The mammary hamartoma: appreciation of additional imaging characteristics

To determine the mammographic and sonographic findings of hamartomas that were not classic on imaging, how pathologists distinguish the hamartoma from benign breast tissue on core samples, and reasons for discrepancies between core and surgical biopsy.

A retrospective review of all image-recommended core biopsies between 1993 and 2001 was performed. There were 41 cases of hamartomas found on either core or surgical biopsy. The mammographic, sonographic, and pathologic findings were reviewed.

Of 41 hamartomas in 38 patients, 18 went on to surgical biopsy. Of these 18 cases, 4 cases of hamartoma on core biopsy were fibroadenoma after excision; 2 cases of hamartoma on core biopsy were confirmed by surgery; and 12 cases of fibrocystic change after core biopsy were hamartoma after surgical biopsy. The 4 cases of fibroadenoma shown at final pathologic examination were excluded from imaging review, leaving 37 cases. In the 20 patients who underwent only core sampling, 23 hamartomas were diagnosed. Seventeen masses were visible on mammography, and 82% were homogeneously dense. Of 36 masses shown on sonography, 86% were uniformly hypoechoic. At histologic examination, only 16% contained fat within the mass.

Hamartomas may appear as homogeneously dense, well-circumscribed masses, varying in appearance from the classically described encapsulated mixed fatty-fibroglandular mass. Pathologists can make the diagnosis of hamartoma without the presence of adipose tissue but may have difficulty in distinguishing the hamartoma from fibrocystic change. However, if there is radiologic-pathologic concordance, further surgical excision is not warranted.