[Imaging of parathyroid adenomas with F‑18 choline PET-CT]

Performance of quantitative measurements in [18F]fluorocholine positron emission tomography/computed tomography for parathyroid imaging (P2TH study)

Objective

[¹⁸F]Fluorocholine positron emission tomography/computed tomography (PET/CT) is used frequently in addition to [^99mTc]Tc-Sestamibi scintigraphy and ultrasonography for the location of hyperfunctioning parathyroid glands. The aim of this study is to evaluate the performance of quantitative criteria in [¹⁸F]fluorocholine PET/CT for localization of hyperfunctioning parathyroid glands. The secondary objective is to highlight a correlation between the detection rate of [¹⁸F]fluorocholine PET/CT and serum parathyroid hormone (PTH) level.

Materials and methods

In two academic centers, we retrospectively included patients with biological hyperparathyroidism (HPT) and who had [¹⁸F]fluorocholine PET/CT. After a visual analysis, to measure the overall performance of [¹⁸F]fluorocholine PET/CT, a blind reading was carried out with standardized measurements of maximum standardized uptake value (SUV_max), liver ratio, thyroid ratio, and size ratio. We analyzed the quantitative criteria of [¹⁸F]fluorocholine PET/CT compared to the histological results, in particular to identify differences between adenomas and hyperplasias. We compared the performance of each quantitative criterion to the overall sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy of [¹⁸F]fluorocholine PET/CT. The detection rate of hyperfunctioning parathyroid glands was calculated in subgroups of serum PTH level.

Results

The quantitative criteria in [¹⁸F]fluorocholine PET/CT were measured for 120 patients (135 lesions). The areas under the receiver operating characteristic (ROC) curve representing SUV_max and liver ratio were significantly increased. The optimal cut-off values represented by the maximum Youden index was >4.12 for SUV_max and >27.4 for liver ratio. Beyond certain threshold values of SUV_max (>4.12) or liver ratio (>38.1), all the lesions were histologically proven adenomas. SUV_max and liver ratio were significantly higher for adenomas than for hyperplasias and differential diagnosis (p = 0.0085 and p = 0.0002). The positivity of [¹⁸F]fluorocholine PET/CT was correlated with PTH level. Detection rates were 55.56, 75.56, and 87.5%, respectively, for serum PTH < 70, 70 to 120, and >120 ng/ml.

Conclusion

Semi-quantitative measurements (SUV_max and liver ratio) should be considered as additional tools in interpretation of [¹⁸F]fluorocholine PET/CT. These quantitative parameters have lower overall performance but higher specificity than overall visual analysis in identifying an adenoma. Above certain threshold values, all lesions are adenomas. [¹⁸F]fluorocholine PET/CT confirms excellent performance for the detection of hyperfunctional parathyroids. For serum PTH levels < 70 ng/ml, the detection rate of [¹⁸F]fluorocholine PET/CT is strongly decreased.

Questionable value of [99mTc]-sestamibi scintigraphy in patients with pHPT and negative ultrasound

PURPOSE

A successful focused surgical approach in primary hyperparathyroidism (pHPT) relies on accurate preoperative localization of the parathyroid adenoma (PA). Most often, ultrasound is followed by [^99mTc]-sestamibi scintigraphy, but the value of this approach is disputed. Here, we evaluated the diagnostic approach in patients with surgically treated pHPT in our center with the aim to further refine preoperative diagnostic procedures.

METHODS

A single-center retrospective analysis of patients with pHPT from 01/2005 to 08/2021 was carried out followed by evaluation of the preoperative imaging modalities to localize PA. The localization of the PA had to be confirmed intraoperatively by the fresh frozen section and significant dropping of the intraoperative parathyroid hormone (PTH) levels.

RESULTS

From 658 patients diagnosed with pHPT, 30 patients were excluded from the analysis because of surgery for recurrent or persistent disease. Median age of patients was 58.0 (13-93) years and 71% were female. Neck ultrasound was carried out in 91.7% and localized a PA in 76.6%. In 23.4% (135/576) of the patients, preoperative neck ultrasound did not detect a PA. In this group, [^99mTc]-sestamibi correctly identified PA in only 25.4% of patients. In contrast, in the same cohort, the use of [¹¹C]-methionine or [¹¹C]-choline PET resulted in the correct identification of PA in 79.4% of patients (OR 13.23; 95% CI 5.24-33.56).

CONCLUSION

[¹¹C]-Methionine or [¹¹C]-choline PET/CT are superior second-line imaging methods to select patients for a focused surgical approach when previous ultrasound failed to identify PA.

Minimally invasive parathyroid carcinoma-A missing entity between parathyroid adenoma and carcinoma: Scintigraphic and histological features

PURPOSE

Minimally invasive parathyroid carcinoma (MIPC) is clinically and biochemically comparable with parathyroid adenoma (PA) though histopathologically differ from PA. MIPC is an intermediate of PA and parathyroid carcinoma (PC). In literature, there is no definite criterion to diagnose MIPC. Our aim was to evaluate and characterize the imaging and biochemical parameters with histological characteristics of MIPC.

METHODOLOGY

Ten patients with MIPC were recruited from (single centre) Indian PHPT registry (www.indianphptregistry.com) from January 2014 to July 2018. Clinical, biochemical, imaging and histological features of MIPC patients were reviewed.

RESULTS

The mean age of MIPC patients (n = 10; 3 males) was 39.9 ± 11.3 years (range: 17-50). All patients had an elevated preoperative parathyroid hormone (iPTH) level ranging from 427 to 2138 pg/mL (median: 1328). MIBI scan showed intensely avid and enlarged parathyroid tumours in all patients; LIPT in 6, RIPT in 3 and ectopic mediastinal in 1 with mean size of the tumours was 2.8 ± 1.1 cm. The mean of maximum standardized uptake value (SUVmax) of MIPC in F-18 fluorocholine PET/CT was 6.7 ± 1.1 (range 6.0-8.3). The mean tumour weight was 12 ± 9.5 g (range: 1.09-28). All MIPC patients had identified capsular invasion in 80% and vascular invasion in 50% only but there was no local invasion, lymph nodal or distant metastasis. The mean Ki-67 labelling index was 3.2 ± 2.7 (range 1.1-10).

CONCLUSION

The study concluded that MIPC patients are less aggressive (on the basis of imaging and histopathological findings) and should be differentiated from parathyroid adenoma and carcinoma.