Introduction
Background
Radiologists must be familiar with a variety of benign breast conditions to confidently distinguish malignant disease from benign disease. Fibroadenomas are benign tumors composed of stromal and epithelial elements. These tumors are commonly seen in young women. Multiple or complex fibroadenomas may indicate a slightly increased risk for breast cancer; the relative risk of patients with such fibroadenomas is approximately twice that of patients of similar age without fibroadenomas.
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Pathophysiology
Fibroadenomas are benign tumors that represent a hyperplastic or proliferative process in a single terminal ductal unit; their development is considered to be an aberration of normal development. The cause of these tumors is unknown. Approximately 10% of fibroadenomas disappear spontaneously each year, and most stop growing after they reach 2-3 cm.
Fibroadenomas may involute in postmenopausal women, and coarse calcifications may develop. Conversely, fibroadenomas may grow rapidly during pregnancy, during hormone replacement therapy, or during immunosuppression, in which case they can simulate malignancy. In immunosuppressed patients, the etiology of multiple or growing fibroadenomas appears to be related to Epstein-Barr virus infection.
Fibroadenoma variants include juvenile fibroadenomas, occurring in female adolescents, and myxoid fibroadenomas, occurring in persons with Carney complex. Carney complex is an autosomal dominant neoplasia syndrome that includes skin and mucosal lesions, myxomas, and endocrine disorders.
Frequency
United States
Fibroadenomas are among the most common breast lesions, particularly in women younger than 40 years. Approximately 10-15% of fibroadenomas are multiple.
Mortality/Morbidity
Fibroadenomas are benign lesions and are not considered to have malignant potential. However, because they contain epithelium, a risk of neoplasia exists, as in other locations in the breast. The risk of a breast carcinoma occurring within a fibroadenoma is about 3%.
- Carcinoma is twice as likely to occur in women who have previously undergone excision of a fibroadenoma.
- The relative risk of carcinoma is increased in women who have fibroadenomas associated with cysts, sclerosing adenosis, calcifications, or papillary apocrine change.
- Juvenile fibroadenomas, otherwise called giant fibroadenomas, are rapidly growing benign tumors that occur in female adolescents. These tumors are cured with excision.
Race
No racial predilection is noted.
Age
Fibroadenomas may occur in girls and women of any age during their reproductive years. After menopause, the tumors often regress. Fibroadenomas rarely appear in older women; therefore, any new solid lesion in an older woman should be considered malignant until proven otherwise. Cancers are the most common solid masses in postmenopausal women.
The prevalence of fibroadenomas is approximately 8-10% in women older than 40 years. Fibroadenomas are the second most common solid tumor after breast cancer and the most common benign tumor in women. In women younger than 30 years, fibroadenoma is the most commonly diagnosed breast tumor.
Fibroadenomas are common in younger women. Because women younger than 40 years are not ordinarily screened with imaging, detection by palpation is the most common method by which fibroadenomas are detected in women in this age group.
Anatomy
Fibroadenomas are tumors that may occur anywhere in the breast. These tumors are composed of both stromal and epithelial elements. Two kinds of breast stroma exist: intralobular stroma and interlobular stroma. Intralobular stroma contains lobules composed of 6-10 major ductal systems surrounded by a myxomatous stroma; it is from this stroma that fibroadenomas arise. Interlobular stroma is composed of dense fibroconnective tissue mixed with adipose and elastic tissue.
Presentation
On clinical examination, fibroadenomas are oval, freely mobile, rubbery masses that may be nonpalpable or palpable. Their size varies from smaller than 1 cm in diameter to as large as 15 cm in diameter in the giant forms. Most commonly, the tumors are removed surgically when they are 2-4 cm in diameter. In young women, the tumors are usually palpable. In older women, the tumors typically appear as a mass on mammograms and may be palpable or nonpalpable.
