Cystic Neutrophilic Granulomatous Mastitis in Accessory Breast Tissue: A Case Report

Abstract

Background

Cystic neutrophilic granulomatous mastitis (CNGM) is a rare inflammatory breast disease characterized by granulomatous inflammation with cystic spaces and neutrophilic infiltration. CNGM involving accessory breast tissue is exceptionally uncommon and has only rarely been reported. Due to its nonspecific clinical manifestations, CNGM may be misdiagnosed, potentially resulting in delayed diagnosis and treatment.

Case Presentation

A 37-year-old woman presented with swelling and pain in the right axillary region. Ultrasonography revealed an inflammatory lesion within accessory breast tissue, and core needle biopsy confirmed the diagnosis of CNGM. Histopathological examination demonstrated granulomatous inflammation with characteristic cystic neutrophilic features. The patient received antibiotic therapy, traditional Chinese medicine, and other conservative treatments. Her clinical symptoms and inflammatory markers improved during short-term follow-up.

Conclusions

CNGM arising in accessory breast tissue is exceptionally rare and may pose a diagnostic challenge because of its nonspecific clinical and imaging features. This case expands the recognized clinical spectrum of CNGM and highlights the importance of considering CNGM in the differential diagnosis of inflammatory lesions arising in accessory breast tissue. Histopathological evaluation is essential for establishing the diagnosis and excluding malignancy or other inflammatory conditions.

Introduction

Accessory breast tissue arises from congenital developmental anomalies and represents ectopic but otherwise normal breast tissue. It can occur anywhere along the mammary ridge, most commonly in the axilla.¹ Both benign and malignant breast diseases may also develop in accessory breast tissue.² Cystic neutrophilic granulomatous mastitis (CNGM) is a rare inflammatory breast disease with distinctive histopathological features.³ Although the relationship between CNGM and granulomatous lobular mastitis (GLM) remains incompletely defined, CNGM is generally regarded as a characteristic histopathological pattern within the spectrum of GLM. Compared with classical GLM, CNGM is characterized by suppurative lipogranulomas containing central lipid vacuoles surrounded by neutrophils and an outer rim of epithelioid histiocytes. In some cases, Gram-positive bacilli may be identified within the lipid vacuoles.^4,5 Recognition of this characteristic pattern is important for distinguishing CNGM from other forms of granulomatous mastitis.

GLM involving accessory breast tissue typically presents with nonspecific symptoms such as redness, swelling, and pain.^6–11 Because of its rarity and nonspecific presentation, recognition of this condition may be challenging and misdiagnosis or underdiagnosis may occur.^12,13 Importantly, inflammatory lesions arising in accessory breast tissue may mimic malignancy or other inflammatory breast diseases. Early histopathological evaluation can therefore facilitate accurate diagnosis and may help avoid unnecessary surgical intervention. Although several cases of granulomatous mastitis involving accessory breast tissue have been reported, CNGM in this location appears to be exceptionally rare. A literature search of PubMed, Web of Science, and Embase identified no indexed previous reports specifically describing CNGM arising in accessory breast tissue. This report aims to describe the clinical presentation, diagnostic evaluation, histopathological findings, management, and short-term clinical outcome of a patient with CNGM arising in accessory breast tissue.

Case Information

General Information

A 37-year-old Chinese woman presented with a 7-day history of redness, swelling, and pain in the right axilla. The symptoms developed insidiously and were not accompanied by fever or other systemic manifestations.

History of Present Illness

Five days prior to admission, she was evaluated at another hospital. Breast ultrasonography revealed glandular echogenicity in the right axilla, along with an irregular hypoechoic to anechoic area measuring up to 3.6 cm in maximum diameter. Empirical antimicrobial therapy was recommended, and the patient received intravenous levofloxacin (0.5 g once daily) for four days; however, the clinical response was suboptimal. One day prior to presentation at our hospital, repeat ultrasonography demonstrated a mixed echogenic mass in the inferior aspect of the right axilla, measuring approximately 3.2 × 2.8 × 2.1 cm. Due to the lack of clinical improvement, the patient was subsequently admitted to our hospital for further evaluation and management.

