T2-FLAIR magnetic resonance imaging sequence for brain abscess
The T2-FLAIR magnetic resonance imaging (MRI) sequence is commonly employed in the imaging of brain abscesses. This specific imaging sequence helps in providing detailed and high-contrast images that are beneficial for the identification and characterization of brain abscesses. Here's how T2-FLAIR is relevant to brain abscess imaging:
T2 Weighting: The T2 weighting in the sequence is crucial for highlighting fluid content. Brain abscesses typically contain pus or other fluid components, which have relatively long T2 relaxation times. T2-weighted imaging helps in emphasizing the contrast between the abscess and the surrounding brain tissue.
FLAIR (Fluid Attenuated Inversion Recovery): The FLAIR component in the sequence is particularly useful for suppressing the signal from cerebrospinal fluid (CSF). This suppression of CSF signal is essential because it allows for better visualization of structures adjacent to fluid-filled spaces, such as brain ventricles. This is important when assessing brain abscesses, as they often occur near or within brain parenchyma.
When applied to imaging brain abscesses, the T2-FLAIR sequence helps in differentiating between the abscess and the surrounding brain tissue. The high signal intensity of the abscess on T2-weighted images, combined with the CSF suppression from FLAIR, enhances the visibility of the abscess and improves the overall diagnostic accuracy.
In summary, T2-FLAIR MRI is a valuable tool in the imaging of brain abscesses, providing detailed information about the location, size, and characteristics of the abscess while minimizing interference from surrounding structures.
Central high intensity (hypointense to CSF, does not attenuate on FLAIR)
Peripheral high intensity (vasogenic edema)
The abscess capsule may be visible as an intermediate to slightly low signal thin-rim
Space-occupying lesion, centered in the right frontal anterior white matter, with estimated diameters of 3.5 x 3 x 3.5 cm. It shows well-defined contours and a practically spherical shape. A predominantly hypointense signal on T1 and homogeneously hyperintense on T2, with a wall with hypointense behavior on T2-weighted sequences. After contrast administration, only enhancement of its wall was observed, finely and linearly, without identifying solid poles. The lesion shows diffusion sequence restriction and low values of rVSC in perfusion. Marked surrounding vasogenic edema, which causes a mass effect on the neighboring sulci, as well as mild subfalcian herniation, with a deviation from the midline of approximately 6 mm (significant improvement compared to previous CT control). The discrete mass effect is also on the knee of the corpus callosum and the frontal horn of the right ventricle. The findings are compatible with a brain abscess. A small solution of continuity is observed in its anterior wall, in contact with the meninge, which is thickened in a laminar manner about inflammatory involvement, without clearly identifying empyema. Extensive occupation of the frontal sinus bilaterally, with an enhancement of its wall. Retrospectively, the CT study showed slight permeation on the posterior wall of one of the loculations of the frontal sinus close to the abscess. Small hyperintense foci in subcortical and periventricular white matter with a chronic ischemic profile of a small vessel, to a mild degree. Diagnostic impression: Findings compatible with a right frontal parenchymal abscess, 3.5 cm in diameter, with inflammatory changes and thickening of the adjacent pachymeninge, although without clear associated empyema.
MR imaging is more sensitive than CT, and MRI can usually detect infection in the early cerebritis stage. The MRI scan in focal cerebritis usually shows an area of Hypointensity on T1- and T2-weighted imaging. The characteristic appearance of a mature brain abscess on MRI is a focal lesion with low intensity on a T1-weighted image, with a smoothly marginated capsule that enhances with IV gadolinium.
Gliomas of the brain may appear as expansile ring-enhancing masses in MRI studies, mimicking the appearance of intra-axial abscesses. This study aimed to compare the MRI features of ring-enhancing gliomas and intra-axial brain abscesses in dogs and cats and to identify the characteristics that might help differentiate them. For this multicenter, retrospective, and observational study, the inclusion criteria were as follows: (a) a definitive diagnosis of glioma or abscess based on cytological or histopathological examination following CSF collection or surgical biopsy/necropsy, respectively; (b) MRI study performed with a high- or low-field MRI scanner, including a same plane T1W pre- and postcontrast, a T2W and a T2 FLAIR sequence in at least one plane. If available, delayed T1W postcontrast, T2*W GE, DWI/ADC, and SWI sequences were also evaluated. Sixteen patients were diagnosed with ring-enhancing gliomas, and 15 were diagnosed with intra-axial abscesses. A homogenous signal on T1W (P = 0.049) and T2W (P = 0.042) sequences, a T2W (P = 0.005) or T2*W GE (P = 0.046) peripheral hypointense halo, and an even enhancing capsule (P = 0.002) were significantly associated with brain abscesses. A progressive central enhancement on delayed T1W postcontrast sequences was correlated with ring-enhancing gliomas (P = 0.009). The combination of the following features was suggestive of brain abscess: homogeneous T1W or T2W signal intensity, a T2W or T2*W GE peripheral hypointense halo, and an evenly enhancing capsule. Central progression of enhancement on delayed T1W postcontrast sequences was suggestive of glioma 1).