Great proportion of the nodule' borders are indistinctive. However, the cause of the blur is very likely not pathological. First, the focus was set wrongly (red arrow), therefore the dorsal part of the nodule is difficult to judge (yellow arrow in the transverse scan). Second, the upper and lower parts of the nodule are blurred (yellow arrows in the longitudinal scan) because of the placement of the transducer. It can be difficult to properly fit the probe all along to the patient's neck.

In contrast with the images of transverse scan where the borders of the nodule seem to be ill-defined, longitudinal scan images present sharp borders. The difference is caused by the placement of the transducer: in the event of transverse scanning to fit the probe all along parallel with the neck structures can be more difficult because of anatomical situation. Note that the images differ not only in nodule' borders but even in the echogenicity of the lesion and the extranodular part.

The thyroid parenchyma is echonormal in the ventral part while moderately hypoechoic dorsal to the iso/hyperechoic nodule. Thicker the nodule in the section, darker the non-nodular thyroid dorsal to the lesion.

Two technical issues are demonstrated in this case. The dark band medial (transverse scan) and upper (longitudinal scan) to the nodule starts ventral to the thyroid. It is caused by the improper fitting of the transducer to the neck of the patient. The non-nodular part dorsal to the nodule is more echogenic. This is similar to the phenomenon that the signal behind a cyst gets amplified and it is not infrequently observed in the event of deeply hypoechoic nodules.

Let's compare the solid areas located in the ventral (yellow arrows) and in the dorsal part (red arrows) of the cystic nodule. The latter is more echogenic because the echo signal gets amplified dorsal to the cystic fluid.