Beyond the normal breast anatomy: A case of benign bilateral accessory breasts

Abstract

Accessory breast tissue, or polymastia, is a rare developmental anomaly resulting from incomplete regression of the embryonic mammary ridge. While often asymptomatic, accessory breast tissue can respond to hormonal fluctuations, leading to pain, swelling, or lactation. We present the case of a 39-year-old woman with bilateral axillary accessory breast tissue and accessory nipples, who reported cyclical pain and lactation from the accessory tissue during nursing. Her symptoms, exacerbated during menstruation, significantly impacted her quality of life. Diagnostic imaging confirmed benign glandular tissue, and surgical excision was performed for symptom relief. Histopathological analysis revealed no malignancy. This case highlights the clinical importance of recognizing accessory breast tissue as a potential source of cyclical axillary symptoms and underscores the need for timely diagnosis and tailored surgical management.

Introduction

Accessory breast tissue (ABT), or polymastia, arises from the persistence of embryologic mammary tissue along the milk line, which extends from the axilla to the groin. Although considered rare, with a prevalence ranging from 0.4% to 6%, ABT is not insignificant and may present bilaterally in up to one-third of affected women.^1,2 Additionally, global prevalence rates range from 0.2% to 6%, with higher detection among women and those of Asian descent.^3–5 The axilla is the most frequent site of occurrence, where ABT can mimic more common benign lesions such as lipomas or lymphadenopathy. ⁶ While ABT may remain unnoticed for years, it is hormonally responsive and can become symptomatic during puberty, menstruation, pregnancy, or lactation. The tissue’s ability to undergo physiological and pathological changes similar to normal breast tissue, such as engorgement, pain, and neoplastic transformation, necessitates clinical attention. ⁷

To better characterize the variability in ABT presentation, the Kajava classification system is commonly used. ⁸ This system categorizes ABT into eight classes based on the presence or absence of glandular tissue, nipple, and areola, providing a useful framework for clinical diagnosis and treatment planning.

Despite its potential impact, ABT is often underdiagnosed or misclassified due to its variable presentation and resemblance to other soft tissue masses.^2,9 Studies have reported delays in diagnosis averaging over 3 years, leading to prolonged patient discomfort and, in some cases, unnecessary interventions.^9,10 For some patients, the associated cosmetic concerns and functional limitations, particularly when ABT interferes with arm movement or causes visible swelling, can substantially affect their quality of life. ¹ Accurate diagnosis through physical examination and imaging, followed by appropriate surgical or nonsurgical management, is essential to improving outcomes. Ultrasound remains the first-line imaging modality for evaluating axillary masses, while mammography or MRI may be utilized when further characterization is needed, particularly in cases with suspicion of malignancy or unclear clinical findings.^11,12

This case report presents a unique case of bilateral axillary ABT in a 39-year-old woman, notable for its chronic cyclical pain, presence of accessory nipples, and lactation during nursing. Lactation from ABT is an uncommon phenomenon, and bilateral presentations with hormonal responsiveness are especially rare. Bilateral axillary involvement with hormonally responsive symptoms is infrequently reported in the literature.^13,14 This addition helps underscore the clinical significance and uniqueness of our case.

The rarity of this presentation, along with its long-standing symptoms and hormonal sensitivity, underscores the importance of early recognition and definitive treatment.

Case report

A 39-year-old female presented for evaluation of persistent axillary swelling and fullness, which began during her first pregnancy and has been ongoing since. Notably, she experienced lactation from a right axillary mass while nursing her second child and reported daily discomfort in the axillary regions, exacerbated during her menstrual cycles. For the past 5 years, she experienced bilateral breast pain 2–3 weeks before the onset of her menstrual period. However, she denied any history of nipple discharge, palpable breast lumps, abnormal vaginal bleeding, or vaginal discharge.

The patient’s gynecological history revealed regular menstrual cycles, with her last menstrual period on September 27, 2024, lasting 3–4 days with moderate flow. She experienced light pelvic and low back pain during her cycles. She has had three full-term pregnancies, no history of sexually transmitted infections, and negative Pap Smear/Human Papillomarius infection (Pap/HPV) screening in November 2022. She does not use hormonal contraceptives, as her husband underwent a vasectomy. There was no significant family history of breast or genital cancers. A comprehensive review of systems was negative for any additional symptoms.

