Fig. 23.56 Venous sampling for parathyroid hormone: inferior thyroid venogram. Venous sampling can be undertaken if CT has failed to locate an ectopic tumour. Samples should be taken from mediastinal as well as from thyroid veins. The right and left inferior thyroid veins may join to form a common trunk, as in this patient. The venous anatomy and pattern of drainage may have been altered by previous surgery and not all ectopic tumours will be located by this technique.
