Diagnostic imaging in Merkel cell carcinoma: lessons to learn from 16 cases with correlation of sonography, CT, MRI and PET

Objective: The authors report imaging findings in a series of 16 patients with MCC, a rare tumour which is often managed primarily by a dermatologist. To our knowledge, no equivalent series of MCC has been described in the nuclear medicine literature.

Material and methods: In this IRB-approved retrospective noncomparative case series 16 patients with biopsy-proven Merkel cell carcinoma were included between January 1999 and October 2007. Twenty-nine whole body PET scans (18F-FDG n=24, 18F-FDOPA n=5) in 16 patients were retrospectively reviewed with regard to tracer uptake in six anatomical sites per patient. For 127/144 of FDG-PET evaluated regions and 68/144 of regions depicted by conventional imaging methods, a valid standard of reference could be obtained. A combined standard of reference was applied, which consisted of histopathology (lymphadenectomy or biopsy) or clinical or radiological follow-up for at least 12 months.

Results: the mean FDG uptake over the clinicopatholigical verified FDG avid areas was 4.7 SUV (1.5-9.9 SUV). The region based assessment of diagnostic value, in consideration of the standard of reference, resulted in a sensitivity of 85.7% and a specificity of 96.2% of FDG-PET (n=127) and in a combined sensitivity of 95.5% and a specificity of 89.1% for morphological imaging methods (n=68). Differences between methods did not reach statistical significance (p=1.00, p=0.18).

Conclusions: FDG-PET is a highly useful whole body staging method of comparable value compared to conventional imaging methods with restricted field of view. The lessons learned from case series are discussed.