BACKGROUND: Neurological symptoms and radiographic abnormalities may remain in a small proportion of patients with metronidazole-induced encephalopathy (MIE). Although experimental animal models of MIE have suggested a Wernicke\'s encephalopathy-like pathology, little is known about the histopathological features of MIE. Here we report the first autopsy case of irreversible MIE.
METHODS: A 72-year-old Japanese woman with pancreatic neuroendocrine tumour and metastatic tumours in the liver developed intraabdominal bleeding from a hepatic abscess. She was administered metronidazole for 79 days (1.5 g/day), which caused dysarthria followed by hand tremor and altered mental status. Brain magnetic resonance imaging at the time of onset revealed hyperintensities in the deep white matter of the bilateral parietal lobes and splenium of the corpus callosum on diffusion-weighted imaging (DWI) with reduced apparent diffusion coefficient (ADC) values. Despite the improvement of dysarthria and hand tremor, her cognition remained affected even after the withdrawal of metronidazole. She died of pancreatic neuroendocrine tumour at the age of 74 years. Histopathological examinations of the brain confirmed a combination of severe demyelination and moderate axonal degeneration, which corresponded to the regions showing abnormal signal intensities on DWI with reduced ADC values. There were no pathological findings suggestive of Wernicke\'s encephalopathy in the brain.
CONCLUSIONS: We have demonstrated the clinical, radiographic and histopathological aspects of irreversible MIE. Hyperintensities on DWI with reduced ADC values in affected regions may indicate a poor clinical prognosis due to irreversible pathological damage.

BACKGROUND: Medulloblastoma is well known as the most common malignant brain tumor identified in children, frequently found at an intra-axial location in the posterior cranial fossa. Extra-axial medulloblastoma is uncommon and often misdiagnosed. We believe that a thorough understanding of atypical medulloblastoma cases is important in daily practice.
METHODS: We present the unique case of a 39-year-old woman of Asian descent who suffered from headaches and right-sided hearing impairment. A right extra-axial medulloblastoma with an extremely low apparent diffusion coefficient of 0.404 × 10-3 mm2/second was detected on magnetic resonance imaging. The initial diagnosis suggested schwannoma or hemangioblastoma. However, the postoperative histopathologic findings indicated medulloblastoma (World Health Organization grade IV). Pre- and postoperative magnetic resonance imaging revealed no drop metastasis, but adjuvant radiation therapy was still required as a standard treatment therapy CONCLUSIONS: Extra-axial medulloblastoma is an uncommon tumor that is often mistaken for other cerebellopontine angle neoplasms. We describe a rare example of extra-axial medulloblastoma, characterized by a low apparent diffusion coefficient. When evaluating an atypical cerebellopontine angle neoplasm, the apparent diffusion coefficient should be considered a relevant indicator.

Oral lymphomas are relatively uncommon. Follicular lymphoma is the second most common subtype of non-Hodgkin lymphoma. We report characteristic multimodal imaging of palatal follicular lymphoma, especially CT, diffusion-weighted MR imaging (DWI) and intraoral ultrasonography. A 67-year-old woman presented with swelling on the right side of the palate within 2 months. On clinical examination, an approximately 35 × 20 mm mass lesion with elastic soft was found to overlay the right side of the palate. Contrast-enhanced CT image showed a mass with homogeneous enhancement on the right side of the palate, and bone tissue algorithm CT showed focal erosion of the right posterior maxilla. Regarding MR imaging, on T1-weighted image, the mass showed low signal intensity and homogeneous enhancement, and T2-weighted and STIR images revealed intermediate and high signal intensity, respectively. Furthermore, DWI and apparent diffusion coefficient (ADC) map showed high and low signal intensity, respectively. ADC value of the mass was 0.60 × 10-3 mm2s-1. On intraoral ultrasonography, the mass showed clear boundary, hypoechoic echogenicity, homogeneous internal architecture, vascular signals using color Doppler imaging and heterogeneous hard using strain elastography. A partial biopsy of the palatal region was performed. Histopathological diagnosis was follicular lymphoma. This case suggests that multimodal imaging, especially CT, DWI with ADC map and intraoral ultrasonography with color Doppler imaging and strain elastography, could be effective for evaluating palatal lesions.

BACKGROUND: Posterior ischemic optic neuropathy (PION) is a rare cause of visual loss, especially in young patients who are more prone to inflammatory demyelinating optic neuritis (ON) compared to other types of optic neuropathy. The diagnosis of PION is usually a diagnosis of exclusion; however, the emergence of modern neuroimaging technique with diffuse-weighted image (DWI) and apparent diffusion coefficient (ADC) sequences in Magnetic Resonance Imaging (MRI) provides more evidence for accurate diagnosis and management.
METHODS: A 30-year-old man with a history of hypertension and chronic renal failure secondary to glomerulonephritis presented with sudden onset of blurred vision, dyschromatopsia, pain, and positive relative afferent pupillary defect (RAPD) in the left eye for 1 week. He was initially admitted for steroid pulse therapy and was further monitored due to suspicion of optic neuritis oculus sinister (OS). However, his brain MRI revealed a focal high hyperintensity signal at the left optic nerve on the T2 DWI series. The area was corresponded with the hypointensity area in the ADC series, which was a powerful clue for PION. We explained the poor visual prognosis of PION to the patient after finishing steroid pulse therapy and referred him to the Nephrology and Neurology department for hypertension control to prevent additional hypertension related complication.
CONCLUSIONS: The diagnosis of PION is usually a diagnosis of exclusion; however, carefully interpreting the DWI and ADC sequence in MRI may give the clinician more evidence for the definite diagnosis and leads to proper management.

Pancreatic hamartoma is a rare tumor-like malformation and could mimic other pancreatic tumors including malignant neoplasm. Due to its rarity, magnetic resonance (MR) imaging findings including those diffusion-weighted (DW) imaging have not been clarified. We present a curious case of pancreatic hamartoma presenting high apparent diffusion coefficient (ADC) value with histopathological correlation. A 49-year-old woman with a pancreatic mass found incidentally on ultrasonography for medical checkup was referred to our institution for further examination and treatment because it slightly enlarged in the follow-up examination. Contrast-enhanced computed tomography (CT) and gadoxetic acid disodium-enhanced MR imaging revealed a well-demarcated solid mass of 13 mm in diameter in the pancreas body, which was gradually and homogeneously enhanced in the delayed/transient phase. It showed hyper intensity on T2-weight and DW images, and the mean ADC value was high (1.86 × 10-3mm2/s). Laparoscopic distal pancreatectomy was conducted with suspicious preoperative diagnosis of pancreatic hypovascular neuroendocrine neoplasm (NEN). Histologically, the mass consisted of many disarranged small ducts without atypia embedded in abundant fibrous stroma and contained scant fatty tissue in the periphery, which was not identified on CT and MR images. There were no islets and peripheral nerves throughout the mass. Finally, it was pathologically diagnosed as a solid-type pancreatic hamartoma. Based on radiological-pathological correlation, it was considered that the abundant fibrous stroma and both the widely distributed myxomatous periductal stroma and scattered edematous stroma corresponded with delayed homogenous enhancement on CT/MR images and high ADC value, respectively. Although it is difficult to distinguish solid-type pancreatic hamartoma from other solid pancreatic neoplasms including hypovascular NEN on the basis of usual radiological findings, the high ADC value reflecting the specific pathology may be helpful for the differential diagnosis.