| ObjectiveTo define the "brainstem hemisection sign", and investigate its MR characteristics and relationships with vascular territories, as an aid to the diagnosis of brainstem infarction and differential diagnosis of other brainstem lesions.Materials and MethodsMRI data were collected and analyzed from 286 consecutive patients with brainstem lesions confirmed by clinical or/and pathology from January to April 2009. There were 196 male and 90 female patients, and their ages ranged from 19 months to 95 years (mean age,58.7 years). Informed consent was obtained from each patient.MR scanning was performed on 3.0-T MR unit (General Electric medical systems, USA) with 8-channel head coil. All specimens underwent routine MR examination, which included the following sequences:Transverse T1-weighted fast spin echo (TR 1750ms, TE 24m), fluid-attenuated inversion recovery (FLAIR) (TR 9000ms, TE 150ms), transverse and saggittal T?-weighted spin echo (TR 3280ms, TE 110ms). All these sequences above use the parameters:section thickness 5.0 mm, intersection gap 1.5 mm, FOV 240 mm×240 mm, and matrix 320x256. 201 cases underwent transverse diffusion-weighted imaging (DWI) (TR 5300ms, TE 81.4ms) and 58 cases performed magnetic resonance angiography (MRA) (TR 20ms, TE 3.0ms, flip angle 15°, section thickness 1.4 mm) as clinically indicated.Two neuroradiologists independently interpreted the MRI data of all cases. The shape, location, and distribution of the lesions were evaluated. Discrepancies were resolved by consensus. The "brainstem hemisection sign" was defined as brainstem lesion located in ipsilateral brainstem with a sharp cutting inner edge without crossing the median line of brainstem.ResultsThe study included a total of 286 cases with brainstem lesions. All were confirmed by clinical examination and/or pathology, including brainstem infarction (n=225), metastatic tumor (n=8), neurogliocytoma (n=2), brainstem encephalitis (n=19), disseminated sclerosis (n=4), CO poisoning (n=2), central pontine myelinolysis (n=1), adrenoleukodystrophies (n=1), brainstem hemorrhage (n=17), brainstem cavernous hemangioma (n=6) and brainstem venous aneurysm (n=1)."Brainstem hemisection sign" was found in 35 cases, all of which were brainstem infarction, occupying 15.6% of all 225 cases of brainstem infarction.All lesions of the 35 cases located in unilateral anteromedial zones, showing as abnormal signal with a sharp cutting inner edge reaching to the median raphe without crossing the median line, combined to the territory of paramedian artery. The lesions were demonstrated as hyperintensity area on T2-weighted and fluid-attenuated inversion recovery (FLAIR) images, and hypointensity area on T1-weighted image. Some acute or subacute infarcts showed hyperintensity on diffusion-weighted images. Of the 35 cases showing"Brainstem hemisection sign",1 (2.9%) located in the midbrain,32 (91.4%) located in the pon and 2 (5.7%) located in the Medulla Oblongata.Conclusion"Brainstem hemisection sign", consistenting with branches and distribution of the brainstem arteries, is a special sign only found in brainstem infarction and mostly occurrs in pons. Non-infarction cases in this study didn't show this sign on MR imaging, as their occurrence did not have a direct and obvious relationship with the distribution of brainstem arteries. As a result, this sign is valuable in diagnosing brainstem infarction and in the differential diagnosis of the brainstem lesions. |
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