Chang June Song

Diffusion MR Imaging of Postoperative Bilateral Acute Ischemic Optic Neuropathy

A 57-year-old woman experienced bilateral acute ischemic optic neuropathy after spine surgery. Routine MR imaging sequence, T2-weighted image, showed subtle high signal intensity on bilateral optic nerves. A contrast-enhanced T1 weighted image showed enhancement along the bilateral optic nerve sheath. Moreover, diffusion-weighted image (DWI) and an apparent diffusion coefficient map showed markedly restricted diffusion on bilateral optic nerves. Although MR findings of T2-weighted and contrast enhanced T1-weighted images may be nonspecific, the DWI finding of cytotoxic edema of bilateral optic nerves will be helpful for the diagnosis of acute ischemic optic neuropathy after spine surgery.

Uremic Encephalopathy: MR Imaging Findings and Clinical Correlation

BACKGROUND AND PURPOSE: Uremic encephalopathy is a metabolic disorder in patients with renal failure. The purpose of this study was to describe the MR imaging findings of uremic encephalopathy. MATERIALS AND METHODS: This study retrospectively reviewed MR imaging findings in 10 patients with clinically proved uremic encephalopathy between May 2005 and December 2014. Parameters evaluated were lesion location and appearance; MR signal intensity of the lesions on T1WI, T2WI, and T2 fluid-attenuated inversion recovery images; the presence or absence of restricted diffusion on diffusion-weighted images and apparent diffusion coefficient maps; and the reversibility of documented signal-intensity abnormalities on follow-up MR imaging. RESULTS: MR imaging abnormalities accompanying marked elevation of serum creatinine (range, 4.3–11.7 mg/dL) were evident in the 10 patients. Nine patients had a history of chronic renal failure with expansile bilateral basal ganglia lesions, and 1 patient with acute renal failure had reversible largely cortical lesions. Two of 6 patients with available arterial blood gas results had metabolic acidosis. All basal ganglia lesions showed expansile high signal intensity (lentiform fork sign) on T2WI. Varied levels of restricted diffusion and a range of signal intensities on DWI were evident and were not correlated with serum Cr levels. All cortical lesions demonstrated high signal intensity on T2WI. Four patients with follow-up MR imaging after hemodialysis showed complete resolution of all lesions. CONCLUSIONS: The lentiform fork sign is reliable in the early diagnosis of uremic encephalopathy, regardless of the presence of metabolic acidosis. Cytotoxic edema and/or vasogenic edema on DWI/ADC maps may be associated with uremic encephalopathy.

Acute carbon monoxide poisoning: MR imaging findings with clinical correlation

PURPOSE To assess the magnetic resonance imaging (MRI) findings, including diffusion-weighted imaging (DWI) in patients with acute carbon monoxide (CO) poisoning and correlate MRI findings with carboxyhemoglobin levels. MATERIALS AND METHODS The MRI examinations and medical records of seven men with a mean age of 43±16.0years (SD) (range: 25-63 years) with acute CO poisoning were reviewed. MRI examinations were analyzed with respect to lesion location, imaging presentation on T1- and T2-weighted images, and diffusion characteristics on DWI and apparent diffusion coefficient (ADC) maps. We also evaluated clinical features and laboratory findings including the presenting symptoms and signs, carboxyhemoglobin level, and treatment. RESULTS All seven patients presented with mental status change. The level of carboxyhemoglobin ranged between 8.3% and 34.8% (normal<1.5%). All seven patients (7/7, 100%) showed restricted diffusion of the lesions on ADC maps and bilateral involvement of globus pallidus. The mean ratios of ADC values was 0.63±0.15 (SD) (range: 0.46-0.92) on bilateral globi pallidi. Cerebral cortex, cerebral white matter, cerebellum, hippocampus, amygdala, splenium of corpus callosum, midbrain and insula were also involved. CONCLUSION Bilateral globi pallidi with restricted diffusion may be a characteristic MRI feature in patients with acute CO poisoning. However, the relationship was not certain between the carboxyhemoglobin levels and the variety or severity of MRI findings.