SPECT/CT characterization of oral activity on radioiodine scintigraphy

CONTEXT

Oral activity on radioiodine scintigraphy is commonly seen and may cause diagnostic dilemma. Determining the precise mechanism of oral uptake on radioiodine scintigraphy will increase the accuracy and confidence of interpretation and avoid possible misinterpretation.

OBJECTIVE

To determine the etiology of focal persistent radioiodine oral uptake seen on radioiodine scans.

DESIGN

Retrospective sequential series at a university clinic and a phantom study experiment.

METHODS

Preablation iodine-131 planar and single photon emission computed tomography/computed tomography (SPECT/CT) scans of 216 patients after total thyroidectomy were reviewed. Planar images were inspected for the presence of oral activity above the salivary gland background and SPECT/CT was reviewed to determine the location and nature of oral activity. A post-hoc phantom study was designed using typodont stone models fitted with various dental materials, immersed in a diluted iodine-131 solution, and imaged with SPECT/CT to characterize radioiodine uptake by high-attenuation dental materials.

RESULTS

Oral activity was seen on planar images in 123 of 216 (57%) patients; 12 patients were excluded from analysis because the SPECT/CT field of view did not cover the entire oral cavity. In the remainding 111 patients SPECT/CT images demonstrated focal uptake localizing to high-attenuation dental material on the CT in 95 of 111 (86%) patients. All cases of oral activity on planar imaging were interpreted as benign etiology on SPECT/CT. The phantom study confirmed focal in vitro uptake within high-attenuation dental materials representing a range of commonly used metal alloys.

CONCLUSION

Focal oral activity on diagnostic radioiodine scans frequently localizes to high-attenuation dental material on SPECT/CT. We postulate that an affinity between negatively charged iodide ions (I(-)) in saliva and positively charged metal ions (eg, Ag(+), Hg(+), Au(2+), Pd(2+)) within the dental materials is at the basis of persistent focal radioiodine uptake in the oral cavity. This represents a new mechanism underlying benign radioiodine activity not previously described in the medical literature.

[MR Sialography]

Indications for sialography have became rare and radiologists are less and less experienced for salivary gland cannulation. MR Sialography allows opacification of salivary ducts without any cannulation and could replace residual indications for sialography. The purpose of this paper is to review the principle of the technique, the normal and pathologic aspects of MR Sialography and to emphasize advantages and limitations compared to other techniques.

Developmental submandibular gland defect of the mandible. Review of the literature and report of a case

The literature relative to developmental submandibular gland defect of the mandible is reviewed, and an interesting case is presented. Evaluation for more serious systemic disease which may manifest radiolucencies in the region of the angle of the mandible is made.