Functional imaging of a large demyelinating lesion

Solitary Acute Inflammatory Demyelinating Lesion of the Cervical Spinal Cord Mimicking Malignancy on FDG PET/CT

A 43-year-old woman presented with numbness of the left hand and leg for 4 weeks. MRI of the spinal cord revealed an intramedullary lesion with central nodular enhancement at the C3 level. Primary tumor or metastasis of the cervical spinal cord was suspected. FDG PET/CT showed focal hypermetabolism of the spinal cord corresponding to the gadolinium-enhanced nodule. The patient underwent resection of the cervical spinal cord lesion. Histopathological findings of the resected specimens were consistent with acute inflammatory demyelinating lesion.

Usefulness of [11C] Methionine PET in the Differentiation of Tumefactive Multiple Sclerosis from High Grade Astrocytoma

Tumefactive multiple sclerosis (tumefactive MS) is an atypical variant of MS characterized by a large isolated demyelinating lesion. Because tumefactive MS mimics high grade astrocytoma clinically and radiologically, it is difficult to distinguish between the two using only traditional diagnostic modalities, such as routine magnetic resonance imaging. [¹¹C] methionine positron emission tomography (MET PET) has been known as a useful diagnostic tool for glioma. However, it has not been established as a diagnostic tool for tumefactive MS yet. Therefore, the objective of this study was to evaluate the performance of MET PET in differentiating tumefactive MS from high grade astrocytoma. We studied patients with tumefactive MS [six patients (three men, three women), 7 lesions] and 77 patients with astrocytoma (World Health Organization grade II: 13 patients, grade III: 28 patients, and grade IV: 36 patients), and we compared MET uptake of tumefactive demyelinating lesions and astrocytoma. For MET PET analysis, Lesion/Normal region ratios (L/N ratios) were calculated and compared between tumefactive demyelinating lesions and astrocytoma. On MET PET, the L mean/N ratio of tumefactive MS was 1.18 ± 0.50, which was significantly lower than that of high-grade glioma (astrocytoma grade III: 1.95 ± 0.62, P = 0.006; grade IV: 2.35 ± 0.54, P <0.0001). The L maximum (L max)/N ratio of tumefactive demyelinating lesion was also significantly lower than that of high grade astrocytoma (tumefactive MS: 1.89 ± 0.55; astrocytoma grade III: 3.37 ± 1.36, P = 0.0232; astrocytoma grade IV: 4.35 ± 1.30, P <0.0001). In conclusion, MET PET can help differentiate tumefactive MS from high grade astrocytoma.

Frontal Tumefactive Demyelinating Lesion Mimicking Glioblastoma Differentiated by Methionine Positron Emission Tomography

BACKGROUND

Tumefactive demyelinating lesion (TDL) is often reported as a rare variation of multiple sclerosis (MS). TDL is difficult to diagnose solely by magnetic resonance imaging (MRI) in patients with no history of MS. This is because the lesion often shows ring enhancement with perifocal brain edema on gadolinium MRI, thus mimicking glioblastoma multiforme (GBM).

CASE DESCRIPTION

A 54-year-old healthy woman complained of headache 1 month before admission. She developed a decline in cognitive function, decreased attention, and executive function disorder 10 days before admission. Gadolinium magnetic resonance imaging showed a ring-shaped enhancement accompanied by massive brain edema in the left frontal lobe. This suggested GBM, but methionine positron emission tomography (MET PET), surprisingly, showed no uptake with a tumor-to-normal brain ratio of 1.18. Accordingly, we eliminated GBM and suspected brain abscess because diffusion-weighted images showed high signal intensity in the lesion. Although we performed drainage, we could not demonstrate the presence of pus. Pathologic analysis of a specimen obtained by needle biopsy revealed broad necrosis and a small number of inflammatory cells. We therefore prescribed steroid therapy, by which symptoms gradually improved. No relapse occurred for 2 years. We finally diagnosed the patient as having TDL.

CONCLUSIONS

MET PET is considered a possible diagnostic modality for demyelinating disease as it can appropriately reflect pathologic findings. MET PET will facilitate decision making regarding surgery in patients with TDL.

