emission tomography (PET). This imaging modality developed from a small number of basic clinical science investigations followed by subsequent work that influenced and enhanced the research of others. Apart from precise anatomical localization by coregistration of morphological imaging and quantification, the most intriguing advantage of this imaging is the opportunity to investigate the time course (dynamics) of disease-specific molecular events in the intact organism. Most importantly, MI represents one of the key technologies in translational molecular neuroscience research, helping to develop experimental protocols that may later be applied to human patients. PET may help monitor a patient at the vertebral level after surgery and during adjuvant treatment for recurrent or progressive disease. Common clinical indications for MI of primary or secondary CNS spinal tumors are: (i) tumor diagnosis, (ii) identification of the metabolically active tumor compartments (differentiation of viable tumor tissue from necrosis) and (iii) prediction of treatment response by measurement of tumor perfusion or ischemia. While spinal PET has been used under specific circumstances, a question remains as to whether the magnitude of biochemical alterations observed by MI in CNS tumors in general (specifically spinal tumors) can reveal any prognostic value with respect to survival. MI may be able to better identify early disease and to differentiate benign from malignant lesions than more traditional methods. Moreover, an adequate identification of treatment effectiveness may influence patient management. MI probes could be developed to image the function of targets without disturbing them or as treatment to modify the target's function. MI therefore closes the gap between in vitro and in vivo integrative biology of disease. At the spinal level, MI may help to detect progression or recurrence of metastatic disease after surgical treatment. In cases of nonsurgical treatments such as chemo-, hormone- or radiotherapy, it may better assess biological efficiency than conventional imaging modalities coupled with blood tumor markers. In fact, PET provides a unique possibility to correlate topography and specific metabolic activity, but it requires additional clinical and experimental experience and research to find new indications for primary or secondary spinal tumors.

News on the genetics, epidemiology, medical care and translational research of Schwannomas

Recent years have seen substantial news and updates in the genetics and diagnosis of schwannomas, even a new hereditary disease with schwannomas; Schwannomatosis has been defined. These developments have consequently led to better evaluation of the incidence of schwannomas. Although there has also been progress in the treatment of schwannomas especially in the field of radiation therapy, hereditary diseases with multiple tumours still represent a therapeutic dilemma. NF2 in particular still causes major morbidity and mortality owing to the neurological deficit of multiple tumour disease and deafness caused by vestibular nerve involvement. Thus there has been great enthusiasm about disease models in the hope that translational research will give rise to new therapies.

Imaging in neurooncology

Imaging in patients with brain tumors aims toward the determination of the localization, extend, type, and malignancy of the tumor. Imaging is being used for primary diagnosis, planning of treatment including placement of stereotaxic biopsy, resection, radiation, guided application of experimental therapeutics, and delineation of tumor from functionally important neuronal tissue. After treatment, imaging is being used to quantify the treatment response and the extent of residual tumor. At follow-up, imaging helps to determine tumor progression and to differentiate recurrent tumor growth from treatment-induced tissue changes, such as radiation necrosis. A variety of complementary imaging methods are currently being used to obtain all the information necessary to achieve the above mentioned goals. Computed tomography and magnetic resonance imaging (MRI) reveal mostly anatomical information on the tumor, whereas magnetic resonance spectroscopy and positron emission tomography (PET) give important information on the metabolic state and molecular events within the tumor. Functional MRI and functional PET, in combination with electrophysiological methods like transcranial magnetic stimulation, are being used to delineate functionally important neuronal tissue, which has to be preserved from treatment-induced damage, as well as to gather information on tumor-induced brain plasticity. In addition, optical imaging devices have been implemented in the past few years for the development of new therapeutics, especially in experimental glioma models. In summary, imaging in patients with brain tumors plays a central role in the management of the disease and in the development of improved imaging-guided therapies.

Myringosclerosis develops within 9h of myringotomy

The aim of the present experimental study was to elucidate the temporal development of myringosclerosis. Twenty-four Sprague-Dawley rats were myringotomized bilaterally. At 3, 6, 9, 12, 18, 24, 30, 36, 48, 60, 72 and 84 h after the myringotomy, 2 animals at each time were examined otomicroscopically and thereafter sacrificed. The pars flaccida and pars tensa were excised and prepared for light- and electron-microscopic studies. Otomicroscopically, myringosclerosis was visible in the pars tensa 24 h after myringotomy, whereas no sclerotic lesions were noted in the pars flaccida. Histologically, sclerotic lesions were present in the pars tensa and pars flaccida 9 and 12 h, respectively, after myringotomy. The pars flaccida responds promptly with an inflammatory reaction characterized by abundant macrophages. Myringosclerosis develops promptly after myringotomy and its establishment is related to an inflammatory reaction.