Myxomatous fibroadenoma of the breast: correlation with clinicopathologic and radiologic features.

Fibroadenoma is a frequently encountered benign tumor that must be differentiated from carcinoma. Fibroadenomas often exhibit myxedematous changes (myxomatous fibroadenoma). We focused on myxomatous fibroadenomas and evaluated their diagnostic imaging and clinicopathologic findings. We examined the (1) clinicopathologic findings of myxomatous fibroadenomas out of 113 fibroadenomas among 592 needle biopsy cases and (2) clinical findings of 27 patients with fibroadenoma who underwent surgical resection. One hundred thirteen (19%) of 592 cases were fibroadenoma, of which 45 cases (40%) were myxomatous fibroadenoma. Based on ultrasonography findings, the depth to width ratio was significantly higher in the myxomatous fibroadenoma group (0.79 ± 0.26) compared with the non-myxomatous fibroadenoma group (0.64 ± 0.26) (P < .01). Forty-two patients were subjected to needle biopsy to differentiate fibroadenoma from carcinomas based on ultrasonography and clinical findings, of which 13 cases (31%) were myxomatous fibroadenoma. These lesions showed a relatively round shape and increased posterior echo enhancement with internal hyperechogenicity on ultrasonography. Among 17 resected cases suspected of malignancy that showed rapid growth and/or size greater than 3 cm, 16 cases were myxomatous fibroadenoma. Tumors showing rapid growth and a relatively large size, a high depth to width ratio, a relatively round shape, and posterior echo enhancement with internal hyperechogenicity on ultrasonography require differentiation from (mucinous) carcinoma but are histologically more likely to be myxomatous fibroadenoma. Understanding the histologic features and combining the ultrasonography findings of myxomatous fibroadenomas may permit reduction in the number of unnecessary needle biopsies for tumor-forming lesions.