Ultrasound Alternative: When Is it the Better Choice for Appendicitis?

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 - Ultrasound
Ultrasound imaging shows submucosal echogenic layer in inflamed appendix.
Source: Am J Roentgenol. 2013;200: 957-962.

When a child has appendicitis, it no longer is a hair-raising emergency bellyache. Instead it is just the beginning of a diagnostic puzzle that imaging helps to sort out. But which type of imaging to use is the question. Ultrasound offers a radiation-free alternative to CT, but it is not without its own drawbacks. The choice is crucial, but often determined by availability and influenced by a hospital’s size and patient base.

Appendicitis, which usually features stomach pain, a fever and vomiting, can be difficult to diagnose because its symptoms resemble those of other maladies. Delayed or incorrect diagnosis can lead to a ruptured appendix.

Usually, with few exceptions, instead of rushing a child straight to the operating room, doctors first make a critical choice to use either ultrasound, CT, or both to find the child’s tiny, worm-shaped appendix, no longer than four inches.

“It’s no longer automatically a middle-of-the-night kind of case,” says Brent A. Townsend, MD, of Wake Radiology in Raleigh, N.C. “A child comes in to the ER with belly pain. A physical exam, white blood cell count and other lab work are done. Serial exams can be done every six to 12 hours, or a full range of imaging, to confirm the diagnosis.”

“It’s rare if children go straight to the OR,” he adds. Often, a child who has appendicitis is given antibiotics and surgery is scheduled for the following day.

Advances in diagnostic imaging—and reliance on it—have steadily increased. Ultrasound produces diagnostic quality images and is free of ionizing radiation. CT scans produce more detailed images than ultrasound, but carry a radiation risk.

Imaging has become so pervasive that some physicians say the diagnosis of appendicitis has shifted from clinical diagnosis to diagnostic imaging for all patients.

Physicians almost inevitably turn to imaging each time a child with a suspected appendicitis turns up at the ED. About 280,000 appendectomies are done yearly in the U.S., making it one of the more frequently performed pediatric abdominal surgeries.

Deciding on which kind of imaging is the best one to use for diagnosing a suspected appendicitis is not cut and dried. “It’s a confusing issue. A multitude of people are advocating many different imaging modalities,” says Robert. C. Orth, MD, PhD, of Texas Children’s Hospital (TCH) in Houston.

Advocates for ultrasound see it as the go-to modality because it doesn’t carry the radiation risk of CT scans.

Ultrasound also is the least expensive modality by any measure. NewChoiceHealth.com, a company that compares medical costs using hospitals’ list prices, pegged the cost for an abdominal ultrasound at about $400, while a recent study using data from Medicare and Medicaid found costs for a limited ultrasound in appendicitis evaluation could be as low as just $88 (Am J Roentgenol. 2014 Jan;202(1):124-35). The same study also found that using ultrasound first then CT for appendicitis saved as estimated $24.9 million per year across the U.S. population despite extra surgeries being conducted.

Many children’s hospitals, including TCH, the nation’s largest, use ultrasound first followed by CT if needed. About 5 to 10 percent of ultrasound exams are followed by CT scans to confirm diagnosis at TCH. Out of the 3,000 cases per year of suspected appendicitis seen at TCH, approximately one third require appendectomies, Orth says. The rest turn out to be stomach bugs, constipation, or other conditions.

Among other advantages, ultrasound doesn’t require IV contrast, unlike CT. Ultrasound is seen as ideal to use on small children because their lack of fat, which is a barrier for sound waves, allows a better image than it might in adults.

Learning curve

One potential drawback of ultrasound is that image quality is heavily operator dependent. “The bottom line is that it depends on whether the ultrasound technologist and radiologist have the skill and experience to perform the exam,” Orth explains. “The sonographer may see the whole appendix, part of it, or none of it. Sound waves don’t travel well through gas. If there is a lot of gas or stool, the appendix can be hard to see.”

