Contrast-enhanced magnetic resonance imaging of tumours of the central nervous system: a clinical review

Delineation of Gliomas with Magnetic Resonance Imaging Using Gd-DTPA in Comparison with Computed Tomography and Positron Emission Tomography

Fourteen patients with cerebral gliomas were investigated by MR imaging using Gd-DTPA (Magnevist), CT with the contrast agent iohexol (Omnipaque) and, as a reference, positron emission tomography (PET) using 11C-L-methionine. Tumour areas with disruption of the blood-brain-barrier (BBB) as seen on MR and CT were compared with areas with increased accumulation of methionine in PET. There were 6 patients with high-grade astrocytoma (grade III-IV), 5 with low-grade astrocytoma (grade I–II) and 3 with oligodendroglioma. In 4 high-grade tumours, PET showed a larger tumour or tumour tissue in additional areas, compared with enhancement on MR and CT, while in 2 cases the tumour extension was similar in the three modalities. In the low grade tumour group, the findings on PET differed from those on post-contrast MR or CT in 7 cases. In 3 of these cases, no disruption of the BBB was seen either on MR or on CT. In 2 of our 14 patients CT showed larger enhancement extension than MR and in 2 cases MR was superior to CT in this respect. The enhancement intensity was higher on MR in 4 patients and on CT in 2 patients. No definite difference in the delineation of tumour tissue between the T1 weighted SE sequences used was found. The gradient echo sequences FLASH and FISP gave limited information that was less than that provided by the T1 weighted SE sequences. A greater increase in signal intensity in T1 weighted images was usually seen 5 min post-contrast in the high-grade tumours than in the low-grade ones.

Usefulness of 11C-methionine positron emission tomography for detecting intracranial ameloblastic carcinoma: A case report

Ameloblastic carcinoma, secondary type, is an extremely rare odontogenic malignant tumor. The present study reports the case of a 58-year-old male with ameloblastic carcinoma that extended into the intracranial space close to the internal carotid artery. Surgical excision was performed, as headaches were being caused via compression by the mass. Small remnants of the tumor remained surrounding the internal carotid artery following surgical resection. Although the remnant tissue was not detected on magnetic resonance imaging or 18F-fluorodeoxyglucose (FDG)-positron emission tomography (PET), it was clearly visualized on ¹¹C-methionine PET in the early post-operative follow-up period. No neurological deficits were exhibited during the follow-up period, and ¹¹C-methionine PET was able to detect the remnant lesion distribution in the intracranial space. The current study presents a rare case of ameloblastic carcinoma that extended into the intracranial space. In addition, several diagnostic imaging tools were compared in order to determine the most suitable imaging modality. At present, the patient is continuing a therapeutic course of radiation and evident mass reduction has been observed. However, the therapeutic effects are currently under consideration. To the best of our knowledge, this is the first study on the effectiveness of using ¹¹C-methionine PET for detecting ameloblastic carcinoma with intracranial extension.

Efficacy and Safety of Gadobutrol (1.0 M) versus Gadopentetate Dimeglumine (.5 M) for Enhanced Mri of Cns Lesions: A Phase Iii, Multicenter, Single-blind, Randomized Study in Chinese Patients

The aim of this study was to compare the efficacy and safety of macrocyclic gadobutrol (1.0 M) with linear gadopentetate dimeglumine (0.5 M) for contrast-enhanced magnetic resonance imaging (MRI) of central nervous system (CNS) lesions in Chinese patients (N = 147) with known or suspected CNS lesions, who were enrolled in this single-blind, randomized, parallel-group study. Three blinded independent readers evaluated all efficacy variables. The primary efficacy variable was the difference between the two agents for the change in contrast-to-noise ratio (CNR) between non-enhanced and contrast-enhanced scans of lesions. Secondary outcomes included mean change in number of lesions detected before and after contrast enhancement, diagnostic confidence, and safety and tolerability parameters. Gadobutrol was non-inferior to gadopentetate dimeglumine in respect to the difference in the mean change in CNR (6.94; 95% confidence interval [CI] lower limit: -3.90; predefined maximum 95% CI lower limit: -6.52). The mean change in the number of CNS lesions detected was greater with gadobutrol versus gadopentetate dimeglumine (1.2 vs. 0.2 lesions). Diagnostic confidence was classified as ‘high’ for more patients with gadobutrol versus gadopentetate dimeglumine by the investigators (58.8% vs. 55.4%) and by the three blinded readers (63.6% vs. 55.7%, 23.7% vs. 18.0% and 81.7% vs. 81.0%). Both agents were well tolerated by participating patients. We concluded that in Chinese patients with CNS lesions, gadobutrol (1.0 M) was as effective and well tolerated in contrast-enhanced MRI as gadopentetate dimeglumine (0.5 M). Gadobutrol provided improved visualization of CNS lesions compared with gadopentetate dimeglumine, with a comparable tolerability profile.