On physical examination, the patient had bilateral axillary ABT. The accessory breasts were ~5 cm in diameter on each side, with a soft and pliable texture consistent with glandular tissue. No overlying skin changes, such as erythema, dimpling, or peau d’orange, were observed. Accessory nipples were present bilaterally, with normal pigmentation and no signs of inflammation or discharge. Palpation of the ABT revealed no discrete masses or nodules. There was no tenderness on palpation outside of the reported cyclical discomfort. Additionally, there was no evidence of axillary lymphadenopathy or signs of infection (Figure 1). The differential diagnosis for axillary masses in this context includes lipomas, epidermal inclusion cysts, lymphadenopathy, and hidradenitis suppurativa; however, the presence of hormonally responsive tissue and accessory nipples helped support the diagnosis of ABT.

Figure 1.

Clinical photograph showing bilateral accessory breast tissue with accessory nipples in the axillary regions.

A mammogram confirmed the presence of bilateral ABT with accessory nipples, all appearing benign. No suspicious masses or abnormalities were identified. Given these findings and the patient’s history of cyclical pain and discomfort during her menstrual cycle, she was referred to a plastic surgeon for surgical excision of the accessory tissue with the primary goal of symptom relief (Figure 2).

Figure 2.

Mammogram images confirming bilateral accessory breast tissue, including accessory nipples, with no suspicious findings or masses. (a) RLM view mammogram showing accessory breast tissue and nipple. (b) RMLO view mammogram showing accessory breast tissue and nipple. (c) LLM view mammogram showing accessory breast tissue and nipple. (d) LMLO view mammogram showing accessory breast tissue and nipple.

The patient was counseled about the surgical procedure, which involved excision of the ABT under general anesthesia. The potential risks, including infection, scarring, hematoma formation, and incomplete resolution of symptoms, were discussed in detail. The surgeon also explained the expected outcomes of significant symptom relief, improved quality of life, and cosmetic enhancement from the removal of the accessory tissue. The patient expressed a clear understanding of the procedure, its risks, and benefits and agreed to proceed with the surgical intervention. This case highlights the importance of recognizing ABT as a cause of cyclical breast pain and axillary swelling, particularly in postpartum patients. Further follow-up is planned to assess the surgical outcomes and the patient’s satisfaction with the intervention.

Histopathological examination of the excised axillary tissue revealed benign glandular breast tissue without evidence of atypia, hyperplasia, or malignancy. These findings were consistent with normal architecture, including ductal, and lobular structures embedded in fibrous stroma, confirming the diagnosis of benign ABT.

Patient perspective

Living with ABT was something I never expected to impact my life so deeply. For years, I dealt with persistent pain and discomfort in both of my armpits, especially around my menstrual cycle. It became part of my routine feeling soreness for 2–3 weeks each month and not understanding why. Things worsened after I had children. I was shocked when I noticed lactation coming from the tissue in my right armpit while nursing. It was not just physically uncomfortable; it made me feel self-conscious and frustrated. I felt like my body was doing something abnormal, and I didn’t have the language or information to understand it. After many years of just managing the symptoms, I finally sought help. When the doctor explained that I had ABT and that this condition was real and treatable, I felt validated for the first time. The surgery was not just about removing the tissue; it was about getting my quality of life back. I no longer feel that constant, nagging pain, and I don’t worry about visible swelling under my clothes. Most importantly, I finally feel like I have control over my body again. I’m incredibly grateful to my care team for listening to me, taking me seriously, and giving me the option of a permanent solution.

