ObjectivesTo characterize the sonographic features of cat scratch disease and to identify features that allow differentiation from other causes of medial epitrochlear masses.MethodsAfter Institutional Review Board approval was obtained, patients who underwent sonography for a medial epitrochlear mass or lymph node were identified via the radiology information system. Patients were divided into 2 groups: cat scratch disease and non–cat scratch disease, based on pathologic results and clinical information. Sonograms were retrospectively reviewed and characterized with respect to dimension, shape (round, oval, or lobular), symmetry, location (subcutaneous or intramuscular), multiplicity, echogenicity (anechoic, hypoechoic, isoechoic, hyperechoic, or mixed), hyperechoic hilum (present or absent), adjacent anechoic or hypoechoic area, hyperemia (present or absent), pattern of hyperemia if present (central, peripheral, or mixed), increased posterior through‐transmission (present or absent), and shadowing (present or absent). Sonographic findings were compared between the patients with and without cat scratch disease.ResultsThe final patient group consisted of 5 cases of cat scratch disease and 16 cases of other causes of medial epitrochlear masses. The 2 sonographic findings that were significantly different between the cat scratch disease and non–cat scratch disease cases included mass asymmetry (P = .0062) and the presence of a hyperechoic hilum (P = .0075). The other sonographic findings showed no significant differences between the groups.ConclusionsThe sonographic finding of an epitrochlear mass due to cat scratch disease most commonly is that of a hypoechoic lobular or oval mass with central hyperemia and a possible adjacent fluid collection; however, the presence of asymmetry and a hyperechoic hilum differentiate cat scratch disease from other etiologies.