https://orcid.org/0000-0002-8792-6185
History
A 72-year-old woman presented for a routine screening mammogram. She had received multiple COVID-19 vaccinations in her left arm over the previous 9 months. She had a family history of breast cancer in her daughter, who was diagnosed at age 38 years, and in two nieces who were diagnosed in their 40s.
Imaging findings
Screening digital breast tomosynthesis mammography was performed (Figure 1). A circumscribed fat-containing mass adjacent to a vessel in the axillary tail of the left breast was noted to be enlarged compared with prior examinations and consistent with an intramammary lymph node (IMLN). A second new small oval mass in the upper outer quadrant was seen for which additional imaging was recommended, and this proved to be benign at subsequent biopsy. No other mammographic abnormalities were seen, even in retrospect. Targeted left US was performed (Figure 2), showing an IMLN with a cortex measuring 2.5 mm and transcapsular vessels on color Doppler. The IMLN was considered suspicious in view of the enlargement. No axillary adenopathy was observed. In view of the enlarging IMLN and lack of any exculpatory history, there was concern for an occult breast mass. US imaging of the retroareolar region at the 12-o’clock position of the left breast unexpectedly demonstrated a 16-mm irregular, spiculated hypoechoic mass with an echogenic rim, palpable in retrospect, with an adjacent dilated duct (Figure 3). US-guided 14-gauge core biopsy of the retroareolar mass and the enlarging IMLN was performed.
Screening mammography images of an asymptomatic 72-year-old woman found to have an enlarging intramammary lymph node (IMLN). A: Screening digital breast tomosynthesis with synthetic reconstructions (craniocaudal views on left, mediolateral oblique views on right) show a circumscribed mass (arrows) adjacent to a vessel in the axillary tail of the left breast. An oval mass was newly noted in the upper outer quadrant (circle) which proved to be fibrocystic change on US-guided core biopsy (not shown). A stable calcifying fibroadenoma was also noted in the central left breast. B: On close-up craniocaudal (left two images) and mediolateral oblique (right two images) 6-mm slab tomosynthesis images, the 12-mm oval circumscribed fat-containing mass (filled arrows) adjacent to a vessel in the axillary tail of left breast is consistent with an IMLN and is enlarging compared with corresponding images from 13 months prior (open arrows) when it measured 8 mm. The patient was recalled for additional imaging.
Images at recall of an asymptomatic 72-year-old woman found to have an enlarging intramammary lymph node (IMLN). A: On full mediolateral synthetic mammogram (left) and close-up (right) 6-mm slab tomosynthesis at the time of recall one month later, the IMLN (arrows) has further enlarged. B: Targeted radial US (left) and antiradial (center) images of the IMLN (arrows) demonstrate a markedly hypoechoic cortex measuring 2.5 mm. Transcapsular vessels were noted on color Doppler (right, open arrow). In view of enlargement, the IMLN was considered suspicious.
US images of the retroareolar region of an asymptomatic 72-year-old woman found to have an enlarging intramammary lymph node (IMLN). Transverse and sagittal US of the left retroareolar region at the 12-o’clock position unexpectedly demonstrated a 16-mm irregular, spiculated hypoechoic mass (curved arrows) with an echogenic rim, palpable in retrospect, with an adjacent dilated duct, occult on tomosynthesis, and BI-RADS 5. US-guided core biopsy of the retroareolar mass showed grade 3 invasive ductal carcinoma, estrogen receptor, progesterone receptor, and human epidermal growth factor receptor-2 negative, Ki-67 proliferation index high at 45%. US-guided core biopsy of the IMLN showed metastatic carcinoma in a lymph node, with pathology that was morphologically similar to the retroareolar mass.
Dynamic contrast-enhanced MRI was then performed. Axial maximum intensity projection image (Figure 4) showed a 16-mm irregular enhancing retroareolar mass corresponding to the mass found on US and an oval circumscribed intensely enhancing mass in the upper outer quadrant with washout kinetics corresponding to the IMLN. Again, no axillary adenopathy was observed.