Development of a MR-visible compound for tracing neuroanatomical connections in vivo

Traditional studies of neuroanatomical connections require injection of tracer compounds into living brains, then histology of the postmortem tissue. Here, we describe and validate a compound that reveals neuronal connections in vivo, using MRI. The classic anatomical tracer CTB (cholera-toxin subunit-B) was conjugated with a gadolinium-chelate to form GdDOTA-CTB. GdDOTA-CTB was injected into the primary somatosensory cortex (S1) or the olfactory pathway of rats. High-resolution MR images were collected at a range of time points at 11.7T and 7T. The transported GdDOTA-CTB was visible for at least 1 month post-injection, clearing within 2 months. Control injections of non-conjugated GdDOTA into S1 were not transported and cleared within 1-2 days. Control injections of Gd-Albumin were not transported either, clearing within 7 days. These MR results were verified by classic immunohistochemical staining for CTB, in the same animals. The GdDOTA-CTB neuronal transport was target specific, monosynaptic, stable for several weeks, and reproducible.

Nonenhancing tumors of the spinal cord

OBJECT

Enhancement of pathological entities in the central nervous system is a common finding when the blood-brain barrier has been compromised. In the brain, the presence or absence of gadolinium enhancement is often an indicator of tumor invasiveness and/or grade. In the spinal cord, however, contrast enhancement has been shown in all tumor types, regardless of grade. In this study the authors explore the incidence of nonenhancing tumors of the spinal cord and the clinical course of patients with these lesions.

METHODS

A retrospective analysis was conducted in which investigators examined the patterns of enhancement of histologically proven intramedullary spinal cord tumors that had been evaluated at the Mayo Clinic between 1998 and 2002. The tumors that did not enhance were the subject of this report.

RESULTS

A total of 130 patients with intramedullary tumors were evaluated. Of those, 11 patients (9%) had tumors that did not enhance. Histologically, a majority of tumors were astrocytomas (eight low-grade and two high-grade lesions); one tumor was a subependymoma. Morphologically, most of the tumors were diffuse and none had associated cysts. Tumors spanned from two to seven levels and were located throughout the spinal cord (four cervical, three cervicothoracic, one thoracic, and three thoracolumbar). Biopsy procedures were performed in eight patients, subtotal resection was performed in two, and gross-total resection in one. After a mean follow-up period of 19 months, tumors remained stable in eight patients but progressed in three, two of whom died.

CONCLUSIONS

A number of intramedullary spinal cord tumors will not enhance after addition of contrast agents. The absence of enhancement does not imply the absence of tumor.

In vivo uptake and metabolism of alpha-[11C]methyl-L-tryptophan in human brain tumors

Abnormal metabolism of tryptophan has been implicated in modulation of tumor cell proliferation and immunoresistance. alpha-[(11)C]Methyl-L-tryptophan (AMT) is a PET tracer to measure cerebral tryptophan metabolism in vivo. In the present study, we have measured tumor tryptophan uptake in 40 patients with primary brain tumors using AMT PET and standard uptake values (SUV). Tryptophan metabolism was further quantified in 23 patients using blood input data. Estimates of the volume of distribution (VD') and the metabolic rate constant (k(3)') were calculated and related to magnetic resonance imaging (MRI) and histology findings. All grade II to IV gliomas and glioneuronal tumors showed increased AMT SUV, including all recurrent/residual tumors. Gadolinium enhancement on MRI was associated with high VD' values, suggesting impaired blood-brain barrier, while k(3)' values were not related to contrast enhancement. Low-grade astrocytic gliomas showed increased tryptophan metabolism, as measured by k(3)'. In contrast, oligodendrogliomas showed high VD' values but lower k(3)' as compared with normal cortex. In astrocytic tumors, low grade was associated with high k(3)' and lower VD', while high-grade tumors showed the reverse pattern. The findings show high AMT uptake in primary and residual/recurrent gliomas and glioneuronal tumors. Increased AMT uptake can be due to increased metabolism of tryptophan and/or high volume of distribution, depending on tumor type and grade. High tryptophan metabolic rates in low-grade tumors may indicate activation of the kynurenine pathway, a mechanism regulating tumor cell growth. AMT PET might be a useful molecular imaging method to guide therapeutic approaches aimed at controlling tumor cell proliferation by acting on tryptophan metabolism.

Chordoid glioma of the third ventricle: CT and MR findings

We present a case of chordoid glioma involving the third ventricle in a 42-year-old woman. CT and MR showed a homogeneously enhancing mass occupying the third ventricle, with a cystic component. Chordoid glioma should be included in the differential diagnosis of uncommon masses of the third ventricle in middle-aged women.

Invited review: biophysical properties and clinical applications of magnetic resonance imaging contrast agents

Contrast enhanced magnetic resonance imaging (MRI) is a very versatile and effective technique for detecting and characterizing lesions, for identifying a variety of patho-physiological abnormalities, and for providing perfusion and functional information. The application of contrast enhanced MRI to many clinical and research indications has emerged because of the rapid evolution in imaging techniques, improved methodology, and the development of efficient and specific contrast agents. Problems related to optimizing parameters and dosage have been due to complex interplay of relaxation times, biophysical mechanisms and acquisition parameters. A knowledge of basic biophysical aspects is therefore essential for a full understanding of the results obtained for different organs under different conditions, and for optimizing the image parameters and dosage of contrast agents. This article underlines the biophysical basis of the effects of contrast agents in MRI, identifies the problems involved in optimizing the parameters for maximum efficiency, and presents a general overview of the clinical studies and research applications in the central nervous system, perfusion abnormalities, hepatobiliary system, musculoskeletal system and the gastrointestinal tract. The section on perfusion studies includes a discussion of quantitative analysis and kinetic models describing the effects of contrast agents. Finally, a critical evaluation of the scope and limitations of contrast enhanced MRI is presented.

