Pathologic nipple discharge is typically unilateral, single-pore, spontaneous and persistent, bloody or occurring during postmenopausal phase. According to the patient age, clinical examination with mammography, US and cytological examination of the nipple discharge should be the first line diagnostic approaches. However, no general consensus exists in the medical literature, and cytological examination of nipple discharge has not been found to provide any significant complementary value [1, 6]. In case of inconclusive mammographic or ultrasonography findings, a second line examination should be considered [17].
Istomin et al. [6] recently reported that galactography is not an obsolete investigation for evaluating pathologic nipple discharge, and it remains a practical, valuable and cost-effective procedure. Conventional FFD-galactography can still represent a useful diagnostic procedure for evaluating patients with pathologic nipple discharge, since it can provide the location of the underlying lesion when a single duct discharge is identified, in contrast with cytology that can be falsely negative in a high proportion of cases [6, 18] and is also unable to provide information on lesion location. Notably, data regarding lesion location is very important for surgical planning. In this field, it has been reported that galactography lesion localisation improves the diagnostic performance of surgical biopsy from the 67% in non-studied patients to 99% in patients receiving a galactogram [18].
The galactogram may show normal findings as well as the presence of ductal dilatation, single or multiple filling defects or filling stops. In particular, suspicious findings on galactogram include distortion and ductal wall irregularity highly suggestive of malignancy, even if it is quite challenging to distinguish between malignant and benign lesions only relying on a galactogram [19].
However, FFD-galactography provide only two-dimensional images, not always allowing for accurate detection of an intraductal lesion due to overlapping effect and for precise lesion localisation in the three-dimensional space. Schulz-Wendtland et al. [16] recently reported a first approach with DBT-galactography (“galactomosynthesis”) in only five patients concluding that this kind of imaging tool could be a useful addition to complementary breast diagnostics and could lead to a renaissance of this method. However, their preliminary findings needed to be confirmed in a larger patient population comparing DBT-galactography with FFD-galactography with intra-individual design.
To the best of our knowledge, this is the first study comparing DBT-galactography with FFD-galactography in patients with pathologic nipple discharge. By assessing 49 patients with pathological nipple discharge, we found a significantly higher sensitivity and accuracy of DBT-galactography (95% and 96%) than those of FFD-galactography (77% and 80%, respectively) without any trade-off on terms of sensitivity (100% for both techniques). In other words, the gain in accuracy was entirely due to a higher sensitivity.
Our study showed that DBT galactography could represent an accurate tool for identifying and localising intraductal lesions being the cause of pathologic nipple discharge, notably also characterised by a higher inter-observer agreement as compared with FFD-galactography (0.86 versus 0.78).
From a general viewpoint, our results confirm the role of DBT in breast imaging, even though further studies of DBT-galactography on larger patient population are still required.
Although DBT-galactography could represent a fast, quite inexpensive, widely available and accurate examination in the field of pathologic nipple discharge, it still remains an invasive procedure to be performed only in case of nipple discharge at the time of the examination and could cause discomfort and pain [1]. On the other side, DBT-galactography uses the same conventional projections of FFD-galactography without significant technical difference. In case of validation on larger series, DBT-galactography could replace FFD-galactography in the workflow of patients with nipple discharge.
Importantly, DBT-galactography could not allow an accurate differential diagnosis between benign or malignant papillary lesions. In this field, MRI provides details in addition to the morphological information of DBT-galactography with a higher potential for lesion characterisation basing on the enhancement features [1, 10, 20]. In fact, MRI allows an accurate imaging of both breasts detecting multifocal, multicentre or occult lesions evaluating at the same time all the ductal system also in the deepest areas of the breast as compared with galactography which allows to study only segmental ductal areas. MRI has also been reported as an accurate tool for the management of nipple discharge especially in case of negative or inconclusive mammography or for a correct preoperative evaluation; despite the higher costs, it allows to exclude malignant lesions with high accuracy and to avoid unnecessary surgical procedures with a crucial role for clinical management [20, 21]. Of note, in our study, MRI has been considered as the next step in case of patients with negative findings on both FFD- and DBT-galactography. However, further studies comparing unenhanced plus contrast-enhanced MRI with DBT-galactography are needed. Finally, the recent introduction of contrast-enhanced mammography [10] needs to be investigated also in patients with pathological nipple discharge to allow for diagnosing benign, borderline or malignant lesions associated with this clinical condition.
We have also to consider that contraindications do exist for DBT-galactography mainly represented by severe allergy to iodinated contrast material, nipple retraction or a history of a prior nipple surgery that would invalidate the examination, as is for conventional galactography [1].
Our study has limitations. First, we did not evaluated differences in terms of average glandular dose (AGD) between the two techniques. This was due to the fact that we used the COMBO mode in which the two imaging techniques are acquired in a combined fashion that prevented a separation of the two doses. However, we can consider that entire AGD was 1.94 ± 0.64. This AGD, even all attributed to the DBT, means that it still remains acceptable for the clinical use, and in case of validation on larger series, the use of DBT-galactography with synthetically reconstructed images will certainly reduce the previous AVG value. Second, we studied a relatively small number of patients that, however, allowed to show a significant difference in terms of sensitivity and accuracy in favour of DBT, but not to get information about possible false positive cases that we did not encounter in our case series for both techniques.
In conclusion, we showed that DBT-galactography provided a sensitivity and a diagnostic accuracy higher than that of FFD-galactography. It could represent a reliable and largely available diagnostic tool in patients with pathologic nipple discharge, potentially avoiding the need for MRI in this clinical setting.