Mammographic Analysis of Breast Calcifications

Normal Breast Anatomy and Calcifications

Breast anatomy explains why calcific shapes or distributions suggest benign or malignant disease. The structures in which calcifications form influence calcification morphology and distribution appearances on mammograms.

The breast is composed of approximately 15 to 20 breast lobes extending from 7 to 9 breast ducts ( Fig. 3.1 ). Each lobe has 20 to 40 lobules and branches over a quarter of the breast. In each lobe, a collecting duct starts in the nipple and branches to smaller ducts, each ending in a terminal ductal-lobular unit (TDLU), which is the basic functional unit that produces milk and contains terminal ducts and a cluster of ductules and acini. A normal TDLU size ranges from 1 to 4 mm. The TDLUs and ducts are surrounded by interlobular stroma, extralobular stroma, and fat.

Calcifications forming within the breast ducts and acini/ductules include benign and malignant entities. For example, both large rodlike calcifications from benign secretory disease and fine-linear or fine linear–branching calcifications from ductal carcinoma in situ (DCIS) have pathognomonic morphologies reflecting the shape of ducts or ductules. Their shapes are very different from each other, even though they both form in ducts. The benign secretory disease calcifications are large and rodlike, as shown in Fig. 3.2 , because they form in larger ducts ( Fig. 3.2A ). Cancer calcifications are tiny and irregular because they generally start in smaller peripheral ducts and form in the interstices of cancers within pathologic ducts ( Fig. 3.2B ).

Calcifications forming in the location of interlobular stroma; in periductal locations; or in blood vessels, fat, or skin are usually benign. By understanding the pathologies in which calcifications form and how they interact with structures in which they develop, one can understand why calcification shapes and distributions suggest either cancer or benign entities.

Breast Ducts, Terminal Ductal Lobular Units, Pathology, and Calcifications

Benign round punctate calcifications often form in normal terminal breast acini or lobules. Benign round (BI-RADS size <1 mm for round) or punctate calcifications (<0.5 mm for punctate) are densely calcified and sharply marginated. These calcifications take on the round shape of the acini in which they form ( Figs. 3.3 and 3.4 ).

Calcifications forming in DCIS are not as dense or sharply marginated as benign round or punctate calcifications because they form within central tumor necrosis or secretions. DCIS is a noninvasive cancer, grows within mammary ducts, and is classified into high-grade, intermediate-grade, and low-grade types. The histologic architecture of DCIS includes the comedocarcinoma, which describes the appearance of the comedos of thick tenacious material extruding from the ducts on its cut surface at pathology, resembling pimples ( Fig. 3.5 ). The terms micropapillary, solid, and cribriform reflect the DCIS architecture showing small DCIS papillary extensions into the duct, a solid tumor, or a tumor with little cribriform holes, respectively.

Because DCIS grows within ducts, and because the comedo and micropapillary DCIS calcifications form in the center of the tumor, these calcifications may take on a ductal or linear shape. In cribriform DCIS, calcifications form in tiny tumor holes and take on a round, irregular shape, and are much smaller, less sharp, and more numerous than the benign round or punctate calcifications. The DCIS calcifications can be as small as 50 to 100 μm, which is equal to or smaller than the width of a human hair (approximately 100 μm). The classic appearance of DCIS calcification is the fine-linear or fine linear–branching individual calcifications, which have a 70% chance of malignancy ( Fig. 3.6A–B ). Also, DCIS is typically suggested by calcifications in linear or segmental distributions, in which individual calcifications can have any morphology, including amorphous, fine pleomorphic, coarse heterogeneous, or fine linear/fine-linear branching ( Fig. 3.6C–D ). Linear and segmental distributions have a 60% to 62% chance of malignancy. Figure 3.7 shows four example cases of DCIS with the correlation of mammographic features and pathologic findings. Not all calcifications seen on pathology can be seen on the mammogram.

