Delayed signal detection by diffusion-weighted imaging in brainstem infarction

Diagnostic benefit of high b-value computed diffusion-weighted imaging in acute brainstem infarction

BACKGROUND AND PURPOSE

Diffusion-weighted imaging (DWI) is a cornerstone in diagnostic of ischemic stroke. The aim of this study was to investigate the usefulness of high-b-value computed DWI (c-DWI) in comparison to standard DWI in patients with acute brainstem infarction.

MATERIALS AND METHODS

56 patients with acute brainstem infarction were retrospectively analysed by two readers. DWI was obtained with the b-values 0, 500 and 1000 s/mm² on either a 1.5 or 3 T magnetic resonance imaging (MRI) scanner. c-DWI was calculated with a monoexponential model with high b-values 2000, 3000, 4000 and 5000 s/mm². All c-DWI series with high-b-values were compared to the standard DWI sequence at b-value of 1000 s/mm² in terms of image artifacts, lesion extent and contrast.

RESULTS

There was no statistically significant difference between 1.5 and 3 T MRI regarding the measured ischemic lesion size. There were no statistically significant differences between the ischemic lesion sizes on DWI at b-values of 1000 s/mm² and on c-DWI at higher b-values. Overall, the contrast between the lesion and the surrounding normal areas improved with increasing b-value on the isotropic DWIs: maximum at b = 5000, followed by that at b 2000 and b 1000 s/mm², in order. The best relation between artifacts and lesion contrast was identified for b 2000 s/mm².

CONCLUSION

High b-value DWI derived from c-DWI has a higher visibility for ischemic brainstem lesions compared to standard DWI without additional time cost. The b-2000 image is recommended to use in clinical routine, higher b-value images lead to more imaging artifacts, which might result in misdiagnosis.

Sagittal diffusion-weighted imaging in preventing the false-negative diagnosis of acute brainstem infarction: Confirmation of the benefit by anatomical characterization of false-negative lesions

Background:

In some cases of acute brainstem infarction (BI), standard axial diffusion-weighted imaging (DWI) does not show a lesion, leading to false-negative (FN) diagnoses. It is important to recognize acute BI accurately and promptly to initiate therapy as soon as possible.

Methods:

Of the 171 patients with acute cerebral infarctions in our institution who were examined, 16 were diagnosed with true-positive BI (TP-BI) and six with FN-BI. We evaluated the effectiveness of sagittal DWI in accurately diagnosing acute BI and sought to find the cause of its effectiveness by the anatomical characterization of FN-BIs.

Results:

Considering the direction of the brainstem perforating arteries, we supposed that sagittal DWI might more effectively detect BIs than axial DWI. We found that sagittal DWI detected all FN-BIs more clearly than axial DWI. The mean time between the onset of symptoms and initial DWI was significantly longer in the TP group (17.6 ± 5.5 h) than in the FN group (5.0 ± 1.2 h; P < 0.0001). The lesion volumes were much smaller in FN-BIs (259 ± 82 mm³) than in TP-BIs (2779 ± 767 mm³; P = 0.0007). FN-BIs had a significant inverse correlation with the ventrodorsal length of infarcts (FN 3.5 ± 1.1 mm, TP 11.4 ± 3.6 mm; P < 0.0004) and no correlation with other size parameters such as rostrocaudal thickness and lateral width.

Conclusion:

Anatomical characterization clearly confirmed that the addition of sagittal DWI to the initial axial DWI in suspected cases of BI ensures its accurate diagnosis and improves the patient’s prognosis.

A retrospective analysis of negative diffusion-weighted image results in patients with acute cerebral infarction

We aimed to investigate the clinicoradiologic determinants of negative diffusion-weighted image (DWI) results in patients with acute cerebral infarction (ACI). The medical records were reviewed of ACI patients. Patients were divided to the DWI positive and negative group. Positive DWI was used as independent variable and patients' clinicoradiologic factors were used as co-variables for multivariate logistic regression analysis. 349 patients received initial cerebral MRI within 72 hours of admission. Lacunar infarction was most common (42.1%) followed by posterior circulation infarction (30.1%) and partial anterior circulation infarction (18.1%). The majority of the patients (72.2%) had an NIHSS score of less than 5 at admission. 316 patients (90.54%) were positive on initial DWI. Patients with smoking, initial SBP ≥ 140 or DBP ≥ 90 mmHg, initial fasting plasma glucose (FPG) ≥ 7.0 mmol/L, initial MRI from onset of disease >1 d and anterior circulation infarction were liable to show positive DWI. Furthermore, DWI negative patients had significantly lower NIHSS scores (IQR 0,1,2) than DWI positive patients (IQR 1,2,4) (P = 0.000) at two weeks post onset of acute cerebral infarction. In conclusion, multiple clinicoradiologic factors are associated with negative and positive DWI and further delineation of these factors is required in future prospective studies.

"Invisible" brain stem infarction at the first day

BACKGROUND

In specific stroke cases, serial diffusion-weighted magnetic resonance imaging (DW MRI) on day 1 was unable to show a lesion, whereas that on day 4 and later clearly revealed a lesion. However, clinical features of this phenomenon ("invisible" brain stem infarction [IBI] at the first day) have not been fully delineated.

METHODS

We retrospectively recruited 212 stroke patients in the Emergency Unit and Neurology Department. Among these, we studied patients with IBI. Definition of IBI is that acute and clear brain stem symptoms/signs on arrival were ameliorated at discharge and appearance of high signal intensity on serial DW images with low apparent diffusion coefficient (ADC) by 1.5 T MRI with 2-mm slices.

RESULTS

IBI were found in only 6 patients. Day 1 invisible stroke was found only in the brain stem (17%, 6 of 35) but none (0 of 177) in the hemispheric infarction (P < .05). In most patients with IBI, DW MRI turned out visible at the third/fourth day. Before the fourth day, DW/ADC signal changes in patients with IBI were minimal. In IBI, lesion size (mean 2.7 mm(2)) was smaller than that of visible cases (mean 7.3 mm(2)). In IBI, lesion location was mostly at the dorsolateral medulla. In IBI, sensory disturbance was significantly more common (67%) than visible cases (24%; P < .05), whereas dysarthria was less common (0%; P < .01) than visible cases (66%; P < .01).

CONCLUSIONS

It is likely that patients with smaller stroke volume, sensory disturbance, and medullary location are prone to develop IBI. When evaluating stroke using MRI criteria, recognition of IBI is important to start early management.