Multiple chemodectomas. Carotid body tumor masked by salivary gland uptake on I-123 MIBG scintigraphy.

Chemodectomas resemble pheochromocytomas in that they are derived from neural crest tissue. Their distribution in the body may be quite different, however, as chemodectomas are more frequently found in the aortic and carotid bodies, while pheochromocytomas are most common in the adrenal medulla. The authors present a case of a patient with a known history of chemodectoma, imaged with I-123 MIBG to rule out recurrent disease. Images of the chest revealed a thoracic tumor representing recurrent periaortic tumor, but an additional carotid body tumor (which was later demonstrated by angiography) was masked by salivary gland uptake. In patients with chemodectomas, SPECT imaging of the neck may be necessary to distinguish normal salivary gland uptake from tumoral uptake of MIBG. In general, knowledge of the characteristics of the individual neural crest derived tumor is mandatory for maximal effectiveness of I-123 MIBG scintigraphy.