Teaching Case

A 33-year old woman presented with a palpable non-tender, rubbery and mobile breast mass which had increased in size during pregnancy, 4 months previously, and continued doing so during breast feeding. Breast feeding had ceased 2 months previously. There was no family history of breast, uterine or ovarian malignancy.

During pregnancy the patient underwent a breast ultrasound (US) scan (Fig.1) that showed a hypoechoic, well delimited mass with minor contour lobulation and posterior acoustic enhancement. A pseudocapsule was present. The mass measured 42x23mm. Colour Doppler (Fig. 1b) did not show flow. (US Bi RADS -2) The mass was not biopsied due to its benign appearance.

After breast feeding cessation, she underwent mammographic (Fig.2) evaluation that showed a well circumscribed mass with similar density to breast parenchyma. The post-lactation US scan (Fig. 3) showed a mass isoechoic to the breast parenchyma containing hypoechoic areas corresponding to dilated ducts. This had increased and now measured 50x38mm. Colour Doppler (Fig. 3b) showed vascular flow within the mass. Spectral analysis of the larger fluid images did not show flow spectrums. (Bi-RADS-2)

Fine needle aspiration (Fig. 4) revealed milky content. Core biopsy was not preformed as the patient was reassured by the benign mass appearance.

Although a histological diagnosis was not obtained, fibroadenoma is the most likely diagnosis as it is the most common solid breast tumour found during pregnancy and lactation. These lesions exist prior to pregnancy but, as hormone-sensitive tumours, enlarge with hormone level increase. Imaging characteristics are the same as for fibroadenomas in non-pregnant women. Hormonal stimulation can result in cystic degeneration, increased vascularity and duct prominence - secretory hyperplasia- as seen in this case.[1] Differentiating fibroadenomas from lactic adenomas can be difficult; fibroadenomas show myoepithelial cell proliferation. Milk may be extracted with fine needle aspiration, as seen here.

Lactating adenomas are benign, well-circumscribed, non-capsuled breast lesions that occur in response to physiologic pregnancy and lactation changes. The tumour origin is controversial; some authors believe it to be a variation of fibroadenomas. During the first trimester of pregnancy these masses can enlarge quickly, with resultant infarction, which occurs in <5% of cases. [1, 2] Mammographically a lactating adenoma's density is slightly higher than normal breast tissue and can present microcalcifications. [3] It is usually evaluated by US and presents as a homogeneously hypoechoic mass with posterior acoustic enhancement. Hyperechoic areas corresponding to septa or fat can exist. On US, differentiation from galactoceles can be difficult, however lactating adenomas usually present vascularity on Doppler. Some have microlobulated or irregular margins, posterior acoustic shadowing and heterogeneity, which can be due to infarcts. They usually regress spontaneously after lactation, but large lesions can be treated with Bromocriptine. [2]

Other less likely differential diagnosis include:

- Galactoceles, are cystic in nature. They usually occur after lactation has ceased. They are seen mammographically as masses of variable density depending on viscosity, fat and protein content (from lucent to a mixed density hamartoma-like masses). On US they present as complicated cysts or echoic masses with posterior acoustic enhancement. Fluid levels can be seen. [1]

- Pregnancy-associated breast carcinoma, defined as breast cancer occurring during pregnancy or up to a year after delivery, accounts for <3% of breast malignancy.[1] These are more aggressive and have worse prognosis than tumours occurring in age matched non-pregnant women. Patients usually present with a palpable mass; less frequently they can have breast inflammatory signs suggestive of locally advanced disease. 50% have lymph node involvement at presentation. Due to increased breast density mammography has a lower sensitivity for detection of these tumours. However, mammographic and US features do not differ from that of other breast tumours.