Ultrasound demonstration of a thyroid carcinoma within a benign cyst.

A healthy 49-year-old woman with no history of thyroid abnormality or radiation exposure had a painless, nontender mass in the left lobe of the thyroid. At physical examination, the mass felt smooth and cystic with slight firmness at its lower edge. Routine laboratory studies were normal. The mass was nonfunctional on ‘ ‘l scanning. Gray scale ultrasonography revealed a 5-6 cm oval cystic structure with a 1 .5-2 cm pedunculated mass projecting into the lumen (figs. lB and 1C). Subsequent surgery and subtotal thyroidectomy revealed a left lobe mass resembling a benign cyst containing clear fluid. However, a fingerlike projection extended into the lumen of the cyst and the adjacent thyroid was firm and yellowish. Figure 1A was rendered from the surgeon’s description of the mass (no photographs were taken before biopsy and sectioning). Frozen and permanent sections of the mass demonstrated a partially collapsed benign cystic lesion and fibrous capsule with inflammatory infiltrate. An accompanying papillary carcinoma was growing in a “small portion” of the cyst wall, extending up to 2 cm into the surrounding thyroid with a partly necrotic, pedunculated extension into the cyst’s center. There was no evidence of local recurrence of metastasis at follow-up 9 months after surgery.