I is for internal structure (LESION)
Next is the internal structure of a lesion. There are only three primary descriptions with this letter. They are radiolucent, radiopaque and mixed radiolucent/radiopaque.
Radiolucent has two subcategories. The first is unilocular. This refers to a lesion/entity that is completely radiolucent. The second is multilocular. This refers to a lesion/entity that has bony septa within the lesion/entity. When describing a radiolucent lesion/entity, you should also note if it is unilocular or multilocular. Radiopaque is a lesion/entity that is completely radiopaque. Mixed radiolucent/radiopaque is a lesion/entity that has both components within the area in question.
Remember the best way to get better and become more comfortable with describing is to practice on more radiographs.