Ultrasonic Anatomy of the Breast

Anatomical structures of the breast are easily differentiated by using modern ultrasound equipment. The image of the mammary gland normally varies widely and depends on the ratio of fat, connective and glandular tissue. Unlike x-ray mammography, ultrasound of the mammary glands allows you to visualize the tomographic section of the image of a fragment of the mammary gland from the skin to the chest wall.

On the echogram of the mammary gland of a woman of childbearing age, the following constituent parts and structures can be differentiated.

1. Leather.
2. Nipple.
3. Subcutaneous zone (subcutaneous fat layer, front sheet of split fascia).
4. Cooper bundles.
5. Parenchyma of the breast, fibroglandular zone (glandular part with tender fibrillar fibers, interparenchymal intraorganic lymphatic network, fatty tissue).
6. Milky channels.
7. Retromammary fatty tissue (not always visualized).
8. Thoracic muscles.
9. Ribs.
10. Intercostal muscles.
11. Pleura.
12. Lymph nodes (not always visualized).
13. Internal thoracic artery and vein.

Leather. On the echogram skin integuments are represented by a more or less even hyperechoic line with a thickness, normally 0.5-7 mm. When the skin thickens, it can be visualized in the form of two hyperechoic lines separated by a thin echogenic layer. Changes in the contours and thickness of the skin can mean an inflammatory, postoperative or malignant process in the superficial or deeper parts of the breast.

The nipple is visualized as a rounded, well-delineated formation from medium to low echogenicity. Often behind the nipple is an acoustic shadow. This acoustic phenomenon is due to connective tissue structures of the milk ducts. Conducting ultrasound studies of the subareolar region in oblique projections makes it possible to clearly visualize the hindfoot region. Skin in the areola area is less echogenic than over the rest of the mammary gland, and subareolar structures are always more echogenic due to the absence of subcutaneous tissue in this area.

The subcutaneous zone. In the early reproductive age, subcutaneous fat is almost completely absent. In very young women, fatty tissue can be represented by a thin hypoechoic layer or elongated hypoechogenic inclusions under the skin. With age, there is an increase in the thickness of the hypoechoic subcutaneous layer on the echogram. With the advent of the processes of involution, the fat tissue becomes less homogeneous. In its hypoechoic echostructure, hyperechoic linear inclusions of connective tissue begin to be determined. Fatty fiber takes the form of rounded, arranged in several rows of hypoechoic structures. This is due to the thickening of Cooper ligaments, which, like a hyperechoic capsule, cover individual accumulations of fat, forming a fatty lobe. Very often on the sides of the fat slice symmetrical lateral acoustic shadows are detected. With excess fat content in the mammary gland, the repeated alternation of lateral acoustic shadows from neighboring fatty lobes prevents a clear differentiation of the organ's echostructure. Pressing the breast tissue sensor allows you to reduce or eliminate these unwanted artifacts. At the border of fatty tissue and parenchyma is the anterior leaf of the split fascia in the form of a hyperechoic band. It leaves perpendicular to the skin hyperechoic septa - Cooper ligaments.

Cooper ligaments are also visualized in the form of linear hyperechoic strands covering the hypoechoic fatty segments. With age, ultrasound differentiation of Cooper ligaments improves. Sometimes behind the ligaments of Cooper is determined by the acoustic shadow, which can mimic the pathological processes in the mammary gland. The change in the angle of incidence of the ultrasonic wave due to the movement of the sensor or the change in the position of the mammary gland allows us to get rid of this artifact.

In the normal state, intraorganic lymphatic vessels are not visualized. In case of their expansion in inflammation or tumor infiltration, the intraorganic lymphatic network of vessels can be visualized as longitudinal and transverse hypoechogenic tubular structures reaching the skin.

