Sonographic evaluation of infiltrating lobular carcinoma.

OBJECTIVE: Infiltrating lobular carcinoma (ILC), which accounts for 7-10% of all breast malignancies, often poses diagnostic difficulties. The purpose of our study was to correlate the clinical, mammographic, and sonographic findings in each histologic subtype of ILC and to evaluate the sensitivity of sonography in its diagnosis. MATERIALS AND METHODS: We reviewed 208 cases of invasive lobular carcinoma. In 81 of these tumors, sonography was performed to further examine a mammographically invisible palpable abnormality or a mammographically subtle lesion. A dedicated breast pathologist classified each of these tumors as pure invasive lobular carcinoma or mixed invasive lobular and ductal carcinoma. Pure ILC tumors were further subclassified as one of five histologic subtypes. We retrospectively studied the clinical, mammographic, and sonographic findings in each histologic tumor subtype. RESULTS: The most common sonographic appearance of ILC was a heterogeneous, hypoechoic mass with angular or ill-defined margins and posterior acoustic shadowing, which was seen in 60.5% (49/81) of tumors. Of the remaining 32 tumors, 15% (12/81) showed focal shadowing without a discrete mass, 12% (10/81) appeared as a lobulated, well-circumscribed mass, and 12% (10/81) were sonographically invisible. Although considerable overlap occurred among histologic subtypes, classic ILC tended to present as focal shadowing without a discrete mass; pleomorphic ILC typically was seen as a shadowing mass; and, of all the tumor subtypes, signet, alveolar, and solid ILC were most likely to be revealed on sonography as a lobulated, well-circumscribed mass. In the 81 mammographically subtle or invisible lesions, sonography detected the tumor in 87.7% (71/81). The sensitivity of sonography in tumors smaller than 1 cm was 85.7% (12/14). CONCLUSION: High-resolution sonography of the breast is a useful adjunct in the evaluation of ILC, a neoplasm that frequently presents a clinical and mammographic diagnostic challenge.