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Background
Radial scars (RSLs), also known as complex sclerosing lesions (CSLs) if > 1.0 cm, are idiopathic proliferative breast lesions defined by a central scar-like area with obliterative ducts in a stellate pattern. It is considered a high-risk lesion, which both increases the future risk of breast cancer and is potentially associated with breast cancer upon excision. The prevalence of RSL ranges from 0.1 to 2/1000 seen on screening digital mammography but its incidence on autopsy is between 14-28%. The incidence of RSLs has increased with the technological the development of tomosynthesis. Since more are found on tomosynthesis, current investigation is underway regarding management of RSLs. Traditionally, all RSLs were excised. Today, management may vary across institutions. While it is well established that surgery is recommended of radial scars with atypia on core biopsy, Piraner et al. suggests that cases of concordant, pure RSLs diagnosed at core-needle biopsy may not require surgical excision. For biopsies yielding RSLs with other high-risk lesions, including ADH, lobular carcinoma in situ, flat epithelial atypia, atypical lobular hyperplasia, and papillomas, excision should still be considered. Research has shown varying degrees of upgrade rates (0-43%); however, later publications and those which use larger-gauge (9 and 9-12G) vacuum-assisted biopsy (VAB) devices show lower upgrade rates.

Educational Goals / Teaching Points
Educational goals include a review of imaging findings, histopathology findings, and management considerations. Management remains controversial, with more studies providing evidence for surveillance after therapeutic excision with VAB or follow-up. The management of single and multiple RSLs will be reviewed.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Radial scars are classically nonpalpable. On mammography, the typical appearance is that of architectural distortion and can mimic cancer, particularly invasive lobular carcinoma. Oftentimes, fine radiolucent lines radiate from the dark center, described as a benign etiology with a sensitivity and specificity of 86.7% and 61.5%, respectively. The spicules of RSLs are described as very long and thin, classically referred to as “black star”. On ultrasound, the appearance can again overlap with that of cancer, often demonstrating a hypoechoic irregular mass with indistinct margins. The appearance on MRI is variable and may appear as a mass and non-mass enhancement. Some research has suggested that suspected mammographic RSL and the absence of enhancement on MRI is an accurate predictor of benignity at excision, with reported negative predictive values of 97.6% and 100%.

Conclusion
The mammographic appearance of radial scars can mimic cancer and therefore radiologists should be aware of the classic imaging findings to determine concordance and further treatment. The management after diagnosis remains controversial, with considerations including excision, follow-up, repeat biopsy and discussion at multidisciplinary conferences.