Primary CNS Lymphomas: Challenges in Diagnosis and Monitoring

Primary Central Nervous System Lymphoma (PCNSL) is a rare neoplasm that can involve brain, eye, leptomeninges, and rarely spinal cord. PCNSL lesions most typically enhance homogeneously on T1-weighted magnetic resonance imaging (MRI) and appear T2-hypointense, but high variability in MRI features is commonly encountered. Neurological symptoms and MRI findings may mimic high grade gliomas (HGGs), tumefactive demyelinating lesions (TDLs), or infectious and granulomatous diseases. Advanced MRI techniques (MR diffusion, spectroscopy, and perfusion) and metabolic imaging, such as Fluorodeoxyglucose Positron Emission Tomography (FDG-PET) or amino acid PET (usually employing methionine), may be useful in distinguishing these different entities and monitoring the disease course. Moreover, emerging data suggest a role for cerebrospinal fluid (CSF) markers in predicting prognosis and response to treatments. In this review, we will address the challenges in PCNSL diagnosis, assessment of response to treatments, and evaluation of potential neurotoxicity related to chemotherapy and radiotherapy.

Molecular and Metabolic Imaging in Multiple Sclerosis

Multiple sclerosis is a multifactorial disease with heterogeneous pathogenetic mechanisms, which deserve to be studied to evaluate new possible targets for treatments and improve patient management. MR spectroscopy and PET allow assessing in vivo the molecular and metabolic mechanisms underlying the pathogenesis of multiple sclerosis. This article focuses on the relationship between these imaging techniques and the biologic and chemical pathways leading to multiple sclerosis pathology and its clinical features. Future directions of research are also presented.

11C-methionine PET/CT findings in benign brain disease

¹¹C-methionine (MET) is one of the most commonly used positron emission tomography (PET) tracers for evaluation of malignant brain tumor, with MET-PET being a sensitive technique for visualization of primary and recurrent malignant brain tumors. However, previous reports have demonstrated MET uptake in lesions associated with benign brain diseases. These diseases usually show an increase in MET uptake similar to that of malignant tumors. This pitfall in MET-PET image interpretation is important not only for nuclear medicine professionals, but also for radiologists. In this review, we demonstrate the imaging characteristics of MET uptake in benign brain disease, and recommend physician interpretation of imaging findings and disease characteristics for optimal patient management. Benign uptake must be identified to prevent misdiagnosis and unnecessary surgical operations.

A patient develops transient unique cerebral and cerebellar lesions after unruptured aneurysm coiling

Background

We describe a case of a very unusual complication following a coiling procedure in which the patient developed transient unique cerebral and cerebellar lesions. Lesions were examined not only by magnetic resonance imaging (MRI) but also by positron emission tomography-computed tomography (PET-CT) and proton magnetic resonance spectroscopy (¹H-MRS).

Case presentation

A 33-year-old woman presented an incidental 3.7 × 3.3-mm unruptured cerebral aneurysm (CAn) in her basilar artery, which was successfully coiled with balloon assistance. A follow-up brain MRI at 1 and 2 months showed a gradual increase in several white matter hyperintense lesions in the left cerebellar, bilateral occipitotemporal and left parietoccipital lobe during fluid-attenuated inversion recovery (FLAIR). These were the only lesions associated with perfused CAn. However, the patient did not show any additional symptoms such as visual disturbance throughout the entire course. ¹¹C-methionine-PET (MET-PET) showed an obvious increase in methionine uptake in the lesion corresponding to enhanced areas with gadolinium-enhanced MRI. MRS showed a decrease in the N-acetylaspartate/creatine (NAA/cr) ratio and a slight elevation of the choline/creatine (cho/cr) ratio and a lactate peak in the lesion. A follow-up MRI at 6 and 12 months showed a gradual decrease in the initial hyperintense lesions in FLAIR without any treatment.

Conclusion

We present a case of an unusual complication after a coiling procedure. Although it is difficult to identify this etiology without a pathological examination, it is importance to increase awareness of such a potential complication arising from coiling procedures, because interventional procedures have become the first choice of treatment for cerebrovascular diseases in many countries.

Tumefactive Demyelinating Lesion Differentiated from a Brain Tumor Using a Combination of Magnetic Resonance Imaging and (11)C-methionine Positron Emission Tomography

A 37-year-old woman gradually developed a gait disturbance due to sensory loss in the left lower extremity three years after being diagnosed with clinically isolated syndrome. Brain magnetic resonance imaging (MRI) demonstrated an incomplete ring-enhanced lesion with perifocal edema in the subcortex of the right parietal lobe. (11)C-methionine positron emission tomography (MET-PET) showed an insignificant uptake in the lesion. The patient was noninvasively diagnosed with tumefactive multiple sclerosis and treated with corticosteroids, and her neurological symptoms and MRI findings improved with treatment. The combination of MRI findings and insignificant uptake on MET-PET is useful for noninvasively differentiating tumefactive demyelinating lesions from brain tumors.

