High Fractional Anisotropy in Brain Abscesses versus Other Cystic Intracranial Lesions
Rakesh K. Guptaa,
Khader M. Hasand,
Asht M. Mishraa,
Deepak Jhac,
Mazhar Husainc,
Kashi N. Prasadb and
Ponnada A. Narayanad
a Department of Radiodiagnosis, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, India
b Department of Microbiology, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, India
c Department of Neurosurgery, King George’s Medical University, Lucknow, India
d Department of Radiology, University of Texas Medical School at Houston, Houston, Texas
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FIG 1. A 4-year-old child presented with right ear discharge and brain abscess with intraventricular rupture and meningitis.
T2-weighted axial image (A) through the lateral ventricles shows hyperintensity in the right periventricular region with mass effect. Note the layering in the left lateral ventricle. Corresponding T1-weighted image (B) shows the periventricular lesion as hypointense that displays rim enhancement on post contrast T1-weighted MT image (C). Note the enhancement of the ventricular lining that is more prominent on the right side, which suggests ependymitis (C). DW image (D) and Dav map (E) at the same level show restricted diffusion in the cavity. Note the area of restricted diffusivity in the layered portion of the left lateral ventricle. FA map (F) shows areas of high FA values in the cavity mixed with intervening low FA values. Note the high FA values in the lower part of the left lateral ventricle medial to the optic radiation. Color modulated FA maps fused with Dav map shows (G) orientation in the abscess cavity as well in the left lateral ventricle similar to what is observed in the oriented white matter. Three sections caudally, postcontrast T1-weighted MT image (H) shows the epicenter of the abscess cavity that appears highly oriented on the color-modulated FA maps fused with Dav images. The measured FA values were higher than corpus callusm in some of the regions of the abscess cavity. The color coding is shown (G and I, lower left corner): red (right–left), green (anteroposterior), blue (superior–inferior).
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FIG 2. Scatter plot of the FA values versus Dav from the abscess cavities, tumor cavities cysts, corresponding contra-lateral normal-appearing parenchyma and whole brain of a healthy adult subject. The plot shows FA and Dav values for the tumor cavity and cyst are separate from the abscess cavity. Note the marked variability of FA values in the abscess cavity.
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FIG 3. An 8-year-old girl presented with fever, tooth infection, and signs of raised intracranial tension.
T2-weighted axial image (A) through the lateral ventricles shows hyperintense lesion with hypointense peripheral rim in the right periventriclular region and is associated with mass effect. Corresponding T1 (B) and postcontrast T1-weighted MT (C) images show central hypointensity with peripheral rim extending to the body of the corpus callosum. DW image (D) and Dav map (E) show areas of restricted diffusivity. FA map (F) show very high values in the medial part of the abscess cavity, and variable FA in the lateral part of the cavity (0.12–0.32). Color-modulated FA map fused on Dav map shows (G) the same with orientation. Following drill aspiration of the abscess cavity, a repeat DTI was done after 5 days. Follow-up T2-weighted image (H) shows residual cavity with mild ventricular dilatation. Postcontrast T1-weighted MT image (I) shows rim enhancement of the residual cavity with ependymal enhancement, which suggests ependimitis. Dav map (J) shows high diffusivity and FA map (K) shows marked decrease in values compared with panel F. Color-modulated FA maps (L) fused with Dav shows the loss of orientation compared with panel G.
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FIG 4. A 55-year-old woman with left frontoparietal low-grade astrocytoma.
T2-weighted axial image (A) through the lateral ventricle shows hyperintense mass on the left side with perifocal edema and mass effect. The lesion appears hypointense on T1WI image (B) and shows rim enhancement on postcontrast T1-weighted MT image (C). Dav map (D) shows high diffusivity and FA map (E) shows little anisotropy. Color-modulated FA map shows no orientation in the cavity.
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FIG 5. A 40-year-old man with neurocysticercosis.
T2-weighted image (A) through the supraventricular region shows a hyperintense cyst on the left side with eccentrically placed hypointense scolex. The lesion appears hypointense with isointense scolex on T1-weighted image (B), and shows minimal rim enhancement on postcontrast T1-weighted MT image (C). Dav map (D) shows high diffusivity, and FA map (E) shows little anisotropy. Color-modulated FA map shows no orientation in the cavity.
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