Original contributionDisappearance of tumor contrast on contrast-enhanced FLAIR imaging of cerebral gliomas
Introduction
Magnetic resonance imaging (MRI) is the most sensitive imaging modality in the detection and delineation of primary intraaxial brain tumors (gliomas) [1]. For detecting cerebral gliomas, T2-weighted sequences were widely accepted to be the most sensitive imaging modality [1] because as in many other pathologic conditions the prolongation of the T2 relaxation time by tumor tissue results in a high contrast between the lesion and brain tissue [2], [3]. Enhancing regions in anaplastic or malignant gliomas are generally equated with the more solid part of the tumors and histopathologic correlation has proved that enhancing areas on contrast enhanced scans largely correspond to the densely cellular, hypervascular tissue of viable tumor [4]. On non-enhanced T1-weighted images, these areas are hypointense to the surrounding normal tissue indicating a substantially prolonged T1 time. In recent studies, a fluid-attenuated inversion-recovery (FLAIR) MR sequence has shown to be a valuable imaging sequence in the assessment of cerebral gliomas [5], [6]. FLAIR produces heavily T2-weighted and cerebrospinal fluid (CSF)-nulled MR images [7], [8] which allows a better delineation of tumors close to CSF filled structures. Therefore, FLAIR MR imaging is currently used as a routine sequence in most MR centers and has replaced proton-density sequences.
Due to a mild T1 weighting of the FLAIR sequence, which is induced by the long inversion time used for the CSF suppression, FLAIR images obtained after administration of i.v. gadolinium can be used to detect pathologic enhancement [9]. This effect has shown to further enhance the delineation of intraaxial tumors and other contrast enhancing CNS diseases [9], [10]. In some circumstances, e.g., radiotherapy planning or neurosurgical navigation, where only a limited number of images can be applied, contrast enhanced FLAIR may be used as a solitary sequence to save time and to avoid potential errors from e.g., image fusion.
In this report, we present a potential pitfall regarding the use of contrast enhanced FLAIR imaging alone in patients with enhancing anaplastic or malignant cerebral gliomas.
Section snippets
Patient studies
Eighty patients (49 female and 31 male, age range 21–68 years, mean age 42 years), with enhancing cerebral tumors histologically confirmed as anaplastic (WHO Grade III) or malignant (WHO Grade IV) cerebral gliomas were examined on a standard 1.5 Tesla clinical MR scanner by FLAIR and conventional MR imaging before and after contrast media application. The first 18 of these patients were previously published [10].
The imaging protocol included T1-weighted SE, PD- and T2-weighted FSE and FLAIR
Results and discussion
FLAIR imaging was found to be superior to conventional MR imaging in the delineation of the gross tumor volume and the delineation of the enhancing from the non enhancing tumor parts (Table 1 , Fig. 1). In the qualitative analysis, the tumor contrast was best on the contrast enhanced FLAIR images (Table 2). However, in ten patients (3 female and 7 male, age range 31–63 years, mean age 44 years) out of the series of 80, the gadolinium enhanced FLAIR images were rated inferior to the
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