Parathyroid adenomas are usually found in the inferior parathyroid gland; however, in 6%-10% of patients, they may be located in the thyroid, thymus, the pericardium, and behind the esophagus. Adenomas usually weigh 0.5-5 g but may weigh as much as 10-20 g (on average, normal glands weigh about 25 mg).
Approximately half of patients with hyperparathyroidism are asymptomatic. The manifestations of hyperparathyroidism primarily involve the skeletal system. Osteitis fibrosa cystica is a constellation of findings pathognomonic of hyperparathyroidism. In osteitis fibrosa cystica, the number of trabeculae on bones is reduced, and the number of giant multinucleated osteoclasts is increased. The surface of the bone may have a scalloped appearance (Howship lacunae). The normal marrow and cellular elements of bones are replaced with fibrous tissue, which weakens the bones and, often, results in pathologic fractures. Other changes include subperiosteal resorption of the phalanges and loss of the lamina dura of the teeth. Tiny punched out lesions (the classic "salt-and-pepper" appearance) are seen on the skull.[1,3]
Although hyperparathyroidism primarily affects the skeletal system, numerous other organ systems may be affected as well. Historically, kidney involvement has been reported in 60%-70% of cases. However, with improvement in early detection, it is now reported to be present in less than 20% of patients. Kidney involvement either results from the deposition of calcium in the renal parenchyma or from recurrent nephrolithiasis. Renal stones are usually composed of calcium phosphate or calcium oxalate. Recurrent nephrolithiasis can result in renal scarring, urinary tract obstruction, infection, and loss of renal function.[1,3]
Muscular manifestations may include proximal muscle weakness, fatigability, and atrophy. Neuropsychiatric findings typically occur only in advanced disease, and they may include confusion, psychosis, agitation, or coma. Band keratopathy is easily detectable in patients undergoing ophthalmologic examination, but these changes are not specific. Gastrointestinal system manifestations are typically subtle and nonspecific; however, they may include significant conditions, such as peptic ulcers, pancreatitis, or paralytic ileus. Chondrocalcinosis and pseudogout are also frequently seen.[1,3]
The diagnosis of hyperparathyroidism is typically made by the detection of an elevated immunoreactive PTH level. The suspicion of hyperparathyroidism should arise in patients with hypercalcemia, hypophosphatemia, and raised alkaline phosphatase levels or in those with the abnormal skeletal findings described above. Parathyroid ultrasonography and technetium-99m sestamibi parathyroid scintigraphy are most useful for the preoperative detection of parathyroid adenoma. Parathyroid scintigraphy can be limited by the presence of thyroid nodules or other metabolically active tissues, such as lymph nodes, diffuse hyperplasia, or metastatic thyroid cancer.
Primary hyperparathyroidism should be established on the basis of biochemical findings before any imaging studies are performed. The use of preoperative localization imaging is controversial in patients with primary hyperparathyroidism who have not undergone previous neck surgery. Shaha and colleagues indicated that, in the following patients, preoperative imaging studies are warranted:
Patients with associated palpable thyroid abnormalities;
Patients in hypercalcemic crisis in whom urgent diagnosis is needed;
Patients with associated malignancies;
Asymptomatic patients with mild hypercalcemia;
Obese patients with short necks;
High-risk patients whose operative time is crucial;
High-risk patients in whom local anesthesia must be used; and
Patients with cervical spinal problems with neck extension difficulties.
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