Urgent and emergent breast lesions – A primer for the general radiologist, on‐call resident and sonographer

Abstract There are very few true breast emergencies. While infrequent, women do present to emergency departments or urgent care centres with breast‐related concerns. In this case‐based review, both common and uncommon urgent and emergent breast lesions are presented, emphasising ultrasound characteristics and imaging optimisation to improve accurate diagnosis and appropriate recommendations.


Introduction
Ultrasound is a modality that is readily available at a low cost and does not use ionising radiation, making it ideal for evaluating patients with breast-related complaints in an urgent or emergent setting. 1 When evaluating the breast in these settings, the primary goal is to efficiently identify the acute cause for the patient's presenting symptoms. This is in contrast to when ultrasound is utilised during a diagnostic imaging evaluation where the rationale is to identify or exclude a malignancy as the aetiology for a patient's presentation. This article reviews the most common causes for breast-related urgent and emergent complaints, including trauma, bleeding and infection. Emphasis is placed on salient ultrasound imaging features to make an accurate diagnosis of a benign process and aid the recognition of a possible underlying malignancy that would require additional diagnostic imaging and biopsy. This review was approved by the Institutional Review Board of our institution's Office for Human Research Protections.
At our institution and at many imaging centres across the country, targeted breast ultrasound examinations performed after-hours are not always interpreted by a Mammography Quality Standards Act (MQSA)-certified breast radiologist. Furthermore, imaging reports often contain a disclaimer such as 'This focused breast ultrasound examination was performed to evaluate for infection and fluid collections only. To assess for malignancy, a full diagnostic workup in the Breast Imaging department would be necessary'. American College of Radiology (ACR) Breast Imaging-Reporting and Data System (BI-RADS) assessments (Table 1) are not used when generating a report for these cases; therefore, these cases are not included in an MQSA audit. 2 Given the infrequency of these after-hours cases and the non-breast subspecialised experience of the interpreting radiologist, consultation with an MQSA-certified breast radiologist the next day or follow-up with a dedicated breast imaging evaluation is a common practice.
Linear ultrasound transducers ranging from 5 to 18 MHz are most commonly used for targeted breast ultrasound. 3 According to ACR practice guidelines, due to concerns of poor spatial resolution at lower frequencies, the lowest frequency considered 'allowable' in breast imaging is a centre frequency of 12 MHz. 4,5 However, curved or lower frequency linear transducers, commonly utilised for body ultrasound, may be used after-hours by the on-call sonographer or radiologist for imaging the breast, and this is another reason patients should be encouraged to pursue dedicated breast imaging evaluation in follow-up. an infectious process involving the breast are depicted in Figure 1. Typically, these patients will complain of breast pain and physical examinations reveal localised erythema and swelling or even a palpable lump. 6 Early infections are localised to the dermis, with isolated skin thickening (>2 mm) that can be appreciated on targeted breast ultrasound examination, confirming the diagnosis of breast cellulitis ( Figure 2). The role of ultrasound is to evaluate the progression of infection into the breast parenchyma. Therefore, it is important that ultrasound images should be taken from the skin to the chest wall for these evaluations as to not miss deeper infections.

