The hook sign for differential diagnosis of malignant from benign lesions in magnetic resonance mammography: experience in a study of 1084 histologically verified cases

Abstract

Background: The hook sign (HS) has recently been introduced as a new descriptor for differential diagnosis in magnetic resonance mammography (MRM).

Purpose: To analyze the diagnostic value of HS in a large collection of 1084 cases.

Material and methods: This study was approved by the local ethics committee, and 1084 consecutive lesions (no manipulations of the breast up to 12 months before MRM) with histological verification after MRM were included. HS was analyzed according to standard study protocols and was rated positive if a hook-like spiculated dendrite connecting a lesion with the pectoral muscle could be visualized. Examinations were rated by experienced observers (>500 examinations). Prevalence of HS was correlated with histological diagnosis, grading, and size (chi-square test). Diagnostic accuracy was assessed using sensitivity, specificity, positive likelihood ratio (LR+), and diagnostic odds ratio (DOR).

Results: HS was significantly associated with malignancy (P < 0.001), providing high specificity, LR+, and DOR (96.8%, 9.1, and 12.5, respectively). Malignant lesions >20 mm presented with HS significantly more often than those <20 mm (P < 0.001). HS was characteristic of invasive cancers and rare in preinvasive malignomas (P < 0.001). Prevalence of HS did not differ between invasive lobular and ductal carcinomas (n.s.). There was no correlation between HS and the grading of invasive carcinomas.

Conclusion: In 1084 lesions, the hook sign was a specific descriptor for differentiation of benign and malignant lesions in MRM, with high evidence for prediction of malignancy, particularly in the case of advanced lesions and invasive carcinomas.