Rethinking orbital imaging - Establishing guidelines for interpreting orbital imaging studies and evaluating their predictive value in patients with orbital tumors

Purpose: To establish guidelines for interpretation of orbital imaging by magnetic resonance imaging (MRI) and/or computed tomography (CT), and to apply these guidelines and examine their predictive value in 131 patients with biopsy-proven orbital tumors. Design: Prospective evaluation of imaging studies. Participants: Imaging studies (CT and/or MRI) from 131 cases with biopsy-proven orbital tumors. Methods: Guidelines for reviewing orbital imaging studies (MRI and/or CT) were established based on 5 major characteristics: (1) anatomic location, (2) bone and paranasal sinuses involvement, (3) content, (4) shape, and (5) associated features. In total, 84 features were established by an experienced orbital surgeon and a neuroradiologist. Applying these 84 features, imaging studies of 131 biopsy-proven orbital tumors were evaluated by 3 physicians. Main Outcome Measures: Imaging features: characteristics, sensitivity, specificity, and positive and negative predictive values in various groups of orbital tumors and K values. Results: One hundred thirty-one cases of biopsy-proven orbital tumors were evaluated. Benign lesions were more likely to be smaller in size, round or oval in shape (29% of all benign tumors, 0% in malignant and inflammatory, P<0.001), and associated with hyperostosis (22% of all benign lesions, P<0.001). They were also more likely to be hyperdense or hypodense on CT imaging (15% and 11%, respectively; P<0.05 in comparison with inflammatory and malignant tumors). Inflammatory processes showed. panorbital involvement (23% vs. 3%, and 0% in benign and malignant tumors, respectively; P<0.001). Orbital fat involvement and fat stranding were noticed only in inflammatory lesions (19% and 16%, respectively; P<0.001). None of the features occurred only in malignant tumors, but they tend to involve the anterior orbit more commonly (54% vs. 20%, and 29% in benign and malignant; P = 0.002), and were more likely to show bone erosion (31 % vs. 6%, and 16% in benign and inflammatory tumors, respectively; P = 0.004) and molding around orbital structures (29% vs. 3% in benign, and 0% in inflammatory tumors, respectively; P<0.001). Features such as panorbital involvement, orbital fat, frontal sinus opacity, molding around orbital structures, perineural involvement, and fat stranding had specificity of 97% to 100%, but low sensitivity. Conclusions: Guidelines for analysis of orbital imaging studies (CT or MRI) are suggested. Based on these guidelines several imaging features showed significantly different occurrences in benign, malignant, and inflammatory processes; although this can help in differential diagnosis, tissue diagnosis may still be required.