Aquaporin-4 autoimmunity masquerading as a brainstem tumor

Brainstem glioma is a highly devastating disease, and any mass-like lesion in the brainstem can raise suspicion of this diagnosis. However, other inflammatory, demyelinating, or degenerative diseases can mimic brainstem glioma in clinical presentation and imaging features. Therefore, diagnosis based solely on imaging is often insufficient for brainstem lesions and may lead to incorrect diagnosis and treatment. This case report is the first description of central nervous system aquaporin-4 (AQP4) autoimmunity confined mainly to the brainstem. It demonstrates the wide spectrum of neuroinflammatory diseases in children and highlights the utility of surgical biopsy for suspicious brainstem lesions with atypical imaging features for glioma.

PET imaging in multiple sclerosis

Positron emission tomography (PET) is a non-invasive technique for quantitative imaging of biochemical and physiological processes in animals and humans. PET uses probes labeled with a radioactive isotope, called PET tracers, which can bind to or be converted by a specific biological target and thus can be applied to detect and monitor different aspects of diseases. The number of applications of PET imaging in multiple sclerosis is still limited. Clinical studies using PET are basically focused on monitoring changes in glucose metabolism and the presence of activated microglia/macrophages in sclerotic lesions. In preclinical studies, PET imaging of targets for other processes, like demyelination and remyelination, has been investigated and may soon be translated to clinical applications. Moreover, more PET tracers that could be relevant for MS are available now, but have not been studied in this context yet. In this review, we summarize the PET imaging studies performed in multiple sclerosis up to now. In addition, we will identify potential applications of PET imaging of processes or targets that are of interest to MS research, but have yet remained largely unexplored.

The role of brain MRI in mitochondrial neurogastrointestinal encephalomyopathy

Leukoencephalopathy is a hallmark of mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) a devastating disorder characterized by ptosis, ophthalmoparesis, gastrointestinal dysfunction and polyneuropathy. To characterize MNGIE-associated leukoencephalopathy and to correlate it with clinical, biochemical and molecular data, four MNGIE patients with heterogeneous clinical phenotypes (enteropathic arthritis, exercise intolerance, CIDP-like phenotype and typical presentation) were studied by magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS). Diffusion weighted imaging (DWI) with apparent diffusion coefficient (ADC) maps were also obtained. In two patients we also investigated the role of brain MRI in monitoring the evolution of leukoencephalopathy by performing follow-up imaging studies at an interval of one and two years. The extension and distribution of leukoencephalopathy were not clearly linked with age, phenotype or disease severity, and did not seem to be related to TYMP mutations, enzyme activity or pyrimidine levels. In the studied patients MRS revealed reduced N-acetyl-aspartate and increased choline signals. Although DWI appeared normal in all patients but one, ADC maps always showed moderate increased diffusivity. Leukoencephalopathy worsened over a two-year period in two patients, regardless of the clinical course, indicating a lack of correlation between clinical phenotype, size and progression of white matter abnormalities during this period. Brain MRI should be considered a very useful tool to diagnose both classical and atypical MNGIE. Serial MRIs in untreated and treated MNGIE patients will help to establish whether the leukoencephalopathy is a reversible condition or not.

Autologous mesenchymal stem cell-derived dopaminergic neurons function in parkinsonian macaques

A cell-based therapy for the replacement of dopaminergic neurons has been a long-term goal in Parkinson's disease research. Here, we show that autologous engraftment of A9 dopaminergic neuron-like cells induced from mesenchymal stem cells (MSCs) leads to long-term survival of the cells and restoration of motor function in hemiparkinsonian macaques. Differentiated MSCs expressed markers of A9 dopaminergic neurons and released dopamine after depolarization in vitro. The differentiated autologous cells were engrafted in the affected portion of the striatum. Animals that received transplants showed modest and gradual improvements in motor behaviors. Positron emission tomography (PET) using [11C]-CFT, a ligand for the dopamine transporter (DAT), revealed a dramatic increase in DAT expression, with a subsequent exponential decline over a period of 7 months. Kinetic analysis of the PET findings revealed that DAT expression remained above baseline levels for over 7 months. Immunohistochemical evaluations at 9 months consistently demonstrated the existence of cells positive for DAT and other A9 dopaminergic neuron markers in the engrafted striatum. These data suggest that transplantation of differentiated autologous MSCs may represent a safe and effective cell therapy for Parkinson's disease.