The anterior contour of the parenchyma is wavy due to bulging at the attachment points of Cooper ligaments. Usually the echogenicity of the parenchyma has an intermediate significance between the echogenicity of fat and fascial structures. At a young age, the parenchyma (fibroglandular part) of the mammary gland is represented by the image of a single granular formation from high to medium degree of echogenicity. In the echostructure of this single array it is practically impossible to differentiate the presence of soft, collagen-free connective tissue fibrillar fibers. The echography allows to detect a change in the parenchyma in the form of an increase in the "grain" of the fibro-glandular complex from the 16th to the 28th day of the menstrual cycle. During this period, the echostructure of the parenchyma is an alternation of more echogenic segments of fibroglandular tissue with tubular hypoechoic structures of the milk ducts. The echostructure of the parenchyma also depends on the number and proportion of fibro-glandular and adipose tissue. This proportion varies with age and hormonal status (state of pregnancy, lactation, menopause), the number of previous pregnancies.

The central sections of the breast are occupied by the milk ducts. In the hormonally calm mammary gland, the milk ducts are always asleep and practically not visualized. If they are determined, the diameter of the terminal and interlobular ducts does not exceed 2 mm. The largest diameter of the ducts (up to 3 mm) is noted in the area of the lacteal sinus (behind the nipple). In the lactating mammary gland, as well as in the 2nd phase of the menstrual cycle, the mammary ducts are visualized as linear and convoluted hypoechoic tubular structures more than 2 mm in diameter, radially converging from the base of the mammary gland to the nipple. Often, in one cut, both transverse and longitudinal fragments of different ducts are visualized in the form of alternation of rounded and elongated hypoechoic structures. In young women with a rich glandular component along the internal contour of the ducts, hyperechoic strands can be visualized along the main axis of the duct. The posterior border of the mammary gland is the image of the posterior sheet of the split fascia in the form of a parallel skin of the hyperechogenic line.

Retromammary area consists of retroammary fatty tissue, pectoral muscles, ribs, intercostal muscles and pleura.

Retro-mammary fat is visualized in the form of small hypoechoic lobes between the hyperechogenic lines of the posterior sheet of the split fascia and anterior fascial box of the large pectoral muscle. In the absence of a retromammary fat layer, the image of the posterior sheet of the split fascia may merge with the image of the anterior fascia of the pectoral muscles.

Large and small pectoral muscles are visualized in the form of multidirectional parallel skin of hypoechoic layers separated by transverse hyperechoic septa. On both sides of the muscles in the form of hyperechoic lines, pectoral fascia are visualized. The identification of muscle layers is a guarantee that the whole array of mammary glands is examined.

In addition, the detection of the posterior border of the gland makes it possible to differentiate tumors of the soft tissues of the thoracic wall from tumors of the actual mammary gland.

The ultrasound picture of the ribs varies depending on the cartilage or bone portion. The transverse image of the cartilaginous part of the ribs shows an oval formation with a small amount of reflections from the internal structure. This image may be mistaken for a benign solid formation of the mammary gland or lymph node. Distinguish these structures helps that the rib is located under the muscle, and the lymph node - anterior or muscle background. With increased calcification behind the cartilaginous segment of the ribs, a weak acoustic shadow may appear. Lateral, always ossified in the normal segments of the ribs are visualized as hyperechoic crescents with a pronounced acoustic shadow.

Intercostal muscles are defined in intercostal spaces in the form of hypoechoic structures of various thicknesses with a typical muscle pattern.

The pleura in the form of a hyperechoic line is the deepest structure that can be discerned during breast ultrasound.

In most cases, the regional lymph nodes of the breast are not normally differentiated from the surrounding tissues. When using ultrasound devices of the highest class equipped with specialized high-frequency sensors, it is sometimes possible to visualize the normal lymph node, especially in the projection of the axillary part of the breast next to the pectoral muscles. Normal lymph nodes have an elongated shape with a hypoechoic rim of the marginal sinus around the echogenic center - the lymph node gates. The horizontal diameter of a normal lymph node usually does not exceed 1 cm. Most often, the internal lymph nodes of the breast can be visualized in the projection of the upper outer quadrant. With increasing size and changing the echomorphological structure, all groups of lymph nodes are well visualized in the form of hypoechoic formations of globular shape. According to Pamilo (1993), the echography allows to detect metastases of breast cancer in the axillary lymph nodes in 73% of cases, while palpation and x-ray mammography - only in 32%.

