According to the Breast Imaging Lexicon (ACR 1998) a mass is a space-occupying lesion seen in two different projections.
The most common circumscribed mass among women in their teens, 20s, and early 30s is the FIBROADENOMA. Radiographically, a fibroadenoma is, for all practical purposes, indistinguishable from a cyst or even a well-circumscribed carcinoma. However, in general it has sharply defined margins that may be slightly more angular than the usually round or ovoid cyst. Like other benign lesions they usually do not distort the breast architecture but rather fit in it. When the typical large calcifications are present within the fibroadenoma, the diagnosis can be made without a biopsy.
CYSTS are probably the most common masses found in the breast. They are rare before the age of 30 and begin to be frequently diagnosed beginning in the fourth decade of life. Although more common in premenopausal women, they can be found in women of all ages and are not that unusual in postmenopausal women. They most likely represent dilatation of the terminal ducts within the lobules that is the result of an imbalance between secretion and resorption. Macrocysts (visible by mammography) are usually multiple and bilateral. They also rarely distort the architecture of the breast, appearing rather as round densities within it.
Cysts may be clearly defined. They more commonly have margins that are partially obscured by the surrounding parenchyma. At times their margins are not visible on the mammogram, causing only focal increased density. Portions of their margins may be seen as bulging, rounded contours within the dense background of the breast.
Ultrasound is a safe, easy, and accurate way of evaluating lesions to determine if they are cysts or solid. Most clinicians agree that if a lesion meets all the criteria for the ultrasound diagnosis of a cyst (round or oval, sharply defined, with no internal echoes and with enhanced through transmission of sound), the diagnosis is virtually ensured.
Most infections of the breast are treated before they form an ABSCESS. Furthermore, most breast abscesses occur in young women and are often associated with nursing. Consequently, it is rare that a mammogram is indicated in a woman with an abscess, and most are treated clinically. They may be round and well circumscribed or irregular and ill defined or only evident by skin and trabecular thickening. Even ultrasound cannot always differentiate an abscess from a cyst or other abnormality; aspiration is generally needed to make the diagnosis.
Intraductal PAPILLOMAS usually extend within the lumen of the duct and are not evident on conventional mammograms. On occasion they form visible masses that may be circumscribed. If the duct is cystically dilated around the papilloma, they may appear as cysts. When present, they are commonly seen within several centimeters of the nipple. They rarely have a lobulated border.
The breast is a fairly dynamic organ and appears to readily produce and resorb collagen. On occasion FOCAL AREAS OF FIBROSIS occur and may appear as isolated islands of density. The margins of such fibrotic islands are sometimes smooth and well demarcated, but usually they are more difficult to evaluate because they fade gradually into the surrounding tissues. Coned-down spot compression may help eliminate concern by showing undisrupted architecture through the density.
More recently some of these lesions have been recategorized as pseudoangiomatous stromal hyperplasia. These are benign lesions that may resemble focal fibrosis or fibroadenomas on imaging. The lesions have clefts that are lined by fibroblasts (spindle cells) that give the appearance of small vessels (hence the name). They have no known malignant potential.
Trauma to the breast can cause a hard mass or thickening that is obvious on physical examination. Radiographically, a contusion may appear as very subtle diffuse infiltration of tissues by blood or edema. Producing only mild architectural changes with some thickening of the breast trabeculations, a contusion rarely produces a radiographically visible mass.
If, on the other hand, trauma results in a true focal collection of blood, a fairly well-circumscribed lesion may be seen. HEMATOMAS are not uncommon after surgery. They should resolve spontaneously within several weeks, but it is not uncommon for architectural change to persist for up to a year after a breast biopsy with benign results and longer if the breast has been irradiated for cancer. Usually there are no long-term sequelae of trauma to the breast, and permanent architectural distortion is fairly unusual.
PHYLLOIDES TUMOR is a rare lesion that used to be more common. It usually forms a slightly lobulated density with sharply defined margins and is often rapidly growing. Usually the tumor is benign, but approximately 15% are malignant and are locally invasive, recurrent, or metastatic beyond the breast. Although their natural history is difficult to determine, this lesion is probably a variant of the fibroadenoma. It is radiographically indistinguishable from the so-called giant fibroadenoma that can be seen in adolescent women and women in their twenties.
Malignant LYMPHOMA of the breast can have varying morphologic characteristics, from diffuse increased density to a sharply marginated lesion. Primary lymphoma of the breast is a relatively rare phenomenon, and lymphoma is usually evident elsewhere in the body when detected in the breast.
As many as 7% of MALIGNANT LESIONS can be well circumscribed. Infiltrating ductal carcinoma is the most common diagnosis when the margins of a cancer are sharply marginated on the mammogram. Although it has been suggested that circumscribed margins indicate that a cancer is slow growing, circumscribed borders do not guarantee indolence.
METASTASES to the breast from another primary malignancy are frequently round and fairly well marginated. When multiple round densities are seenâ€”particularly when they occur unilaterally, a metastatic process should be considered. Although it is not common, virtually any other malignancy can be metastatic to the breast. When metastatic disease is found in the breast, the primary cancer is usually already known.
The most common lesion to metastasize to the breast is melanoma, followed by lymphoma and lung cancer. Metastatic lesions are usually multiple. Although metastatic lesions may be ill defined, they are frequently distinguished from primary breast malignancy by their often well-defined margins.
There are other extremely rare lesions that may be circumscribed. These include such unusual lesions as sarcomas, malignant fibrous histiocytomas, and myoid hamartomas. None has distinguishing features by imaging.