Utility of diffusion tensor imaging parameters for diagnosis of hemimegalencephaly.
BACKGROUND
Hemimegalencephaly is a rare hamartomatous entity characterised by enlargement of all or part of the cerebral hemisphere ipsilaterally with cortical dysgenesis, large lateral ventricle and white matter hypertrophy with or without advanced myelination. Although conventional magnetic resonance imaging (MRI) is useful for detecting these diagnostic features, hemimegalencephaly is not always easily distinguished from other entities, especially when hemimegalencephaly shows blurring between the grey and white matter. Diffusion tensor imaging (DTI) is a functional MRI technique commonly used to assess the integrity of white matter. The usefulness of DTI in assessing hemimegalencephaly has not been fully elucidated. In this study, we clarified the characteristics of hemimegalencephaly with regard to DTI and its parameters including fractional anisotropy and apparent diffusion coefficient.


METHODS
Three patients with hemimegalencephaly underwent MRI including DTI. We first visually compared fractional anisotropy mapping and conventional MRI. Next, we quantitatively measured the fractional anisotropy and apparent diffusion coefficient values in the subcortical white matter of the hemisphere with hemimegalencephaly and corresponding normal-appearing contralateral regions and analysed the values using the Mann-Whitney U test.


RESULTS
On fractional anisotropy mapping, we could clearly distinguish the junction of grey and white matter and observed thicker white matter in the hemisphere with hemimegalencephaly, which was unclear on conventional MRI. The white matter in the hemisphere with hemimegalencephaly showed significantly higher fractional anisotropy (P<0.0001) and lower apparent diffusion coefficient (P=0.0022) values than the normal contralateral side.


CONCLUSIONS
DTI parameters showed salient hemimegalencephaly features and could be useful in its assessment.
Department of Diagnostic Radiology, Tohoku University Graduate School of Medicine, Japan tomomis1016@gmail.com.
Tomomi
T
Oikawa
Department of Diagnostic Radiology, Tohoku University Graduate School of Medicine, Japan.
Yasuko
Y
Tatewaki
Department of Diagnostic Radiology, Tohoku University Graduate School of Medicine, Japan.
Takaki
T
Murata
Department of Diagnostic Radiology, Tohoku University Graduate School of Medicine, Japan.
Yumiko
Y
Kato
Department of Diagnostic Radiology, Tohoku University Graduate School of Medicine, Japan.
Shunji
S
Mugikura
Department of Diagnostic Radiology, Tohoku University Graduate School of Medicine, Japan.
Kei
K
Takase
Department of Diagnostic Radiology, Tohoku University Graduate School of Medicine, Japan.
Shoki
S
Takahashi
D000293:Adolescent; D000328:Adult; D000368:Aged; D016880:Anisotropy; D001931:Brain Mapping; D056324:Diffusion Tensor Imaging / Q000379:methods*; D005260:Female; D007839:Functional Laterality; D066128:Gray Matter / Q000473:pathology; D065705:Hemimegalencephaly / Q000175:diagnosis*; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D066127:White Matter / Q000473:pathology; D055815:Young Adult
Hemimegalencephaly; apparent diffusion coefficient; diffusion tensor imaging; fractional anisotropy; magnetic resonance imaging