Common mistakes - “The wrong kidney”

It can be pretty embarrassing if you miss a pathology or an important finding. But it is even worse if you mistaken a pathologic finding for an entire organ. When I was new to abdominal ultrasound this is what almost happened to me.

Falling into a pit hole:

I was examining a patient with a history of abdominal discomfort and stool abnormalities, performing an ultrasound scan right at the first contact and this is what I saw in the right upper quadrant in a subcostal view. While the structure had an awkward shape it did have the echogenicity of a kidney. So this is what I thought the structure is.
Imaging the right upper quadrant. Imaging a structure that resembles the right kidney

I then imaged what I thought was the “kidney in a transverse view and saw this image:
Echolucent structure with a rather irregular surface in the right upper quadrant

Again there were several features that made me believe it was the kidney such as a central hyperechoic reflex with a hypoechoic surrounding. I guess you already suspect that I was wrong. The true kidney was located further lateral and dorsal. Can you appreciate the difference?
Right kidney with its typical features (10-12 mm in size, typical internal structure, hyperreflexive smooth capsular contour

The truth behind

But what is the rather large structure then? As it turned out what I saw was a large colon carcinoma . The central highly reflective structure depicts the colon gas, the hypoechoic surrounding was the thickened colon wall. Because of the carcinoma infiltrating the colon wall this structure had a bizarre form, mimicking the kidney. I am happy that my superior pointed me to the mistake.

As it turns out this pitfall is not as uncommon as you might think. It actually has a name:

The “Pseudo Kidney sign”. Several pathologies can mimic a kidney. Especially those, which cause thickening of the bowel wall. Here you will see an outer rim with an echogenic central reflex and a hypoechoic surrounding

What are some of the specific pathologies that can mimic a kidney:
  • colon carcinomas
  • inflammatory colitis,
  • necrotizing enterocolitis,
  • lymphoma, in some cases even,
  • intussusception.
  • How to avoid?

    Here are some tips and tricks that will help you avoid falling into this trap:

    Always examine the entire abdomen then you will find the “real kidney“. If you find three kidneys in a patient, be aware that one could be a pseudo kidney. Look at the details of the suspected kidney such as: internal structure, mark pyramides, the size ( 10- 12 cm in longitudinal diameter, 4-6 cm transversal), shape and the capsular contour (which should be a smooth, hyperreflexive thin line, surrounding the kidney).

    If you are uncertain compare it with the true kidney of the contralateral side. And keep in mind: the kidneys are normally positioned in the retroperitoneum and slide up and down the psoas muscle during respiration. Finally, bowel often shows movement of stool. Something you will not see in the kidney


    Ulli Handler and the 123sonography team