Sebaceous cysts are not cysts at all, but result from keratin accu- mulation in plugged ducts. They have an epithelial cell lining from the sebaceous gland, whereas epidermal cysts have a true epidermal cell lining and no sebaceous glands. Because they have almost no malignant potential, biopsy is not required unless the patient desires removal.
Clinically, sebaceous cysts can produce a palpable mass or a blackhead that when squeezed will yield cheesy yellow or white material. On mammography, sebaceous and epidermal inclusion cysts are identical, with subcutaneous oval or round well-defined
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FIG. 4.63 Galactoceles in two different cases. (A and B) Mammogram (A) shows a dense round mass with corre- sponding ultrasound (B) showing an oval, shadowing mass. Excisional biopsy revealed a galactocele. Most likely the fluid components of the galactocele resorbed, resulting in the apparent solid mass. (C and D) Mammogram (C) shows a palpable equal-density mass under a skin marker that is difficult to see against the dense fibroglandu- lar tissue. Ultrasound (D) shows an oval hypoechoic galactocele that yielded milk on aspiration.
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FIG. 4.64 Necrotic invasive ductal carcinoma in two different cases. (A and B) Photographically magnified mam- mogram (A) shows a high-density 4-cm irregular mass with mixed fine pleomorphic and coarse heterogeneous calcifications. Corresponding ultrasound (B) shows a complex cystic and solid mass with calcifications. Biopsy showed invasive ductal carcinoma. (C) Ultrasound of another patient with invasive ductal carcinoma shows a complex cystic and solid mass containing fluid. Note a fluid/fluid level is seen within the necrotic cavity.
A B
FIG. 4.65 Intracystic carcinoma. (A) Mammogram shows a dense oval mass. (B) Corresponding ultrasound shows a fluid-filled cyst with an irregular mural mass. Although this mass was an intracystic carcinoma, the dif- ferential diagnosis includes papilloma or debris in a benign cyst.
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masses that are often overexposed because of their location near the skin surface (Fig.4.66). They occasionally contain calci- fications and US shows an oval, well-circumscribed, hypoechoic or anechoic mass in a subcutaneous location with a little tail extending into the skin, representing the dilated hair follicle (see Fig. 4.66 D–E).
Displacement of epidermal fragments from the skin surface to locations deep within the breast parenchyma cause epidermal
inclusion cysts after percutaneous biopsy or surgery. The epider- mal inclusion cyst produces a round or oval mass located within breast tissue far away from the skin surface. Because epidermal inclusion cysts have an epithelial lining, they can produce a growing mass on the mammogram as a result of accumulating inspissated material within them. Because they cause a growing solid mass, the epidermal inclusion cyst often requires biopsy to exclude cancer.
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FIG. 4.66 Sebaceous cyst in two different cases. (A and B) Left mediolateral oblique (A) and craniocaudal (B) mammograms in a man with gynecomastia (under skin BB marker) show an upper inner quadrant mass (arrows) that was in the skin. Ultrasound (US; C) showed an oval, hypoechoic, well-circumscribed mass between the two bright lines of the skin. This is a sebaceous cyst. (D–F) In another patient, longitudinal US (D and E) shows an oval hypoechoic sebaceous cyst at the junction of the skin surface and subcutaneous fat, with the typical thin tail (arrows) extending into the skin. Note that on the transverse scan (F) this sebaceous cyst is an oval mass that appears to be below without the tail. The tail connecting the mass to the skin surface is seen only with careful scanning and clinches the diagnosis.
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Key Elements
A mass is a three-dimensional object seen on at least two mammographic projections.
On mammography, the mass repeat includes a description of the shape, margins, density, location, associated findings, and how it has changed if previously present.
Mass shapes are round, oval, lobular, and irregular, with the probability of cancer increasing with increasing irregular- ity of the shape.
Mass margins are circumscribed, microlobulated, obscured, indistinct, or spiculated, with the probability of cancer in- creasing with increasing spiculation of the margin.
Fat-containing masses are almost never malignant.
Mass density is lower, equal to, or higher than an equal amount of fibroglandular tissue. High-density masses are suspicious for cancer.
The differential diagnosis for spiculated masses includes inva- sive ductal cancer, invasive lobular cancer, tubular cancer, postbiopsy scar, radial scar, fat necrosis, and sclerosing adenosis.
To determine whether a spiculated mass represents a postbi- opsy scar, correlate the postbiopsy mammogram with the prebiopsy study showing where the finding was removed.
Spiculated masses that do not represent postbiopsy scars should undergo biopsy to exclude cancer.
Radial scars cannot be distinguished from spiculated breast cancer on mammography.
Invasive lobular cancer accounts for approximately 10% of all cancers but is one of the hardest to see on mammography because of its single-file cellular growth pattern.
The differential diagnosis for solid masses with round or ex- pansile borders includes fibroadenoma, cancer, phyllodes tumor, papilloma, lactating adenoma, tubular adenoma, metastases, sebaceous cyst, and epidermal inclusion cyst.
The most common round cancer is invasive ductal cancer, an uncommon form of the most common breast cancer.
Medullary and mucinous breast cancers are commonly round in shape, but they are much rarer than invasive ductal cancer.
Fat-containing masses include lymph nodes, hamartoma, oil cyst, lipoma, and the rare liposarcoma.
Normal lymph nodes are oval, have an echogenic fatty hilum, and may contain a central pulsating blood vessel on color or power Doppler US in the fatty hilum.
Abnormal lymph nodes lose their fatty hilum and become larger and rounder than previously.
Fluid-containing masses include cysts, hematoma/seroma, necrotic cancer, intracystic carcinoma, intracystic papil- loma, abscess, and galactocele.
Hamartomas look like a breast within a breast and should be left alone.
Galactoceles may rarely show a fat/fluid level on upright mammographic views.
Know the typical appearance of “don’t touch” benign lymph nodes, hamartomas, oil cysts, lipomas, galactoceles, cysts, and postbiopsy scars.
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