Mr Diagnosis And Analysis Of Signs In Spontaneous Intracranial Hypotension Syndrome

ObjectiveTo explore the MRI features of spontaneous intracranial hypotension syndrome (SIH) and evaluate the diagnostic value of fluid-attenuated inversion recovery (FLAIR) MR images in SIH. The purpose of this study was also to provide objective criteria in the MRI evaluation of SIH.Materials and MethodsWe retrospectively studied the MR imaging and clinical records of10patients (5men and5women; age range,31-49years; mean age,39.8±5.1years) treated for clinical diagnoses of SIH at our institution from September2011through January2014. Control subjects were selected from the same imaging time period and were matched for age and sex. For the control group, we enrolled20consecutive patients (10men and10women; age range,29-52years; mean age,40.0±5.8years) who had undergone MR imaging examination, including both T2-FLAIR and T2-weighted images, Patients with tumor, ischemic and hydrocephalus were excluded. We performed MR imaging in all subjects by using a3.0Tesla MRI system (Achieva3.0T TX, Philips Healthcare, Best, The Netherlands), facilitated by the standard circularly polarized head coil. The SIH patients were underwent pre-and post-contrast brain MR imaging.Binary evaluation of MRI features included diffuse pachymeningeal(dural mater) enhancement, shrinkage of ventricle size, engorgement of cerebral venous sinuses, cerebellar tonsillar herniation, subdural effusion/hematomas and enlargement of the pituitary gland. Signal intensities of the thickened dura and subdural effusion/hematomas were compared on the T1-weighted, T2-weighted, and T2-FLAIR MR images of all10patients. The final classifications were determined by consensus of the2observers. The following factors were evaluated on the MR images: presence of diffuse pachymeningeal enhancement on T1-weighted images with gadolinium, presence of diffuse pachymeningeal hyperintensity on T2-FLAIR imaging, and thickness of subdural effusion/hematomas (thin, thickness≤6mm; thick, thickness>6mm).The measurements were performed by1observer, who measured3times.The following parameters were assessed for both groups, A mid sagittal T1W or T2W image or MRV was selected in which the internal cerebral vein (ICV) and the vein of the Galen (VOG) were seen in the same plane. A straight line was drawn along the main axes of the ICV and VOG.The angle between these two lines was measured. The angle between the VOG and the straight sinus (SS) was measured on saggital midline T2W or T1W images or MRV. Because of the curvature of the VOG, the direction of its final8-10mm was considered. The pontomesencephalic angle was defined as the angle between a line tangential to the anterior margin of the midbrain and the line tangential to the superior margin of the pons. The mamillopontine distance was defined as the distance between the inferior aspect of the mamillary bodies and the superior aspect of the pons. We focused on the T2-weighted and T2-FLAIR MR images at the level of the centrum semiovale and measured the signal intensities of the subcortical white matter of the bilateral middle frontal gyri and inferior partial lobules. To calculate the ratio of the signal intensity of the subcortical white matter to the adjacent cortex, we measured the signal intensities of them by using a region of interest with a fixed area (0.1cm2).Mean and standard deviation (SD) was calculated for the angle between the ICV and VOG, the angle between the VOG and SS, the pontomesencephalic angle and the mamillopontine distance in patients with IHS and normal controls. Mean and SD was also calculated for the ratio of the signal intensity of the subcortical white matter to the adjacent cortex on the T2-weighted and T2-FLAIR MR images. An unpaired t test was used. Statistical significance was established at the P<0.05level.ResultsThe characteristic MR findings of SIH included dural thickening and homogeneous enhancement (10/10), shrinkage of ventricle size (7/10), engorgement of venous structures (7/10), downward herniation of the cerebellar tonsils (4/10), subdural fluid collections (6/10), subdural hematomas (1/10). Mean and SD of the enlargement of pituitary was8.1mm±1.1mm (range6.0mm-9.5mm).In the10patients with