Outcome and discussion

ABT, or polymastia, is a congenital anomaly resulting from the incomplete regression of the embryonic mammary ridge, or “milk line,” which extends bilaterally from the axilla to the groin. ¹⁵ ABT affects ~0.4%–6% of the population, with accessory nipples occurring in around 1%. ¹⁴ The axillary region is the most common site of ectopic breast tissue, and although ABT is often asymptomatic, it can present clinically as soft, palpable masses that respond to hormonal fluctuations such as those during puberty, menstruation, pregnancy, or lactation.^4,16,17 Hormonal stimulation, particularly elevated estrogen, progesterone, and prolactin levels, can cause cyclical pain, enlargement, and even lactation from the ectopic tissue.^18–20 Diagnosis relies on physical examination and imaging modalities such as ultrasound or mammography to confirm the glandular nature of the mass and exclude malignancy. While ABT is benign in most cases, it can undergo the same pathologies as normal breast tissue, including fibroadenoma and, rarely, carcinoma.^21,22 Treatment may be conservative or surgical, depending on symptom severity, cosmetic concerns, and the presence of pathological changes. While conservative management, including observation and hormonal regulation, may be considered in asymptomatic or mildly symptomatic patients, it often provides limited relief in cases of hormonally responsive ABT. In contrast, surgical excision is the preferred approach when patients experience recurrent pain, lactation, cosmetic concerns, or interference with daily activities. In this case, the patient’s history of cyclical discomfort, lactation from the axillary region during nursing, and the impact on her quality of life warranted definitive treatment through surgical removal. Excision not only provides symptom relief but also eliminates the risk of future pathological changes within the ectopic tissue. Surgical excision remains the gold standard, particularly when the tissue is symptomatic or cosmetically distressing.

The clinical behavior of ABT is strongly influenced by hormonal changes, particularly during periods such as puberty, pregnancy, lactation, and the menstrual cycle.^23,24 Elevated levels of estrogen and progesterone during the luteal phase of the menstrual cycle can stimulate proliferation of glandular elements, leading to swelling and cyclical pain.^25,26 During pregnancy and postpartum lactation, increased prolactin levels may induce milk production from ectopic tissue, as was observed in our patient.^27,28 These hormonally driven symptoms often mimic those experienced with normal breast tissue, making ABT particularly prone to misdiagnosis when located in atypical regions like the axilla. In our case, the patient reported chronic cyclical tenderness and lactation during nursing, which is both consistent with hormonally responsive accessory tissue. Recognizing these patterns is critical for differentiating ABT from other benign axillary masses and for determining the need for definitive surgical intervention. Recognizing these patterns is critical for differentiating ABT from other benign or malignant axillary masses. A recently published case report describing invasive ductal carcinoma arising in axillary breast tissue underscores the importance of including ABT in the differential diagnosis and highlights the potential for malignant transformation in ectopic breast tissue. ²⁹

Complementary to our benign, hormonally responsive presentation, malignant transformation in ABT, although rare, has been documented. These cases, including those involving invasive ductal carcinoma arising in ectopic axillary tissue, illustrate the importance of maintaining a high index of suspicion when evaluating persistent axillary masses.^30,31 These malignancies frequently present as persistent, often painless, axillary masses, which may delay diagnosis due to their atypical location and nonspecific presentation. ³² Moreover, malignant ectopic breast tissue can exhibit similar patterns of regional lymphatic spread as orthotopic breast cancer, underscoring the need for thorough clinical evaluation and appropriate imaging.^17,33 In contrast, benign ABT, as seen in our case, tends to exhibit hormonally driven changes such as cyclic enlargement or tenderness, often correlating with menstrual phases, pregnancy, or lactation. Importantly, benign ABT lacks the architectural distortion, nodularity, and invasive features typically associated with malignancy. ³⁴ Despite these differences, distinguishing between benign and malignant presentations can be challenging, especially when the clinical history is limited or the mass is long-standing. Taken together, benign and malignant ABT presentations underscore the need for standardized diagnostic pathways, potentially including targeted imaging (ultrasound, mammography, MRI) and tissue biopsy when indicated. ³⁵ This approach ensures that malignant cases are not missed, and benign conditions are appropriately managed. By presenting a clearly benign, hormonally driven case alongside the growing body of literature on malignant transformation, we aim to enhance clinical awareness of the full spectrum of ABT and promote vigilant, evidence-based evaluation of persistent axillary masses.

