Purpose: To correlate the sonographic findings of tissue oedema with histopathological changes in order to find an explanation for the different sonographic appearances of oedema.
Materials and methods: Subcutaneous and cutaneous tissue of the chest wall, the abdominal wall, and the thigh of 4 human cadavers with clinically evident oedema were examined sonographically. A specimen was then taken from each region for histological examination.
Results: Twelve cutis-subcutis-regions underwent sonographic-histological correlation. 9 out of 12 subcutaneous regions exhibited a diffusely increased echogenicity. 5 of the 9 regions with increased echogenicity also showed hypoechoic bands (up to 3 mm) within the subcutaneous tissue. Histologically, all of the 9 sonographically altered subcutaneous regions displayed lentiform or band-like optically empty spaces within the connective tissue between lobules of fatty tissue as well as between groups of fat cells within lobules of fatty tissue corresponding to fluid. Hypoechoic stripes at sonography represented very broad bands of fluid. The cutis appeared hyperechoic in all cases. At histology, 9 of 12 cases exhibited uniformly distributed optically empty spaces between connective tissue fibres of the dermis. Dermal thickness corresponded to the degree of oedema.
Conclusion: Subcutaneous oedema results in diffusely increased echogenicity, which is caused by the difference in acoustic impedance occurring at the edges of numerous bands of fluid. In addition, hypoechoic bands are observed if broad spaces of fluid are present in severe cases. Encased fluid in the dermis is uniformly distributed between connective tissue fibres. Sonographically, the homogenous hyperechoic appearance of normal dermis remains unaltered in cases of oedema, but dermal thickness increases.