Fig 1.
PET/CT study in a 43-yr-old patient with papillary thyroid cancer and central nodal disease.
He presented a detectable rhTSH-stimulated serum Tg level (4 ng/ml) three years after initial surgery. The neck US and diagnostic 131I whole-body (WB) scan were negative. Hybrid CT scan of the PET/CT study is presented in Panel a. On the WB PET (Panel b) there was a faint FDG uptake (SUVmax = 2.1) in a left lateral LN which was considered as probably benign (score 2) by Reader 1 and indeterminate (score 3) by Reader 2. On head and neck (HN) PET (Panel c), both readers reported a probably malignant (score 4) FDG focus (SUVmax = 3.4). Node/muscle background ratio was 4.3 on HN PET vs. 2.3 on WB PET. A LN without suspicious features (short-axis: 6 mm; long axis: 14 mm) was described in front of this FDG focus on hybrid CT scan (Panel a).
Table 1.
Characteristics of the 15 patients operated on in the neck with at least one FDG focus scoring 4 or 5 on PET/CT.
Fig 2.
PET/CT study in a 63-yr-old patient (Patient 4) with a pT1aN1aM0 papillary thyroid cancer and a detectable serum Tg level under levothyroxine (6 ng/ml).
Hybrid CT scan of the PET/CT study is presented in Panel a. Whole-body (WB) PET (Panel b) was considered as normal whereas a small grade 4 FDG focus was reported on head and neck (HN) PET (Panel c) by both readers. Node/muscle background ratio was 3.9 on HN PET vs. 1.9 on WB PET. A small LN without suspicious features (short-axis: 7 mm; long axis: 9 mm) was described in front of this FDG focus (Panel a). Neck US examination was normal. Central neck lymph node dissection was performed and pathology confirmed HN PET/CT data. The tumor size of the left central LN was 8 mm at histology (Panel d).
Fig 3.
PET/CT study in a 74-yr-old patient (Patient 11) with a pT4aN1bM1 papillary thyroid cancer (tall-cell variant).
She presented with a detectable serum Tg level under levothyroxine (14 ng/ml) 5 years after initial diagnosis. Both whole-body (WB) and head and neck (HN) PET (Panels b and c) evidenced a grade 5 FDG focus in front of an abnormal LN (short-axis: 10 mm; long axis: 16 mm) in the right lateral compartment IV (Panel a). A small grade 4 FDG focus was also reported by both readers on HN PET (Panel f) in front of an apparently normal LN (short-axis: 4 mm; long axis: 8 mm) located in the left lateral compartment II (Panel d). This FDG focus was not reported on WB PET (Panel e). Node/muscle background ratio was 6.0 on HN PET vs. 3.9 on WB PET. After bilateral neck dissection, pathology confirmed HN PET/CT data.
Fig 4.
SUVmax values of the malignant lesions on head and neck (HN) and whole-body (WB) PET (Panel a), SUVmean values on HN and WB PET for vascular (Panel b) and muscle (Panel d) background, and the resulting node/background (N/B) ratios when considering either vascular (Panel c) or muscle (Panel e) background.
Fig 5.
Size of the largest LN metastasis detected neither by whole-body (WB) nor head and neck (HN) PET (3 ± 1 mm), for the metastasis detected by HN but not by WB PET (7 ± 3 mm) and for those detected by both acquisitions (13 ± 5 mm) (P = 0.0004).
Table 2.
Metastatic lymph nodes removed during surgery: relationship between tumor size, PET detection on either WB or HN PET and FDG uptake.
Fig 6.
Receiver-Operating Characteristic (ROC) curve analysis for SUVmax on head and neck (HN) and whole-body (WB) PET.
The area under the curve (AUC) is higher for HN PET than for WB PET (0.97 [95%CI, 0.90–0.99] vs 0.88 [95%CI, 0.78–0.95], P = 0.009).