Objective: Sonography of the normal gastric wall delineates five distinct layers: from the luminal side, a first, inner hyperechoic layer; a second, hypoechoic layer; a third, middle hyperechoic layer; a fourth, hypoechoic layer; and a final, outer hyperechoic layer. The anatomic origin of the inner two sonographic layers has been a matter of controversy. To verify the histologic origin of the inner two sonographic layers, we attempted to correlate sonographic and histologic layers of resected gastric specimens. Because we hypothesized that the fluid covering the mucosa and the mucosa may be responsible for the sonographic inner two layers of the stomach, we selected specimens in which the mucosa was sloughed or thickened.
Materials and methods: We selected five resected gastric specimens with ulcerative carcinoma in which the mucosa was totally sloughed, one specimen with a mucosal polyp, and two specimens with a polypoid lesion and partial surface ulceration. The gastric specimens were immersed in normal saline and examined with 5-MHz high-resolution sonographic equipment. Sonographic findings were correlated with gross and microscopic pathologic findings. Two phantoms were immersed in normal saline and examined with the same technique to evaluate the thickness of the sonographic interface between water and phantoms.
Results: The inner hyperechoic layer was constant in thickness, measuring 1 mm, and covered the surface of the normal areas and the areas where the mucosa was lost or thickened. The hypoechoic layer underlying the hyperechoic layer was obliterated where the mucosa was defective and thickened where the mucosa was thickened. The sonographic interface between water and phantoms was 1 mm thick.
Conclusion: Our results show that the inner hyperechoic layer of the stomach seen on sonograms is due to echoes arising from the interface between fluid in the gastric lumen and the mucosal surface. The underlying hypoechoic layer is caused by the mucosa itself.