Kidney ultrasound pitfalls: don’t forget to fan
When performing kidney ultrasound, we emphasize on fanning through the entire organ (anteroposterior in the long axis and superoinferior in the transverse axis) so that small lesions such as cysts and stones are not missed. Fanning is nothing but tilting the transducer along its short axis as shown below.
However, even larger lesions can be missed sometimes if you don’t fan. Here is an excellent example. At first glance, this long axis view of the kidney appears OK with no hydronephrosis or other notable lesions. Parenchyma appears relatively thin (h/o chronic kidney disease). Image is obtained using a handheld ultrasound device in cardiac preset, hence appears grainy.
Once the transducer is fanned posteriorly, three large anechoic lesions (simple cysts) appear with a maximal diameter of more than 5 cm.
Review of the previous CT scan demonstrated these cysts. Below image shows the polar cysts.
Below is another nice example illustrating how stone(s) and associated hydronephrosis could be missed on still images. Shared by Dr. Martínez.
The purpose of POCUS is to answer focused clinical questions (e.g., hydronephrosis vs no hydronephrosis) but if you are a nephrologist and fail to document large (and otherwise obvious) lesions like this, it won’t look good! Not only that, but inadequate fanning often leads to confusion between cysts and hydronephrosis. So, always remember to fan through the entire kidney and follow SECONDS checklist while interpreting the images.