Echo-planar DW MR imaging can help characterize indeterminate orbital masses.

BACKGROUND AND PURPOSE DWI has been increasingly used to characterize orbital masses and provides quantitative information in the form of the ADC, but studies of DWI of orbital masses have shown a range of reported sensitivities, specificities, and optimal threshold ADC values for distinguishing benign from malignant lesions. Our goal was to determine the optimal use of DWI for imaging orbital masses through aggregation of data from multiple centers. MATERIALS AND METHODS Source data from 3 previous studies of orbital mass DWI were aggregated, and additional published data points were gathered. Receiver operating characteristic analysis was performed to determine the sensitivity, specificity, and optimal ADC thresholds for distinguishing benign from malignant masses. RESULTS There was no single ADC threshold that characterized orbital masses as benign or malignant with high sensitivity and specificity. An ADC of less than 0.93 × 10−3 mm2/s was more than 90% specific for malignancy, and an ADC of less than 1.35 × 10−3 mm2/s was more than 90% sensitive for malignancy. With these 2 thresholds, 33% of this cohort could be characterized as “likely malignant,” 29% as “likely benign,” and 38% as “indeterminate.” CONCLUSIONS No single ADC threshold is highly sensitive and specific for characterizing orbital masses as benign or malignant. If we used 2 thresholds to divide these lesions into 3 categories, however, a majority of orbital masses can be characterized with >90% confidence.

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A wide variety of space occupying lesions may be encountered in the orbit. CT and MR imaging frequently help confirm the presence of a mass and define its extent. Characteristic imaging features may help distinguish among lesions that have overlapping clinical presentations. This review focuses on some of the common orbital masses. Common vascular lesions that are reviewed include: capillary (infantile) hemangioma, cavernous hemangioma (solitary encapsulated venous-lymphatic malformation), and lymphangioma (venous-lymphatic malformation). Benign tumors that are reviewed include: optic nerve sheath meningioma, schwannoma, and neurofibroma. Malignancies that are reviewed include: lymphoma, metastasis, rhabdomyosarcoma, and optic glioma. Key imaging features that guide radiological diagnosis are discussed and illustrated.

BACKGROUND AND PURPOSE Orbital inflammatory syndrome (OIS) has clinical features that overlap with orbital lymphoid lesions and orbital cellulitis. Prompt diagnosis is needed in all 3 conditions because the management of each one differs greatly. CT and MR imaging, though useful, do not always distinguish among these conditions. The aim of this study was to identify the role of diffusion-weighted imaging (DWI) in differentiating these 3 diagnoses. MATERIALS AND METHODS A retrospective analysis of orbital MR imaging was conducted. T1- and T2-weighted and postcontrast images were analyzed. Region-of-interest analysis was performed by using measurements in areas of abnormality seen on conventional MR imaging sequences and measurements of the ipsilateral thalamus for each patient. The DWI signal intensity of the lesion was expressed as a percentage of average thalamic intensity in each patient. Similarly, lesion apparent diffusion coefficients (ADCs) and lesion-thalamus ADC ratios were calculated. Statistical significance was determined by the Kruskal-Wallis test, and post hoc pairwise comparisons, by the Mann-Whitney U test for DWI-intensity ratio, ADC, and ADC ratio. RESULTS A significant difference was noted in DWI intensities, ADC, and ADC ratio between OIS, orbital lymphoid lesions, and orbital cellulitis (P < .05). Lymphoid lesions were significantly brighter than OIS, and OIS lesions were significantly brighter than cellulitis. Lymphoid lesions showed lower ADC than OIS and cellulitis. A trend was seen toward lower ADC in OIS than in cellulitis (P = .17). CONCLUSIONS DWI may help differentiate OIS from lymphoid lesions and cellulitis and may allow more rapid management.