Cysts with masses and masses with cysts: An imaging review of cystic breast masses

Simple and complicated cysts are the most common cystic breast lesions. Cysts are fluid filled and develop secondary to dilatation of the terminal ductal lobular unit (TDLU). They are commonly multiple, bilateral and may wax and wane in size. Cysts typically present as circumscribed masses on mammography that maybe obscured by overlying breast tissue. ¹ Sonographically, simple cysts are circumscribed anechoic masses with posterior acoustic enhancement and absent vascularity. Simple cysts are benign, requiring no further assessment unless aspiration is requested due to symptoms. Complicated cysts contain internal echoes and are associated with less than 2% incidence of malignancy.^1-2 Clustered microcysts are multiple grouped cysts and in some instances may require aspiration to distinguish them from solid masses. Follow up, however, is supported by the Berg et al study, where none of the simple, complicated or clustered cysts were found to be malignant.⁴

Fluid collections appearing as cystic masses include hematomas and abscesses. The clinical scenario is typically specific so that when paired with imaging, the diagnosis is definitive. Hematomas are associated with trauma, anticoagulation therapy or interventional procedures. The incidence of post core-needle biopsy hematoma is less than 1% when using lidocaine with epinephrine and sufficient compression.⁵ The sonographic imaging appearance varies with the age of the hematoma.⁶ Acute hematomas are hypoechoic collections with layering debris (Figure 1A). Over time, the hematoma organizes developing internal echoes depending on the ratio of clotted and fluid blood and can present as a complex mass (Figure 1B).¹ Follow-up ultrasound evaluation of hematomas is often recommended to document resolution. ²

Abscesses are collections of fluid and pus resulting from infection and are more frequent in younger women. They may be related to progressive mastitis or, less commonly, a complication of an interventional procedure. Symptoms include pain, warmth, skin thickening and erythema.^1,5Staphylococcus aureus is the most common pathogen.⁵ Puerperal abscesses occur in 1-24% of lactating women and occur as a complication of mastitis in 5-11% of these women. Non-puerperal abscesses occur in non-lactating women. Puerperal abscesses respond better to treatment. ⁷ Abscesses features on ultrasound are complex multi-loculated fluid collections with internal debris and surrounding hyperemia (Figure 2).⁵Abscesses are typically managed by antibiotics with or without drainage. Surgical intervention is declining, as percutaneous drainage is less invasive and equally effective, with reported success in 54-100% of patients. ⁷ Follow-up imaging is recommended if the clinical response is prolonged. This is to evaluate for the presence of an underlying malignancy, which may be the cause of the lymphatic or duct obstruction that preceded abscess formation. Rarely, inflammatory breast cancer can result in the development of malignant breast abscesses and a punch biopsy may be necessary for diagnosis. ⁶

A galactocele is the most common mass seen in women during late pregnancy, lactation, and shortly after cessation of lactation. ⁸ This entity presents as a painless, palpable lump. Ultrasound is the best assessment modality, as mammography is limited in the setting of lactation due to stromal proliferation leading to increased mammographic density. Galactoceles are focal dilations of the ductal system resulting from distal duct obstruction of the TDLU. They are fluid filled, containing differing amounts of proteins, fat, and lactose.⁹ Initially, galactoceles appear cystic, and complexity increases over time as fat-fluid levels develop, with the milk eventually curdling, resulting in solid components (Figure 3). A biopsy or aspiration may be required if they present as a complex cystic mass.¹

Fat necrosis typically develops after trauma or surgery and frequently occurs as evolution of a hematoma. The degree of trauma may be insignificant enough that many women do not recall the inciting event. Disrupted fat cells and associated hemorrhage result in inflammatory changes that may eventually be replaced by fibrosis. Fat necrosis may result in cystic changes containing oily fluid from necrotic lipid content. ^1,10 On ultrasound, oil cysts appear as either simple or complicated cysts. As oil cysts evolve, solid components may appear as complex cystic masses on sonographic imaging (Figure 4A).¹ Studies have demonstrated fat necrosis to present as cystic masses in as many as 47-48% of cases, as outlined in Table 1.^11-12 Echogenic internal bands that change orientation with changes in patient positioning were found to be specific for fat necrosis.¹¹ Mammographically, it may present as a fat-containing mass with calcification (Figure 4B). On MRI, fat necrosis may enhance but with fat signal on all sequences. Correlating ultrasound, mammography and MRI results in the correct diagnosis, and eliminates the need for biopsy. ¹⁰

Fibroadenomas are benign neoplasms that develop in the TDLU. On imaging, fibroadenomas may present as solid masses with cystic clefts and less often as a predominantly cystic mass with solid components. The cystic appearance of fibroadenomas ranges from 6.6 -11%.^13-14 A cystic appearance may be related to complex histology and Dupont et al found there was a 3.1-increased relative risk of malignancy with complex fibroadenomas compared to simple ones.¹³ Juvenile fibroadenomas, also known as giant fibroadenomas, are a rare variant, with a prevalence of approximately 2-7.6%. These are typically seen in the teenage years and may also present with cystic changes (Figure 5).¹⁵

