Incidence and Significance of Incidental Focal Thyroid Uptake on (18)F-FDG PET Study in a Large Patient Cohort: Retrospective Single-Centre Experience in the United Kingdom.

OBJECTIVE: To assess the prevalence and pathological nature of incidental focal thyroid uptake on (18)F-FDG (2-[(18)F]-fluoro-2-deoxy-D-glucose) PET (positron emission tomography) and examine the role of the maximum standardised uptake value (SUVmax) to differentiate benign from malignant thyroid pathology. MATERIAL AND METHODS: (18)F-FDG PET reports were retrospectively reviewed. Incidental focal tracer uptake in the thyroid was noted in 147 patients (0.5%). Patients with known primary thyroid malignancy were excluded. The final diagnosis was made following ultrasonography of the neck, fine-needle aspiration cytology (FNAC) or histopathology of the surgically resected specimen where surgery was indicated. A Mann-Whitney U test was used to compare the SUVmax of benign and malignant thyroid pathology. Receiver operating characteristic (ROC) analysis was performed to identify an SUVmax cutoff in differentiating benign from malignant pathology. RESULTS: A final diagnosis was achieved in 47/147 (32%) of the patients. The diagnoses included benign lesions in 36 patients and malignancy in 9 patients. In 2 patients, FNAC demonstrated indeterminate follicular lesions; however, surgical excision was not performed. There was a highly significant difference in the mean SUVmax of malignant focal thyroid uptake (15.7 ± 5.9) compared to that of benign lesions (7.1 ± 6.8) with a p value of 0.000123. An SUVmax of 9.1 achieved a sensitivity of 81.6%, specificity of 100% and area under the curve of 0.915 in the ROC analysis differentiating benign from malignant disease. CONCLUSION: The malignancy potential of incidental focal thyroid uptake remains high and warrants prompt and appropriate follow-up by the clinician. The SUVmax may aid in further characterisation of the lesion and its management.

Metastasis to the thyroid from non-small cell carcinoma of the lung: findings in (18)F-FDG PET/CT study.

The incidence of thyroid metastasis from other primary malignancy is rare. In this case, we present the findings of (18)F-FDG PET/CT in thyroid metastasis from underlying non-small cell carcinoma of the lung and highlight the importance of tracer uptake pattern recognition within the thyroid on (18)F-FDG PET/CT study.

Beware of the focal uptake at the ischium on the bone scan in prostate cancer.

RATIONALE: The isotope bone scan is routinely used in the management of prostate cancer as the skeleton is the second most common area of metastasis after lymph nodes. A classic site of involvement in the pelvis is the ischium, and the aim of this study was to assess the value of single-photon emission computed tomography/computed tomography (SPECT/CT) imaging in patients with focal ischial uptake on the planar scan. MATERIALS AND METHODS: This was a retrospective study of consecutive 150 patients with prostate cancer who were referred for a whole-body bone scan between August 2007 and 2008. Two experienced nuclear medicine consultants along with a musculoskeletal radiologist reviewed the scans. RESULTS: Sixty-eight patients were diagnosed with widespread metastases and 46 patients showed typical degenerative disease changes on planar whole-body imaging. SPECT/CT imaging was done in 36 patients to clarify the diagnosis in areas of indeterminate uptake noted on planar whole-body imaging. Ten of these 36 patients who had focal increased ischial uptake were included in the study. Only three of these 10 patients were diagnosed as having a metastatic lesion with the presence of an enthesopathy, a common finding. CONCLUSION: Isolated focal uptake in the ischium is a relatively common finding in patients with prostate cancer and there is concern that this, on occasion, could be misinterpreted as metastasis. SPECT/CT imaging has an important role in differentiating a benign from a malignant lesion.