Correlation of Body Mass Index with Cervical Prevertebral Soft Tissue Thickness

Purpose: Radiologists rely on normative values including upper limits of normal for cervical prevertebral soft tissue thickness (PSTT) to aid in detection of osseous or soft tissue injuries in the setting of neck trauma. Given the epidemic increase in obesity rates over multiple decades, evaluation of the effect of body habitus as measured by body mass index (BMI) on these normative values is needed to assess their reliability in obese patients. Methods and Materials: PSTT measurements were made retrospectively at C1, C2, C3, C6 and C7 in 166 patients who underwent computed tomography of the neck, after excluding patients with known or suspected pathology affecting PSTT. Mean PSTT was calculated within clinical BMI categories (normal, overweight, obese, and morbidly obese) and compared to normative values from the literature at each cervical level. A multivariate linear regression analysis was performed using BMI, age, and gender as predictive variables for PSTT. Results: The morbidly obese group had significantly increased mean PSTT compared to normative mean values from the literature at all measured cervical levels (p < 0.001 at C1, C2, C3 and C6; p < 0.05 at C7), and were near or above described upper limits of normal at C1, C2 and C3. Mean PSTT was also increased in the overweight group at C2 and C6 (p < 0.05) and obese group at C1, C2 and C3 (p < 0.001). Multivariate linear regression found BMI was significantly associated with increased PSTT at all cervical levels (p < 0.001 at C1, C2, C3 and C6; p < 0.05 at C7). Male gender was also associated with increased PSTT at all levels except C3 (p < 0.001). BMI was the strongest predictor of PSTT in the regression model at all cervical levels when comparing standardized beta coefficients. PSTT was estimated to increase by approximately 1 mm for every increase of 10 in BMI. Conclusions: Increased BMI is associated with increased PSTT and is the strongest predictor of PSTT compared to age or gender. Established PSTT normative values may be unreliable in overweight and obese patients and are likely to produce increased false-positive results, particularly in the upper cervical spine and in morbidly obese patients. This unreliability is expected to worsen as obesity rates continue to increase. Further study is needed to assess whether BMI-corrected models improve the reliability and accuracy of these normative PSTT values. Clinical Relevance/Application: Cervical PSTT is an important indicator of osseous or soft tissue injury in the setting of trauma. The current study shows a significant effect of BMI on PSTT. Established normative PSTT values may not be reliable to assess obese patients who make up an increasingly larger percentage of the population.