Plunging goitre is

Refer Robbins page no 1092 Multinodular goiters are multilobulated, asymmetrically enlarged glands that can reach weights of more than 2000 gm. The pattern of enlargement is quite unpredictable and may involve one lobe far more than the other, producing lateral pressure on midline structures, such as the trachea and esophagus. In other instances the goiter grows behind the sternum and clavicles to produce the so-called intrathoracic or plunging goiter. Occasionally, most of it is hidden behind the trachea and esophagus; in other instances one nodule may stand out, impaing the clinical appearance of a solitary nodule. On cut section, irregular nodules containing variable amounts of brown, gelatinous colloid are present (Fig. 24-15A). Older lesions have areas of hemorrhage, fibrosis, calcification, and cystic change. The microscopic appearance includes colloid-rich follicles lined by flattened, inactive epithelium and areas of follicular hyper- plasia, accompanied by degenerative changes related to phys- ical stress. In contrast to follicular neoplasms, a prominent capsule between the hyperplastic nodules and residual com- pressed thyroid parenchyma is not present