Towards Standardized Language to Describe the Pathological Enhancement of the Nipple in NAC-Infiltrating Breast Tumors: A Retrospective Case Series Study

Background: The normal pattern of nipple enhancement on magnetic resonance imaging (MRI) is defined based on healthy individuals, as it correlates with the structural anatomy of the nipple–areola complex (NAC). Understanding the normal range of nipple morphology and enhancement on MRI allows radiologists to better identify abnormalities. Some authors have previously detailed the morphology and characteristics of nipple–areola complex enhancement, both in normal and pathologically infiltrating conditions. Our aim is to present a case series involving a population of women with breast cancer infiltrating the NAC, retrospectively evaluated at our institution. Furthermore, based on previously published literature and our own experience, we intend to propose potential standardized language to describe tumor-infiltrating NAC enhancement on MRI and compare it with CT and PET findings. Methods: Our study included 110 breast cancer patients with NAC infiltration, who were referred to our hospital from August 2023 to July 2024. All patients were candidates for neoadjuvant chemotherapy and therefore underwent MRI and CT; 33 of them also underwent PET/CT. We distinguished the MRI enhancement pattern based on morphology and intensity. There were three types of morphology: SLE (superficial linear enhancement) at the skin level, NEZ (non-enhancing area immediately below the SLE), and INE (nipple enhancement below the NEZ but above the nipple base). In INE, the pattern could be linear or patchy. Depending on the intensity, the enhancement could be minimal, mild, moderate, or marked. The enhancement on CT depended on the distribution of pathological tissue in the infiltrated NAC and could be present or absent; it could involve the nipple base, the nipple body, or both. For quantitative analysis, we used the maximum standardized uptake value (SUV) measured in early-stage PET/CT images, obtained by delineating a three-dimensional volume of interest (VOI) on the NAC. Results: In our population, the most represented enhancement pattern was INE (110), while slightly less than half of the patients showed invasion of the NEZ (49). Approximately one quarter of the patients presented linear ductal INE (36), while the majority presented patchy INE (74). On CT and PET/CT, NAC enhancement was detectable in almost all patients (102), mainly involving the base and the body together. Correlation analysis in the following pairs of variables showed a high association, with a Kendall’s tau value greater than 0.7 (p < 0.001): (1) involvement of the NEZ on ce-MR and pattern of nipple involvement on ce-CT (CT score); (2) morphological pattern of INE on ce-MR (INE score) and intensity of INE enhancement on MR; and (3) pattern of nipple involvement on ce-CT (CT score) and intensity of INE enhancement on MR. The calculated mean SUV of pathological NACs on PET/CT for early-stage images was 3.59, while the mean SUV of contralateral normal NACs was 2.12. The calculated mean NAC-SUV ratio was 1.7. Conclusions: Although pathological involvement of the NAC cannot always be assessed in the final surgical specimen due to the effects of neoadjuvant chemotherapy, so the “gold standard” of histological reference is missing, MRI and CT with morphology and enhancement descriptors, and additionally PET/CT with SUV measurement can, in our opinion, provide valuable information on the infiltrated nipple. Standardized language for describing breast tumors infiltrating the NAC is desirable to ensure consistent interpretation across different radiologists.