Rapidly growing breast masses in lactating or pregnant women can be due to many underlying etiologies including physiologic glandular hyperplasia, cysts, fibroadenomas, abscesses, galactoceles, lactating adenomas, phyllodes tumors, and breast cancer (123). In particular, phyllodes tumor is rare during pregnancy or breast feeding (1). Furthermore, spontaneous infarction of these pregnancy-related breast diseases is rare and is usually not included in the list of differential diagnoses. Here, we report the first case of spontaneous infarction of a benign phyllodes tumor in a postpartum woman.

A 30-year-old woman visited our hospital one month after delivery, with a huge palpable non-tender mass in her left breast. The mass had progressively grown during pregnancy and hardened during the postpartum period. After delivery, she breastfed for 2 weeks and then stopped. In addition, she had a history of vacuum-assisted breast biopsy in the left breast for fibroadenoma 5 years back.

Physical examination revealed a hard, palpable mass with erythematous skin change in the bulging left breast (Fig. 1A). Mammography showed a large oval hyperdense mass in the left breast (Fig. 1B). Breast ultrasound (US) depicted a 14 cm sized oval circumscribed mass with a multiloculated cystic portion, and color Doppler US showed penetrating vascularity within the solid portion (Fig. 1C). This complex cystic and solid mass was classified as Breast Imaging Reporting and Data system (BI-RADS) category 4. US-guided core needle biopsy was performed using a 14-gauge needle, and subsequent histological analysis revealed a fibroadenoma with infarction. Magnetic resonance imaging (MRI) was recommended due to the imaging-histologic discordance, and to identify any suspicious features of this mass. MRI revealed a huge, heterogeneous, circumscribed mass containing multiloculated fluid. The solid portion of the mass exhibited iso- to high signal intensity and dark septa on T2-weighted images (T2WI), with no diffusion restriction on diffusion-weighted image (DWI) and isointensity on apparent diffusion coefficient (ADC) map. A gadolinium-enhancement study visualized a heterogeneous, well-enhanced mass, and a dynamic contrast enhancement study revealed a 77% persistent and 20% plateau kinetic pattern in the solid portion of the mass (Fig. 1D). The mass was classified as BI-RADS category 4.

The patient underwent mass excision of a 14.0 × 11.5 × 8.0 cm white-to-yellow colored mass containing a multiloculated cystic portion with inflammation and necrosis (Fig. 1E). Histopathologic analysis revealed benign phyllodes tumor with infarction (Fig. 1F).

Physiologic glandular hyperplasia, cysts, fibroadenomas (influenced by estrogen), abscesses, galactoceles, lactating adenomas, phyllodes tumors, and breast cancer are normally included in the differential diagnoses of rapidly growing breast masses in lactating or pregnant women (123). Since the treatment options of these conditions differ, it is very important to establish an accurate diagnosis (1).

Phyllodes tumor is a rare breast tumor, accounting for 1% of primary breast tumors, and rarely occurs during pregnancy and lactation. A previous study of 15 cases reported that phyllodes tumors arising during pregnancy or lactation could be benign, borderline, or malignant. Phyllodes tumor is rare in lactating breasts due to the presence of lobular and acinar hyperplasia, which are required to satisfy the physiological requirements during lactation. Thus, it is hypothesized that as stromal hyperplasia is not a feature of the lactating breast, the probability of developing phyllodes tumor is low (1). Furthermore, it is unknown if this rapidly growing mass is hormone dependent in pregnant women (4).

Spontaneous infarction of a breast mass is rare. However, it may be associated with pregnancy, lactation, recent fine needle aspiration, cardiovascular disease, or the use of oral contraceptives (3). Although the mechanism of breast mass infarction is unknown, some hypotheses have been proposed, especially for fibroadenomas. One suggestion concerns relative vascular insufficiency due to increased metabolic need during pregnancy or lactation. Additional hypotheses suggest that infarction may be secondary to calcification with hyalinization and mechanical factors related to mass mobility, which may reduce the blood supply, or thrombo-occlusive vascular changes in feeder vessels (35). In the case of giant juvenile fibroadenomas, the rapid growth and large size are proposed as the mechanisms of infarction, as the tumor may outgrow its blood supply (6).

There are few publications on the imaging findings of infarcted breast disorders. The majority of reported cases of infarcted benign tumors involve fibroadenomas, and some reports have described infarcted fibroadenomas or lactating adenomas during pregnancy or lactation (3). In one previous report, the sonographic findings of an infarcted fibroadenoma include a circumscribed complex cystic and solid mass with internal multiple small anechoic portions having posterior acoustic shadowing (35).

US features of infarcted breast tumors include inhomogenous, low echoic, circumscribed lesions that may be accompanied by posterior acoustic enhancement. Oh et al. (7) concluded that an inhomogenous, low echoic lesion suggests infarction, and combined high echoic lesions indicate hemorrhage. The radiologic features of these tumors depend on the stage of infarction. The imaging findings of our patient were similar to those previously reported, and consisted of a huge, inhomogeneous mass lesion with an internal anechoic portion histopathologically related to necrosis.

Typical MR findings of infarcted breast tumors are yet to be established. For infarcted juvenile fibroadenomas, MRI findings of infarcted tumors include solid portions that exhibit less pronounced enhancement, and edema, which is sometimes associated with hemorrhage and progressive enhancement (6). In one case of an infarcted phyllodes tumor in a non-pregnant woman, the MRI revealed a 3 cm sized slightly irregular mass of predominantly cystic appearance due to massive infarction (8).

The MRI findings need to be correctly analyzed to enable the differentiation of benign and malignant phyllodes tumors, since the histologic features of the phyllodes tumor influences the treatment decision making and prognosis. Yabuuchi et al. (9) reported equal to lower signal intensity of tumor than normal breast tissue on T2WI, cystic change with an irregular wall, and low ADCs on DWIs as features of histopathologically malignant phyllodes tumor. Another study reported that larger tumor size, non-enhanced T2 low signal intensity septations, and silt-like patterns in enhanced images, are correlated significantly with the malignant histologic grade (10).

In our case, the MRI depicted a huge, heterogeneous, well-enhancing mass with cystic change and non-enhanced T2 low signal intensity septations mimicking malignant phyllodes tumor. However, high signal intensity of the mass on T2WI was comparative with normal breast tissue, cystic change with a smooth thin wall, delayed persistent kinetic patterns of the solid portion during the dynamic contrast enhancement study, and no significant diffusion restriction of the mass, indicating a benign nature.

MRI is a useful imaging modality to help differentiate an infarcted benign tumor from a malignant tumor with hemorrhagic necrosis, in pregnant patients presenting with a rapidly growing well circumscribed mass with cystic features on US examination. Here, we report the first case of spontaneous infarction of a benign phyllodes tumor in a postpartum woman.