Phyllodes tumors are uncommon, comprising 0.3%-1.0% of breast neoplasms. These have stromal and epithelial elements, and therefore share similarities with fibroadenomas. Histologic sampling is required to differentiate benign and malignant tumors, and surgical resection may be needed as well. The local recurrence rate ranges from 16-28% secondary to incomplete excision; therefore, wide margins are needed to prevent recurrence. Approximately 29% of malignant tumors develop metastases.¹⁶ There is a wide range in the percentage of phyllodes presenting with cystic changes. Liberman et al found that cystic changes were present in more malignant tumors than benign, but the difference was not statistically significant.¹⁷ Buchberger et al concluded that cystic changes were not pathognomonic and found biopsy was needed.¹⁶ Studies describing incidence of cystic changes in these fibroepithelial lesions are outlined in Table 2.^13-17

Infiltrating ductal carcinoma (IDC) and ductal carcinoma in situ (DCIS) are the most common malignancies to present as complex cystic and solid masses. ² Of invasive ductal malignancies, grade 3 cancers may present as cystic masses with posterior acoustic enhancement due to their increased cellularity mimicking a benign lesion (Figure 7).²³In papillary DCIS, malignant cells grow with papillary projections into the duct (Figure 8). This variant is associated with a higher rate of microinvasion and multicentric disease in comparison to other DCIS.²⁴ Infiltrating lobular carcinoma (ILC) accounts for 7-10% of breast malignancies. Invasive malignancies typically present as irregular masses and less commonly, can present as complex cystic masses. Suspicious masses may present with thick walls and thick septations (Figure 9) or as solid masses with cystic foci.²⁵ Studies have demonstrated a wide range in the incidence of primary breast malignancy presenting as cystic masses, as outlined in Table 4.^4,18 Of 18 that were found malignant by Berg et al, the pathologies were the following: 50% IDC, 22% IDC/DCIS, 17% DCIS, 6% ILC, and 6% a combination of IDC, DCIS and ILC (Figure 10).⁴ Therefore, the percentage of malignancies presenting as complex cystic and solid masses varies, but it is high enough that ultrasound-guided biopsy is warranted.

Papillary carcinomas represent only 1-2% of all breast malignancies. They occur mostly in postmenopausal women, often present with nipple discharge, and have a good prognosis, as they are well differentiated. Papillary carcinomas are seen on ultrasound as solid masses, complex cystic and solid lesions or intracystic masses (Figure 11). Intracystic papillary carcinomas are seen in fluid-filled ectatic ducts as a vascular solid component. As these are vascular, hemorrhage may occur, resulting in fluid-debris levels on ultrasound imaging. ²⁴ In the study by Berg et al, 75% of the malignant intracystic masses were papillary in origin. ⁴ Additional studies have shown papillary malignancies present as complex cystic masses in 24-57% of cases as outlined in Table 3. ^{4, 18-22}

Mucinous carcinomas, also called colloid carcinomas, are most common in older women, associated with a good prognosis these lesions comprise 1-7% of invasive breast cancers. ²⁶ Mucinous carcinomas often appear as hypoechoic to anechoic, round, circumscribed masses on ultrasound and as dense round, circumscribed masses on mammography. ^27-28 In a study by Lam et al, 37.5% presented as a complex mass with solid and cystic components and were more common in mixed variants and grade 1 tumors.²⁹ Other studies however were unable to correlate sonographic features with histologic grade (Figure 12). ²⁷

Metastatic disease to the breast often indicates late-stage disease and has a poor prognosis. Clinical history is critical, as a primary malignancy or other metastatic lesions narrow the differential diagnosis. The most common origins of metastatic disease from extra-mammary malignancies include lymphoma/leukemia and melanoma. Metastatic disease to the breast is uncommon with incidence ranging from 1.7-6.6% in autopsies series, with variable rates dependent on whether lymphoma/leukemia were included in the studies. Additional studies have demonstrated the clinical incidence to average around approximately 2%.³⁰

Metastatic lesions are most commonly located in the upper outer quadrant ³⁰ typically in superficial breast tissue with rich blood supply.³¹ Metastases can spread to the breast via hematologic or lymphatic pathways. The hematogenous metastases are more likely to form breast masses. Metastases have a variety of presentations, most commonly seen on ultrasound as solid hypoechoic masses with circumscribed margins. Imaging is often unable to distinguish metastases from other processes.³² Breast metastases can present as cystic masses on ultrasound with reports of intratumoral cystic lesions.³¹ In a study by Lee et al, 21% of patients had breast metastases from an extramammary malignancy presenting as a cystic mass with complex echo pattern. 80% of these lesions were lymphoma metastases and 20% from malignant fibrous histocytoma .³² Other metastatic lesions to the breast include lung, ovarian and gastric carcinomas (Figure 13).³³ In another institution, metastatic disease with cystic foci was seen in patients with synovial sarcoma, hepatocellular carcinoma and insular carcinoma of the thyroid gland.³¹ Cystic metastases are uncommon, but regardless of the imaging presentation, biopsy is required for final diagnosis.