The rose among the thorns: A rare and harmless mimic of a spiculated breast mass

INTRODUCTION

A spiculated breast mass on mammography is a typical sign of malignancy, with a positive predictive value of about 90%.^[1] Due to their high positive predictive value, they are considered malignant unless proven otherwise, and a benign biopsy report for a spiculated mass is often regarded as discordant. In malignancy, spicules represent tumor cell invasion into the surrounding parenchyma, accompanied by fibrosis.^[2] Less commonly, specific benign breast pathologies such as sclerosing adenosis, radial scar, fat necrosis, hemorrhage, and post-surgical scar can cause spiculations.^[3] In this case report, we discuss a rare cause of a spiculated breast mass, along with its radiological and pathological features.

CASE REPORT

A 38-year-old woman presented to our breast center with a painless lump in her right breast that had persisted for 1 week. Clinical examination revealed an irregular, firm, non-tender mass approximately 2 cm in diameter at the 9 o’clock position of the right breast, along with skin retraction.

We performed mammography with tomosynthesis of both breasts using the Hologic Selenia Dimensions (Hologic, Massachusetts, United States). The mammogram revealed an irregular, high-density mass with spiculated margins, measuring 2.8 × 2.1 cm, located in the middle third of the upper outer quadrant of the right breast. It was associated with architectural distortion, focal skin and trabecular thickening, and focal retraction of the overlying skin. No suspicious microcalcifications were observed [Figure 1]. Ultrasound examination was performed using a Supersonic Mach 30 (Aix-en-Provence, South France), which showed an irregular hypoechoic, non-parallel mass with spiculated margins measuring 2.8 × 1.9 × 1.5 cm at the 9 o’clock position in the right breast, 3 cm from the nipple, with a thick, irregular echogenic halo and posterior acoustic shadowing with internal vascularity on Doppler. Shear-wave elastography indicated the mass was hard, with a mean value of 262 kPa. No suspicious axillary lymph nodes were identified [Figure 2]. These imaging findings were highly suggestive of malignancy (Breast Imaging Reporting and Data System [BI-RADS] CATEGORY 5), according to the American College of Radiology BI-RADS 5^th edition.^[4]

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Figure 1:

A 38-year-old woman presented with a painless lump in her right breast. Mammogram (a-d) revealed an irregular, equal-density mass with spiculated margins in the upper outer quadrant (solid pink arrow). Another mass with circumscribed margins in the lower inner quadrant of the right breast (solid yellow arrow) was identified, which is a biopsy-proven fibroadenoma.

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Figure 2:

The ultrasound correlation revealed (a) an irregular hypoechoic, non-parallel mass with spiculated margins and an echogenic halo in the right breast, (b) showing internal vascularity. On shear wave elastography (c), the mass appears hard, with a mean elastography value of 262 kPa. The image (d) also shows a normal right axillary lymph node.

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Ultrasound-guided biopsy of the mass was performed under local anesthesia using a 14-G automated biopsy gun (Bard Maxcore biopsy needle, New Jersey, USA). The histopathology report revealed acute-on-chronic inflammation with no evidence of in situ or invasive malignancy. In view of discordance between radiological and pathological findings, a repeat biopsy of the mass was performed, revealing a dense sheet-like infiltrate of mononuclear cells, predominantly plasma cells, within intralobular and interlobular areas, along with stromal hyalinization, consistent with plasma cell mastitis (PCM).

Furthermore, due to persistent radiological and pathological discordance, a wide local excision of the mass, along with a sentinel lymph node biopsy, was planned. Before surgery, a magnetic resonance imaging (MRI) of the breast was performed as part of pre-operative staging. The MRI revealed an irregular, heterogeneously enhancing mass with spiculated margins measuring 3.1 × 2.5 × 2.1 cm in the outer central quadrant of the middle third of the right breast. It showed associated architectural distortion, focal trabecular and skin thickening, and skin retraction. The mass was isointense on T1-weighted imaging and hyperintense on T2 short tau inversion recovery, with diffusion restriction (apparent diffusion coefficient (ADC) value: 0.78 × 10⁻³ mm²/s). On post-contrast dynamic images, the mass demonstrated washout (type 3) kinetics [Figure 3]. Based on its morphological and kinetic features, the mass was classified as BI-RADS category 5.

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Figure 3:

Magnetic resonance imaging (MRI) was performed as part of pre-operative staging. Axial MRI images showed an irregular mass with spiculated margins in the right breast. The mass (a) appears isointense on T1, (b) hyperintense on T2 and (c & d) diffusely restricted on diffusion-weighted images. On post-contrast dynamic images (e & f), the mass exhibits heterogeneous enhancement with washout kinetics.

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Breast conservation surgery with sentinel lymph node biopsy of the axilla was performed. The lumpectomy specimen was sent for a frozen section, which identified PCM without evidence of malignancy, and the sentinel node was also negative. The final histopathology confirmed dense periductal, perilobular, and interlobular inflammation, mainly composed of plasma cells mixed with lymphocytes, consistent with PCM [Figure 4].

