For many years bilateral cervical exploration with identification of four glands remained the gold standard in parathyroid surgery, and rou­tine preoperative imaging for initial surgery was considered unnecessary and not cost effective. In 1986, John L. Doppman stated ‘‘Inmy opinion, the only localizing study indicated in a patient with untreated primary hyperparathyroidism (HPT) is to localize an experienced parathyroid surgeon’’ [1]. Times have changed, and undoubt­edly it is the progress of imaging studies that has modified the surgical management of patients with HPT and helped the development of new surgical techniques.

linear transducer (7.5–10 MHz) is used to obtain optimal depth penetration of 3–4 cm. A bilateral and comparative scan should be performed in transverse section, then in longitudinal section. In transverse section, the examination concen­trates on an area defined by the longus colli muscles posteriorly, the thyroid gland ante­riorly, the trachea medially, and the carotid artery laterally. The scan is then performed in cranial and caudal directions. An additional scan can be performed with the head of the patient turned away to the side, and during deglutition to optimize the latero-esophageal images. The anterosuperior mediastinum is examined by inclining the transducer deeply in a retrosternal direction.

Enlarged parathyroid glands appear as a homogeneous well-demarcated mass, which is hypoechoic in contrast to the hyperechoic thyroid tissue. They are usually solid, but large adenomas may have a cystic component.

The examiner should note the precise loca­tion with respect to surrounding structures, particularly the thyroid gland, and the depth from the skin. Enlarged superior parathyroid glands are usually found adjacent to the poster­ior aspect of the thyroid lobe (Fig. 17.1). They tend to migrate posteriorly and in a downward direction (Fig. 17.2), sometimes into the pos­tero-superior mediastinum. Enlarged inferior

in parathyroid hyperfunctioning lesions whereas it washes out more rapidly from normal thyroid tissue. This retention is presumably related to oxyphil cells in parathyroid lesions which are rich in mitochondria. The dual protocol requires early (15 min postinjection) and delayed images (at 1 and 2–3 h, depending on thyroid washout). Image acquisition is centered over the 140 Kev photopeak. On the early images, activity of the parathyroid lesion may be more intense, intense as, or less intense than thyroid activity. The detectability of disease is dependent on parathyr­oid–thyroid activity ratio and location of the tumour. On the delayed images, parathyroid lesions are easily identified (Fig. 17.5). However, washout of parathyroid lesions compared to thyroid may vary between subjects.