A study of 645 normal adult parathyroid glands in 160 cadavers revealed that there is a definite pattern of anatomic distribution on the basis of the embryologic development of the parathyroid, thyroid, and thymic glands. The sites of predilection of the upper gland (Parathyroid IV) are, in order of frequency, the cricothyroid junction; the dorsum of the upper pole of the thyroid; and the retropharyngeal space. Those of the lower gland (Parathyroid III) are at the lower pole of the thyroid and the thymic tongue; rarely in the upper, the lateral neck, or the mediastinum. An understanding of the developmental relationship of the parathyroid glands to the thyroid and the thymus is fundamental in the delineation of the embryologic origin of the parathyroid glands. The parathyroid gland, located within the surgical capsule of the thyroid (subcapsular), when diseased, remains in place locally. A gland outside of the capsule (extracapsular) is often displaced into the posterior or anterior mediastinum. A collective assessment of the size, weight, color, shape, and consistency of the parathyroid gland is mandatory in the determination of its normalcy. Frozen section examination for stromal and intracellular fatty content is an added assurance of normalcy. That parathyroid glands sink in saline solution, and fat globules float, may aid in differentiating the two types of tissue. Supernumerary, fused, and intrathyroidal parathyroids, albeit rare, are of surgical importance.

We have developed a highly sensitive, two-site immunoradiometric assay (IRMA) for human parathyrin (PTH) that is specific for the intact, secreted, biologically active 84-amino-acid peptide. This assay has several technical advantages: it does not detect even high concentrations of inactive carboxyl-terminal fragments, results are available within 24 h, and the detection limit for intact hormone is low (1 ng/L). The assay readily measures concentrations of PTH in all healthy subjects and distinguishes these values from low or undetectable PTH values observed in clinical situations in which PTH secretion is expected to be suppressed. We found complete separation of results from 37 patients with surgically proven hyperparathyroidism and those from 23 patients with hypercalcemia associated with malignancy, the latter having PTH values at or below the lower limits of normal for this assay. The sensitivity, specificity, and rapid turnaround time of this two-site IRMA should advance the laboratory evaluation of patients with disorders of calcium metabolism.

The literature on substernal goiter from the seventeenth century to the present is reviewed. Substernal goiter may be defined as any thyroid enlargement that has its greater mass inferior to the thoracic inlet. Truly ectopic mediastinal goiters are rare, and most substernal goiters arise from and maintain some attachment to the cervical thyroid gland. Patients are generally in the fifth decade of life, and women predominate. Most patients experience dyspnea, stridor, or dysphagia, but 15 to 50% are asymptomatic; symptoms are often positional, and acute stridor may occur. Ten to twenty percent have no cervical mass or tracheal deviation on examination, and virtually all patients are euthyroid. Standard chest roentgenograms are often diagnostic, but computed tomographic or radioactive iodine scans may be helpful. The presence of a substernal goiter in all but the highest-risk patients is an indication for resection, usually through a cervical collar incision; an occasional patient will require sternotomy or thoracotomy. Death or major complications should be rare postoperatively. Substernal goiters are adenomatous and benign, but carcinoma occurs in 2 to 3% and may be occult. Patients should be followed closely, as these goiters may recur.

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