The volume of the testicles increases
When twisted, testicles increased in size due to the congestion of parenchyma and presented a full and spherical shape, which is often misdiagnosed as orchitis. A difference in the size of testicles at both sides, with the affected testis larger in volume than the asymptomatic side, is a crucial feature, suggestive of testicular torsion(16). The testicular volume of the affected side in the present study is larger than that of the contralateral side in all patients (Figure1).
The testes are commonly in an upright position. If the long axis of the testicle is inclined or even horizontally relative to the long axis of the thigh or long axis of the femur, especially if the orientation of the testicular mediastinum changes in the cross section, it may indicate testicular torsion(18). Four testicles were oblique (Figure 2).
Besides, previous studies have also reported that testicular torsion is more likely to occur on the left side (4,19) because the left spermatic cord is longer than the right. This study also found that four testicular torsions occurred on the left, whereas three testicular torsions happened on the right side, which was consistent with previous studies. But the study with a larger sample size is warranted.
Heterogeneous echotexture of the testicles
Testicular torsion can have a various twisting degree and thus result in heterogeneous parenchymal echotexture seen in testicular torsion. The presence of significant heterogeneity indicates a late torsion and testicular nonviability. Whereas, the homogeneous signal of testicular parenchymal may indicate the variability of testicles(20,21). In the present study, there were five cases with the heterogeneous echo of testis parenchyma and fissure anechoic around mediastinum (Figure3), and the result matched with surgical findings. Careful mapping of the testicular echotexture can help with the early diagnosis of potential segmental necrosis and can also aid the follow-up exam when the echotexture returns to normal.
The epididymis is inevitably involved in the torsion, and it is often enlarged. In our study, the epididymis was enlarged in various degrees, and it thus can be commonly misled to epididymitis. An 8 years 3month-old boy from the current cohort with the third episode of acute left scrotal pain for five days and was initially misdiagnosed as epididymitis. In addition, the increased epididymis and the convoluted spermatic cord are also easily entangled together to form pseudo mass (Figure 4, Video1). The appearance of the pseudo mass is similar to that of an inflamed epididymis. Sonographic review of the spermatic cord can differentiate testicular torsion with pseudo mass formation from epididymitis. The presence of a straight spermatic cord with a hyperemic epididymis but no pseudo mass can be seen with both epididymitis and torsion of an appendage, both of which should be treated medically, not surgically(14).
The spermatic cord--“whirlpool sign”
The diagnosis of torsion is based on a lack of blood flow in the testes or a marked reduction in blood flow in the affected testes(22). However, in the present study, three cases showed an increased blood flow signal, and four cases had preserved blood flow (Figure5), which indicated the low yield of blood perfusion in diagnosing testicular torsion by US. Four cases with even hyperperfusion were given by the reasons as follows:1) enlarged testicular volume may increase the diagnostic sensitivity of color doppler US(23);2) inflammatory response happening surround the ischemic testicular parenchyma may increase the parenchymal perfusion(24); 3) There are different types of testicular torsion including complete testicular torsion, intermittent testicular torsion, and partial or incomplete torsion based on the various twist degrees(14).
In the present study, all of the patients were intrathecal testicular torsion which was confirmed by surgery with various twisting situations from 90° to 540°. Taken together, the residual blood flow in all cases may be caused by intermittent or spermatic cord torsion. In this case, the ‘whirlpool sign' was the key feature(Figure6), which was consistent with early studies(5,14,18,25). The "whirlpool sign" of the spermatic cord is considered to be a more direct and specific sign of testicular torsion and is valuable for the diagnosis of complete, intermittent, and incomplete torsion of the testis, regardless of color doppler US findings(5,18,25). In patients with preserved blood flow, the position of the spermatic cord and testes should be assessed comprehensively. Therefore, in the diagnosis of testicular torsion, ultrasound examination needs to evaluate the full length of the spermatic cord.
This study had some limitations. First, the study has a small sample size. Second, all the patients we had tested color doppler, but resistive index (RI) and venous flow were not assessed. Third, we did not recruit normal volunteers but using the opposite healthy side of the testis as the reference group. The prospective case-control study with a larger sample size should be conducted to confirm our findings in the future.