The rate of breast-conserving surgery among Asian women with breast cancer (50–60 %) is relatively lower compared with the rate among American or European patients (70–80 %) (15, 16). This difference may be attributed to the small- to moderate-sized breasts and dense breasts of Asian women (reference). Therefore, the incidence of breast reconstruction after partial or total mastectomy may be higher among Asian breast cancer patients.
Fat necrosis can appear as a postoperative complication after breast reconstruction, and the incidence of fat necrosis after flap-based breast reconstruction is approximately 4–25 % of patients treated with breast-conserving surgery and adjuvant radiotherapy for breast cancer (8, 9, 11, 12, 17, 18). In the current study, the incidence of fat necrosis was 11.6 %. Even if fat necrosis is only a minor complication, physicians should carefully evaluate their patients because it is necessary to distinguish it from tumor recurrence (19-21).
The identification of fat necrosis can be achieved with clinical examination, mammography, ultrasonography, MRI, or PET/CT (13). Several studies have reported the imaging findings of fat necrosis using various imaging modalities (8, 17, 18, 22, 23). Patient who received breast reconstruction for breast cancer can detect a newly formed nodule, including fat necrosis or tumor recurrence. However, because the Asian female patients commonly have high density of breasts, it would be not easy to distinguish between normal parenchyma and newly formed nodule (24).
The mammographic findings of fat necrosis typically show coarsely calcified nodules with occasional lipid-containing complex cysts, increased opacity, microcalcification, or architectural distortion. On the other hand, the ultrasonographic findings of fat necrosis are variable (ranging from a simple or complex cyst to a complex solid nodule). Although solid lesions typically have well-circumscribed margins, they occasionally have indistinct or spiculated margins mimicking carcinoma (18, 25-28). Cystic lesions appear as complex cysts with a mural nodule, complex cysts with echogenic bands, or round anechoic lipid cysts (29, 30). Breast MR imaging of fat necrosis also shows a wide range of findings. The internal signal characteristics may be identical to those of the adjacent fat or there may be no enhancement after the administration of contrast material, indicating that the lesion is benign and consistent with fat necrosis. However, contrast enhancement may be present in early periods, complicating efforts to distinguish this entity from recurrent cancer. Enhancement can be focal or diffuse and homogeneous or heterogeneous. Furthermore, enhancement patterns may vary from slow, gradual enhancement to rapid enhancement, and a washout curve may be present (13, 25, 29, 31).
Several surgeons have reported that symptomatic fat necrosis led to a significantly worse cosmetic outcome and that asymptomatic fat necrosis did not demonstrate evidence of cosmetic abnormality (8, 9, 32, 33). However, they did not observe a significant deterioration in cosmetic outcome for patients who developed fat necrosis. Most cases of fat necrosis may be resolved without intervention or do not show any changes (17, 34). In this study, more than 60 % of fat necrosis cases were spontaneously resolved without any procedures. Around 2 years after the occurrence of fat necrosis, the size of the necrotic nodules was decreased by half and remained constant without significant changes.
According to the literature, the timing of fat necrosis development after breast reconstruction varies widely. Wazer et al. reported the development of fat necrosis as early as 7.5 months (35). Chen et al. reported fat necrosis at a median time of 66 months (36). In this study, the mean period until the detection of fat necrosis was 21.1 months from surgery with clinical examination or imaging modalities including mammography, ultrasonography, or breast MR imaging. In addition, the location of fat necrosis after breast reconstruction has been reported to be different based on the surgical techniques used. As fat necrosis is affected by poor blood supply from the breast or flap tissues, the location could be identified with various techniques.
Several risk factors associated with the occurrence of fat necrosis after surgery have been proposed, which include neoadjuvant chemotherapy, adjuvant radiotherapy, high BMI, and uncontrolled underlying disease (37-40). However, there was no significant factor associated with fat necrosis in our study. The performance of neoadjuvant chemotherapy was only associated with fat necrosis in univariate analysis but not multivariate analysis.
In our study, the radiologist who is an expert in breast with more than 15 years of experiences performed and analyzed about the fat necrosis. If she had been a less experienced radiologist, there would be more cases which requires the pathologic confirmation. In addition, the fat necrosis after breast reconstruction could not be observed as prospective study and this is another limitation in our study.
If the imaging findings of fat necrosis reveal a suspicious lesion, pathologic confirmation should be obtained to rule out tumor recurrence. However, as fat necrosis may resolve independently within 2–3 years, the management of fat necrosis can be performed only through observation if fat necrosis is highly probable or pathologically confirmed. An understanding of the natural course of fat necrosis would be helpful for the management of fat necrosis.
In conclusion, fat necrosis after breast reconstruction for breast cancer is relatively common; nevertheless, it is only a benign complication. Sometimes, it can mimic tumor recurrence, and pathologic confirmation is needed. However, if fat necrosis after breast reconstruction is confirmed, it can only be observed based on its natural course and more than half of the cases will be resolved within 2–3 years.