ESWL is increasingly used in clinical practice, leading to a greater number of potential complications. The parenchymal injury is originated by the shock waves that affect the blood vessels, leading to hematomas. The degree of damage depends on the technique, kidney morphology, patient co-morbidities and stone characteristics [4,5,6]. Most of them are asymptomatic, but a few present with ipsilateral pain, as described above. Clinical evaluation, including physical evaluation, is important but frequently not enough to clearly differentiate between the most frequent complications of ESLW. It is our understanding that the addition of POCUS to the clinical evaluation can improve diagnostic accuracy of the possible complications, as this case shows. Ultrasound has many advantages, including a favourable safety profile, without ionizing radiation, increasing availability and can be easily performed multiple times on the bedside.
In this particular scenario, POCUS helped in the differential diagnosis of lumbar pain after ESWL, favoring subcapsular renal hematoma against other potential diagnoses, including incomplete stone fragmentation and, less frequently, kidney rupture [7].
The sonographic appearance of a subcapsular renal hematoma is usually a crescent-shaped or ellipsoid hyper-, iso- or hypoechoic lesion located around the kidney in the subcapsular space. Hematomas can appear heterogenous and hyperechogenic in the acute phase, becoming more hypoechoic or cystic over time [8, 9]. Technically, the kidneys are usually well identified using a standard curvilinear probe. The visualization of the hyperechoic renal capsule helps to differentiate between the fluid in the intraabdominal cavity and the hematoma, as subcapsular hematomas are between this capsule and the cortex. Subcapsular renal hematomas can be more difficult to see in the acute phase because they may have the same echogenicity of the renal cortex.
It is important to note that the sensitivity of renal ultrasound for subcapsular renal hematomas is low compared to CT [10]. So, a normal POCUS should not be used to rule out a subcapsular renal hematoma (or other complications). When there is a clinical suspicion, a more sensitive exam like a CT scan should be obtained.
Treatment of these conditions depends on hemodynamic stability. Most of the patients, like this one, stay hemodynamically stable and the treatment should be conservative, consisting of clinical observation and exclusion of other complications [11]. POCUS can also be a useful tool in this setting, as it allows for continuous monitoring, especially in case of worsening of the symptoms. More severe cases may require blood transfusions, percutaneous drainage [12], that can be guided using ultrasound, or even, in very rare cases, nephrectomy.