Soundings: Ultrasound Anatomy

No Comments

When you use ultrasound to identify specific problems, can you also identify surrounding anatomic structures? 

It’s 7am and your first patient is a 71-year-old male with abdominal pain and vomiting. From the triage notes, you see he takes metformin for diabetes and atenolol for hypertension. He smiles at you while answering your questions in broken English. After a brief interview you surmise that he has been having generalized abdominal pain since midnight and has vomited three times. When you ask about diarrhea or his “BM’s” the communication gap seems to widen, so you proceed to examine him. He does not look particularly uncomfortable. His blood pressure is a bit on the low side–the low 90’s to be precise–but the rest of his vital signs are normal. His mouth looks a tad dry. His heart and lungs sound normal, but his abdomen seems tympanic and possibly distended, with a well-healed midline scar. You ask what surgery he has had while pointing to the scar. He smiles and answers, “in my country”. Palpation and percussion reveal only mid generalized tenderness without rebound or guarding. His legs are notable for bilateral 1+ edema.

You go through a differential diagnosis in your head. His symptoms are suggestive of a small bowel obstruction, but he’s not really that tender and his low blood pressure is concerning. It could be an abdominal aortic aneurysm; better rule that one out fast. Perhaps he’s in DKA. Other conditions are lower on your list: appendicitis, cholecystitis, gastritis, mesenteric ischemia, coronary syndrome… porphyria. You order two IV’s, some labs, an EKG, 5mg of metoclopramide and a 500ml bolus, hoping that the fluids will bump up his blood pressure a little. An upright chest X-ray is a no-brainer. You figure you’ll eventually get an abdominal series, a CT abdomen, or both, but first you want to wheel in the department’s ultrasound machine to make sure he doesn’t have a “triple-A”. No sense running a code in the CT scanner; the last one you heard about didn’t go too well.
While scanning his abdomen, you do note that his aorta is enlarged to about 3cm (image 1) but that is as large as it gets. While searching for his aorta, you also obtain the following two images of apparent fluid filled structure (2 & 3). Have you adequately ruled out a ruptured triple-A? What are these other structures that you see?
What should you do next, assuming that his blood pressure remains stable? If your answer is “order a CT scan” what kind of contrast, if any, should you use? And if you do decide to use IV contrast, what must you remember to warn both the patient and the PMD about?
•    71-year-old diabetic presents with abdominal pain and vomiting.
•    Blood pressure is in the low 90’s.
•    Abdominal scar and mild generalized tenderness noted on exam.
•    Differential diagnosis is broad but includes AAA and SBO.
•    Bedside ultrasound shows a 3cm aorta plus additional fluid filled structures.
{mospagebreak title=ANSWER}
If you see an enlarged aorta on bedside ultrasound, and your patient is hemodynamically stable, you should consider obtaining a CT scan to delineate your findings further.  If the patient is unstable call the surgeon.  A CT scan of the abdomen and pelvis may also reveal information to support what you discovered on ultrasound images 2 & 3 (fluid filled loops of small bowel).  During your scan, you note that these fluid filled loops of bowel are not only distended, but also quite rigid.  Although you can clearly see that peristaltic activity is almost completely absent, you cannot seem to find any collapsed bowel distal to the dilated proximal loops seen in images 2 & 3.  You can also almost imagine the valvulae conniventes of the bowel on these images if you look closely.
A follow-up CT scan should help define whether the dilated bowel is secondary to ileus or to mechanical obstruction, meanwhile defining the elusive transition point. What about the contrast decision?  In many institutions, the evaluation of a small bowel obstruction is performed without contrast.  This eliminates the delay from the oral contrast, which most patients with bowel-obstruction tolerate poorly, if at all.  It also avoids the renal risk of IV contrast in a patient who is likely somewhat dehydrated.  In this case an added benefit is avoiding the issue of metformin metabolism following IV contrast administration. 
If IV contrast is given to a patient who takes metformin (Glucophage, Avandamet and other combo meds) both the patient and the PMD should be made aware of the necessary precautions that must be taken.  I find the advice given to patients, both by the radiology department and by the treating physician, is often incomplete and therefore dangerous.  Most people are advised, “Don’t take your metformin for two days.”  This is actually a dangerous simplification.  If the patient does go into renal failure from the IV dye and subsequently restarts their metformin on the third day, they will still be at risk to develop lactic acidosis and could die.  Since metformin is contraindicated if the creatinine is greater than 1.4, the proper advice should be, “Stop your metformin until you have your kidney function rechecked.  Your doctor should do this in two to five days.  If everything is fine, you should be able to restart the metformin about a week from now.”  Why is this better advice?  The answer is that although contrast induced rise in creatinine usually starts within 48 hours, the creatinine level doesn’t peak until 3-5 days post contrast.  If all goes well, the creatinine will usually return to baseline by 7-10 days.  A patient who gets the impression that they can restart metformin on the third day could run into big trouble.
After considering all this, you go for the non-contrast, or “unenhanced” scan.  Your radiologist calls back afterwards letting you know the patient does have a bowel obstruction, which appears to be of the “closed-loop” variety.  He only mentions the 3cm AAA after you ask.  You call the surgeon, place an NG tube, notice the blood pressure is improving and book your patient a bed on the surgical floor.  Your work here is done.  Next customer!?

