Vagus Nerve Preservation Selectively Restores Visceral Fat Volume in Patients with Early Gastric Cancer who Underwent Gastrectomy

Background

Body weight loss is a well-known complication after gastrectomy, and is mainly due to reduced fat volume. The effect of vagotomy on the postoperative fat volume was investigated in patients with early stage gastric cancer who underwent gastrectomy.

Methods

Subcutaneous fat area (SFA) and visceral fat area (VFA) were separately measured in a computed tomographic (CT) image at the level of the umbilicus using Fat Scan software. The changes in these two fat areas were determined by comparing CT images taken before and more than 6 mo after gastrectomy, and the ratio of postoperative to preoperative fat area was calculated in 77 patients.

Results

VFA was reduced significantly greater after total gastrectomy (TG) than distal gastrectomy (DG) (P = 0.0003). In 63 patients who underwent DG, the reduction in VFA, but not in SFA, was significantly less in vagus nerve-preserved than in vagus nerve-nonpreserved cases (59.0% ± 24.2% versus 74.9% ± 28.2%, P = 0.027). If compared in each case, VFA showed a significantly greater decrease than did SFA in vagus-nonpreserving, but not in vagus-preserving, gastrectomy (68.2% ± 37.0% versus 52.7% ± 25.2%, P < 0.0001; 76.3% ± 30.0% versus 74.9% ± 28.2%, P = 0.79).

Conclusions

The vagus nerve has a function to locally regulate the amount of intra-abdominal fat tissue, and selective vagotomy in gastrectomy results in a preferential reduction of visceral fat in gastrectomy. Surgical denervation of vagus may be reconsidered as a reasonable treatment for excessive obesity.

Introduction

Body weight loss is a common, but sometimes serious, problem for patients who undergo gastrectomy. Postoperative body weight loss could be explained by various mechanisms such as reduced food intake, appetite loss caused by the reduced reservoir or delayed gastric emptying 1, 2, diarrhea [3], and malabsorption possibly caused by reduced secretion of gastric acid [4], or pancreatic insufficiency 5, 6. In addition, it has recently been suggested that alteration of the endocrine status, such as reduced gastrin [5] or ghrelin [7], and increased cholecystokinin 2, 5, might be involved in weight loss after gastrectomy. Previous studies have shown that the degree of body weight loss differs with the extent of gastrectomy, i.e., weight loss after conventional distal gastrectomy (DG) is significantly less than that after total gastrectomy (TG) 7, 8, while more than that after pylorus-preserving gastrectomy (PPG) 9, 10. However, the mechanism of body weight loss after gastrectomy has not yet been fully clarified.

It has been shown that loss of adipose tissue is the main cause of postoperative weight loss after gastrectomy [8]. Recent studies have suggested that adipose tissue is an endocrine organ that can produce a variety of secretory peptides, named adipokines, and thus plays important roles in the pathophysiology of various disorders 11, 12. In particular, it has been proposed that visceral, rather than subcutaneous, fat tissue is closely related to development of the metabolic syndrome 13, 14. In general, men have more visceral fat than women, while subcutaneous fat is more prominent in women than in men, suggesting that the volumes of these two adipose tissues are differently regulated in the body. However, the detailed mechanisms selectively controlling visceral fat are not understood.

In this study, we hypothesized that various surgical procedures in gastrectomy could affect the postoperative volume of each fat tissue, and investigated the changes in subcutaneous and visceral fat separately after various types of gastrectomy using Fat Scan software, which can separately calculate the area of subcutaneous (SFA) and visceral (VFA) fat from a fat density computed tomographic (CT) scan. Recent studies have shown that the metabolism of adipose tissue is controlled by autonomic nervous system and the visceral fat tissues were totally innervated by vagus nerve 15, 16. In this study, therefore, we paid special attention to the effect of vagus nerve preservation, because vagotomy in gastrectomy might lead to loss of the parasympathetic anabolic effect on intra-abdominal adipose tissue.