This learning curve of ultrasound training is something that Einat Blumfield, MD, of the Jacobi Medical Center of the Albert Einstein College of Medicine, in the Bronx, N.Y., is very familiar with. She trains the ultrasound operators at the adult and pediatric trauma center, which uses ultrasound first followed by CT, if needed. 

“It takes about a year to train them to be sure that what they see is an appendix, and to be good at finding it and demonstrating the appendix,” Blumfield says.

The appendix is even harder to find in obese children, and the obesity epidemic sweeping the country has had an impact. “It has taken me up to 20 minutes to find the appendix,” she says.  

Blumfield has advocated for the use of ultrasound to diagnose appendicitis, and has conducted research into its effectiveness. She was the lead author of a retrospective study that looked at 161 children with acute appendicitis who had ultrasound before undergoing appendectomies. It found that ultrasound could effectively detect the difference between perforated and nonperforated appendicitis (Am J Roentgenol. 2013;200: 957-962).

Availability of ultrasound can be problematic though, especially at smaller institutions that do not have ultrasound operators on site all of the time. Many appendicitis cases are not seen at children’s hospitals or at large medical centers.

“One of the key things to understand is ultrasound is great, except people don’t always have access,” Townsend says. “At one hospital, we don’t offer ultrasound of the appendix if no radiologist is present, because it is hard to read remotely. What happens at outside (satellite) clinics is kids go straight to CT.”

Townsend, like Blumfield, supports ultrasound as an alternative to CT. “I am passionate about it,” he says, and he notes that stakeholders are becoming more judicious when weighing the risks and benefits of CT scans.

Despite cancer concerns, CT use for diagnosing abdominal pain in children has been increasing, from 2 percent of all pediatric ER visits in 1999 to 16 percent in 2007 (Radiology 2012;263:778-785). The automated nature of CT makes it less dependent on the skill of the operator, and CT images are considered easier to read. “Most body radiologists are comfortable reading CT scans for suspected appendicitis,” says Orth.

MRI waiting in the wings

Given the limitations of ultrasound and CT, Orth sees a future for MRI because it yields more comprehensive images and, like ultrasound, it lacks radiation. It can detect the appendix when it is in an atypical location as well as the inflammatory processes occurring in the surrounding area.

“At community hospitals, they might start using MRI instead of CT,” says Orth, adding that while it is unlikely that institutions routinely using ultrasound would switch to MRI, some might consider MRI rather than CT to confirm appendicitis.

Orth was the lead author of a study published in the July 2014 issue of Radiology that looked at 81 patients, of whom 37 percent had acute appendicitis. The study found sensitivity and specificity were 93.3 percent and 98 percent, respectively, for MRI, compared with 90 percent and 86.3 percent, respectively, for ultrasound.

Some institutions have embraced an MRI first model of care. For example, Orth cites Penn State Hershey Children’s Hospital, in Hershey, Pa., as one that uses emergent MRI to diagnose appendicitis.

But MRIs have limitations too. It can’t be used for some children with implants, and young children may not be able to lie still during the exam without sedation.

The lack of flexibility for scheduling an MRI also can be problematic. “Even at our hospital, with seven to eight MRIs running, they are less flexible for scheduling than ultrasound,” says Orth. “And with ultrasound, you can bring it to the room.”

Many MRIs are booked solid with outpatient exams. For example, Blumfield says at the trauma center in the Bronx, there is one MRI, and its outpatient schedule does not allow it to be used in place of CT scans.

In the end, institutions will proceed based on their capabilities, keeping the safety of the patient at the forefront of the decision making process. Young children are more sensitive to radiation, and both the American College of Radiology and the Society for Pediatric Radiology have issued joint guidelines advising physicians to limit the exposure of children to radiation from CT scans.

“There is a lot of controversy over whether CT scans really cause cancer. There are opposing viewpoints,” says Townsend. “But you think, ‘first, do no harm,’ especially with kids. Is this test worth it to this child? Every scan needs to be governed by risk analysis.”

However, when only a CT scan can find an appendix, the risks are reasonable, says Blumfield. “The radiation risk is very low,” she says, adding that if a child had surgery instead of a CT scan that “anesthesia also has its risks.”