A rare case report of fibroadenoma in accessory breast tissue

INTRODUCTION

Accessory breast tissue refers to residual breast tissue remaining along the “milk line” in the axillary region. Unlike the main breast parenchyma, it is anatomically separate and situated superficially, anterior to the subcutaneous fat layer. In contrast, the axillary tail of Spence represents a natural, deeper extension of the breast into the axilla, positioned posterior to the subcutaneous fat layer and maintaining continuity with the primary breast tissue. Clinically, it is essential to recognize that accessory breast tissue can develop the same range of pathological conditions as normal breast tissue. These include benign disorders such as fibrocystic changes, mastitis, and fibroepithelial lesions; precancerous conditions like atypical ductal or lobular hyperplasia; and malignancies. Accurate differentiation between these entities is critical for diagnosis and management.^[1]

CASE REPORT

A 38-year-old woman presented to the surgical Outpatient department (OPD) with complaints of lumps in both axillae for the past 3 months. She had no similar complaints in the past and no family history of breast carcinoma or any prior surgical history. She had not undergone mammography before. There was no significant increase in the size of the lumps. On clinical examination, these axillary lumps were hard, non-tender, and freely mobile, without any palpable axillary nodes. Subsequently performed ultrasound (USG) revealed the presence of two circumscribed, oval, parallel-oriented hypoechoic masses with posterior acoustic enhancement and no internal vascularity in the left axilla with a background of fibroglandular tissue [Figures 1–4]. The right axilla showed a circumscribed, oval, parallel-oriented hypoechoic mass with posterior acoustic enhancement and no internal vascularity [Figures 5 and 6]. No solid or cystic mass could be seen in the breast parenchyma. Mammography was performed to rule out any microcalcification, and it showed circumscribed, round-to-oval, isodense masses within the fibroglandular tissue of both axillae—consistent with USG findings [Figure 7].

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Figure 1:

(a and b) shows fibroglandular tissue in left axilla.

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Figure 2:

(a–c) shows an oval, circumscribed, parallel-oriented hypoechoic mass measuring 1.3 cm × 0.9 cm × 0.6 cm in the left axilla; (d) no internal vascularity.

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Figure 3:

shows an oval, circumscribed, parallel-oriented hypoechoic mass measuring 0.7 cm × 0.5 cm noted in the left axilla showing, (b) no internal vascularity.

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Figure 4:

(a and b) shows a tiny cyst of size 4 cm × 3 mm noted in the left axilla—benign—BIRADS II. (c) shows a cyst with no internal vascularity. BIRADS: Breast imaging reporting and data system.

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Figure 5:

(a and b) shows fibroglandular tissue in the right axilla.

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Figure 6:

(a-c) Oval circumscribed parallel-oriented hypoechoic mass measuring 1.2 cm × 0.7 cm noted in the right axilla.

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Figure 7:

(a) MLO view, (b) Axillary view shows fibroglandular tissue in the bilateral axilla (yellow arrows). MLO: Medio-lateral oblique.

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An MRI was undertaken for academic interest and to completely evaluate these masses before making a management decision. Both axillae show the presence of fibroglandular tissue on MRI as well, and these masses showed circumscribed margins with hypointense signal on T1, hyperintense on T2-weighted sequences, and no diffusion restriction [Figures 8–10].

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Figure 8:

(a-c) Axial T2 image shows normal fibroglandular tissue in bilateral breasts. Yellow arrows in Axial T2 images show fibroglandular tissue in bilateral axilla.

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Figure 9:

(a) Axial T1, (b) Axial T2 and (c) Sagittal STIR images show oval circumscribed T1 hypointense and T2 hyperintense mass in the left axilla (yellow arrows).

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Figure 10:

(a) Axial T1, (b) Axial T2 and (c) Sagittal STIR images show oval circumscribed T2 heterogeneous masses (yellow arrows) in right axilla.

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In view of these features, the patient was categorized as BIRADS-3 and kept on 6-month follow-up which determined lesion stability.

DISCUSSION

Accessory breast tissue, a vestigial remnant from embryonic growth, is present in approximately 6% of individuals.^[2] It typically manifests along the “milk line,” a bilateral ectodermal ridge stretching from the axilla to the groin that forms by the fourth gestational week. Normally, these ridges regress except at primary breast sites. The predominant embryologic explanation suggests that residual or displaced cells from these ridges lead to accessory tissue. However, occurrences beyond the milk line have spurred alternative theories. Hughes (1950) hypothesized sporadic migration of early breast cells, whereas Craigmyle linked it to transformed apocrine glands.^[2]

The Kajava system organizes accessory breast tissue into eight structural categories^[2]:

• Class 1 (Polymastia): Fully formed breast with nipple, areola, and glandular tissue.

• Class 2: Glandular tissue and nipple, lacking an areola.

• Class 3: Glandular tissue and areola, without a nipple.

• Class 4: Solely glandular tissue (most frequent in the axilla).

• Class 5 (Pseudomamma): Nipple and areola present, absent glandular tissue.

• Class 6 (Polythelia): Isolated nipple.

• Class 7 (Polythelia Areolaris): Only areola.

• Class 8 (Polythelia Pilosis): Localized hair growth.

Accessory tissue is anatomically separate from the primary breast, situated superficially above the subcutaneous fat. Comparatively, the axillary tail of Spence—a natural extension of breast tissue into the axilla—resides deeper and integrates with the main gland.^[2,3,4]

Mirroring standard breast tissue, accessory tissue may develop benign pathologies (e.g., fibrocystic disease, inflammation) or malignancies.^[5] High-risk individuals, such as those with prior breast cancer, should undergo accessory tissue evaluation during screenings.^[1,2,4]

Asymptomatic cases rarely necessitate intervention. Symptomatic or cosmetically bothersome tissue (e.g., painful axillary masses) typically requires surgical removal, as liposuction fails to address glandular components. Radiologic recognition is vital to avoid overlooking malignancies during cancer surveillance.^[2,4]

The clinical differentials would include entities like lipoma and axillary lymph nodes. Where lipomas may appear as hyperechoic masses on USG, radiolucent (consistent with fat density) on mammograms, and follow fat signals on all MRI sequences, including suppression on fat-saturated images, the lymph nodes have oval shape, and echogenic fatty hilums on USG. On a mammogram, the node will have a reniform (kidney-shaped) appearance with visible hilar fat, and MRI can confirm the presence of a fatty hilum across all sequences.

CONCLUSION

Present in up to 6% of individuals, accessory breast tissue predominantly arises in the axilla but may emerge anywhere along the milk line. Radiologists must recognize its imaging features across modalities to prevent misinterpreting it as pathologic. Importantly, all breast-related diseases, benign or malignant, can also affect accessory tissue, underscoring the need for thorough evaluation.^[2,3,4]

Accessory breast tissue (superficial to fat) must be distinguished from the deeper axillary tail. Ultrasound is the best initial tool for evaluation, with mammograms for correlation. Reserve MRI only for atypical cases.