Radiologia Brasileira - Publicação Científica Oficial do Colégio Brasileiro de Radiologia

^IInstitute of Radiology at Hospital das Clínicas of Faculdade de Medicina da Universidade de São Paulo
^IIDepartment of Radiology at Faculdade de Medicina da Universidade de São Paulo

Mailing Address

Mammography, ultrasound and magnetic resonance imaging play amajor role in detection, diagnosis and management of breastdiseases. Besides these methods, other technologies have beenconsidered for breast study, such as positron emission tomography(PET), spectroscopy, computed tomography, tomosynthesis andcontrast-enhanced ultrasound. However, additional studies arenecessary to determine the cost-benefit ratio of thesemethods.

Mammography still remains as the major breast imagingtechnique. It is the modality of choice for population breastcancer screening in asymptomatic women, and is the first imagingtechnique indicated for evaluating the majority of breastalterations. There is ample consensus that the mammographicscreening reduces mortality from breast cancer in asymptomaticwomen^(1,2). Other benefits from the earlydetection include increase in the number of therapeutic options,in the probability of treatment success, and in the survival.

Presently, there are two modalities of imaging in terms ofmammographic equipment. The first generation is constituted bythe screen-film technique characterizing the conventionalmammography. The second generation is represented by solid-statedetectors defining the digital mammography. The technique ofmammographic images acquisition (digital detector versusscreenfilm) defines the majority of differences betweenconventional and digital mammography. In the conventionalmammography, the film is the media for recording, displaying andstoring mammographic images, and, although generatinghigh-spatial resolution images, this technique leaves very littleroom for improvements.

In the digital mammography, the processes of imagesacquisition, display and storage are independent and may beindividually improved; additionally, the analysis of digitalmammographic images in workstations with high-resolution displaysallows images processing for enhancing and improvingvisualization. The digital mammography also includes an array ofnew technologies like CAD (computer aided detection),tomosynthesis, use of intravenous contrast agents, and imagesinterpretation at distance (teleradiolology).

Recently, Pisano et al.⁽³⁾ have comparedconventional and digital mammography in a study with 42,760women, and concluded that the overall accuracy of theconventional and digital mammography for breast cancer screeningwas similar for both methods. However, the digital mammographyhas presented higher accuracy in some specific subgroups ofwomen, namely: women aged less than 50 years, pre- andperimenopausal women with radiologically dense breasts.Notwithstanding, a great deal of debate has raised questions onthe meaning and reasons for the higher accuracy of digitalmammography in these subgroups. It is important to note that,currently, both the conventional and the digital mammography canbe employed for population breast cancer screening. A consensusis still to be reached about the preferential use or conventionalor digital mammography, even in specific subgroups of women.

The mammography capability to detect breast cancer variesamong women according to some factors, and the most important oneis the radiological breast density; the mammography sensitivitybeing lower in dense breasts than in those where adipous tissuepredominates⁽⁴⁾. For this reason, supplementaryimaging methods for dense breast screening and evaluation,particularly ultrasound and magnetic resonance imaging, have beenstudied.

Ultrasound is the main adjuvant method in conjunction withmammography and clinical examination for detecting and diagnosingbreast diseases⁽⁵⁾, and has increasingly beenused for years. Main indications and potential indications forbreast ultrasound are: differentiation and characterization ofsolid nodules and cysts identified by mammography or clinicalexamination; guidance in interventional procedures; evaluation ofyoung patients, pregnant and breastfeeding women with breastsalterations; investigation of mastitis abscesses; evaluation ofpalpable nodules in radiologically dense breasts; analysis ofbreast implants; locoregional staging of breast cancer;characterization of focal asymmetries which may correspond tonodules; evaluation of response to neo-adjuvant chemotherapy;and, as an adjuvant method, in the screening of breast cancer inwomen with radiologically dense breasts, aiming at identifyinglesions missed by previous clinical examination and mammography.This latest indication is quite controversial and must not beutilized as an alternative to mammography, considering itslimitations regarding detection and characterization ofcalcifications, architectural distortions and nodules localizedin areas with predominance of adipous tissue. Ultrasoundlimitation for detecting microcalcifications is particularlyrelevant, since this is the most frequent finding in ductalcarcinomas in situ.

Breast magnetic resonance imaging also has increasingly beenused as an adjuvant method for characterization of malignantbreast lesions and therapy planning. Many indications have beenidentified and evaluated, and usually are based principally onthe high sensitivity of the method for detecting breast cancer,including lesions which have been missed by conventional methods(mammography and ultrasound). The use of magnetic resonanceimaging has been investigated for the screening of women at highrisk for breast cancer; screening of synchronous neoplasms in thecontralateral breast of women diagnosed with cancer; in thesearch for an occult primary lesion in patients with axillarymetastasis; characterization of dubious findings at mammographyor ultrasound; determination of the local extent of the breastcancer; verification of the presence and extent of residualdisease, especially in cases of histologically positive surgicalmargin; evaluation of response to neo-adjuvant chemotherapy;differentiation between surgical scar and tumor recurrence inpatients previously treated for breast cancer; evaluation ofbreast implants integrity. Magnetic resonance imaging must not beutilized as a criterion for indication, or not, of histologicalinvestigation of clinically, mammographically or sonographicallysuspect lesions. Also, there is no study providing scientificbasis for the use of MRI in the screening of breast cancer inwomen who are not at high risk for the disease.

