The spectrum of findings on gray-scale and color Doppler US imaging of a STI differs depending on the time between the onset of testicular pain and the US examination (1
). It was shown that lesions identified earlier were more often rounded and nearly isoechoic to the testis and have ill-defined margins (8
). Based on the gray-scale US features at an early presentation, differentiation from a testicular neoplasm is difficult. Interestingly, we found a softer area compared to the normal testicular parenchyma at the initial SWE examination (within 24 hours after onset of pain). Increase in water content and swelling of the tissues secondary to ischemia may be the pathophysiological mechanism for the infarcted area that appeared soft on SWE led us to follow the patient rather than to go to surgery.
On gray-scale US, a STI became more conspicuous and smaller over time, hypoechoic to testis, and often having a wedge shape (8
). A follow-up of our case showed that the lesion became wedge-shaped but still had ill-defined margins. On SWE, the lesion appeared stiffer than the testicular parenchyma, probably due to the organization of hemorrhage and necrosis and the shrinkage in size of the lesion. Interestingly, the lesion had the shape of a testicular lobule on SWE images that was more easily appreciated than the gray-scale US, enabling us to confidently diagnose a STI.
On color Doppler US, a typical STI has complete loss of vascularity; however, diminished vascularity has also been reported (1
). Presence of color Doppler signal within the lesion results in diagnostic difficulties, with a tumour being a possibility (4
). Testicular tumours are normally vascular on color Doppler ultrasonography and may demonstrate a characteristic pattern of vascular flow (10
). The demonstration of vascularity in a focal testicular mass is thought to be dependent on the size of the abnormality. Horstman et al. (10
) failed to demonstrate an increase in lesion vascularity when the lesion was smaller than 16 mm in diameter. However, with modern ultrasonography equipment, color Doppler flow may be demonstrated in focal, solid lesions as small as 5 mm (11
). In our case, at the initial examination, there was complete loss of vascularity; however, on follow-up Doppler US, there was some vascularity within the lesion. In our case, without knowing the previous Doppler US findings, the presence of vascularity within the lesion at follow-up may cause difficulties for the diagnosis.
Contrast-enhanced US was successfully used to improve lesion conspicuity and depict the anatomic characteristics in a STI (8
). Infarction presents as one or more avascular areas separated by normal vessels at contrast-enhanced US, which is consistent with ischemic testicular lobules. The perilesional rim enhancement is a useful finding frequently seen in patients with a STI on contrast-enhanced US (8
). A more pronounced perilesional rim enhancement and lobular distribution differentiates STI from an abscess. Similar to contrast enhanced US, gadolinium-enhanced magnetic resonance imaging demonstrates an enhanced halo delimiting the avascular area in a STI (3
In summary, similar to gray-scale and Doppler US, the SWE features may depend on the evolution of a STI that is soft at initial presentation and hard the late stages compared to normal testicular parenchyma. The use of SWE in addition to gray-scale and Doppler US may prevent unnecessary orchiectomies.