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Figure 4:

Histopathology images in (a) 10x & (b) 40x magnification views show dense infiltration of plasma cells within interlobular (solid yellow arrow) and intralobular areas (solid lack arrow), consistent with plasma cell mastitis. No in situ or invasive malignancy is observed.

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DISCUSSION

PCM is a chronic, non-infectious inflammatory condition of the breast, mainly occurring in women who are neither pregnant nor breastfeeding.

The pathophysiology of PCM remains unknown; however, a proposed hypothesis suggests an autoimmune response.^[5]

There are four stages of PCM: The duct dilatation stage, the acute inflammatory stage, the abscess stage, and the fistula formation stage. The condition begins with ductal dilatation caused by duct obstruction, which leads to the retention of secretions within the duct. As ductal dilatation progresses, the duct ruptures, allowing secretions to leak into the periductal connective tissue, triggering an inflammatory response and infiltration of lymphocytes, neutrophils, and numerous plasma cells into the periductal, perilobular, and interlobular connective tissue. The abscess forms secondary to superimposed bacterial infection. In the chronic phase, a fistula to the skin may develop.^[5]

The clinical signs of PCM differ depending on the disease stage. In the ductal dilation stage, the primary symptom is nipple discharge with a cheesy appearance. During the acute inflammatory and abscess stage, common symptoms include pain, redness, swelling, a lump, and yellowish nipple discharge. Skin retraction and fistulas develop in the chronic stage.^[5-7]

The imaging features of PCM also vary with disease stage. The duct dilatation phase is characterized by retroareolar duct ectasia with or without echogenic debris on ultrasound, and the mammogram may be normal at this stage. In the acute inflammatory phase, imaging features include dilated ducts with thickened ductal walls and periductal inflammatory changes, accompanied by increased vascularity.^[7] The abscess stage involves the formation of single or multiple abscesses, which require incision and drainage. In the chronic phase, typical imaging features of PCM include bilateral, symmetrical, thick, linear, rod-like calcifications measuring up to 10 mm, which are distributed along the course of ducts and their branches, converging toward the nipple on mammography.^[8] Overall, the most common imaging feature of PCM on mammogram is calcifications, and less common presentations include masses or asymmetries.

MRI is not routinely performed to diagnose PCM. However, MRI is indicated if there are suspicious masses or asymmetries on the mammogram, or if the mammogram and ultrasound are inconclusive, or when there is radiology–pathology discordance. Because MRI provides both morphological and functional information, it is possible to characterize lesions seen on mammograms and to help establish rad-path concordance.

The primary differential diagnoses for the PCM include invasive breast cancer and granulomatous lobular mastitis. On a mammogram, the morphology of calcifications can help differentiate between PCM and ductal carcinoma in situ/ invasive breast cancer. The calcifications of PCM are longer and thicker, and smoother in outline, compared to those in breast cancer, which appear as fine linear or linearly branching structures along the ductal distribution with irregular outlines.^[8] It is often difficult to distinguish the spiculated mass of PCM from the malignancy because PCM presenting as a spiculated mass is an infrequent entity, as shown in our case. MRI may be a problem-solving tool, and certain features can help differentiate between the two. T2 hyperintensity, a higher ADC value, multiple rim enhancement in cases of abscesses, a type 1 or type 2 time-intensity curve, and the absence of a choline peak are indicators of PCM.^[9] However, as in our case, some MRI findings can overlap with those of invasive ductal carcinoma, including an irregular mass with spiculated margins, heterogeneous enhancement, and washout kinetics. The formation of abscesses characterizes both granulomatous lobular mastitis and PCM, and the two entities can be differentiated by biopsy.

The management of PCM depends on the severity of the disease and the presence of complications, such as abscesses. Treatment options include antibiotics, corticosteroids, and surgery. Antibiotics and corticosteroids are used to treat infections and inflammation, respectively. For large abscesses and masses that do not respond to medical treatment, surgery is necessary.^[7]

CONCLUSION

PCM is a benign breast condition that commonly manifests as thick, rod-like calcifications on mammography. PCM, presenting as a spiculated mass on imaging and masquerading as malignancy, is an infrequent presentation, making differentiation from malignancy challenging and often requiring biopsy and surgery.

COMMON DIFFERENTIAL DIAGNOSES FOR A SPICULATED MASS ON A MAMMOGRAM

TWO TEACHING POINTS FROM THE CASE REPORT

1. There are various etiologies for the spiculated mass on mammography, and it is often difficult to differentiate the cause based on imaging.

2. A spiculated mass on mammography is a typical feature of malignancy and requires biopsy and excision if there is rad path discordance.

MCQs

1. All of the following are the causes for a spiculated mass except

   1. Invasive breast cancer, NST

   2. Radial scar

   3. Fibroadenoma

   4. Tubular carcinoma

   Answer key: c

2. Which is the most common imaging presentation of plasma cell mastitis?

   1. Calcifications

   2. Mass

   3. Asymmetry

   4. Architectural distortion

   Answer Key: a

3. Which is the most common clinical manifestation of plasma cell mastitis?

   1. Pain

   2. Lump

   3. Nipple discharge

   4. Asymptomatic

   Answer Key: d