A direct comparison between benign and malignant manifestations of ABT reveals key clinical and diagnostic distinctions that can guide evaluation. Benign ABT, such as in our case, often presents with cyclical, hormonally mediated symptoms and imaging findings consistent with glandular tissue without signs of atypia or masses. In contrast, malignant ABT may present as firm, irregular, or rapidly enlarging axillary masses and may not follow a cyclical pattern. A recently published case report describes invasive ductal carcinoma arising within axillary ectopic breast tissue, emphasizing the need for histopathologic evaluation in suspicious or atypical presentations. ²⁹ Incorporating both benign and malignant possibilities into the clinical framework reinforces the importance of individualized imaging and, when indicated, biopsy to rule out underlying malignancy.

A primary limitation of this case report is the lack of long-term follow-up data to assess postoperative outcomes, including recurrence of symptoms and patient satisfaction over time. While the initial surgical outcome was favorable, future visits are necessary to evaluate sustained symptom relief and quality-of-life improvements. Additionally, as a single case report, the findings may not be generalizable to all patients with ABT. Broader studies are needed to better understand the variability in presentation and response to treatment.

Given the hormonal responsiveness and potential for recurrence or symptom persistence, long-term follow-up is critical to monitor postoperative outcomes, including the recurrence of pain, residual tissue growth, and patient-reported satisfaction. Continued surveillance may also help detect any delayed complications or overlooked pathology. In addition, there is a clear need for prospective studies and larger case series to better understand the natural history, optimal management strategies, and long-term outcomes of patients with ABT, particularly those with rare bilateral and lactational presentations. These data would help establish standardized guidelines and further delineate when surgical versus conservative management is most appropriate.

Several case reports have described axillary ABT; however, many focus on unilateral presentations, isolated nipple variants, or incidental findings with limited symptomatic impact.^19,22,36 In contrast, our patient presented with bilateral axillary ABT with coexisting accessory nipples, a rarer subtype consistent with Kajava Class I, the most complete form of polymastia, involving glandular tissue, nipple, and areola. ⁸ Additionally, her history of cyclical pain, lactation during nursing, and symptom persistence over multiple years distinguishes this case from more transient or asymptomatic presentations. Previous reports often lacked a comprehensive hormonal history or failed to document lactation as a key symptom, both of which were prominent in our patient’s clinical course. Another important distinction in this case is the thorough use of imaging. While many case reports rely solely on clinical suspicion or ultrasound, this case included diagnostic mammography, which confirmed the benign nature of the accessory tissue and guided surgical planning. Postoperative histopathological analysis further validated the diagnosis by revealing benign glandular architecture with no evidence of malignancy.

The novelty of this case lies in its combination of rare bilateral presentation, coexisting accessory nipples, long-term symptom duration, and hormonally triggered lactation, all supported by a structured diagnostic workup and definitive surgical intervention. It emphasizes the need for heightened clinical awareness of ABT in reproductive-age women with unexplained axillary swelling or cyclical pain. Furthermore, this case supports the integration of the Kajava classification in clinical assessments to better inform diagnosis and treatment decisions. By contributing a well-documented, symptomatic bilateral case of Kajava Class I ABT with lactational features, our report adds to the growing body of literature advocating for early recognition and appropriate surgical management of symptomatic ABT.

Conclusion

This case highlights a rare presentation of bilateral axillary ABT with accessory nipples, classified as Kajava Class I, in a reproductive-age woman experiencing cyclical pain and lactation. The patient’s symptoms, closely tied to hormonal fluctuations, significantly impacted her quality of life. Through thorough clinical evaluation, imaging, and surgical intervention, a definitive diagnosis was made and effective symptom relief was achieved. This report emphasizes the importance of considering ABT in the differential diagnosis of axillary masses, especially in patients with cyclical or lactational symptoms. Early recognition and appropriate management, including the use of diagnostic imaging and histopathological confirmation, are essential to avoiding misdiagnosis and unnecessary delays in treatment. Incorporating classification systems such as Kajava’s may further support clinical decision-making. By documenting this unique presentation, we aim to raise awareness of symptomatic ABT and advocate for timely, patient-centered care.