Radiopaque lesions are primarily seen in which of the following conditions?

The primary reason Paget's disease is associated with radiopaque lesions is due to the abnormal bone remodeling that characterizes this condition. In Paget's disease, there is an increase in both the rate of bone formation and resorption, leading to a disorganized pattern of bone structure. The excessive bone formation can give rise to areas that appear radiopaque on imaging studies, as the newly formed bone is denser than normal bone. This results in distinctive findings such as radiopaque lesions that can be observed in affected areas.

In contrast, conditions like multiple myeloma often result in radiolucent lesions due to bone marrow infiltration and destruction of the bone structure. Hyperparathyroidism can also present with a mixed pattern of radiolucent and radiopaque areas but is generally associated with more radiolucent lesions since it leads to increased bone resorption. Chronic renal failure tends to cause systemic bone changes that can also lead to radiolucency rather than radiopacity.

Thus, the characteristic radiopaque lesions seen in Paget's disease makes it the correct answer in this context.