•    Know your limitations: Ultrasound may help clarify findings elicited by history and physical exam.  When used correctly, it can greatly improve diagnostic accuracy, and help guide patient management, especially for time-critical diagnosis and treatment in unstable patients.  There is no substitute for hands-on practice to improve your skills, but if you use ultrasound in your ED, your department should also have a quality improvement program set up that is approved by both ED administration and radiology.
•    Hollow Viscus Imaging: Imaging the bowel is not part of the core-curriculum in Emergency Medicine Bedside Ultrasound Applications.  However, if you do come across abnormal bowel images during your scan of the other areas of the abdomen, it is useful to understand what those findings may imply. 
•    Bowel Obstruction: Dilated loops of bowel will measure >3cm in diameter and contain anechoic (black) fluid within their lumen.  Gas-filled bowel may be difficult to visualize and will cause scatter over far-field structures. 
•    Pseudo-mass: A loop of bowel may occasionally look like a mass.  This is especially common when imaging the gallbladder.  The duodenum may look like a solid mass just behind and below the gallbladder.  If the duodenum is filled with solid matter, it may also produce acoustic shadowing and confuse you to think you are looking at a gallbladder filled with gallstones.  When in doubt, scan through the structure in question and see if it connects to the common bile duct. 
•    Peristalsis: If you keep your probe steady, you may be able to see the bowel peristalsing.  This may help you to identify certain structures as bowel.  It is also interesting to watch or show your patients.
•    Other Applications: Ultrasound evaluation of the bowel is a time-intensive process and requires additional training and credentialing.  Although you may not have the requisite skill to detect appendicitis or intussusception by ultrasound, your ultrasound tech may.  Always keep in mind the potential advantages of ultrasound when ordering imaging tests on patients in whom you may want to minimize exposure to ionizing radiation, such as pregnant patients and young children. An added benefit of imaging the appendix with ultrasound is that there is no delay for the passage of oral contrast.
•    Practice Makes Perfect: With bedside ultrasound there is no substitute for experience.  The more ultrasounds you do, the better you will be able to differentiate abnormal from normal, even when you may not be sure exactly what the abnormality is.  An image library of normal and abnormal images helps immensely and has just that.  To see more, go to, chose Departments, chose Real-Time-Readings and click on the Ultrasound Library link.

Brady Pregerson, MD, oversees QI for ED Ultrasound at Cedars-Sinai Medical Center in Los Angeles.
Teresa Wu, MD, a clinical assistant professor in EM at Florida State University, completed her ultrasound fellowship at Stanford University Medical Center.

function CheckMultiple3(frm, name) { for (var i=0; i; if (fldId) { var; if (fieldnamecheck != -1) { if (fldObj.checked) { return true; } } } } return false; } function CheckForm3(f) { if ( == “”) { alert(“Please enter your email address.”);; return false; }if (f.format.selectedIndex == -1) { alert(“Please choose a format to receive your email campaigns in”); f.format.focus(); return false; } return true; };


Leave A Reply