In approximately 50% of women who receive cyclosporine after renal transplantation, fibroadenomas develop, and these tumors are often multiple and bilateral. The size of fibroadenomas also can vary during the menstrual cycle and during pregnancy. During postmenopause, tumors regress and often develop calcifications. Cancer may arise in a fibroadenoma, occurring in about 2.9% of cases; an increase in size, a change or irregularity in the margin, the development of small pleomorphic calcifications, and the presence of cystic spaces all suggest a developing malignancy.
Preferred Examination
A patient's age determines the preferred imaging method. In general, ultrasonography (US) is preferred if a palpable mass is found, if a patient is younger than 30 years, or if the patient is pregnant. Mammography and US are both useful if the patient has a palpable mass, is older than 30 years, and is not pregnant.
In patients younger than 30 years, the most appropriate modality is US because the patient is spared radiation exposure and the likelihood for fibroadenoma is high. Positron emission tomography is expensive and not universally available. Mammography is not indicated as the primary imaging study in women younger than 30 years, unless high-risk factors are present. Computed tomography (CT) scanning is not initially indicated for assessing a palpable lump in a woman in this age group because of radiation exposure, the inability of CT to demonstrate microcalcifications, and the lack of specificity in the findings. Magnetic resonance imaging (MRI) is not initially indicated for assessing a palpable lump in a woman in this age group mainly because of its high cost and the high likelihood of false-positive findings.
On mammograms, fibroadenomas typically appear as circumscribed oval or round masses, which occasionally have coarse calcifications.
On ultrasonograms, fibroadenomas appear as circumscribed, homogeneous, oval, hypoechoic masses that may have gentle lobulations; a smooth, thin, echogenic capsule; variable acoustic enhancement; and homogeneity.
On MRIs, fibroadenomas typically appear as smooth masses with high signal intensity on T2-weighted images and enhancement with the administration of gadolinium-based contrast agent.
Limitations of Techniques
Mammography cannot be used to distinguish whether a mass is a fibroadenoma, a cyst, or a carcinoma with certainty because of some overlap in the findings. All of the entities may appear as smooth masses.
On ultrasonograms, fibroadenomas often demonstrate a typical appearance and may be distinguished clearly from cysts and carcinomas; however, fibrocystic disease with complicated hypoechoic cysts and, rarely, smooth carcinomas may mimic fibroadenoma. Atypical fibroadenomas, which are inhomogeneous or irregular in shape, may simulate carcinomas.
On MRIs, enhancement characteristics may help distinguish fibroadenomas from carcinomas, although the enhancement kinetics and morphologic features of the 2 tumors overlap. Fibroadenomas are hypointense or isointense lesions as compared with adjacent breast tissue on T1-weighted images, and they are hypointense or hyperintense on T2-weighted images. With gadolinium, the majority of fibroadenomas are hyperintense, with slow initial contrast enhancement and a persistent delayed phase, but some have rapid enhancement and either a plateau or a washout phase. Large phyllodes tumors may typically have smooth margins, internal cysts, septations, and hemorrhage or perifocal or unilateral edema, but it is not possible to definitely differentiate between phyllodes tumors and fibroadenomas. Septations occur in about half of fibroadenomas and have been reported to be a strong indicator of this diagnosis, but phyllodes tumors also may have septations. Fibroadenomas may have a contrast-enhancement pattern
suggestiveofmalignancy in up to one third of cases; on MRIs, they cannot be distinguished from phyllodes tumors with certainty.
Definitive diagnosis often requires palpation or image-guided biopsy.
Differential Diagnoses
Magnetic Resonance Mammography
Other Problems to Be Considered
With mammography or US, circumscribed masses may also represent simple or complex cysts, hamartomas, cystosarcoma phyllodes, lactation adenomas, papillomas, mucinous carcinomas, or medullary carcinomas.
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References
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Further Reading
Keywords
benign breast tumors, breast tumors, breast lesions, stromal tumors, myxomatous stroma, intralobular stroma, interlobular stroma, epithelial tumors, multiple fibroadenomas, complex fibroadenomas, breast hyperplasias, juvenile fibroadenomas, giant fibroadenomas
