Breast Cysts, Intracystic Tumors, and Cystic-Appearing Masses

The most frequent clinical application of breast ultrasonography is to characterize masses initially detected by mammography as cystic or solid. Cysts are the most common breast mass and occur in an estimated 7% to 10% of all women. Cysts are lined by apocrine cells that actively secrete material, predisposing these types of cysts to recur after aspiration. Sometimes, cysts are lined by a flat epithelial lining that is less active. The accuracy of ultrasound in distinguishing cystic from solid masses can be as high as 98% to 100%, as reported by Hilton and colleagues.

Strict ultrasound criteria for a simple cyst include a mass with well-circumscribed margins, sharp imperceptible anterior and posterior walls, a round or oval contour, absence of internal echoes, and posterior acoustic enhancement (Box 5-4 and Fig. 5-7A). Cysts may be single or multiple, gathered into small clusters, or contain thin septations (see Fig. 5-7B to D). Cysts are not malignant or premalignant, but examination of them is important because they may cause lumps that mimic round cancer on physical examination or mammography. When palpable, a cyst is a smooth, mobile mass on physical examination. Occasionally cysts appear as a visible mass if the patient is supine and the cyst is large. Cysts may be painful and may wax and wane with the patient’s menstrual cycle. If a mass is proven to be a cyst by ultrasound, the patient can be monitored by screening mammography because cysts are not cancer. Symptomatic cysts that are painful or cause a lump that disturbs the patient can be treated by aspiration. Cysts may be simple or “complicated,” meaning that the cyst contains sloughed debris. These complicated cysts contain material within them rather than being anechoic. Some complicated cysts require aspiration to confirm that they are cysts rather than solid masses (see Fig. 5-7E).

Figure 5-7 Examples of breast cysts. A, This simple cyst has an anechoic interior, an imperceptible wall, sharply marginated smooth borders, and enhanced transmission of sound. B, This simple cyst is lobulated and contains thin septations and imperceptible walls. C, A typical anechoic simple cyst with imperceptible walls and enhanced through-sound transmission. D, Two typical anechoic simple cysts that are sharply marginated with imperceptible walls and enhanced through-sound transmission. E, Two cysts adjacent to each other include a simple cyst (arrow) with lobulated borders that is anechoic and has an imperceptible wall and enhanced through-sound transmission. Adjacent to the simple cyst are complicated cysts (double arrows) that contain debris and have indistinct margins and enhanced through-sound transmission; needle aspiration showed simple cyst fluid. F, This simple cyst does not show enhanced through-sound transmission because of focal zones that are located too deep for proper evaluation of the cyst. G, Acorn cyst. An oval, well-circumscribed mass has a lower cystic component and a possible solid upper component, comprising the “acorn cyst,” which has a fluid/fluid level (arrow). Aspiration showed a cyst with debris in it.

Attention to technical detail is especially important because increasing the TCG curve may produce artifactual echoes in benign cysts that suggest a solid mass. An improperly set DCG curve may inaccurately evaluate the internal matrix of the mass and make a cyst look solid and may make a solid mass appear to be a cyst. On real-time imaging, cyst contours may be flattened with compression, whereas solid masses are less compressible. Alternatively, small, clustered, or deeply located cysts may be at the technical limits of ultrasound to distinguish the usually anechoic cyst from a solid mass.

Deeply located cysts may not show enhanced through-sound transmission because of their location close to the chest wall, and lateral cyst walls may be obscured by refractive shadows (see Fig. 5-7F). These problems may be resolved by repositioning the patient or the transducer to scan from a different angle. This permits visualization of distal acoustic enhancement or eliminates the refractive shadows obscuring the sharp cyst walls. Acorn cysts contain a fluid/fluid level, with the dark dependent portion of the cyst representing clear fluid (the acorn) and the lighter top representing layering fluid above it (the acorn cap) (see Fig. 5-7G). Changing the patient’s position may cause the layer to move dependently, clinching the diagnosis of an acorn cyst.

