Predicting Underlying Neoplasms in Appendiceal Mucoceles at CT: Focal Versus Diffuse Luminal Dilatation

OBJECTIVE. The purpose of this study was to determine whether a novel morphologic characteristic of appendiceal mucoceles at CT-focal distal appendiceal dilatation with a segment of morphologically normal appendix proximally-could predict an underlying neoplastic pathologic abnormality before surgery and histopathologic assessment. MATERIALS AND METHODS. A retrospective study was performed that assessed CT cases from 2012 through 2014. Cases showing morphologic features of a mucocele were identified and categorized into two subgroups: focal distal dilatation with a segment of normal appendix proximally and generalized appendiceal dilatation. The underlying histopathologic diagnosis for each case was assessed and categorized as neoplastic or nonneoplastic. Several additional morphologic findings were also assessed. RESULTS. Forty-nine cases with confirmed histopathologic diagnoses were identified. Of those, 20 of 23 (87.0%) cases with the finding of focal distal dilatation had an underlying neoplastic cause, whereas 14 of 26 (53.8%) cases with generalized dilatation had an underlying neoplastic cause (p = 0.012). The findings of periappendiceal fat stranding (p = 0.004), mural calcification (p = 0.006), and degree of luminal dilatation (p = 0.002) also reached statistical significance. When seen in combination with focal distal dilatation, the positive predictive value for underlying neoplasm approached or reached 100%. CONCLUSION. Our study shows that isolated focal distal appendiceal dilatation with a segment of morphologically normal appendix proximally is significantly associated with an underlying neoplastic histopathologic cause. When seen in combination with mural calcification, a diameter of more than 2 cm, and absence of periappendiceal stranding, an underlying neoplastic cause is strongly suggested.