Benign milk of calcium forms in enlarged cystic acini or ductules. Large rodlike calcifications representing benign duct ectasia, secretory disease, or plasma cell mastitis form in proximal ducts. Both milk of calcium and ductal ectasia have unique pathognomonic calcification shapes caused by their morphology and distribution, which allows them to be left alone.

Thus individual calcification morphologies and distributions are clues as to whether calcifications are associated with benign or malignant disease based on the anatomic structures in which they form ( Fig. 3.8 ).

Technique for Finding Calcifications

Calcifications are bright white specks, like grains of sand, to be detected against dense white glandular tissue. To find calcifications on two-dimensional (2D) screen-film mammography (SFM), radiologists use a bright light to illuminate the darker parts of the film. They view the mammogram with a handheld magnifying glass, enlarging the image and making calcifications easier to see. On 2D digital mammography, the radiologist adjusts the viewing monitor window and level to optimize the whiteness of the calcifications against the glandular tissues and then views the entire breast in magnified sections. The radiologist uses a systematic search pattern for calcifications to make sure no areas are missed. It is common to search the entire breast in a zigzag pattern or in strips, like mowing a lawn with a lawnmower or searching for a lost boat at sea in a rescue helicopter ( Fig. 3.9 ).

To find calcifications on tomosynthesis studies, the radiologist first reviews the conventional 2D mammogram or tomosynthesis-synthesized 2D mammogram to detect calcifications initially using the method described earlier. The 2D mammograms show a better overall view of calcifications compared with tomosynthesis slices alone. After finding calcifications on one 2D image, the radiologist looks for the calcifications on the orthogonal view to figure out the calcifications’ location within the breast and to determine whether the calcifications are grouped or scattered. The radiologist then knows where to search for the calcifications on individual tomosynthesis slices and confirms their location and grouping. Then he or she analyzes the targeted calcifications on the individual tomosynthesis slides in detail and looks for additional findings ( Fig. 3.10 ; ). Optical magnification and the systemic search of images using zigzag reading on the tomosynthesis slices are keys to detecting and evaluating tiny calcifications appropriately. Sometimes calcifications are detected initially on tomosynthesis slices because they are shown better than when obscured by overlapping breast tissue.

However, tomosynthesis may not be as effective as conventional 2D mammography in detecting microcalcifications. Tomosynthesis microcalcification detection varies in the literature, partly because of variations in image reconstruction techniques, and placing individual slice combinations into slabs to optimize calcification visualization. A subgroup analysis from a large study in England (Comparison of Tomosynthesis with Digital Mammography [TOMMY] Trial) showed that synthetic 2D plus tomosynthesis was less optimal than conventional 2D or 2D plus tomosynthesis in calcification detection or in detecting 11- to 20-mm DCIS (mostly detected by microcalcifications). Because of this, a 2D mammogram could possibly be required for optimal microcalcification detection when using tomosynthesis. Adding 2D mammography to tomosynthesis would increase radiation dose. However, other groups have suggested that the decreased dose from not using 2D mammograms may be worth the trade-off in not detecting a small numbers of DCIS cases (shown by calcifications). Tomosynthesis imaging improvements will continue to evolve, and no doubt there will be continuing changes in viewpoints on the use of synthesized 2D plus tomosynthesis views as the only imaging modality for calcification detection.

After detecting calcifications on conventional mammograms or tomosynthesis, 0.1-mm focal spot air-gap magnification mammography should be performed on all calcifications requiring further analysis (see Fig. 1.2 ). Air-gap magnification mammography increases the resolution power of the imaging system by about 1.8 times, separates closely grouped calcifications into their individual forms, sharpens individual calcification shapes for analysis, and displays faint calcifications not detected on standard mammography ( Fig. 3.11 ). Magnifying screen-film mammograms with a magnifying glass or electronically magnifying digital mammograms makes the original image bigger but does not sharpen the calcification shapes or show faint calcifications displayed only on true magnification mammography.