Past Medical History

The patient had no history of diabetes mellitus and was a non-smoker. She had two full-term pregnancies and had breastfed her children for approximately 18 and 15 months, respectively. Her last episode of lactation occurred approximately three years prior to presentation. Menstrual cycles were regular.

Clinical Examination

On presentation, her vital signs were within normal limits, with a temperature of 36.5 °C, pulse rate of 78 beats per minute, respiratory rate of 17 breaths per minute, and blood pressure of 110/85 mmHg. Bilateral axillary fullness was noted, with visible accessory nipples. In the right axilla, a firm mass measuring approximately 10 × 8 cm was palpable, with overlying redness involving an area of approximately 7 × 5 cm (Figure 1A and B). In the left axilla, soft glandular tissue was palpable (Figure 1D). Examination of both breasts revealed no abnormalities, including absence of nipple retraction, discharge, or palpable masses. Mild tenderness was noted, but no discrete lesions were identified. No clinically enlarged axillary lymph nodes were detected bilaterally. Cardiopulmonary and abdominal examinations were unremarkable, and no erythematous nodules were observed on the lower extremities.

Figure 1.

Clinical findings of the accessory breast tissue at presentation and after treatment. (A) Initial presentation showing accessory breast tissue in the right axilla, with a visible accessory nipple and localized swelling accompanied by overlying erythema. (B) The extent of the accessory mass outlined with a skin marker at presentation. (C) Post-treatment findings demonstrating a reduction in erythema with residual hyperpigmentation. (D) The left accessory breast showing no significant abnormality, unchanged from baseline.

Diagnostic Approach

The patient subsequently underwent breast ultrasonography at our hospital (Figure 2). Imaging demonstrated subcutaneous soft-tissue edema and thickening in the right axilla, with glandular echogenicity and multiple interconnected hypoechoic areas. A larger mixed-echogenic lesion measuring approximately 3.4 × 1.3 cm was also identified, consistent with inflammatory changes. Laboratory investigations showed a normal complete blood count and cytokine profile, including interleukin (IL)-1β, IL-2, IL-4, IL-5, IL-6, IL-8, IL-10, IL-12p70, IL-17, interferon (IFN)-α, IFN-γ, and tumor necrosis factor (TNF)-α. In contrast, C-reactive protein (CRP) was elevated at 11 mg/L (reference range: 0.0–8.0 mg/L), erythrocyte sedimentation rate (ESR) was 36 mm/h (reference range: 0–20 mm/h), and serum prolactin was mildly elevated at 34.25 ng/mL (reference range: 2.80–29.20 ng/mL).

Figure 2.

Ultrasonographic findings of bilateral accessory breast tissue. (A) Glandular echogenicity in the right axilla with subcutaneous soft-tissue edema and thickening. Multiple communicating hypoechoic inflammatory areas are present (blue arrows), measuring approximately 33.5 × 13.2 mm. (B) Dilated ducts within the right accessory breast tissue are indicated by the orange arrow, with a maximal diameter of approximately 6.9 mm. (C) A hypoechoic inflammatory lesion within the right accessory breast tissue is indicated by the green arrow, with a small amount of internal vascularity demonstrated on color Doppler imaging. (D) Ultrasonographic appearance of the left accessory breast tissue, showing glandular echogenicity without focal inflammatory changes.

An ultrasound-guided core needle biopsy was then performed, and purulent material was obtained for microbiological analysis. Histopathological examination demonstrated prominent acute and chronic inflammatory cell infiltration within the interstitium, with abscess formation and lipid vacuoles, consistent with CNGM (Figure 3). Gram staining of the purulent specimen revealed a small number of Gram-positive cocci. Bacterial culture yielded Staphylococcus aureus, which was identified using the VITEK 2 Compact automated microbial identification system. Antimicrobial susceptibility testing showed that the isolate was susceptible to levofloxacin.

