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PET/CT Alone Should Not Be Used to Exclude Tonsillar Cancer

by Amy E. Hamaker •

Comment: Increased and asymmetric PET/CT FDG uptake in the tonsils is a frequent reason for referral to otolaryngology. However, it is unclear what uptake threshold should prompt biopsy. Certainly, we don’t want to miss primary tonsillar cancer; we also don’t want to perform unnecessary procedures. This small study showed that an SUVmax ratio between tonsils >1.6 (62% sensitive, 100% specific) is highly suspicious and warrants biopsy. They also note that malignant tonsils can have normal FDG uptake. Thus, PET/CT alone should not be used to exclude
cancer. —Jennifer Villwock, MD

What is the maximum standardized uptake value (SUVmax) ratio between tonsils in patients with and without tonsillar carcinoma to determine useful diagnostic thresholds?

Bottom Line:
An SUVmax ratio between tonsils of ≥1.6 is highly suspicious for squamous cell carcinoma (SCC) and could be used to direct site of biopsy. Some malignant tonsils had normal FDG uptake; therefore, positron-emission tomography (PET)/computed tomography (CT) should not be used to exclude tonsillar cancer. Minor asymmetrical uptake is frequently seen in non-malignant tonsils and does not necessarily require further investigation.

Study design: Retrospective.

Summary: PET/CT examinations of patients with suspected head and neck SCC and controls from April 2013 to September 2016 were reviewed retrospectively. Tonsillar SUVmax ratios (ipsilateral/contralateral for malignant tonsils, maximum/minimum for patients without [controls]) were calculated and used to construct a receiver operating characteristic (ROC) curve. Twenty-five patients had tonsillar carcinoma (mean SUVmax ratio of 2, range 0.89–5.4) and 86 patients acted as controls (mean SUVmax ratio of 1.1, range 1–1.5). Using the ROC, the most accurate SUVmax ratio for identifying malignancy was >1.2 (77% sensitivity, 86% specificity). A potentially more clinically useful SUVmax ratio is ≥1.6 with 62% sensitivity and 100% specificity.

Citation: Pencharz D, Dunn J, Connor S, et al. Palatine tonsil SUVmax on FDG PET-CT as a discriminator between benign and malignant tonsils in patients with and without head and neck squamous cell carcinoma of unknown primary. Clin Radiol. Published November 16, 2018 online ahead of print. doi: 10.1016/j.crad.2018.10.007.