CASE REPORT 

Annals of Nuclear Medicine Vol. 10, No. 3, 335-338, 1996 

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

Ali S. ARBAB, Kiyoshi KOIZUML Takao ARAI Keiji TOYAMA and Tsutomu ARAKI 
Department of Rediology, Yamanashi Medical University 

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. 

Key words : salivary gland, Warthin's tumor, 99mTcO4- 201TlCl 

INTRODUCTION 

THE DIAGNOSIS of Warthin's tumor by a nuclear medicine procedure is straight forward. Both early and delayed images, with or without lemon stimulation, by Tc-99m pertechnetate (Tc-99m) is quite suitable for diagnosing Warthin's tumor.1-3 But diagnosis of other tumors of the salivary glands requires imaging by other radionuclides. To date, many radiopharmaceuticals have been used to detect salivary gland tumors.4-6 Though gallium-67 (Ga-67) provided some promising results in the diagnosis of salivary gland disorders, it had certain limitations in differentiating benign from malignant tumors.7 To over-come the limitations of Ga-67, we have changed our protocol for diagnosing salivary gland tumors to dual isotope (Tc-99m and Tl-201) single photon emission computerized tomography (SPECT) acquisition (early and delayed) with triple energy window (TEW) scatter correction method.8 We also analyze the Tl-201 scan semiquantitatively. In a patient with left parotid gland tumor, both Tc-99m and TI-201 images showed increased uptake on the early images and retention on the delayed images, and the final diagnosis was Warthin's tumor. 

CASE PRESENTATION 

A 57-year-old female presented with left parotid gland swelling and the mass was moderately soft. Ultra-sonography showed hypoechoic, and X-ray CT showed a hyperdense mass with enhancement (Fig. 1). She was referred to our department for further evaluation with radionuclides. According to our new protocol, she under-went dual isotope SPECT acquisition with the TEW method. After injection of Tc-99m (1 85 MBq) and Tl-201 (111 MBq), early and delayed images were acquired at 10 minutes and 3 hours, respectively, with a GCA-9300A/DI triple head gamma camera from Toshiba Co., Japan, using low-energy-high-resolution collimators. SPECT data were obtained by continuous acquisition for 20 minutes (5 rotations, 4 minutes/rotation) in a 128 x 128 matrix at 4' step. The projection images were reconstructed using Butterworth and ramp filters but cut-off values were selected according to the count density in Tc-99m and Tl-201 images. To minimize the factors affected by the cut-off values of the filter in semiquantitative analysis, both early and delayed Tl-201 images were reconstructed with the same cut-off value . For image interpretation, matched slices of Tc-99m and Tl-201 were chosen. For semi-quantitative analysis of Tl-201 images, a 1 x 1 cm region of interest (ROI) was drawn over the tumor and the normal gland on matched slices. The count ratio of tumor to normal gland was calculated and referred to as the uptake ratio. Early Tc-99m images (Fig. 2A) showed increased uptake at the site of the mass in the left parotid gland with retention on delayed images (Fig. 2B). Tl-201 scan also showed increased uptake on early and retention on de-layed images (Fig. 3). The early uptake ratio was 3.0 but delayed uptake ratios of Tl-201 became 2.3 due to retention of activity in the normal gland. We suggested a case of Warthin's tumor according to the Tc-99m scan findings. At surgery the tumor was 3 x 2.5 cm in size and was confirmed histologically as a Warthin's tumor (Fig. 4). 

DISCUSSION 

To date, many radionuclides have been used to detect salivary gland tumors.4-6 Tc-99m scan provided very consistent results in the diagnosis of Warthin's tumor. 1,2 A combination of Tc-99m and Ga-67 has been used for salivary gland tumors though Ga-67 showed non-specificity in detecting malignant tumors.7 Moreover, combined Tc-99m and Ga-67 scans is a time consuming study; that is, the patient has to come twice for the study. Tl-201 has shown potentiality in detecting malignant tumors in various organs.9-11 To utilize the potentiality of Tl-201 for the detection of malignant tumors and to reduce the patient's and technologist's inconvenience, we changed our protocol to combined Tc-99m and Tl-201 dual isotope acquisition with the TEW method. With this new protocol, all scans are completed in 3 hours in a single day. Our preliminary study showed the advantage of Tl-201 over Ga-67 in detecting salivary gland tumors regarding specificity and patient scheduling. 12 A phantom SPECT studies in our department showed that the cross talk of Tc-99m on Tl-201 images was 8.2% and that of Tl-201 on Tc-99m images was 2.2%.
 The development of Warthin's tumor is believed to be from heterotropic salivary ducts within pre-existing lymphoid tissue.13 The uptake and retention of Tc-99m in Warthin's tumor may be explained by the Warthin's tumor cells retaining their capacity to concentrate Tc-99m but not being able to secrete it, since Warthin's tumor does not communicate with the gland's ductal system.3,13 The uptake and retention of Tl-201 may be due to increased cell membrane potential resulting from increased mito-chondrial density13 and thereby increased metabolic activity. Increased uptake of Tl-201 was observed in a tumor cell line with increased mitochondrial density.14 
 Though Tc-99m images alone may be enough for tentative diagnosis of Warthin's tumor, Tl-201 scan was performed in this case according to our clinical protocol. Increased uptake with retention of Tl-201 must be interpreted carefully along with Tc-99m scan results. If a Tc-99m scan also shows increased uptake with retention, a Warthin's tumor is most likely. If a Tc-99m scan provides cold or photopenic results, tumors other than Warthin's tumor should be considered. 

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