Figure 3.

Histopathological findings of axillary biopsy specimens (hematoxylin and eosin staining; ×10; scale bar = 100 μm). (A) Representative histopathological features of CNGM. The red arrowhead indicates a lipid vacuole, the orange arrowhead indicates neutrophils, and the green arrowhead indicates lymphocytes. The blue dashed outlines indicate granulomatous inflammation surrounding the lipid vacuole and an adjacent area of inflammatory exudate and necrotic debris. (B) Representative histopathological image demonstrating dense inflammatory cell infiltration. The black dashed box outlines the area of dense inflammatory cell infiltration.

Treatment Outcome

A multimodal conservative treatment strategy was adopted. Based on the antimicrobial susceptibility results, the previously initiated intravenous levofloxacin regimen (0.5 g once daily) was continued for an additional 3 days, completing a total 7-day course. Adjunctive therapy included oral administration of a traditional Chinese herbal decoction, topical application of a Chinese herbal ointment, ultrashort-wave therapy, and ultrasound-mediated drug delivery for one week. During treatment, the patient’s local symptoms, including erythema and pain, improved (Figure 1C). Repeat laboratory evaluation showed a decrease in CRP from 11.0 to 3.3 mg/L and in ESR from 36 to 29 mm/h. The patient was subsequently discharged with recommendations for continued outpatient management and regular follow-up.

Discussion

Accessory breast tissue arises from incompletely regressed mammary ridges during embryologic development, with a reported incidence of approximately 1–6%.¹⁴ Similar to orthotopic breast tissue, accessory breast tissue is subject to hormonal influences and can develop a spectrum of benign and malignant conditions, including mastitis, fibroadenoma, phyllodes tumors, and carcinoma, the latter being the most frequently reported.^15,16

CNGM is a rare inflammatory breast disorder characterized by a distinctive histopathological pattern within the spectrum of GLM.^17,18 First characterized by Paviour et al in 2002, this entity exhibits a characteristic histological pattern consisting of suppurative lipogranulomas with central lipid vacuoles surrounded by neutrophils and an outer layer of epithelioid histiocytes, accompanied by mixed inflammatory infiltrates including lymphocytes and multinucleated giant cells. In some cases, Gram-positive bacilli may be identified within the lipid vacuoles.¹⁹ Subsequently, Renshaw et al formally introduced the term “cystic neutrophilic granulomatous mastitis” in 2011 to describe this distinctive histopathological pattern.²⁰

The pathogenesis of CNGM remains incompletely understood; however, several risk factors have been proposed. The condition predominantly affects parous women in their late 30s and typically develops within six years following the last pregnancy.²¹ Increasing evidence suggests a strong association with bacterial infection, particularly Corynebacterium kroppenstedtii and Corynebacterium parakroppenstedtii.^22–25 Additional proposed contributing factors include milk stasis, hyperprolactinemia, autoimmune mechanisms, and the use of psychotropic medications.^26–30 In the present case, serum prolactin was mildly elevated at admission, which may have represented a contributing factor.

Clinically, CNGM most commonly presents as a palpable breast mass, often accompanied by inflammatory signs such as erythema and ulceration. Systemic manifestations, including erythema nodosum, fever, and cough, may also occur in a subset of patients.^5,21 In the present case, the patient presented with a 7-day history of erythema and pain in the right axilla. Physical examination revealed a firm, palpable mass with associated inflammatory changes, including redness and swelling, which is consistent with the typical clinical presentation of CNGM described in the literature.

There are currently no established serum biomarkers for the diagnosis or prognosis of CNGM. Previous studies have suggested that inflammatory markers such as CRP and ESR may be associated with disease activity in granulomatous mastitis.^31–34 In the present case, both CRP and ESR were elevated at admission and decreased following treatment, in parallel with improvement in local clinical symptoms. These findings suggest that CRP and ESR may provide supportive information for monitoring inflammatory activity, although their role specifically in CNGM requires further investigation.