The internal thoracic artery and vein are visualized on longitudinal echograms parallel to the pectoral muscles in the 1 and 2 intercostal spaces in the form of hypoechoic tubular structures. According to Adler (1993), normal blood flow in the mammary glands is determined in color Doppler mapping in 69% of cases. There are works in which the authors differentiate normal blood flow in the mammary gland from the changes that occur in these vessels when a malignant tumor occurs (the ratio of maximum and minimum blood flow velocities). In other publications, the impossibility of such differential diagnosis with Dopplerography is emphasized. Thus, in view of the insufficient experience of these studies and the inconsistency of the published results, it is inappropriate to recommend using the Doppler method as an independent diagnostic technique separately from ultrasound in the B-mode.

Ultrasonic image of mammary glands in different age periods

The pubertal mammary gland consists of fat, underdeveloped ducts, glandular elements and is visualized as a mixed echogenicity of the structures behind the nipple.

Post-pubertal mammary gland is characterized by a hyperechoic image of the glandular tissue, surrounded by small hypoechoic areas of fat structures.

The mammary gland of an adult woman has many options for ultrasound imaging, in particular, the following types can be distinguished.

The juvenile type. The skin is visualized as a thin hyperechoic line 0.5-2.0 mm thick. The bulk of the gland is represented by the image of glandular structures in the form of a single fine-grained layer of increased echogenicity. In the second phase of the menstrual cycle, the hyperechoic image of the glandular structures alternates with the hypoechoic tubular (in longitudinal section) or rounded (in cross section) structures of the milk ducts.

Early reproductive type. The skin is visualized as a thin hyperechoic line 0.5-2.0 mm thick. Subcutaneous fatty tissue is defined either as a small amount of elongated hypoechoic structures or as a single hypoechoic layer 2-3 cm thick. The glandular part is visualized as a single hyperechoic fine-grained bed, or hypoechoic rounded adipose tissue accumulations are determined against it. In the second phase of the menstrual cycle, the image of the hyperechoic glandular tissue alternates with the image of the hypoechoic fragments of the milk ducts. The anterior contour of the parenchyma of the gland has a wavy form due to protrusions at the attachment points of Cooper ligaments. Cooper ligaments, fascia, fibrillar interlobar tissue poorly differentiated.

Premenopausal type. The skin is visualized as a hyperechoic line with a thickness of 2.0-4.0 mm. A well-pronounced subcutaneous fat layer is defined as rounded hypoechoic structures. Accumulations of hypoechoic fat, surrounded by hyperechoic rims of connective tissue, are fat slices. Partial replacement of glandular tissue by fat is characterized by the appearance of numerous areas of hypoechoic fat on the background of hyperechoic glandular tissue. In the 2nd phase of the menstrual cycle, multiple images of hypoechoic structures of the milk ducts appear on this background. Often in the retromammary space, the fat tissue is determined in the form of hypoechoic small rounded inclusions. Cooper ligaments, fasciae, fibrillar interlobar tissue are well differentiated as multidirectional hyperechoic strands.

Postmenopausal type. The skin is visualized as two hyperechoic lines, between which a thin hypoechoic layer is defined. The thickness of the skin can be different. Almost all of the mammary gland consists of hypoechoic fatty lobules in the form of rounded hypoechoic structures with a pronounced hyperechoic rim. Sometimes between the fatty lobules, single inclusions of the hyperechoic glandular tissue are determined. Connective tissue structures are characterized by thickened hyperechoic Cooper ligaments, as well as by hyperechoic linear inclusions in adipose tissue and in the image of the outer contour of the milk ducts.

The mammary gland during pregnancy and lactation. The skin is visualized as a thin hyperechoic line 0.5-2.0 mm thick. Virtually the entire image of the gland consists of coarse-grained hyperechoic glandular tissue (hypoechoic fat is pushed to the periphery). At late stages of pregnancy and during lactation against a background of hyperechoic glandular tissue, hypoechoic, more than 2.0 mm in diameter, milky ducts are well differentiated.