The internal characteristics of cysts must be analyzed to exclude mural masses or irregular thick walls, which indicate complex masses. Complex masses contain cystic and solid components; intracystic tumors and necrotic neoplasms are in the differential diagnosis. Complex masses are different from complicated cysts, which contain debris. Complex masses might be cancer, but complicated cysts are benign (Table 5-3 and Boxes 5-5 and 5-6).

Table 5-3 BI-RADS® Ultrasound Special Cases (Cystic)

Real-time ultrasound imaging can help distinguish speckle artifact from debris in cyst fluid from a solid mass. Real-time ultrasound can show particulate matter slowly moving inside the cyst. On real-time imaging, the debris causes speckle artifact, which swirls in the cyst like fake snow in a snow globe (Fig. 5-8A to C). Placing the patient in the decubitus position can cause a difference in the sedimentation pattern in the complicated cyst, but not always. Color Doppler or power Doppler ultrasound can detect movement of particulate matter within complicated breast cysts or blood vessels in solid masses (see Fig. 5-8D and E). Doppler imaging will show no blood vessels in breast cysts. Unfortunately, the absence of blood flow in a mass is not diagnostic of a cyst because Doppler imaging does not always detect blood flow in solid masses or even in cancers.

Figure 5-8 Complicated cysts and Doppler ultrasound. A, This complicated cyst had debris within it that did not move at real-time imaging. Color Doppler ultrasound shows pulsating blood vessels around the cyst but not within it. Aspiration yielded cloudy fluid. B, Ultrasound of a palpable mass showed speckle artifact within a complicated cyst that moved at real-time imaging. C, Color Doppler ultrasound detected movement of the debris in real time. In contradistinction, color Doppler (D) and power Doppler (E) imaging show a pulsating vessel flowing into a round cancer, thus differentiating it from complicated cysts.

In everyday clinical practice, cysts do not always fulfill all the strict sonographic criteria for cysts because of a variety of technical factors, or they may contain echoes from debris within the fluid. Posterior enhanced through-transmission of sound was not seen on all images in 25% of 80 cysts reported by Hilton and colleagues. Internal cyst echoes may be produced by reverberation artifacts, although the near-field reverberations may be reduced by scanning through an offset. However, Berg and colleagues (2003, 2005) and other researchers have shown that complicated cysts with low-level internal echoes, no mural masses, thin walls, and thin septations rarely represent cancer and can either be monitored or aspirated with little or no morbidity.

Differentiation of complicated cysts from benign or malignant cystic masses can be tricky (see Table 5-3). Some cysts contain true internal echoes as a result of thick tenacious fluid or hemorrhage from previous aspirations. Some cysts have thick walls as a result of inflammation from cyst fluid leaking into the surrounding tissues. In cases in which all the sonographic criteria of a simple cyst have not been met, fine-needle aspiration may obviate the need for core needle biopsy or surgical biopsy. Once the needle is within the mass, the presence of cyst fluid rather than solid tissue can be confirmed by moving the needle, as suggested by Stavros and colleagues (Fig. 5-9). Cysts that do not fulfill all criteria for simple cysts, in the right clinical setting, require aspiration (see Fig. 5-9C to E). Cyst fluid should be sent for cytologic analysis if it is bloody, if there is an intracystic mass on ultrasound or pneumocystography, or if the patient has had prior intracystic carcinoma. Clear cyst fluid can be discarded if there are no clinical factors that would require cytologic examination.

Figure 5-9 Simple cyst fluid compared with cyst fluid containing debris. A, The complicated cyst fluid in the left test tube, which contains debris consisting of particulate matter, causes speckles within the cyst on ultrasound. The simple cyst fluid in the right test tube is clear and contains no debris. Both fluids are normal and may be discarded after aspiration. B, A simple way to tell whether a mass is cystic at needle biopsy is to move the needle tip within the mass. In a complicated cyst, the needle will move within the mass. In a solid mass, the needle will move the mass up and down. C, Complicated cyst. This patient felt a palpable mass; ultrasound shows an oval, hypoechoic mass with sharp walls and enhanced through-sound transmission, suggesting cystic or solid material. Doppler ultrasound showed no flow. Aspiration showed yellow fluid with debris within it compatible with a cyst. D and E, Deeply located complicated cyst and simple cyst. Ultrasound shows an oval, well-circumscribed hypoechoic mass with an imperceptible wall anterior to a simple cyst near the chest wall. Despite scanning from several angles, the hypoechoic mass could not be shown to be a simple cyst and Doppler imaging showed no flow. Fine-needle aspiration under ultrasound guidance showed cystic fluid from both masses. The anterior mass represented a complicated cyst and the deeper mass represented a simple cyst.

