Elastofibroma Dorsi in a Patient with Right Breast Carcinoma: A Potential Diagnostic Pitfall

Elastofibroma dorsi is a rare benign soft tissue pseudotumour typically located in the infrascapular region deep to the serratus anterior and latissimus dorsi muscles. It is often detected incidentally on cross-sectional imaging and is usually asymptomatic. However, in oncological patients, it may mimic metastatic soft tissue disease and therefore represent a significant diagnostic pitfall. We report the case of an 80-year-old female with known right breast carcinoma who underwent staging contrast-enhanced computed tomography (CT) of the thorax. Imaging demonstrated an ill-defined, non-encapsulated lenticular soft tissue lesion in the right infrascapular region, deep to the latissimus dorsi and serratus anterior muscles, showing characteristic internal linear fat streaks and a striated internal architecture without calcification, necrosis, or adjacent bone destruction. Based on its typical morphology, location, and internal fat attenuation, a confident diagnosis of elastofibroma dorsi was established without the need for biopsy. This case emphasises the importance of recognising the characteristic CT and magnetic resonance imaging (MRI) appearances of elastofibroma dorsi in oncologic imaging to avoid misinterpretation as metastatic disease, thereby preventing erroneous upstaging and unnecessary invasive procedures.