Clinical presentation: A 39-year-old woman was referred for evaluation of a "recurrent nodule" described on screening. In fact, the patient hasn't been operated on.

Palpation. No abnormality.

Laboratory tests: TSH 6.09 mIU/L, aTPO 893 U/mL.

Ultrasonography. Connective tissue replaced the right lobe. The left lobe was moderately hypoechogenic and presented more hypoechogenic areas. On longitudinal section, the central part of the left lobe was described as nodule. However, this area was clearly not a nodule.

Aspiration cytology of the area in question resulted in Hashimoto's thyroiditis.

Diagnosis: Agenesia of the right thyroid lobe. Hashimoto's thyroiditis. Primary hypothyroidism.

Suggestion. Daily 50 microgram levothyroxine.