Multinodular Goiter: The presence of multiple nodules in both lobes of the thyroid gland, with varying echogenicity and well-defined borders, is consistent with a multinodular goiter. The nodules are also of different sizes, which further supports this diagnosis.

Thyroid Adenomas: The well-defined, isoechoic nodule in the right lobe and the hypoechoic nodule in the left lobe could be thyroid adenomas. The absence of calcification, abnormal vascularity, and the presence of a thin rim of lucency around the nodules also support this diagnosis.
Thyroid Cysts: The spongy, well-defined nodule in the mid-portion of the left lobe could be a thyroid cyst. However, the absence of a clear fluid-filled structure makes this diagnosis less likely.

Papillary Thyroid Carcinoma: Although the nodules are well-defined and lack calcification, it is essential to consider papillary thyroid carcinoma, especially given the presence of multiple nodules. A thin rim of lucency around the nodule in the right lobe could be a sign of capsular invasion.
Medullary Thyroid Carcinoma: This rare tumor can present with multiple nodules, and the absence of calcification does not rule out this diagnosis. However, the lack of specific ultrasound features, such as a "starry sky" appearance, makes this diagnosis less likely.

Thyroid Lymphoma: This rare tumor can present with multiple nodules, but it is often associated with other symptoms, such as weight loss, night sweats, and fatigue. The ultrasound features are non-specific, making this diagnosis challenging to consider without additional clinical information.
Metastatic Disease to the Thyroid: Although rare, metastatic disease to the thyroid gland can present with multiple nodules. However, this diagnosis would require a known primary malignancy and other supporting clinical features.