The usefulness and limitations of combined Tc-99m pertechnetate and Ga-67 citrate imaging of salivary gland disorders

Identification of Warthin tumor: magnetic resonance imaging versus salivary scintigraphy with technetium-99m pertechnetate

OBJECTIVE

The aim of this study was to evaluate the accuracy of technetium-99m (Tc-99m) pertechnetate scintigraphy and magnetic resonance (MR) imaging in the diagnosis of Warthin tumor.

METHODS

Sixteen cases of Warthin tumor and 17 cases of non-Warthin tumor were examined by Tc-99m pertechnetate scintigraphy with lemon juice stimulation and MR imaging, including T1-weighted, T2-weighted, short inversion time inversion recovery, diffusion-weighted, and contrast-enhanced dynamic images. We used the receiver operating characteristic (ROC) curve to evaluate diagnostic accuracy.

RESULTS

The mean area under the ROC curves of MR imaging in the diagnosis of Warthin tumor (0.97) was higher than that of Tc-99m pertechnetate scintigraphy (0.88).

CONCLUSION

Magnetic resonance imaging is more useful in the evaluation of Warthin tumor than Tc-99m pertechnetate scintigraphy.

Increased Uptake on I-131 Whole-Body Scintigraphy in Warthin Tumor Despite False-Negative Tc-99m Pertechnetate Salivary Gland Scintigraphy

Whole-body I-131 scintigraphy is an important component of the postoperative follow-up of patients with well-differentiated thyroid cancer. However, false-positive scans showing abnormal uptake in the absence of residual thyroid tissue or metastases may occur. Unless recognized as false positive, these abnormal sites of uptake may lead to unnecessary administration of therapeutic doses of I-131. The authors report a patient with Warthin tumor whose I-131 whole-body scan demonstrated increased uptake in the parotid gland, despite a negative Tc-99m pertechnetate salivary gland scintigraphy.

The limitations of gallium scintigraphy in the differentiation between benign and malignant salivary gland mass lesions

The aim of this study was to evaluate the ability of gallium scintigraphy to differentiate between benign and malignant salivary gland mass lesions and to identify what types of lesions surpass its diagnostic utility. By considering the uptake of 67Ga, 193 salivary gland masses were graded visually as negative, weakly positive, moderately positive or strongly positive in comparison to the uptake in the nasal cavity and the liver. The uptake was compared with histopathological findings. Among 39 malignant tumours, uptake was positive in 31 (79%) (strongly positive in 18, moderately positive in seven and weakly positive in six) and uptake was negative in eight (21%). Adenoid cystic carcinoma was the most common malignant tumour in our study (11/39), and uptake was negative in five (45%) of these tumours. Malignant tumours did not differ significantly in size despite differences in uptake. Among 154 benign lesions, uptake was negative in 101 (66%) and positive in 53 (34%) (strongly positive in 12, moderately positive in 19 and weakly positive in 22). Out of 88 pleomorphic adenomas, 41 (47%) showed positive uptake. Sensitivity, specificity and accuracy for gallium study were 80%, 66% and 68%, respectively, when the malignancy criterion was weakly positive uptake. Accuracy was greatest (83%) when the criterion was strongly positive uptake, but this criterion failed to detect more than a half of malignant tumours (46% sensitivity). In conclusion, gallium scintigraphy had limitations in differentiating between benign and malignant salivary gland mass lesions. Adenoid cystic carcinomas and pleomorphic adenomas were the principal sources of false negative and false positive results, respectively.

Various imaging modalities for the detection of salivary gland lesions: the advantages of 201Tl SPET

The aim of this study was to compare dual-isotope (99Tc(m) and 201Tl) SPET imaging with computed tomography (CT) and magnetic resonance imaging (MRI) in the differentiation of various lesions of the major salivary glands. Twenty-two patients underwent dual-isotope SPET imaging, of whom 12 also had CT and 15 also had an MRI study. The uptake ratio and retention index for 99Tc(m) and 201Tl were calculated by drawing regions of interest on the involved and normal glands. Both CT and MRI were interpreted by two radiologists. All malignant tumours were detected by all three modalities. Warthin's tumours were detected by dual-isotope SPET imaging; however, MRI failed to differentiate Warthin's tumour from pleomorphic adenoma. Of 13 other benign tumours, dual-isotope SPET correctly diagnosed 12. Of 16 tumours showing a cold defect on the 99Tc(m) images, parametric analysis with 201Tl gave an accuracy of 94%, whereas CT gave an accuracy of 70-90%. MRI was 73-91% accurate in differentiating between benign (Warthin's) and malignant tumours. We believe that dual-isotope SPET imaging (99Tc(m) and 201Tl), together with semi-quantitative analysis, is the method of choice for differentiating between various lesions of the major salivary glands.

Tl-201 uptake and retention in a Warthin's tumor

We report scan findings of Tl-201 in a case of histologically proved Warthin's tumor. Dual isotopes acquisition was performed in a case of left parotid Warthin's tumor. Both early and delayed Tc-99m-pertechnetate (Tc-99m) images showed increased uptake at the tumor. Tl-201 scan also showed an increase of uptake on the early image and retention on the delayed image. The uptake ratios of Tl-201 were 3.0 (early) and 2.3 (delayed). Scan findings of Tl-201 in a case of Warthin's tumor were similar to those of Tc-99m, and the interpretation of Tl-201 images should be accompanied with Tc-99m images.