SIH, the mean angle between the ICV and VOG was66.1°(SD,9.6°),the mean angle between the VOG and SS was52.3°(SD,±14.2°),the mean pontomesencephalic angle was48.1°(SD,±3.6°),and the mean mamillopontine distance was5.1mm (SD,±1.0mm). In the control group of20subjects, the mean angle between the ICV and VOG was91.0°(SD,±12.0°),the mean angle between the VOG and SS was74.0°(SD,±10.3°),the pontomesencephalic angle was58.7°(SD,±3.7°),and the mean mamillopontine distance was7.8mm (SD,±1.0mm). The difference in the angle between the ICV and VOG values for the SIH group versus the control group was statistically (P<0.05). Similarly, the differences in the angle between the VOG and SS, the pontomesencephalic angle, and the mean mamillopontine distance between the two groups were also statistically respectively (P<0.05).The MR images of10paients showed diffuse pachymeningeal thickening, appearing as hypointense in2patients, isointense in8patients on the T1-weighted MR images, and hyperintense in all cases on both T2-weighted and T2-FLAIR MR images. Subdural effusion was observed in6of the10patients, appearing as hypointense in5patients, isointense in1patient on the T1-weighted MR images, and hyperintense in all cases on both T2-weighted and T2-FLAIR MR images. Subdural hematoma was observed in1of the10patients, appearing as hypointense on the T1-weighted MR images, and hypointense on both T2-weighted and T2-FLAIR MR images. The subdural effusion was observed over the frontal convexity and the frontoparietal convexity in6patients, and4patients were bilateral. Among them,5cases appear very thin and one thick.Diffuse pachymeningeal hyperintensitiy on T2-FLAIR imaging was located at the the supratentorial convexity, falx, and tentorium in all patients. Diffuse pachymeningeal hyperintensitiy on T2-FLAIR imaging was also observed parallel to the posterior fossa convexity in4patients. Diffuse pachymeningeal enhancement on Tl-weighted images with gadolinium was observed over the the supratentorial convexity, falx, posterior fossa convexity and tentorium in all10patients.The mean ratios of the signal intensity of the subcortical white matter to that of the adjacent cortex on T2-FLAIR images were0.794±0.077in images of patients with SIH and0.873±0.057in the control images; those on T2-weighted images were0.747±0.053in images of patients with SIH and0.780±0.027in the control images. On T2-FLAIR images, the unpaired t test revealed a significant difference in the signal intensity ratio between the images in patients with SIH and the control images (P=0.004). In the case of the T2-weighted images, the ratio of the signal intensity between the images in patients with SIH and the control images revealed a significant difference (P=0.029).ConclusionDiffuse pachymeningeal gadolinium enhancement, shrinkage of ventricle size, engorgement of venous structures, subdural effusion/hematomas, sagging of the brain and enlargement of the pituitary gland were typical MR findings of SIH.If used in patients with a clinical suspicion of SIH and if supported by qualitative MR findings, the angle between the ICV and VOG, the angle between the VOG and SS, the mean pontomesencephalic angle, and the mamillopontine distance are valuable for more definitive diagnosis of SIH. Recognition of the reduction in them, in addition to the other imaging signs may aid in diagnosis of cases without the "classic" findings.T2-FLAIR MR imaging has the potential to provide a simple, noninvasive method for the diagnosis of SIH. The appearance of diffuse pachymeningeal hyperintensitiy on T2-FLAIR imaging almost paralleled that of diffuse pachymeningeal enhancement on T1-weighted images with gadolinium. The distribution of the thicked dural is observed over the the supratentorial convexity, falx, posterior fossa convexity and tentorium. T2-FLAIR MR imaging is also superior for the detection of the thin subdural effusion.In patients with SIH, the decrease in signal intensity of the subcortical white matter on T2-FLAIR MR imaging should be useful to support a dianosis of SIH. Particularly in cases having no characteristic MR findings of SIH, such as pachymeningeal thickening or enhancement, awareness of this MR finding, if present, could help as a diagnostic clue to SIH.