On the other hand, complex cystic masses (i.e., fluid-filled masses with thick walls or mural projections) require biopsy to exclude the rare intracystic papilloma, intracystic carcinoma, phyllodes tumor with a marked cystic component, or solid cancers with central necrosis. Other complex masses include hematoma, abscess, galactocele, and seroma; management of these masses is based on their appearance and the clinical situation (Fig. 5-10).

Figure 5-10 Complex cystic masses that contain both anechoic (cystic) and echogenic (solid) components. This large palpable mass, in a patient with diabetes, has an anechoic center and a solid, irregular rim in transverse (A) and longitudinal (B) scans. C, Doppler ultrasound showed pulsation in the rim. Another complex cystic mass is oval and has small cystic structures with some solid components on transverse (D) and longitudinal (E) scans. This was a phyllodes tumor. Phyllodes tumors have solid leaflike components floating in small cystic structures, which give the tumor its name and account for the cystic and solid appearance in this image. The cystic versus solid components vary according to each tumor.

Intracystic carcinomas are a rare subgroup of tumors that arise from the walls of a cyst; they represent 0.5% to 1.3% of all breast cancers (Fig. 5-11A). These tumors have a better prognosis than other malignant breast neoplasms do. On ultrasound, intracystic carcinomas often appear as solid mural excrescences projecting into the cyst fluid. Differentiation of intracystic carcinoma from benign intracystic papilloma is not possible, and surgical biopsy is thus necessary. The finding of a mural nodule within a cyst has the differential of an intracystic carcinoma, papilloma, a cyst with debris, and reverberations in a simple cyst produced by high gain settings (see Fig. 5-11B to D). Color or power Doppler imaging may be helpful if a blood vessel can be identified in the intracystic mass.

Figure 5-11 Intracystic tumors. A, An intracystic carcinoma is shown as a mural mass projecting into the fluid-filled center of a cyst on ultrasound. B, In another patient, an intracystic papilloma is shown as a mass surrounded by air after fluid aspiration and pneumocystography. C, In a third patient, an apparent intracystic mass was shown to represent debris stuck to the side wall of a complicated cyst at aspiration. D, This oval, well-circumscribed cystic mass has a round, solid mural nodule. Because it is not completely anechoic, it cannot be considered a simple cyst and is a complex mass; the differential is intracystic cancer papilloma or debris in a cyst. Aspiration was performed, showing cystic fluid and debris without atypia or cancer on cytology.

Benign Solid Masses: Fibroadenoma and Fatty Pseudolesions

Fibroadenomas arise from breast lobules and are the most common solid benign masses in women younger than age 30 years. Once diagnosed, fibroadenomas may remain stable in 80% of cases, regress in about 15%, and grow in 5% to 10%. Fibroadenomas are benign, although cancer can occur within a fibroadenoma. Women with a specific histologic diagnosis of complex fibroadenomas have cysts or histologic elements other than the fibroadenoma and have a small increased risk of future breast cancer, as described by DuPont and colleagues. Fibroadenomas may be single or multiple and are called giant fibroadenomas if larger than 8 cm.

On ultrasound, Cole-Beuglet and colleagues describe typical fibroadenomas as solid masses with well-circumscribed, round or oval borders and containing weak low-level homogeneous internal echoes with enhanced, decreased, or unchanged sound transmission. Stavros and colleagues and Fornage and colleagues have described fibroadenomas as smooth, wider than tall solid masses. Stavros and colleagues further characterize fibroadenomas as having at most four gentle lobulations and homogeneous internal echo texture (Box 5-7 and Fig. 5-12A to C).