Case-based review
Mastitis is present when infection and inflammatory changes progress deeper to involve the breast parenchyma. Ultrasound findings include skin thickening and underlying increased breast echogenicity with associated hyperaemia on colour Doppler. These subtle breast parenchyma changes may make diagnosis difficult, particularly in the setting of heterogeneously dense breast tissue. In such cases, obtaining comparison images of normal parenchyma in an asymptomatic ipsilateral quadrant or the contralateral breast can confirm subtle changes of infection ( Figure 3). Additional findings include oedema manifested as interstitial fluid and dilated ducts without a focal fluid collection. 7 Again, the role of targeted imaging in such cases is to exclude an abscess that has formed deeper in the breast, and commonly, the ultrasound frequency may need to be decreased to appropriately penetrate oedema, fluid and dense breast tissue. Furthermore, harmonic imaging may be used for troubleshooting as there is more tissue contrast between breast lesions and surrounding tissue. 8 More severe stages of a breast infection include the development of an abscess as the inflammatory response breaks down the infected tissues with the accumulation of bacteria and white blood cells. Only phlegmonous change may be present during the early changes of abscess formation, which on ultrasound presents as breast oedema and non-contained complex fluid ( Figure 4) or non-drainable thick collections. As the infection continues, a discrete drainable fluid collection with surrounding oedema and increased vascularity may develop ( Figure 5). This collection may contain mobile internal echoes and occasional septations. 7 Thorough ultrasound imaging at the site of clinical symptoms and adjacent breast parenchyma is important to evaluate the extent of the infection for possible intervention  and follow-up. Once an abscess is identified, image-guided aspiration should be recommended for both diagnostic and therapeutic purposes. 6 Clinical follow-up within a week is indicated in these cases and will direct the need for subsequent targeted ultrasound examinations or serial aspirations. If symptoms rapidly progress, patients should be instructed to return to care sooner, or if symptoms are resolving, follow-up may be extended out further to document complete resolution. Recognising ultrasound features of potential breast malignancy, which may appear as a solid mass, is imperative to avoid misdiagnosis and delayed treatment ( Figure 6). 9 Additionally, malignancies such as inflammatory breast cancers will have a different clinical course. If a patient does not show a clinical response or there is an (a) (b) Figure 3: 42-year-old woman with a history of breast conservation therapy performed 9 months prior presented to the emergency department with worsening right breast pain and redness despite being treated empirically with clindamycin. In the upper outer right breast at the site of clinical concern, ultrasound was performed with an L3-12 MHz transducer with harmonics and the images were captured from the skin to the chest wall. Targeted ultrasound demonstrated skin thickening measuring 6 mm (bracket) and underlying oedema manifested as subtly increased echogenicity (chevrons), but no drainable fluid collection (a). A comparison with the contralateral (left) breast was performed, which showed normal skin thickness measuring 1 mm (bracket) and normal heterogeneously dense fibroglandular tissue (asterisk) (b). Imaging findings are consistent with right breast mastitis and overlying cellulitis without an underlying abscess. Clinical follow-up of the right breast erythema and pain with repeat targeted imaging in the setting of worsening symptoms was recommended. Fortunately, this patient's symptoms were fully resolved, and she did not require additional targeted imaging.  Ultrasound was performed with a ML6-15 MHz transducer with the frequency set to 11 MHz, and the images were captured from the skin to the chest wall. Targeted ultrasound evaluation at 6 o'clock 2 cm from the nipple demonstrated mild skin thickening measuring 4 mm (bracket), linear hypoechoic regions of interstitial fluid (chevrons) and associated hypervascularity (arrows). No discrete drainable fluid collection was identified. Constellation of findings was consistent with left breast mastitis with phlegmon. The patient was instructed to continue breastfeeding on a frequent basis, with warm compresses and massage in between, and to complete her 10-day course of Keflex. Her symptoms were fully resolved, and she did not require a follow-up ultrasound. incomplete response to the appropriate antibiotic therapy within 1-2 weeks, then inflammatory breast cancer should be considered. 10 As a result, all patients with a breast complaint in an urgent care or after-hours setting should be advised to have a dedicated imaging evaluation at a breast imaging centre. A rare but potentially life-threatening breast emergency is necrotising fasciitis (NF), most commonly observed in   patients with diabetes and obesity. 11 This soft tissue infection shows rapid progression and results in extensive necrosis of the fascia and subcutaneous tissue, leading to severe systemic sepsis. Targeted ultrasound can identify air as echogenic foci with posterior dirty shadowing (Figure 7). 12 However, for this particular type of infection, computed tomography (CT) can readily depict the presence of subcutaneous emphysema resulting from the gas-producing infection and evaluate the extent of disease. 13 Body piercing, including nipple piercing, is becoming more common. These adornments can cause various complications including an infection (Figures 8 and 9), allergic reaction or even scarring. 14 As with any infection, the patient may present with focal breast pain, erythema, swelling and even a palpable mass. 14,15 These symptoms have been reported to occur anywhere from 2 weeks to 17 months after the piercings have been placed. 14 Male patients can also present to the emergency department with complaints of a possible breast infection. However, unlike with women, infections in the male breast are typically a result of trauma such as piercings (Figure 9). 16

Iatrogenic haemorrhage
Haematoma is the most common post-procedural complication. Bleeding typically occurs immediately or within 24 h of a biopsy. The goal for post-procedural imaging in this setting should be to determine whether there is active bleeding from a vessel with an expanding haematoma or a stable thrombosed haematoma ( Figure 10). 17 If active bleeding is present, dedicated images to evaluate a pseudoaneurysm (PsA) with colour Doppler imaging to evaluate a typical yin-yang sign are important. If a PsA is present, images of the neck, including size and spectral Doppler looking for characteristic to-and-fro or bidirectional flow, can assist the interventionalist (Figure 11). Based on the neck size and shape, it is possible to determine whether the percutaneous thrombin injection can be used to treat pseudoaneurysm. 18 A narrow neck is optimal for consideration of either compression or thrombin injection. Furthermore, a PsA should be differentiated from a true aneurysm, which involves all three layers of the blood vessel (Figures 12 and 13).
Very rarely patients present with 'spontaneous' bleeding from the breast. A physical examination will often reveal an associated wound or underlying breast mass suspicious of malignancy. 19 The neoangiogenesis that occurs with malignancies results in friable vessels, which are prone to haemorrhage. 7,20 Papillary tumours have vascular stalks, which, when severed, can lead to repeated bleeding into a cystic component. Ultrasound will show a mixed solid and cystic mass. 21 Identifying flow in the solid components of these lesions can aid in an accurate diagnosis and often requires lightening the manual pressure and reducing the colour scale to detect colour flow ( Figure 14). Non-emergent next-day sampling of the solid portion should be completed by a dedicated breast imaging team.

Trauma
Blunt force trauma to the breast is commonly seen in motor vehicle accidents and falls, which can result in haematoma formation and subsequent fat necrosis. 22 In the acute setting, ultrasound of the affected area will show predominantly hyperechoic breast tissue due to breast oedema ( Figure 15). In the subacute phase, multiple cystic spaces develop with or without surrounding echogenic fat ( Figure 16). As there is evolution of the fat necrosis, the sonographic findings may fully resolve the patient's symptoms, or the cystic components may become discrete oil cysts, which can be calcified over time. 23,24 Seat belt injuries will have a discrete pattern and location depending on if the patient is sitting in the driver's seat or the passenger's seat ( Figure 17). 25 The orientation of the seat belt is such that the appearance of the injury on subsequent mammograms will be in a non-ductal distribution (Figure 18). Imaging findings will vary depending on the timing of the injury and subsequent patient presentation for care. Acute presentation may show increased echogenicity due to trauma or even a developing haematoma if the injury is severe, whereas a delayed presentation may show the later stages of fat necrosis. 15,26 Ethics approval This review was approved by the Mayo Clinic IRB.