Gallbladder Visualization on I-131 Post-Ablative Whole Body Imaging Mimicking Hepatic Metastases.

A 52-year-old woman with follicular thyroid carcinoma presented for ablative radioiodide and whole body I-131 imaging following subtotal thyroidectomy. An abnormal focus of increased activity was present in the region of the gallbladder fossa, persistent on delayed imaging. Subsequent CT revealed no hepatic metastases. Contemporaneously, the patient described right upper quadrant abdominal pain. Abdominal ultrasound demonstrated cholelithiasis. Cholecystectomy revealed extensive cholelithiasis and evidence of chronic cholecystitis; no hepatic metastases were identified. This case demonstrates the potential pitfall of gallbladder activity on I-131 whole body imaging secondary to cholecystitis mimicking hepatic metastases.

Introduction

Cholecystitis is a relatively common condition and can rarely mimic hepatic metastases in patients undergoing post-ablative I-131 imaging for thyroid cancer. Additional clinical workup is necessary in these cases to distinguish between these possibilities.

Case Report

A 52-year-old woman with follicular thyroid carcinoma presented for ablative radioiodide therapy (97.7 mCi Iodine-131; I-131) and whole body imaging 8 weeks following subtotal thyroidectomy. Residual thyroid activity was noted, which is not atypical. An abnormal focus of increased activity was present in the region of the gallbladder fossa on 48 and 72 hour post-ablative imaging (Fig. 1). Initially, this activity was felt to likely represent activity within the bowel near the hepatic flexure, however delayed imaging at 11 days post ablation demonstrated persistent activity in this area (Fig. 2).

Figure 1

52-year-old woman with follicular thyroid carcinoma treated by subtotal thyroidectomy. Pre- (A, B) and Post-ablative (C, D) whole body and spot I-131 imaging performed at 8 and 9 weeks status post subtotal thyroidectomy respectively demonstrated residual activity in the thyroid bed (straight arrows in A-D). Post-ablative imaging (C, D) additionally demonstrated an intense focus of abnormal activity in the region of the gallbladder fossa (curved arrows in C, D), which was persistent on delayed imaging (see Fig. 2). Liver (arrowheads in C, D), bowel (dashed arrows in A-B), and bladder (tapered arrows in A-C) activity is also noted.

Figure 2

52-year-old woman with follicular thyroid carcinoma treated by subtotal thyroidectomy. Delayed spot I-131 imaging performed at 11 days post ablative therapy. Intense focal activity (curved arrows) remains visible in the region of the gallbladder fossa. The liver (arrowheads) shows lower level diffuse activity. Anterior (A) and posterior (B) views are shown.

Iodine avid hepatic metastases, although somewhat unlikely given the normal appearing liver on recent ultrasound, could also give a similar appearance, although a solitary hepatic metastasis of the size suggested by the nuclear imaging would be unusual. Due to the somewhat limited sensitivity of ultrasound for evaluation of small lesions in the liver and the potential to significantly change management, an abdominal CT was performed to exclude hepatic metastases. Consideration was given to the possibility that the patient may require additional radioiodine therapy and that a contrast enhanced CT may diminish the efficacy of such treatment. As the question to be addressed by the CT was of substantial clinical importance and would impact management and additional radioiodide therapy could potentially be administered in an only mildly delayed time frame, the clinical team and patient elected to proceed.

Contrast-enhanced abdominal CT performed 5 weeks after ablative therapy revealed no hepatic metastasis or other abnormalities in the liver. No inflammatory changes were present in the hepatic flexure and the remainder of the bowel was also normal in appearance. Numerous calculi were noted in the gallbladder (Fig. 3).

Figure 3

52-year-old woman with follicular thyroid carcinoma treated by subtotal thyroidectomy. Intravenous contrast-enhanced abdominal CT performed 3 weeks following ablative therapy and whole body imaging demonstrated cholelithiasis (white arrowheads), but no evidence of hepatic metastases.

Review of the patient's chart revealed that she had described right upper quadrant abdominal pain 7 weeks after thyroidectomy (5 days prior to ablative therapy). Abdominal ultrasound shortly thereafter also demonstrated extensive cholelithiasis (Fig. 4). Laparoscopic converted to open cholecystectomy was subsequently performed 7 weeks after ablative therapy, where cholelithiasis and evidence of chronic cholecystitis were confirmed; no gross hepatic abnormalities were noted intra-operatively. At this point, the previously demonstrated abnormal I-131 activity was attributed to gallbladder pathology. Chronic cholecystitis was confirmed on post-operative pathology.

Figure 4

52-year-old woman with follicular thyroid carcinoma treated by subtotal thyroidectomy. Abdominal sonogram performed 7 weeks after subtotal thyroidectomy and prior to ablative therapy demonstrated extensive cholelithiasis, with classic wall-echo-shadow sign (white arrows). The visualized portions of the liver (dark arrowheads) were normal in appearance.

Discussion

This case demonstrates the potential pitfall of gallbladder activity on I-131 whole body imaging secondary to chronic cholecystitis mimicking hepatic metastases. Only two cases of gallbladder I-131 uptake after ablative therapy have been previously described in patients with chronic cholecystitis [1, 2]. Activity in the gallbladder and biliary tree on whole body I-131 scans has also infrequently been described in the context of biliary ductal dilatation [3], acute cholecystitis [4], and in the absence of any inflammatory or infectious processes involving the gallbladder [5, 6]. Numerous other causes of false positive results on whole body I-131 scans have also been described [7, 8, 9, 10, 11].

Acute and chronic cholecystitis are relatively common conditions that can in rare instances be a source of false positive results in patients undergoing post-ablative whole body I-131 therapy. Additional clinical workup is necessary to distinguish between metastatic disease and various causes of false positives in these situations. Delayed I-131 imaging should be included to exclude bowel activity. Correlation with the patient's history can also help determine if ultrasound or enhanced abdominal CT is warranted to determine the source of activity in the region of the gallbladder fossa. Even when cholecystitis is suspected to be responsible for this type of abnormal increased activity, contrast enhanced CT is often unavoidable to search for hepatic metastases as these entities may obviously coexist and the presence of metastatic disease would have significant clinical implications.