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Detection of Breast Abnormalities on Enhanced Chest CT: Correlation with Breast Composition on Mammography

Mammography and breast sonography are currently the preferred modalities for screening and diagnosing breast cancers. On mammography, breast composition is classified into four types as defined by the Breast Imaging Reporting and Data System (BI-RADS) (1). Increased breast composition not only impairs the detection of breast lesions, but it also has been considered as a risk factor of breast cancer (2). Breast sonography is useful for evaluation of masses or asymmetries. There are several studies that investigated the sonographic findings for differentiating benign breast lesions from malignant breast lesions. With the increasing use of chest computed tomography (CT) in a variety of diagnostic pathways, breast abnormalities are being identified more frequently on chest CT (3). It is important that radiologists should not overlook breast lesions on chest CT and they should be aware of CT appearances of malignant and benign breast lesions (4). In a previous study, chest CT showed a higher interreader agreement for readings of breast composition as compared to mamDetection of Breast Abnormalities on Enhanced Chest CT: Correlation with Breast Composition on Mammography 조영증강 흉부단층촬영검사에서 유방 병변의 발견: 유방 실질의 구성과의 연관성


INTRODUCTION
Mammography and breast sonography are currently the preferred modalities for screening and diagnosing breast cancers.
On mammography, breast composition is classified into four types as defined by the Breast Imaging Reporting and Data System (BI-RADS) (1). Increased breast composition not only impairs the detection of breast lesions, but it also has been considered as a risk factor of breast cancer (2). Breast sonography is useful for evaluation of masses or asymmetries. There are several studies that investigated the sonographic findings for differentiating benign breast lesions from malignant breast lesions.
With the increasing use of chest computed tomography (CT) in a variety of diagnostic pathways, breast abnormalities are being identified more frequently on chest CT (3). It is important that radiologists should not overlook breast lesions on chest CT and they should be aware of CT appearances of malignant and benign breast lesions (4).
In a previous study, chest CT showed a higher interreader agreement for readings of breast composition as compared to mamjksronline.org J Korean Soc Radiol 2017;76(2):96-103 mography and breast composition on chest CT might provide additional information for predicting risk of breast cancers (5).
The purpose of our study is to investigate the capability of enhanced chest CT for detecting breast abnormalities and to assess the influence of breast composition on this detectability. Moreover, we tried to evaluate the CT features helpful in differentiating malignant breast lesions from benign breast lesions.

MATERIALS AND METHODS
The Institutional Review Board of our institution did not require any approval or informed patient consent for this type of retrospective study.

Patient Population
From January 2000 to December 2013, we retrospectively identified 983 patients who underwent mammography, breast sonography, and enhanced chest CT within one month at a tertiary medical center. Patients with known breast cancer and a history of surgery for breast cancer were excluded. Finally, 75 women (age range, 35-80 years; mean age, 53.6 years), who had abnormalities on breast sonography, were included in this study.
Clinical indications for enhanced chest CT in these 75 patients included health screening (n = 35), staging work-up for non-pulmonary malignancies (n = 18), various manifestations such as fever, dyspnea, and chest pain (n = 14), abnormality on plain radiography (n = 6), and evaluation of pulmonary neoplasms (n = 2).

Imaging Technique
CT scans were acquired using a multi-detector CT system (So- Breast sonography was performed with a sonographic unit (Acuson Antares, Siemens Medical Solutions, Inc., Malvern, PA, USA) using a standard 5-13 MHz linear array transducer by radiologists who had breast sonography experience ranging from 2-3 years (including reader 1-4).
All patients in this study underwent two-view mammography (both craniocaudal and mediolateral oblique views) of both breasts by a mammography unit (Affinity, Lorad/Hologic Company, Danbury, CT, USA) with the film-screen system (Carestream CR reader, Kodak DirectView, Rochester, NY, USA).

Image Review
All mammography and breast sonography examinations were retrospectively reviewed in consensus by two radiologists (reader 1, 2) who had two and three years of experience. On breast sonography, the reviewers (reader 1, 2) selected the largest lesion as the target lesion in each patient and described the largest diameter, location and BI-RADS assessment categories; category 0 corresponds to an incomplete result with need for additional imaging evaluation; category 1, corresponds to a negative finding; category 2, corresponds to a benign finding; category 3, corresponds to a probably benign finding; category 4, corresponds to a suspicious result ranging from low suspicion to high suspicion for malignancy; category 5, corresponds to a result that is highly suggestive of malignancy; and category

Statistical Analysis
In evaluation of detectability of chest CT and mammography, differences according to the BI-RADS type of breast composition as well as the two types of breast composition were analyzed by chi-square test. Logistic regression was conducted to assess the contribution of the two types of breast composition and size and enhancement of target lesions to detectability of enhanced chest CT.
We compared the differences in CT morphology between benign and malignant breast lesions by the t-test for continuous variables or chi-square test for categorical variables. A p-value of less than 0.05 was considered to indicate statistical significance.
This has also been known that supplemental breast sonography can aid in detection of breast cancers in women with dense breasts (11). In our study, about half of the cases with breast abnormalities were identified on enhanced chest CT. Thus for women who undergo only chest CT, it may provide information on breast lesions and further evaluations including mammography or breast sonography can be suggested, especially in high risk patients.
It is known that the features favoring a benign lesion on breast sonography were oval shape, parallel orientation to the skin, circumscribed margin, abrupt boundary, and anechoic and hyperechoic pattern. On the other hand, malignant features on breast sonography were irregular and round shape, non-parallel orientation, microlobulated, indistinct, angular, or spiculated margin, and boundary of echogenic halo (12)(13)(14)(15). There are several studies which reported the CT features of incidental breast lesions suggestive of malignancy, including irregular or spiculated mar- gins, irregular shape, and rim enhancement. A washout pattern on postcontrast images and diffuse regional enhancement had high positive predictive values for malignancy (16)(17)(18)(19). Similarly, in our study, malignant breast lesions were more irregular in shape and they demonstrated a non-circumscribed margin more frequently, compared with benign lesions (p = 0.023 and 0.031).
But the difference in enhancement between malignant and benign lesions was not significant (p = 0.646).
March et al. (20) studied 35 patients of breast cancer for evaluating detection of axillary lymph nodes on preoperative chest CT scan. They reported a positive predictive value of 89%. Another study concluded that chest CT in prone position with 5 mm sections accurately predicted axillary lymph node involvement in breast cancer (21). Results of our study correlated with conclusions of these studies. In our study, additional findings such as axillary lymphadenopathy (p = 0.006) and skin thickening (p = 0.005) were more frequently observed in malignant breast lesions.
There are several limitations in our study; first, the small study population and the retrospective nature of the study design may have reduced the power of this study. Contrast-enhanced chest CT for a variety of indications may be less sensitive than dedicated breast CT in detecting and characterizing breast lesions (22).
Also various types of CT acquisition and injection protocols were used during the period. Therefore, delayed-phase scanning time may not have been standardized. It was limited to detect breast tumors and measure the accurate size of tumors, because breasts were compressed by gravity in the supine position. Another limitation was that there might be a discrepancy between the target lesions on chest CT and breast sonography, although we compared each of the lesions with their location and size. Because we did not consider all lesions on breast sonography, but we only considered the largest lesions, it may have influenced the detectability of breast lesions on chest CT.
Our study suggested that about half of the cases (45.3%) demonstrated breast lesions on enhanced chest CT which corresponded with target lesions on sonography. Also, breast composition defined on mammography did not affect the detectability of enhanced chest CT for breast lesions. Therefore, cautious interpretation of enhanced chest CT might help detect breast abnormalities covered with dense parenchyma.