Calcification Classifications Based on Breast Imaging Reporting and Data System 2013

The American College of Radiology (ACR) BI-RADS provides terminology to describe benign and suspicious calcification morphology and distributions on mammography ( Box 3.1 ) as well as associated findings ( Box 3.2 ). The BI-RADS report of calcifications includes size of calcific group, location, morphology/distribution, associated findings, change from previous studies, BI-RADS Final Assessment category, and management recommendations ( Box 3.3 ). The BI-RADS helps radiologists classify calcifications into benign or malignant entities, prompting patient management, and provides powerful descriptors that help clinicians understand the seriousness of a finding. For example, the suspicious BI-RADS calcification term fine pleomorphic prompts the radiologist to classify the calcifications into BI-RADS Final Assessment category 4 Suspicious and prompts biopsy. The BI-RADS term large rodlike indicates benign ductal ectasia and prompts classification to BI-RADS Final Assessment category 2 Benign, return to screening. This chapter will illustrate and classify breast calcifications in benign or malignant categories using BI-RADS terminology.

Typically Benign Calcifications

Recognizing typically benign calcifications as “don’t touch” lesions allows the radiologist to leave them alone ( Box 3.4 ). Generally, benign calcifications are dense and have a unique morphology or location. Classic benign calcifications require no further workup and should prompt no further action. However, some benign calcifications mimic malignant calcifications ( Box 3.5 ), and tiny, subtle calcifications may be difficult to classify as benign or malignant in particular. However, recognizing clues for classification into appropriate BI-RADS lexicon terms may help the radiologist make the correct diagnosis. Box 3.6 shows characteristics of benign calcifications according to individual morphologies and distributions that distinguish them from malignancy. Artifacts mimicking calcifications are not included in the BI-RADS lexicon, but these fake “calcifications” will also be illustrated in this chapter ( Box 3.7 ).

BOX 3.4

Typically Benign Calcifications (American College of Radiology Breast Imaging Reporting and Data System Terminology): Don’t Touch Calcifications

• Skin calcifications

• Vascular calcifications (tram-track appearance)

• Coarse or “popcorn-like”

  • Fibroadenoma (mass with round, coarse peripheral calcifications)

• Large rodlike

  • Plasma cell mastitis or secretory disease (needle-like or sausage-shaped calcifications pointing toward the nipple; found in middle-aged women; benign entity, usually asymptomatic)

• Round calcifications

• Rim calcifications (with radiolucent centers)

  • Calcifying oil cysts

• Intraparenchymal calcifications

• Skin calcifications (obtain tangential views)

• Fat necrosis (postbiopsy, posttrauma)

• Dystrophic calcifications (be alert for such calcifications in women after biopsy for cancer)

• Milk of calcium (linear on the mediolateral view, smudgy on the craniocaudal view)

• Suture calcifications (cat gut, postradiation)

BOX 3.5

Benign Calcifications that Simulate Ductal Carcinoma in Situ

Skin Calcifications

• Scattered calcifications projecting as a group in one projection

• Sclerosing adenosis

• Fibrocystic change

BOX 3.6

Terms for Tiny Benign Calcifications

Individual Calcification Form

• Round

• Punctate

Calcification Distribution (if Individual Shapes are Benign, Stable)

• Grouped

• Regional

• Diffuse

BOX 3.7

Other Typically Benign Calcifications (Non-American College of Radiology Breast Imaging Reporting and Data System Terminology)

• Artifacts (deodorant, hair, fingerprints)

• Skin artifacts: antiperspirant, material in moles

• Calcifications in the fibrous implant capsule

• Calcifications in polyurethane-type implant coverings

• Silicon/paraffin injections

• Dermatomyositis

Skin Calcifications

Skin calcifications are tiny, the size of skin pores, are single or clustered, and often (but not always) have a calcific rim surrounding a radiolucent center. On mammograms, they look like little calcified eggshells within the white line of the skin ( Fig. 3.12 ). Skin calcifications deserve special attention because sometimes they have no lucent center and simulate grouped intraparenchymal calcifications that need biopsy ( Fig. 3.13 ). Attempts to needle localize skin calcifications will result in dismal failures because the hookwire tip will never project onto the calcifications (because the calcifications are in the skin and not in the breast).

