Doina E. Tanasescu

False-positive iodine-131 body scan caused by a large renal cyst.

Focal I-131 accumulation is generally a reliable indicator of functioning thyroid tissue or a differentiated thyroid cancer metastasis. Normal accumulation of activity may be seen in areas such as the intestinal tract, liver, and salivary glands. This report describes a patient with significant accumulation of I-131 in the right upper quadrant of the abdomen. The abnormality, first thought to represent metastastic thyroid carcinoma, was subsequently proven to be accumulation within a large renal cyst.

Correlation of thyroglobulin measurements and radioiodine scans in the follow-up of patients with differentiated thyroid cancer

Correlation of radioiodine (131I) scans and serum thyroglobulin (Tg) concentrations were performed in the follow‐up of 85 differentiated thyroid cancer patients who had undergone total thyroidectomy. Tg results were also compared with the control group of 33 thyroidectomized patients with no evidence of thyroid carcinoma and normal values for Tg established. Excellent correlation between Tg and scans was noted in patients with scan evidence of metastasis distant from the neck. Poor correlation was present in patients with scan evidence of local neck metastasis only, thyroid bed activity, and those with mediastinal activity. In addition, in 8% of the patients, the Tg assay could not be performed because of interfering antibodies. The conclusion is that elevated Tg concentration is a good indicator of metastasis outside of the neck as detected by 131I scans. Caution should be used when Tg alone is used in evaluating local neck metastasis demonstrated on scans. The significance of mediastinal activity warrants further investigation.

Evaluation of low-dose radioiodine ablation therapy in postsurgical thyroid cancer patients.

Nineteen patients with differentiated thyroid carcinoma were given low dose (30 mCi) radioiodine therapy for the ablation of residual thyroid tissue following total thyroidectomy. Using 5- to 10-mCi diagnostic I-131 scans, ablation was achieved in two of 19 patients following the first low dose and three of 12 patients following the second low-dose therapy. The ablation response was 53% (ten of 19) following one large dose (100 mCi) in another concurrent group of 19 patients. The ablation response following the first low dose when compared with the first high-dose therapy was significantly lower (P=0.015). The combined ablation response following first and second low doses (five of 14) when compared to a single large dose was not significantly different (P=0.534). The use of low-dose-l-131 therapy, although not as effective as large dose therapy, may be warranted in patients resistant to entering the hospital for therapy. However, ablation as defined by a five- to ten-mCi I-131 scan can be expected to occur in only one third of the patients after two attempts at ablation, while a single 100-mCi regimen can be successful in achieving ablation in over one half of the patients after the first attempt.

Failure of episodic high-dose oral verapamil therapy to convert supraventricular tachycardia: a study of plasma verapamil levels and gastric motility.

The practicality of administering large oral doses of verapamil tablets to terminate supraventricular tachycardia (SVT) was investigated in 10 patients. A pilot study in four patients showed that unexpectedly low plasma levels (less than 40 ng/ml) were obtained 60 minutes after administering 160 mg or 240 mg of verapamil during SVT. Nuclear studies in the six other patients showed that fractional liquid gastric emptying times (T) were significantly prolonged in SVT compared to sinus rhythm (SR), p less than 0.05 from T 1/3 onward. Further verapamil absorption studies (200 to 360 mg) performed during SVT and SR in five of six patients showed that peak verapamil levels in four patients in SVT were 23% to 71% lower than in sinus rhythm, where they had peaked at greater than 250 ng/ml 60 minutes post verapamil ingestion, and areas under the plasma concentration time curves were 26% to 100% (mean 67%) less in SVT than in SR for all five patients. SVT was terminated by verapamil in one patient after 40 minutes and the rate of SVT was slowed after 90 minutes in two other patients. Thus plasma verapamil levels are considerably reduced during SVT as compared to SR, and changes in gastric emptying are likely a contributing cause. Since SVT was converted to sinus rhythm in only 1 of 10 patients within 1 hour, large oral doses of verapamil tablets appear unsatisfactory for the episodic treatment of SVT.

Scintigraphic findings mimicking focal nodular hyperplasia in a case of hepatoblastoma.

Hepatoblastoma is a primary liver neoplasm in which prompt diagnosis and resection are critical to long-term survival. Liver scintigraphy using Tc-99m sulfur colloid and Tc-99m iminodiacetic acid (IDA) derivatives has been used in the evaluation of hepatic masses. Most space-occupying lesions of the liver appear as photopenic regions following either Tc-99m SC or IDA agents. Two exceptions have been reported. Focal nodular hyperplasia (FNH) has been shown to have variable colloid uptake, which is dependent upon the number of Kupffer cells per given volume. Many patients with FNH will demonstrate activity within the FNH to be greater or equal to the normal liver. In addition, two cases of hepatoblastoma have been reported to show colloid activity within the tumor, and in one patient slight uptake of Tc-99m IDA was noted in the tumor 15 minutes postinjection. The current case demonstrates a hepatoblastoma in which the scintigraphic findings with Tc-99m SC and Tc-99m IDA were similar to those reported, with retention of IDA far greater than the previously reported case.