Ultrasonography is the preferred initial imaging modality for the evaluation of suspected inflammatory breast disease and plays an important role in the assessment of CNGM.³⁵ Sonographic findings in CNGM typically include localized parenchymal thickening and the presence of multiple hypoechoic lesions, often irregular in shape and occasionally demonstrating internal liquefaction. However, these features are nonspecific and may overlap with those of GLM, breast carcinoma, and other inflammatory conditions, thereby limiting diagnostic specificity.^21,36 In the present case, ultrasonography revealed subcutaneous soft tissue thickening and edema in the right axilla, with multiple interconnected hypoechoic areas, findings that are consistent with previously reported imaging characteristics of CNGM. Mammography in GLM often demonstrates a focal, asymmetric, and irregular mass. Although it is superior to ultrasonography in detecting microcalcifications, it similarly lacks specificity. Moreover, in the context of acute inflammation, mammography may exacerbate patient discomfort and potentially increase the risk of inflammatory dissemination; therefore, it is not routinely recommended in such cases.³⁷

Histopathological examination remains the gold standard for the diagnosis of CNGM. Commonly employed diagnostic techniques include fine-needle aspiration cytology (FNAC) and core needle biopsy (CNB), with CNB generally demonstrating higher diagnostic sensitivity.³⁸ The hallmark histopathological feature of CNGM is the presence of suppurative lipogranulomas composed of central lipid vacuoles surrounded by neutrophils and an outer rim of epithelioid histiocytes, often accompanied by mixed inflammatory infiltrates. In some cases, sparse, rod-shaped Gram-positive bacilli may be identified within the lipid vacuoles.^39,40 Recent taxonomic studies have identified closely related species within the Corynebacterium kroppenstedtii complex, including C. parakroppenstedtii, which may complicate species-level identification in clinical isolates.^24,41 However, in vitro isolation and identification of lipophilic Corynebacterium species can be challenging because of their fastidious growth requirements. Consequently, microbiological confirmation is not achieved in all cases of CNGM.⁴²

Although CNGM has been frequently associated with Corynebacterium species, particularly C. kroppenstedtii, Corynebacterium was not detected in the present case. Negative microbiological findings are not uncommon in CNGM. In our previous retrospective study of 141 patients with CNGM, pus samples from 54 patients were subjected to microbiological culture, and C. kroppenstedtii was identified by mass spectrometry in only four cases.²¹ The 2025 Guidelines for the Management of Infectious and Inflammatory Lesions of the Breast similarly note that Gram staining and microbiological cultures in CNGM may have false-negative rates exceeding 50%, largely because of the scarcity of organisms, prior antibiotic exposure, and special culture requirements for Corynebacterium.⁴³ In the present case, prior levofloxacin treatment may also have reduced bacterial recovery. In contrast, bacterial culture yielded Staphylococcus aureus, which was identified using VITEK 2 Compact. However, because S. aureus is a common skin colonizer, contamination during specimen collection cannot be completely excluded, and its precise role in this case remains uncertain.

The diagnosis of CNGM can be challenging because of its rarity and the lack of specific clinical, laboratory, and imaging features. In patients presenting with inflammatory lesions in accessory breast tissue, initial evaluation should include careful clinical examination and ultrasonography, with microbiological assessment performed when purulent material is available. Early core needle biopsy should be considered when the lesion is persistent, when imaging findings are atypical or concerning, or when there is an inadequate response to initial empirical treatment. Histopathological evaluation is particularly important for confirming the diagnosis and excluding malignancy and other inflammatory breast diseases.

Regarding treatment, no standardized guidelines for CNGM therapy have been established to date, and the optimal treatment approach remains controversial. Common methods include antibiotics, immunosuppressants, surgery, and traditional Chinese medicine (TCM).^44–48 The treatment principles for accessory breast CNGM are consistent with those for breast CNGM, but the unique anatomical location of accessory breasts must also be taken into consideration. In previous reports of accessory breast GLM, initial treatment primarily involved antibiotics and glucocorticoids.⁴⁹ In some cases, surgical intervention was subsequently performed when the initial medical treatment did not achieve sufficient clinical improvement.^8,9 However, some patients experienced temporary relief of local symptoms but later experienced recurrence, necessitating surgical intervention.¹¹ Such treatment courses may prolong the overall management period while still exposing patients to surgery-related sequelae, such as scarring.