Breast MRI of an asymptomatic 72-year-old woman found to have an enlarging intramammary lymph node (IMLN). Dynamic contrast-enhanced MRI with axial maximum intensity projection image (left) demonstrates a 16-mm irregular enhancing retroareolar mass (curved arrow) corresponding to the known primary malignancy and an oval intensely enhancing mass in the upper outer quadrant (arrow) corresponding to the biopsy proven metastatic IMLN. No axillary adenopathy was observed. The retroareolar cancer (curved arrows, top-right images) is isointense on the T2-weighted image (STIR, left image), intensely enhancing (T1-weighted fat-suppressed post-contrast image, middle image), and shows mostly plateau kinetics (right image). As expected, the metastatic IMLN (arrows, bottom-right images) is hyperintense on the T2-weighted image (left image), intensely enhancing (with clip artifact, T1-weighted fat-suppressed image, middle image), and shows washout kinetics (right image).
Differential diagnosis
An abnormal IMLN may be due to benign or malignant etiologies. The most common cause is metastasis from an ipsilateral breast cancer (1). Other malignant etiologies include lymphoma or metastatic disease from a nonbreast primary, such as melanoma or gastric, lung, or ovarian carcinoma. Benign etiologies include silicone-induced lymphadenopathy because of breast implant rupture or silicone leakage, reactive hyperplasia following recent surgery or radiation, or inflammation such as from autoimmune diseases, breast abscess, or granulomatous mastitis (2). Intramuscular vaccine injections in the deltoid muscle can cause superior axillary and supraclavicular adenopathy because of the lymphatic drainage pattern of the upper extremity but are not reported to cause IMLN enlargement.
Diagnosis: Grade 3 invasive ductal carcinoma detected because of enlarging (metastatic) IMLN
Discussion
Intramammary lymph nodes are common benign findings on imaging and 48% of mastectomy specimens show IMLNs (3). Normal IMLNs are typically smaller than 1 cm with a reniform shape, discernable fatty hilum, and an adjacent artery and vein, and 76% are found in the upper outer quadrant (4).
Distinguishing malignant from reactive or normal IMLNs can sometimes be challenging. In the absence of known ipsilateral breast cancer, Dialani et al (5) found a low breast malignancy rate on biopsy of suspicious IMLNs of only 5/77 (6%) (with 2 additional malignant lymphomas). All 5 malignant IMLNs in that setting had a cortical thickness greater than 5 mm and loss of the fatty hilum. However, in women with known ipsilateral malignancy, IMLNs with a cortical thickness greater than 3 mm and loss of the fatty hilum were suspicious, with 60/94 (64%) of such nodes found to be malignant; the sensitivity here was 60/64 (94%) (5). Features such as round shape, noncircumscribed margin, size greater than 1 cm, calcifications, absent or eccentric hilar fat, and enlargement when compared with prior imaging should prompt further investigation (2). It should be noted that in one series, 15/19 (79%) of metastatic IMLNs were under 1 cm in size (6).
Sentinel node injections are typically performed by injecting 99mTc-sulfur colloid in the subcutaneous space within the periareolar region because the retroareolar Sappey plexus of lymphatics drains to the axillary nodes. Although the sentinel node is often the most inferior level I axillary node, IMLNs are identified as sentinel nodes in 0.7% to 14% of patients (4). In a review of 20 case series, Abdullgaffar et al (7) found that 313/30 784 (1.0%) of breast cancers had metastatic IMLNs. In that review, for the subset of cases with sufficient data, 162/274 (59%) of patients with IMLN metastases also had axillary nodal disease. Isolated IMLN metastasis is considered N1, node-positive disease (8), and IMLN metastasis should be excised.
In this case, the primary breast malignancy was occult on tomosynthesis. The retroareolar breast and inframammary fold are common locations for mammographically occult cancer. In the retroareolar region, mammographic challenges include reduced anterior compression and often suboptimal positioning with the nipple not in profile. The astute radiologist evaluating this patient identified the primary malignancy by performing US of the retroareolar region, and the finding was also demonstrated on subsequent MRI.
Funding
None declared.
Conflict of interest statement
W.A.B. discloses a research grant to the Department from Koios Medical, Inc, for which she is the principal investigator. W.A.B. is an Associate Editor for the Journal of Breast Imaging and was recused from all aspects of review of this manuscript. W.A.B. is voluntary Chief Scientific Advisor to DenseBreast-info.org. A.E.S. discloses a pending patent application, “System, Device and Method for Automated Auscultation,” Skysong Innovations, Arizona State University, unrelated to this manuscript.
