Teaching Case

A 34-year-old female patient presented with a palpable lump in the right axilla. It is noteworthy that the patient had a pertinent medical history of bilateral prophylactic mastectomy due to BRCA2 mutation carrier.

The breast MRI in 2021 demonstrated post-surgical findings after bilateral mastectomy without remaining breast tissue detected beneath the skin (Figures 1a and 1b). Additionally, imaging of the axillae appeared normal (Figure 1c).

The breast MRI in 2023 demonstrated post-surgical findings after bilateral total breast reconstruction using autologous fat transfer (AFT), including bilateral retroareolar heterogeneity. Axial T1-weighted (Figure 2a) and contrast-enhanced T1-weighted fat-saturation (Figure 2b) images of the bilateral breasts revealed centrally located fat-containing masses with peripheral thin enhancement.

Axillary imaging displayed bilateral spherical-shaped masses that were hypointense on T1-weighted images. T1-weighted contrast-enhanced fat-saturated images revealed tiny areas of fat attenuation on heterogeneously highly enhanced axillary masses (Figures 3a and 3b). Ultrasound of the right axilla demonstrated a well-circumscribed, complex heterogeneous mass with small cystic appearances, echogenic internal bands, and areas of fat echogenicity (Figures 4a, 4b and 4c). A core biopsy was recommended for these axillary masses.

Autologous fat transfer (AFT) is frequently utilised in reconstructive and aesthetic contexts, including breast reconstruction following mastectomy [1]. Recently, total breast reconstruction using AFT was introduced by Piatkowski et al. [2].

Fat necrosis is one of the most frequently reported benign nonsuppurative inflammatory processes after AFT [3,4]. Rijkx et al. recently introduced additional imaging findings associated with AFT, including seroma, calcifications, and pectoral muscle fat depositions. Notably, they were the first to report pectoral muscle fat deposition in the literature, illustrating these deposits on MRI as changes in fat intensity within the muscle [5].

No studies have reported fat infiltration of axillary lymph nodes following AFT to date. However, our case demonstrated this phenomenon with pathological confirmation. Imaging findings revealed these fat deposits as small areas of fat attenuation on T1-weighted MRI images and as fat echogenicity on ultrasound.

Studies have shown that the axillary lymphatic pathway is the primary drainage route for breast tissue, where lymph is either directly channelled or transported via Sappey’s plexus into the axilla [6,7]. The migration of cells or particles through lymphatic channels has been observed in various contexts, indicating that fat cells introduced through AFT could follow these established lymphatic pathways. This provides a plausible mechanism for the presence of fat and its phagocytic cell deposits in axillary lymph nodes, as corroborated by our imaging and pathological findings (Figure 5).

Distinguishing benign enlarged axillary lymph nodes with tiny fat content from malignancy based on clinical findings alone is challenging, especially in high-risk patients like those with BRCA mutations. In a patient with a history of AFT, axillary fat infiltration should also be considered as a potential diagnosis, particularly if MRI reveals a fat signal in the lymph node that appears atypical on ultrasound. Accurate diagnosis often requires combined clinical and radiological evaluation, and biopsy.

Take Home Message / Teaching Points

• Autologous fat grafting may lead to the migration of fat cells through the breast’s lymphatic system into the axilla.
• Distinguishing fat infiltration from malignancy, especially in high-risk groups like BRCA mutation carriers, can be challenging based solely on clinical presentation.
• Accurate diagnosis often requires clinical and radiological evaluation, and biopsy.
• In a patient with a history of AFT, axillary fat infiltration should also be considered as a potential diagnosis, particularly if MRI reveals a fat signal in the lymph node that appears atypical on ultrasound.

All patient data have been completely anonymised throughout the entire manuscript and related files.