Rising Obesity Rate Creates Unique Imaging Challenges

With approximately two thirds of the U.S. population estimated as overweight or obese, ultrasonographers should be aware of imaging considerations—as well as pathological findings—that are often specific to overweight patients, according to presenters at RSNA 2009.

"We were taught fatty liver was a benign and reversible process and there was no concern about having fat in your liver," said Stephanie Wilson, M.D., a professor of radiology at the University of Calgary in Canada, who led an interactive session with a discussion of how obesity affects the liver. "Since I've been practicing, I've seen fatty liver become recognized as one of the major risks for westernized societies. A consensus prediction is that by 2020, fatty liver will be the major cause of liver cancer in North America." Currently, about 50 percent of tumors manifest with untreatable disease at the time of detection, she said.

Dr. Wilson urged radiologists who diagnose fatty livers on ultrasound exams to refer patients for liver consultations due to the increased risk for developing chronic liver disease with its increased risk for development of hepatocellular carcinoma.

Obesity Impacts Image Interpretation

Growing numbers of radiology reports are classified as "habitus limited," meaning a patient's size interfered with proper diagnoses, said Raul Uppot, M.D., an assistant professor of radiology at Harvard University in Boston. Using an electronic audience-response system, 78 percent of session attendees reported that obesity had impacted their ability to interpret images on ultrasound exams.

Dr. Uppot suggested alternatives to aid ultrasonographers working with overweight patients, including reducing transducer frequency from the standard 4-5 MHz to 2-3 MHz, allowing the ultrasound beam to better penetrate tissues and target the abnormal area. On the technical exhibits floor at RSNA 2009, said Dr. Uppot, he has seen transducers go as low as 1 MHz.

High-Quality Ultrasound Critical During Pregnancy

Phyllis Glanc, M.D. University of Toronto

According to Phyllis Glanc, M.D., an assistant professor of radiology and obstetrics/gynecology at the University of Toronto, the ability to perform high-quality ultrasound exams on obese pregnant women is especially critical due to increased risks to mother and baby. "One-third of maternal deaths occur in obese patients," she said.

Dr. Glanc also outlined some of the physical risks to the fetus including stillbirth, congenital anomalies and birth trauma.

While highlighting the barriers to acquiring useable images during ultrasound, Dr. Glanc also presented imaging tips. She recommended low-frequency probes and that both patients and technicians change positions to achieve better fetal access and reduce fatigue among technicians.

Optimal timing for ultrasound exams can also minimize difficulty, said Dr. Glanc. "In the obese population, a routine fetal anatomic scan is probably best performed after 20 weeks, providing better visualization." She also pointed out the possible benefits of transvaginal ultrasound exams for visualization of the fetus at around 15 weeks of gestation.

When obesity is a factor, a so-called "normal" ultrasound exam may not give accurate information needed for counseling and management, Dr. Glanc reminded attendees. She also explained that obesity is the most visible clue to "metabolic syndrome," a combination of major and minor health conditions including hypertension, diabetes and insulin resistance that affects women of reproductive age.

Ultrasonographers should be aware of imaging considerations specific for overweight patients, stressed Stephanie Wilson, M.D., during an RSNA 2009 presentation.

Dr. Glanc concluded by stressing the importance of communicating to obese, pregnant patients the limitations of obstetrical ultrasound and necessity for longer clinical exam times. Utilizing newer imaging techniques and industry aids to position patients and pre-planning for surgical delivery when necessary can help assure better medical outcomes for both mother and child, she said.

MR Imaging Reveals Lumbar Disc Disease in Overweight Children

Another RSNA 2009 scientific presentation revealed that lumbar disc disease in pediatric patients occurs more frequently than commonly thought and at a higher rate in children who are overweight.

The link between lumbar spine abnormalities and increased body mass index (BMI) in children had been poorly established in research, according to the study's co-author, Judah Burns, M.D., a radiologist in the Division of Neuroradiology at The Children's Hospital at Montefiore Medical Center in New York.

When Dr. Burns saw MR images from two overweight teenage patients with disc herniations, he wondered if there was a connection to their BMI.

"There is growing medical literature about the effects of obesity in children with various diseases and the radiologic manifestations of those processes," Dr. Burns said. "But in terms of musculoskeletal disease as it relates to obesity in young people, there is not much research about it."

Dr. Burns conducted a retrospective study of four years worth of existing MR imaging data in patients aged 12 to 20 complaining of back pain. He also considered a patient's height and weight to establish age-corrected BMI. Of the 188 patients who met his criteria, 52 percent exhibited abnormal lumbar spine MR imaging exams, the study showed.

"A lot of kids actually have some abnormality of the spine, which was surprising to me and others who saw the results," Dr. Burns said. "Often it is widely assumed that musculoskeletal pain in children is due to back spasm or pulled muscle. My conclusion is that you shouldn't just assume that kids don't get disc disease."

The study further showed that patients with elevated BMI had a much higher rate of lumbar disc abnormalities than other groups. Height and weight information was available on 108 of the 188 patients. Of those, 49 percent in the highest BMI quartile exhibited MR imaging abnormalities, a statistically significant difference when compared to children with lower BMI.

Dr. Burns pointed out that obesity in children doesn't automatically mean pathology. "From a public health perspective, the fact that it's happening at greater rates in children who are obese doesn't mean that if you see an obese kid you have to do an MRI to find their disc disease," he said. "It's more of a statement that this is yet another documented consequence of pediatric obesity that we have to be aware of."