Skin calcifications may be diffuse and bilateral, scattered, or occasionally grouped ( Fig. 3.14 ). The radiologist suspects skin calcifications if calcifications are in the breast periphery; if there are other skin calcifications on the mammogram; if they occur at sites where skin touches skin, such as in the axilla, the inframammary fold, in the cleavage areas; or if the calcifications show up on the first or last tomosynthesis slice (that displays the skin; Fig. e3.1 ; Video 3.2 ; Box 3.8 ).

BOX 3.8

Reasons to Suspect Skin Calcifications ^a

a A skin calcification study should be performed to exclude calcifications (see text).

• Peripheral location in the breast

• Location close to the skin surface on one view

• Location in the axilla, inframammary fold, or medial part of the breast

• Size similar to skin pores

• Other skin calcifications present

• Location on the first or last tomosynthesis slice

To prove that calcifications are in the skin, one does a “skin calcification study.” This is a mammographic procedure in which a metallic marker, usually a BB, is placed directly on top of the skin containing the calcifications. A technologist takes a mammogram tangential to the BB to show the calcifications in the skin, virtually excluding malignancy.

To do a skin calcification study, the technologist uses a mammographic compression plate containing a rectangular hole that has letters and numbers around the edge of the hole (a “localizing grid”). The technologist places the grid directly over the skin containing the calcifications and takes a mammogram ( Fig. 3.15 ). With the patient still in compression, the technologist looks at the mammogram to find the coordinates of the calcifications. A metallic BB is placed on the patient’s skin at the calcification grid coordinates, superimposing the marker on the calcifications. The mammogram is repeated to make sure that the marker superimposes on the calcifications. The technologist then takes a mammogram tangential to the skin marker. Skin calcifications will be directly under the BB in the skin. Intraparenchymal calcifications will be in breast tissue under the marker away from the skin ( Fig. 3.16 ). This process can take from 10 to 30 minutes, depending on whether the facility performs digital (10 minutes) or analog mammography (30 minutes).

It is a common mistake to put the localizing grid on the breast opposite from where the calcifications lie, particularly if the calcifications are in the lower breast. For example, calcifications at the 6 o’clock position (lower breast) will project in the midbreast on a craniocaudal (CC) view. One could mistakenly place the grid on the upper breast, thinking the calcifications are at the 12 o’clock position. A BB placed here will superimpose over the calcifications on the CC view. A tangential view to the 12 o’clock position BB will show no skin calcifications and mislead the radiologist (because the skin calcifications actually lie in the lower breast at the 6 o’clock position). Therefore it is important to look at both CC and lateral views to determine which part of the breast contains the calcifications so that the localizing grid can be placed on the skin containing the calcifications.

Vascular Calcifications

Arterial calcifications have a characteristic appearance of two parallel calcified lines, representing calcification in the arterial wall on edge, with sheetlike calcifications between the lines representing calcifications in the arterial wall en face ( Fig. 3.17 ). Early arterial calcification along vascular walls may simulate suspicious linear calcifications in DCIS. Seeing a noncalcified vessel leading to the calcifications may establish that the calcifications are in a calcified part of the blood vessel. Tomosynthesis may be helpful to visualize the noncalcified portion of blood vessels adjoining the calcified part, which resolves if the calcifications are arterial or not ( Fig. 3.18 ; Video 3.3 ). Magnification views of vascular calcifications will show arterial tram-track calcifications in two parallel lines, with coarse calcifications en face in the vessel wall between them, and also magnify and separate any grouped suspicious calcifications mimicking vascular calcifications from them ( Fig. 3.19 ).

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