Primitive neuroectodermal tumours (PNETs) are a group of malignant soft tissue tumours of neuroepithelial origin that arise from primitive neural crest cells. Most of the PNETs occur in the central nervous system (CNS). If the origin is outside the CNS it is called peripheral primitive neuroectodermal tumour (pPNET). Histopathologically, PNETs consist of small round cells with a hyperchromatic nuclei, high nuclear-cytoplasmic ratio and varying degrees of neural differentiation detectable by immunohistochemical or ultrastructural techniques. pPNETs occur predominantly in children and young adults and show no gender difference. Occurrences of pPNETs in the orbit are infrequent and to the best of our knowledge only eighteen cases have been reported in the literature up to now. In this study, we present clinic, radiologic and histopathologic features of an orbital mass in an 8-year-old boy, which was diagnosed as a primary orbital pPNET confirmed by immunohistochemistry.

Objectives: The purpose of our study was to determine apparent diffusion coefficients (ADCs) of focal liver lesions on the basis of respiratory triggered diffusion-weighted single-shot echo-planar MR imaging (DWI-SS-EPI) sequence and to evaluate whether ADC measurements can be used to characterize lesions. Results: Results were correlated with characteristic MRI findings, histopathologic data and follow-up imagings. The ADCs of different lesion types were compared and lesion differentiation using optimal thresholds for ADCs was evaluated. Mean ADCs (x10 -3 mm 2 /s) were 2.15, 1.57, 1.16, 1.08, 1.03 for cysts, hemangiomas, FNHs, metastases and HCCs, respectively. Mean ADCs differed significantly for all lesion types except metastases, HCCs and FNHs. Overall, 88.5% of lesions were correctly classified as benign or malignant using a treshold value of 1.20x10 -3 mm 2 /s. Conclusion:Measurements of the ADCs of focal liver lesions on the basis of a respiratory triggered DWI-SS-EPI sequence may constitute a useful supplementary method for lesion characterization.

Level I-diagnostic studies.

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