A 78-year-old man presented to the ED with hyperglycemia, abdominal pain, and confusion. The history was obtained from a relative because of his confusion. He had been having right-sided abdominal pain for 2-3 days associated with nausea and vomiting. The emesis was reported to be non-bloody. He was having normal bowel movements. His son noticed that on the evening of presentation, the patient had become more confused in his speech and thought process. He had not had any previous abdominal surgeries. He had a history of chronic urinary tract infections that had been treated intermittently with Nitrofurantoin. He was on metformin for his type II diabetes, and his blood glucose had been up to 600 on the day of presentation.
Initial VS: BP 152/70, HR 110, T 36.8 °C (98.2 °F), RR 18, SpO2 100%
Physical exam was significant for tenderness to palpation of the abdomen in the right upper and lower quadrants. There was also right-sided costovertebral angle tenderness.
The initial differential was broad, and a work-up was initiated that included a CBC, chemistry panel, UA, lipase, liver function tests, lactate, and venous blood gas. Given the right-sided nature of his pain, a bedside ultrasound of his gallbladder and kidneys were performed.
His gallbladder appeared normal without gallstones.
Here are the images of his left kidney:
You can see that the renal pelvis appears hyperechoic with small anechoic areas present. This could be the normal appearance of the renal pelvis, or it could also be mild hydronephrosis. You can see there is a simple renal cyst present in the cortex.
Sometimes the vasculature in the renal pelvis makes it look like there is mild hydronephrosis present. If there is a question whether or not there is hydronephrosis, put color Doppler over the area. Vasculature will have color Doppler flow present. Conversely, hydronephrosis will have no color Doppler flow present in the anechoic areas. Here is the image with color Doppler:
You can see that there are small anechoic areas that do not have color Doppler flow present. There is mild hydronephrosis present.
Here are the images of the right kidney:
What do you notice?
It does not appear like there is hydronephrosis, but the kidney has something else abnormal present. There is SHADOWNING. There is a lot of shadowing. In the kidney, this is usually indicative of renal calculi. The provider taking care of the patient realized this was abnormal and interpreted the image as having a staghorn calculus present. This was an incorrect conclusion, but why?
Renal calculi will produce a clean, dark (hypoechoic) shadow. The shadow in the clips obtained was brighter (hyperechoic) and irregular. This is called a DIRTY SHADOW. Dirty shadowing is created by air. The shadow from air is described as being dirty because it contains lighter, irregular gray level echos. Dirty shadows are most commonly seen from air within the bowel.
Now the big question is why is there air in the kidney?
The patient’s labs returned with many abnormalities:
Lactate: 3
Sodium: 125
Blood Glucose: 629
Anion Gap: 17
Creatinine: 3.3 (baseline unknown)
WBC: 21
His UA was nitrite negative, but did have >50 WBCs present.
Even though the ultrasound images were initially interpreted incorrectly, the team taking care of the patient realized that he was very ill. A CT scan of his abdomen was obtained which revealed why there was air in his kidney. Here are the images:
There is a large right renal abscess and emphysematous pyelonephritis of the right kidney. There is additional gas within the retroperitoneum, right ureter, and bladder. There was also noted to be mild hydronephrosis of the left kidney.
The patient was admitted to ICU with broad-spectrum antibiotics and a urology consult. He initially had a drain placed into the abscess by interventional radiology, but the infection continued to worsen despite this. The patient eventually underwent an emergent right-sided nephrectomy. His blood cultures grew out E. Coli, and he was continued on antibiotics. Despite his complicated course, he did rather well post-operatively, and his creatinine was 2.9 on the day of discharge. He was discharged on hospital day 7 with plans to continue daily IV antibiotics. He was doing well at follow-up.
Bottom Line:
- Clean, hypoechoic shadows are created by dense structures, such as, bone, gallstones, and renal calculi.
- Dirty, irregular shadowing is created by air.