Treatment Rationale in Thyroid Carcinoma Effect of Scan Dose

The authors have previously shown that the definition of ablation of thyroid tissue in patients treated with thyroidectomy and radioiodine (l-131) for thyroid carcinoma depends upon the dose of l-131 used to scan the patient. The therapeutic response to l-131 therapy was evaluated in a group of ten differentiated thyroid cancer patients who had a negative 2-mCi (-2 mCi) diagnostic study, but had a positive 10-mCi (+10 mCi) diagnostic study (group 1) during their follow-up evaluation. These results were compared to another group of ten differentiated thyroid cancer patients who received l-131 ablation therapy based on a positive 2-mCi (+2 mCi) l-131 scan (group 2). Six patients in group 1 and eight in group 2 had improvement or ablation of residual tissue based on the 10-mCi scan following therapy. The difference in response between the two groups was not statistically significant (P=0.63) by two-tailed Fishers exact test, indicating that even patients with -2-mCi, but +10-mCi scans may respond to l-131 therapy. Whether the large dose therapy makes any impact on the clinical outcome has not been answered by this study.

Critical Evaluation of 99mTc Glucoheptonate as a Brain Imaging Agent

99mTc glucoheptonate was used as a brain imaging agent in a consecutive series of 859 patients. Sensitivity was 94% in patients with proved CNS tumors. Static imaging of patients with infarction showed a sensitivity of 62%. When the perfusion study was included, this valve increased to 90%. Overall sensitivity was 83%, specificity 99%, and accuracy 95% without inclusion of perfusion results. When these results were included, overall sensitivity was 93%, specificity 99%, and accuracy 98%.

Comparison of magnetic resonance imaging and radionuclide imaging in the evaluation of renal transplant failure

Magnetic resonance imaging (MRI) was compared with radionuclide scintigraphy (RNS) in 16 patients with renal transplants undergoing renal failure to determine which modality could best discriminate between rejection, acute tubular necrosis (ATN), and cyclosporin nephrotoxicity (CN). Although all rejecting transplants had reduced corticomedullary dilferenttation (CMD) on T1-weighted MR images, four of live cases of ATN had appearances that could not be distinguished from rejection. A normal CMO suggests nonrejection, but diminished CMO is nonspecific. Tc-99m DTPA/I-131 hippuran RNS was superior to MRI In differentiating rejection from ATN. Although ATN and CN have similar RNS patterns, this distinction can usually be made based on the clinical time course. Other potential uses of MRI in the evaluation of the renal transplants are discussed.

False-positive lung imaging: inadvertent injection into a pulmonary artery catheter.

A case of a ventilation-perfusion mismatch seen postoperatively in a patient with chest pain is reported. There was absence of perfusion to the right lung, with relatively normal ventilation. The study was initially interpreted as indicating a high probability of pulmonary embolus. It was then discovered that the injection had been inadvertently made into a Swan-Ganz catheter, with its tip in the left main pulmonary artery. The mismatch was therefore iatrogenic and not related to pulmonary embolus. The false-positive lung imaging which resulted has not been previously reported in the literature.

A METHOD FOR DETERMINING CHANGES IN V-Q RATIOS DUE TO INTERVENTION: THE EFFECT OF EXERCISE ON RESTING LEVELS

Changes in regional V–Q ratios in response to various interventions have been evaluated using complex techniques. The purpose of this study was to develop a new and practical technique for accurately assessing changes in relative perfusion and ventilation in response to an intervention. For this purpose we have chosen to evaluate this method to access changes in V–Q values at rest and exercise. 18 male subjects underwent resting ventilation images using krypton-81 followed by perfusion images using 300 uCi of Tc-99m-MAA. All images contained 500,000 counts and were obtained in the posterior position. Using a cycle argometer, 80% of the maximal predicted heart rate was obtained and maintained for a 5− minute period. The subjects again breathed krypton, and an exercise ventilation image was obtained. This was immediately followed by a 3 mCi Tc-99m-MAA perfusion study. All information was acquired on computer using a 64x64 matrix. Positioning was kept constant by alignment of cobalt sources attached to the subjects back. The lung was trisected, allowing for regional analysis of V–Q ratios. This method was capable of demonstrating a significant increase in perfusion of upper lung zones in response to exercise. The resting perfusion to the right lung was significantly greater than the left, and during exercise there was a major trend to equalize perfusion between the two lungs. Ventilation increased over the right lung, resulting in a relatively higher V–Q ratio on the right than on the left. This method is simple to perform and analyze, and may have a role in determining the effects of therapeutic regimens in cardiovascular or pulmonary disease.