In this patient, the treatment strategy involved continuation of the antibiotic regimen initiated prior to admission to complete a total 7-day course, together with traditional Chinese medicine and other conservative therapies. Clinical symptoms and inflammatory markers improved during treatment. However, because multiple therapeutic interventions were administered simultaneously and this report describes a single patient, the relative contribution of each treatment modality cannot be determined. The observed improvement occurred in the context of antibiotic therapy, TCM, other conservative measures, and the natural course of the disease.

Limitations

This report has several limitations. First, it describes a single patient, which limits the generalizability of the clinical observations. In addition, the limited number of published cases involving accessory breast CNGM restricts meaningful comparison with previous reports. Although Staphylococcus aureus isolated from the purulent specimen was identified using VITEK 2 Compact, 16S rRNA sequencing or other molecular methods were not performed to further assess the possible presence of Corynebacterium species that may not have been recovered by routine culture. Furthermore, multiple therapeutic interventions were administered simultaneously, making it impossible to determine the independent contribution of each treatment modality to the observed clinical improvement. Finally, the follow-up period was relatively short, limiting assessment of long-term outcomes and recurrence.

Conclusion

In summary, this represents one of the few reported cases of CNGM arising in accessory breast tissue. This exceptionally rare presentation has nonspecific clinical and imaging features, which may complicate recognition and diagnosis. CNGM should therefore be considered in the differential diagnosis of inflammatory lesions arising in accessory breast tissue. Ultrasonography and microbiological evaluation may provide supportive information, while histopathological examination remains essential for establishing the diagnosis and excluding malignancy or other inflammatory conditions. Inflammatory markers such as CRP and ESR may be useful for assessing disease activity. Given the rarity of this condition and the limited evidence available, multicentre case series and prospective studies would be valuable for better defining its epidemiology, clinical characteristics, optimal diagnostic strategy, microbiological profile, and management.

Funding Statement

This work was supported by the Clinical Collaboration Project of Traditional Chinese and Western Medicine for Major and Difficult Diseases (ZDYN-2024-A-112); State Administration of Traditional Chinese Medicine of the People’s Republic of China ([2022] No. 256); National Natural Science Foundation of China (82575052); Beijing High-level Young Top-notch Talents in Innovation and Entrepreneurship (20250568); Beijing Nova Program (02604841123); and the National Key Research and Development Program of China (2025YFC3511200).

Abbreviations

CNGM, Cystic neutrophilic granulomatous mastitis; CNB, Core needle biopsy; GLM, granulomatous lobular mastitis; IL, Interleukin; IFN, Interferon; TNF, Tumor necrosis factor; CRP, C-reactive protein; ESR, Erythrocyte sedimentation rate; FNAC, Fine-needle aspiration cytology; TCM, Traditional Chinese medicine.

Data Sharing Statement

All data generated or analyzed during this study are included in this published article. Further details are available from the corresponding author upon reasonable request.

Ethical Approval

Institutional ethics committee approval was not required for the publication of this single-patient case report according to the institutional policy of Beijing Hospital of Traditional Chinese Medicine, Capital Medical University. Written informed consent was obtained from the patient for the publication of this case report and any accompanying images. All diagnostic and therapeutic interventions described were part of routine clinical care. Patient information and clinical data were used exclusively for the preparation of this case report.

Author Contributions

All authors made a significant contribution to the work reported, whether that is in the conception, study design, execution, acquisition of data, analysis and interpretation, or in all these areas; took part in drafting, revising or critically reviewing the article; gave final approval of the version to be published; have agreed on the journal to which the article has been submitted; and agree to be accountable for all aspects of the work.

Disclosure

The authors declare no conflicts of interest.