Obesity is defined as a body mass index (BMI) greater than 30 kg/m2. It is described as being a "modern epidemic" due to increased rates of metabolic syndrome and other complications in these patients, along with a high and increasing prevalence.
Obesity rates vary around the world but over 60% of the American population is classified as overweight, obese or morbidly obese.
- lifestyle obesity (95%) 8,9
- overconsumption of calories with decreased energy expenditure
- ready availability of calorie-dense food
- secondary obesity (5%) 8,9
Body mass index (BMI), which is calculated as the weight of an individual (in kilograms) divided by their height (in meters), is the basis for the most widespread classification system, but its generality is questionable, and race/ethnicity and gender should be accounted for 6. The World Health Organization and National Institute of Health have proposed the following classification 7:
- overweight: 25-29.9 kg/m2
- obese: 30-39.9 kg/m2
- extremely/severely/morbidly obese: ≥40 kg/m2 or ≥35 kg/m2 with comorbidity
However, in a radiology patient the weight and thoracoabdominal circumference may be more useful to know in terms of being able to scan due to physical restrictions, e.g. table weight limits and bore diameter 3.
There are numerous challenges when imaging morbidly obese patients, from practical considerations such as transportation, weight limits for imaging equipment and technical points of gaining diagnostic imaging studies. Ultrasound is the most affected modality 4.
Moreover in obese patients, additional numbers of x-ray photons are required to achieve images of the same quality, resulting in a small, but increased ionizing radiation dose.
Obese patients produce a challenge to the ultrasound practitioner for two main interrelated technical reasons 13:
- increased adipose tissue increases the distance that the ultrasound waves have to travel to reach the target tissue
- fatty soft tissue attenuates the beam, reducing the strength of the waves reaching, and also returning from, the target tissue
In combination this results in a decrease in signal-to-noise ratio.
Moreover obese patients may also find it more difficult:
- to change position to allow the sonographer to use the best acoustic window
- to hold their breath, which may be required to optimize the image
Treatment and prognosis
A variety of non-surgical treatments have been attempted in these patients with disappointing results. Surgical approaches to treating obesity, collectively known as bariatric procedures, have been far more promising and are now routinely used to treat patients with morbid obesity 1,2.
Obesity increases the risk of many conditions including being an independent risk factor for cancer. It has a significant negative effect on life expectancy 10,11:
- diabetes mellitus
- coronary artery disease
- gastro-esophageal reflux disease
- malignancy, e.g. esophageal cancer, endometrial cancer, renal cancer, colorectal cancer, breast cancer
- spinal epidural lipomatosis
- obesity hypoventilation syndrome
- increased mortality in severe trauma 12
- 1. Fisher BL, Schauer P. Medical and surgical options in the treatment of severe obesity. Am. J. Surg. 2002;184 (6B): 9S-16S. Am. J. Surg. (link) - Pubmed citation
- 2. Lockhart ME, Tessler FN, Canon CL et-al. Internal hernia after gastric bypass: sensitivity and specificity of seven CT signs with surgical correlation and controls. AJR Am J Roentgenol. 2007;188 (3): 745-50. doi:10.2214/AJR.06.0541 - Pubmed citation
- 3. Uppot RN, Sahani DV, Hahn PF et-al. Impact of obesity on medical imaging and image-guided intervention. AJR Am J Roentgenol. 2007;188 (2): 433-40. doi:10.2214/AJR.06.0409 - Pubmed citation
- 4. Uppot RN, Sahani DV, Hahn PF et-al. Effect of obesity on image quality: fifteen-year longitudinal study for evaluation of dictated radiology reports. Radiology. 2006;240 (2): 435-9. doi:10.1148/radiol.2402051110 - Pubmed citation
- 5. Ginde AA, Foianini A, Renner DM et-al. The challenge of CT and MRI imaging of obese individuals who present to the emergency department: a national survey. Obesity (Silver Spring). 2008;16 (11): 2549-51. doi:10.1038/oby.2008.410 - Pubmed citation
- 6. Rahman M, Berenson AB. Accuracy of current body mass index obesity classification for white, black, and Hispanic reproductive-age women. Obstet Gynecol. 2010;115 (5): 982-8. doi:10.1097/AOG.0b013e3181da9423 - Free text at pubmed - Pubmed citation
- 7. Obesity and Cardiovascular Disease. CRC Press. ISBN:1574448633. Read it at Google Books - Find it at Amazon
- 8. Obesity: Science to Practice. Chichester: John Wiley & Sons, Ltd., 2009. ISBN:047071221X. Read it at Google Books - Find it at Amazon
- 9. Oxford Textbook of Medicine. Oxford University Press. ISBN:0198529988. Read it at Google Books - Find it at Amazon
- 10. Segula D. Complications of obesity in adults: a short review of the literature. Malawi Med J. 2014;26 (1): 20-4. Free text at pubmed - Pubmed citation
- 11. Wolin KY, Carson K, Colditz GA. Obesity and cancer. Oncologist. 2010;15 (6): 556-65. doi:10.1634/theoncologist.2009-0285 - Free text at pubmed - Pubmed citation
- 12. Hoffmann M, Lefering R, Gruber-Rathmann M, Rueger JM, Lehmann W. The impact of BMI on polytrauma outcome. Injury. 43 (2): 184-8. doi:10.1016/j.injury.2011.05.029 - Pubmed
- 13. Paladini D. Sonography in obese and overweight pregnant women: clinical, medicolegal and technical issues. (2009) Ultrasound in obstetrics & gynecology : the official journal of the International Society of Ultrasound in Obstetrics and Gynecology. 33 (6): 720-9. doi:10.1002/uog.6393 - Pubmed