Review article: computed tomography and magnetic resonance in the diagnosis of intraventricular cerebral masses

We describe a series of 60 cases of patients with masses arising within the cerebral ventricles. The site and relative frequency is noted for each histological type. The differential diagnosis depends on patient age and sex, site, morphology and number of masses, presence and type of hydrocephalus and the characteristics of the mass on computed tomography (CT) and magnetic resonance (MR) images. A review of the literature has been performed and this information collated with our own experience to give detailed descriptions of the typical features of each intraventricular mass. Attention is drawn to intraventricular neurocytoma, a recently described tumour that may be mistaken histologically for intraventricular oligodendroglioma or ependymoma. A comparison is made of the value of CT and MR in the diagnosis of intraventricular masses.

Volumetric analyses of central nervous system neoplasm based on MRI

Morphometric analyses were performed using an objective semiautomated algorithm on 5 sequential three-dimensional T1-weighted magnetic resonance imaging scans of a metastatic choroid plexus carcinoma, concurrent with a course of chemotherapy. The 5 scans were positionally normalized in a three-dimensional coordinate system for uniform definition of the borders of the mass. Volumes were calculated for the gadolinium-DTPA enhancing and nonenhancing cystic-appearing regions. Volumetric changes of up to 145% were measured using this method which were associated with changes in the calculated (spherical) radii of only up to 2.7 mm. Volumetric changes of up to 59% were not appreciated by visual inspection, most probably due to irregular borders and positional variability across the scans. Volumetric analyses were also performed on the right cerebellar hemisphere, producing a 1.83% coefficient of variability across the 5 scans. The growth rates of this mass were estimated from the sequential computations, permitting in vivo observations on tumor behavior otherwise not obtainable. These analyses demonstrate the potential of this morphometric method to detect significant volumetric changes, and illustrate its use to define in vivo the growth properties of central nervous system tumors in response to therapeutic interventions.

Gadolinium-DTPA enhanced magnetic resonance imaging in acoustic neuroma diagnosis and management

Gadolinium-DTPA (Gd-DTPA) is a paramagnetic contrast agent that increases the intensity of acoustic neuromas (AN) on T1-weighted magnetic resonance imaging (MRI) scans. Over a 9-month period we have reviewed Gd-DTPA-enhanced MRI scans on 32 consecutive cases (35 tumors) involving the internal auditory canal (IAC) and cerebellopontine angle (CPA). The majority of patients (84%) were imaged on latest generation 1.5 Tesla scanners. Every tumor studied showed marked enhancement after Gd-DTPA administration. This improved contrast permitted identification of three small tumors that were not evident on unenhanced scans. Gd-DTPA appears to be particularly useful in the evaluation of recurrent or residual AN. In three patients with known residual tumor after planned subtotal excisions, the remaining tumor could only be differentiated from surrounding scar, cerebral spinal fluid (CSF), and brain parenchyma after contrast enhancement. In one of these, a small rim of tumor capsule left on the facial nerve was evident only on Gd-DTPA-enhanced T1 images. Gd-DTPA also provides a more reliable estimate of the depth of tumor penetration in the IAC. This information is useful in selecting candidates suitable for a hearing conservation approach.

Unenhanced and gadolinium-DTPA-enhanced MR imaging in postoperative evaluation in pediatric brain tumors

Gadolinium-diethylenetriaminepenta-acetic acid (Gd-DTPA) is a chelated paramagnetic contrast agent under clinical trial for use in magnetic resonance (MR) imaging. The increased signal intensity following the intravenous infusion of contrast medium may improve the ability of MR imaging to delineate tumors. The use of this method in 15 pediatric patients with suspected brain-tumor recurrence was analyzed. All 15 patients underwent postoperative Gd-DTPA-enhanced MR imaging, and residual tumor was demonstrated in nine of them. Based on the findings of the enhanced MR studies, four patients had additional surgery, two underwent radiation therapy, and one was given immunotherapy. Continued surveillance was recommended for the remaining eight patients. In all cases the enhanced MR imaging studies were superior to the unenhanced studies in regard to the qualitative and quantitative assessment of the residual tumor. Gadolinium-DTPA-enhanced MR imaging appears to be a safe and effective means of providing an accurate postoperative assessment of residual disease in pediatric brain-tumor patients. It is as effective as contrast-enhanced computerized tomography and has the sensitivity and anatomic resolution provided by MR imaging. The most useful role of this agent was in the postoperative period, in assessing the adequacy of surgical resection. This technique is recommended as the procedure of choice in the postoperative assessment and long-term surveillance of patients with brain tumors.