Yolanda Y. P. Lee MBChB, Presenter: Author, Amirsys, Inc Author, Oxford University Press

Gary Cook, Abstract Co-Author: Nothing to Disclose

Val Lewington, Abstract Co-Author: Nothing to Disclose

Bhupinder Sharma MBBS, Abstract Co-Author: Nothing to Disclose

Sue Siew-Chen Chua MBBS, Abstract Co-Author: Nothing to Disclose

Uncommonly, 18F-FDG avid cutaneous foci may occur as an incidental finding during oncolgical PET/CT scanning. The precise nature of these foci, and in particular whether they represent cutaneous metastatic deposits, may have an important bearing on tumor staging and subsequent clinical management. We evaluated the diagnostic features and clinical significance of unexpected cutaneous foci of 18F-FDG uptake detected on oncological 18F-FDG PET/CT studies.

We retrospectively reviewed all 18F-FDG PET/CT reports in our institution over a 5 year period. All cases with unexpected focal skin uptake were reviewed. Cases of focal cutaneous uptake in patients with previous biopsy-proven skin metastases, a primary malignancy with propensity to metastasize to the skin (melanoma and ipsilateral breast carcinoma) and a recent percutaneous/transcutaneous procedure were regarded as expected findings and excluded. PET/CT scans were evaluated for the lesions’ PET and CT characteristics. Biopsy results, clinical and imaging follow up were reviewed for definitive diagnosis and patient outcome.

Of 4779 consecutive oncological 18-F FDG PET/CT scans, 50 cases showed unexpected focal skin uptake. A definitive diagnosis could be made in 40 of these cases. This was by biopsy (12.5%), clinical examination (42.5%) or imaging/clinical follow up (45%). 12 cases (30%) were metastases and 28 cases (70%) were benign. SUVmax and SUVmean were significantly higher in malignant than in benign lesions (p=0.008 and 0.03). Morphologically, a non-solid appearance on CT is predictive of benignity, whereas a solid appearance was associated with malignancy(p=0.03). All patients diagnosed with metastases showed poorer survival than the benign group (p=0.001).

30% of cases of unexpected skin uptake on oncological 18F-FDG PET/CT represent metastases. A higher SUVmax, SUVmean and a solid appearance are features associated with malignancy in unexpectedly detected skin lesions in oncologic patients.

18F-FDG avid cutaneous foci are an uncommon incidental finding at oncological PET/CT. Imaging findings may aid the distinction of benign from malignant lesions, which is highly relevant to prognosis.

Lee, Y, Cook, G, Lewington, V, Sharma, B, Chua, S, The Significance of 18F-FDG Avid Cutaneous Foci Incidentally Detected on Oncological PET/CT.  Radiological Society of North America 2010 Scientific Assembly and Annual Meeting, November 28 - December 3, 2010 ,Chicago IL. http://archive.rsna.org/2010/9008541.html