Phonological processing is uniquely associated with neuro-metabolic concentration

Reading is a complex process involving recruitment and coordination of a distributed network of brain regions. The present study sought to establish a methodologically sound evidentiary base relating specific reading and phonological skills to neuro-metabolic concentration. Single voxel proton magnetic resonance spectroscopy was performed to measure metabolite concentration in a left hemisphere region around the angular gyrus for 31 young adults with a range of reading and phonological abilities. Correlation data demonstrated a significant negative association between phonological decoding and normalized choline concentration and as well as a trend toward a significant negative association between sight word reading and normalized choline concentration, indicating that lower scores on these measures are associated with higher concentrations of choline. Regression analyses indicated that choline concentration accounted for a unique proportion of variance in the phonological decoding measure after accounting for age, cognitive ability and sight word reading skill. This pattern of results suggests some specificity for the negative relationship between choline concentration and phonological decoding. To our knowledge, this is the first study to provide evidence that choline concentration in the angular region may be related to phonological skills independently of other reading skills, general cognitive ability, and age. These results may have important implications for the study and treatment of reading disability, a disorder which has been related to deficits in phonological decoding and abnormalities in the angular gyrus.

Use of PET in the diagnosis of primary CNS lymphoma in patients with atypical MR findings

OBJECTIVE

The diagnosis of primary central nervous system lymphoma (PCNSL) in immunocompetent patients with atypical magnetic resonance (MR) findings such as disseminated lesions or no (non-enhancing) lesion is sometimes difficult because of mimicking other tumorous and non-tumorous diseases. Positron emission tomography (PET) with (18)F-fluorodeoxyglucose (FDG) and (11)C-methionine (MET) can measure the glucose and amino acid metabolism in the lesions and may provide useful information for diagnosing PCNSL in patients with such subtle MR findings.

METHODS

We performed PET studies with FDG and MET in 17 histologically proven PCNSL and compared the uptake of FDG and MET qualitatively and quantitatively in the tumors between 12 typical and 5 atypical MR findings.

RESULTS

All typical PCNSL showed strong uptake of FDG and MET; however, visual analysis of FDG and MET uptake in atypical PCNSL was not very useful for finding lesions in the brain. Semiquantitative FDG and MET uptake values (SUVmax) and quantitative FDG influx rate constant (K ( i )) in the tumors are significantly lower in atypical PCNSL compared with those in typical PCNSL. These values obtained in the lesions with atypical MR findings were also not useful for differentiating PCNSL from other tumorous and non-tumorous diseases. The k (3) values evaluated by FDG kinetic analysis in atypical PCNSL were similar to those obtained in typical PCNSL.

CONCLUSIONS

Visual analysis of FDG and MET uptake in atypical PCNSL was not useful for finding the lesions in the brain. Semiquantitative and quantitative values obtained in the lesions with atypical MR findings were also not useful for differentiating PCNSL from other tumorous and non-tumorous diseases. The k (3) values evaluated by FDG kinetic analysis in atypical PCNSL may provide valuable information in the diagnosis of PCNSL.

MR spectroscopy of the brain in Leigh syndrome

Brain magnetic resonance spectroscopy in two patients with Leigh syndrome revealed the presence of lactate in gray and white matter brain tissue and relatively high choline levels in the white matter. The latter observation, most probably related to an ongoing demyelination process, underlines specific involvement of white matter metabolism in Leigh syndrome even in cases without involvement of the white matter as visualized on MRI. Magnetic resonance spectroscopy might thus be of help in differentiating Leigh syndrome from a range of other mitochondrial diseases, such as ophthalmoplegia and Kearns-Sayre syndrome, showing lack of lactate in brain tissues appearing normal on MRI.

Cancer imaging with fluorine-18-labeled choline derivatives

The choline transporter and choline kinase enzyme frequently are overexpressed in malignancy. Therefore, positron-emitter-labeled compounds derived from choline have the potential to serve as oncologic probes for positron emission tomography. The fluorine-18 ((18)F)-labeled choline derivative fluorocholine (FCH) in particular has demonstrated potential utility for imaging of a variety of neoplasms, including those of the breast, prostate, liver, and brain. The pharmacokinetics of FCH and other choline tracers allow for whole-body imaging within minutes of injection while still achieving high tumor-to-background contrast in most organs, including the brain. These features, along with the possibility of imaging malignancies that have proved elusive with the use of (18)F-fluorodeoxyglucose positron emission tomography support further clinical investigations of (18)F-labeled choline tracers.