Figure 21. 123I-mIBG scan of a child with residual abdominal neuroblastoma seen as activity distributed on both sides of the midline (arrow).

Imaging with 123I-mIBG is indicated to confirm the functional diagnosis prior to surgery and to exclude metastatic or multifocal sites. Uptake is seen in over 90% of pheochromocytomas and is pathognomonic (Fig. 23).

Patients with extra-adrenal and pediatric presentations have a high likelihood of developing malignant pheochromocytoma in the future and should be followed for life with catecholamine estimations, which if abnormal or equivocal, should be supplemented with 123I-mIBG scintigraphy. Metastatic involvement may be extensive and involve bone and soft tissue (Fig. 24)

111In-pentetreotide also has a sensitivity of 80-90% for pheochromocytoma and should be used if 123I-mIBG is not available or if it is negative in the presence of high clinical suspicion.

Parathyroid adenoma

Primary hyperparathyroidism is characterized by excess secretion of parathyroid hormone (PTH) which manifests clinically as hypercalcemia and hypophosphatemia. It occurs in 0.02% of women over age 40 and in 0.005% of men, and is caused either by adenoma (80% single and 5% multiple), hyperplasia (10-20%) or carcinoma (very rare). Secondary and tertiary hyperparathyroidism are not indications for radionuclide imaging and will not be discussed further. Treatment is usually surgical removal of the affected gland(s). Medical therapy with bisphosphonates and/or estrogen can be considered in cases of mild hypercalcemia (serum calcium <3 mmol/ L) without symptoms or complications, or when there are medical contraindications to surgery.

Radionuclide imaging has been reported to be effective in the following indications: (i) urgent or difficult diagnostic questions such as hypercalcemic crisis, equivocal calcium measurements, or where parathyroid carcinoma is suspected; (ii)

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