After the detection of an alteration by any imaging method,its characterization is necessary for establishing the benignityor potential malignancy of the lesion. The likelihood ofmalignancy is determined principally by evaluation of themorphological and progression characteristics of the lesion(decrease, stability and increase along time). Many times, thepractical utility of mammography, breast ultrasound and magneticresonance imaging is limited by the relatively low specificity ofthese methods, leading to biopsy or early follow-up. Thislimitation results from the known findings overlapping of benignand malignant lesions in these imaging methods, but also isrelated to the standardization and understanding of thepredictive value of each criterion utilized for findingsinterpretation.

Two studies included in the present issue of RadiologiaBrasileira address the criteria for interpretation offindings and characterization of breast lesions.

One of them evaluates the predictive value for malignancy ofBI-RADS^® categories 3, 4 (A, B, C) and5⁽⁶⁾ in non-palpable breast lesions. TheBI-RADS^®(6), standardizing the definitionof criteria employed for characterizing lesions at mammography,ultrasound and magnetic resonance imaging, has contributed tofacilitate the comparison between different studies, and,consequently, the understanding of the findings. Additionally, ithas established categories for final evaluation utilized forclassifying nodules according to their probability of malignancy,facilitating the subsequent steps.

The category 0 indicates an incomplete characterization of thealteration, an additional evaluation being required. Categories 1and 2 indicate no mammographic evidence suggesting malignancy.Category 3 indicates the presence of probably benign findings(less than 2% chance of malignancy) for which the preferentialprocedure is the early follow-up. The category 4 is related to asuspect abnormality for which biopsy should be considered, and issubdivided into A, B and C. Category 4A indicates findingsrequiring some intervention, but with low suspicion formalignancy; malignant histology is not expected and a six-monthor routine follow-up after biopsy or benign cytology isappropriate. Category 4B includes lesions with intermediatesuspicion for malignancy; the findings in this category require acareful anatomoradiological correlation and the follow-up ofbenign findings in the biopsy of these lesions depends on thiscorrelation. Category 4C indicates moderate concern but notclassic for malignancy like category 5. Category 5 is dedicatedto findings highly suggestive of malignancy, and category 6 isutilized in cases where there is already a biopsy indicating amalignant lesion. There are not many studies allowing a cleardefinition of which lesions are in categories 4A, 4B and 4C, aswell as their respective positive predictive value.

The other study analyzes the predictive capability of breastnodules sonographic characteristics. Currently it is known that aseries of characteristics are associated with a higher risk formalignancy. These characteristics are: poorly circumscribedmargins, irregular shape, complex echogenicity, posterioracoustic shadowing, nonparallel orientation, echogenic halo, andchanges in adjacent tissues. The sonographic identification ofprobably benign nodules, which are candidates to an earlyfollow-up, requires the ruling out of any sign of malignancy, andthe presence of an association with benignity criteria. Thisaspect implies a careful sonographic analysis, and theidentification of any sign suggesting malignancy indicates theneed for biopsy. The biopsy of a solid nodule found at ultrasoundshould not be disregarded based only on a benign finding,circumscribed margins, for example.

A consensus is being sought on solid nodules that can besonographically classified as probably benign. Stavros etal.⁽⁷⁾ have demonstrated that nodules with nosign of malignancy, with either ellipsoid shape and pseudocapsuleor the presence of two or three lobulations and pseudocapsule, oran intense homogeneous hyperechogenicity, associated with anegative predictive value for malignancy of 99.5%; withsensitivity of 98.4%. Chala et al.⁽⁸⁾ havereported that round-, ovoidshaped or lobulated nodules with lessthan three lobulations, with circumscribed margins, parallelorientation and absence of an accentuated hypoechogenicity,posterior acoustic shadowing, calcifications and alterations inadjacent tissues, independently from echotexture and presence ofpseudocapsule, presented sensitivity and negative predictivevalue for cancer, respectively of 98.1% and 99%.

The progress in the understanding of the predictive value ofthe different criteria utilized isolatedly or in combination forcharacterizing breast lesions detected by different imagingmethods is a significant step towards reducing the number ofbiopsies with benign results. However, it is important to notethat imaging techniques are not histological diagnostictechniques. Therefore, the biopsy with histological investigationpurposes will remain necessary for many breast lesions, and themajority of such lesions, fortunately, will be benign.

REFERENCES

1. Humphrey LL, Helfand M, Chan BK, Woolf SH. Breast cancer screening: a summary of the evidence for the U.S. Preventive Services Task Force. Ann Intern Med 2002;137:347–360.

2. Fletcher SW, Elmore JG. Mammographic screening for breast cancer. N Engl J Med 2003;348:1672–1680.

3. Pisano ED, Gatsonis C, Hendrick H, et al. Diagnostic performance of digital versus film mammography for breast-cancer screening. N Engl J Med 2005;353:1773–1783.

4. Barton MB, Elmore JG, Fletcher SW. Breast symptoms among women enrolled in a health maintenance organization: frequency, evaluation and outcome. Ann Intern Med 1999;130: 651–657.

5. Basset LW, Kim CH. Breast imaging: mammography and ultrasonography. Magn Reson Imaging Clin N Am 2001;9:251–271.

6. ACR Breast Imaging Reporting and Data System. Breast Imaging Atlas. 4th ed. Reston: American College of Radiology, 2003.

7. Stavros AT, Thickman D, Rapp CL, Dennis MA, Parker SH, Sisney GA. Solid breast nodules: use of sonography to distinguish between benign and malignant lesions. Radiology 1995; 196:123–134.

8. Chala L, Endo E, Kim S, et al. Gray-scale sonography of solid breast masses: diagnosis of probably benign masses and reduction of the number of biopsies. J Clin Ultrasound 2007;35:9–19.

Mailing Address:
Dr. Luciano F. Chala
E-mail: lucianochala@ terra.com.br