[Gray-scale histogram analysis in thyroid sonography. Critique of visual evaluation of echogenicity]

Three hundred and eighteen grey scale histograms of thyroid glands in 121 patients have been analysed. The arithmetic average grey scale value (GWMi) and the most commonly appearing grey value (GWMa) were determined electronically. The normal range of GWMi was 24 +/- 4.6 (x +/- s) grey scale units (GWE), for GWMa it was 26 +/- 5.6 GWe (x +/- s). Macrofollicular thyroid adenomas (8 cases) and thyroids with diffuse autonomy (12 cases) differed with a GWMi of 21 +/- 3.8 and 23 +/- GEW (x +/- s) respectively and a GWMa of 23 +/- 3.9 and 25 +/- 4.8 GWE and were within the normal range (p greater than 0.05). Microfollicular thyroid adenomas (12 cases), immunological thyroid lesions (25 cases) and parathyroid adenomas (6 cases) had reduced GWMi (6 +/- 3.1 and 8 +/- 1.8 GWE respectively) and GWMa (5 +/- 3 and 7 +/- 2 GWE, p less than 0.005). Thyroid carcinomas (9 cases) and lymph node metastases (8 cases) were also significantly below normal, with a GWMi of 11 +/- 2.3 and 11 +/- 3.4 respectively (p less than 0.05). Analysis of grey scale histograms makes it possible to evaluate changes in the thyroid without reference to surrounding tissues.