Distribution of Epididymal Involvement in Mumps Epididymo‐orchitis

OBJECTIVES: To evaluate characteristic sonographic findings for mumps orchitis with epididymal involvement. METHODS: This study included 18 patients (aged 12-18 years) with mumps orchitis. We assessed the volume, echogenicity, and vascularity of the testes and the transverse diameter, echogenicity, and vascularity of the epididymal head, body, and tail. We classified 4 types of epididymal involvement: 1A, focal swelling of the epididymal head with hypervascularity only on the swollen head; 1B, focal swelling of the epididymal head with hypervascularity on the entire epididymis; 1C, diffuse swelling of the entire epididymis with hypervascularity; and 2, no epididymal involvement. The Student t test was used to evaluate the significance of the size of each part of the epididymis and the epididymal head-to-tail diameter ratio. RESULTS: Orchitis was unilateral in 13 patients and bilateral in 5. Of 23 affected hemiscrotums, 7 (30.4%) were type 1A, 4 (17.4%) type 1B, 2 (8.7%) type 1C, and 10 (43.5%) type 2. In 11 patients with unilateral epididymal involvement, the mean diameters ± SDs of the epididymal heads on the affected and contralateral sides were 1.11 ± 0.19 (range, 0.7-1.7) and 0.65 ± 0.14 (0.3-0.9) cm (significantly different, P <.001). The diameters of the epididymal tails on the affected and contralateral sides were 0.51 ± 0.41 (0.2-0.8) and 0.46 ± 0.21 (0.3-0.6) cm (not statistically different, P = .106). The mean head-to-tail ratios on the affected and contralateral sides were 2.28 ± 0.49 (1.29-3.00) and 1.41 ± 0.22 (1.00-1.75; significantly different, P < .001). In all types 1A and 1B, the ratio was higher than 2.00; in 22 of 23 unaffected epididymides, the ratio was lower than 2.00. CONCLUSIONS: Focal swelling of epididymal heads was a characteristic sonographic finding of mumps epididymo-orchitis, and a head-to-tail ratio higher than 2.00 can be a useful diagnostic finding.