Endocrine Abstracts

Introduction: Waist circumference is a validated tool to measure obesity-associated cardiovascular risk factor. However it does not differentiate between superficial and visceral abdominal fat. Ultrasonography has many advantages over TC/DEXA in abdominal fat assessment, specially imaging pre-peritoneal, omental and retroperitoneal fat. Our aims were to validate the diagnostic technique and to observe correlations between different abdominal fat layers with clinical and analytical parameters related to obesity comorbidities.

Methods: n=274 patients, mean age 53, 82 (30%) males, 192 (70%) females (59% menopause), mean BMI 31 kg/m² (19.2% normal weight, 28,8% overweight, 52.2% Obesity), came for conventional abdominal US. Thickness of 6 different consecutive layers of abdominal fat at the L4 level were assessed using a 12 MHz linear and 3–6 MHz convex probes (GE logic E): Superficial and deep subcutaneous fat; Pre-peritoneal fat; Peri-aortic (omental) fat; Hepatic steatosis area (cm²) and hepatic US noise (dB) (visceral fat); Pre-renal fat (Left and Right) (retroperitoneal fat). We also obtain: Waist circumference (WC), Glucose, insulinaemia, HOMA index, leptin, Total cholesterol, LDL, HDL, Triglycerides, DM2 diagnosis, Hypothyroidism and Metabolic Syndrome according to ATPIII criteria.

Results: We found a different sex distribution pattern at the SC (mean range 23.28 mm F and 20.16 mm M), pre-peritoneal (10.47 mm F and 11.34 mm M) and peri-aortic fat layers (44.33 mm F and 66.63 mm M) (P<0.05). Only peri-aortic fat correlates with BMI (r=0.446; P<0.001) and WC (r=0.456; P<0.001). Peri-aortic, Right pre-renal, but specially Pre-peritoneal fat (P<0.001, CI 8–20 mm) correlate with steatohepatitis. Menopause predisposes to greater peri-aortic fat (P<0.001, CI 6–18 mm) as well as Metabolic Syndrome (P<0.001, IC 16–27 mm). In a multi-variant analysis, only peri-aortic fat layer thickness and Waist Circumference may predict metabolic syndrome. Peri-aortic fat >34.5 mm in F (AUC=0.761; P<0,001; 74% sensibility and 60% specificity) and >56.5 mm in M (AUC=0.763; P<0,03; 75% S and 70% E), are predictive for metabolic syndrome (ROC curves).

Conclusions: US is an easy method for the stratification of different abdominal fat layers. More than global visceral fat, US highlights the clinical importance of strict peri-aortic (omental) fat layer, with good correlations with BMI, WC and steatohepatitis. We suggest a cut-off point of 34 mm in F and 56 mm in M to consider the thickness of the omental layer as pathological and predictive of metabolic comorbidities. Pre-peritoneal fat thickness with a linear probe may also be an easy way to estimate Steatohepatitis.