Z017

 

The use of computed Tomography as a first-line imaging modality in patients with primary Hyperparathyroidism

 

MC de Jong2, Z Hussein1, K Jamal2, S Morley3, T Beale3, T Chung1, S Jawad3, S Hurel1, H Simpson1, U Srirangalingam1, S E Baldeweg1, V Rozalén García2, S Otero3, M Shawky2, TE Abdel-Aziz2, TR Kurzawinski2, 1Department of Endocrinology, University College London Hospital, London, United Kingdom, 2Center for Endocrine Surgery, University College London Hospital, London, United Kingdom, 3Department of Radiology, University College London Hospital, London, United Kingdom

 

Introduction: Successful outcomes in primary hyperparathyroidism (PHPT) relies on accurate localisation of the culprit parathyroid glands. Concordant findings on the neck ultrasound (US) and Sestamibi (99mTc scintigraphy) are currently considered the ‘gold’ standard. However, Computed Tomography (CT) scan has also been used in the pre-operative planning of parathyroidectomy.

We report a 73-year-old lady, presented to her GP with fatigue and tiredness. Biochemically proven to have PHPT. CT parathyroid and US scans were performed for adenoma localisation and both scans revealed descended right superior parathyroid adenoma.

In our centre we conducted a study to assess the accuracy of CT scan in localising abnormal parathyroid glands in such patients.

 

Study Methods: This is a prospective study of 75 patients with PHPT who underwent neck US and CT scans as their first line imaging between January 2017 and January 2019. Sestamibi was reserved for patients with diagnostic uncertainty (n=7), although many patients (n=47) had already a Sestamibi scan performed at the referring centres.

During surgery, the identification and extirpation of the abnormal gland was followed by intra-operative PTH measurements. The modified Miami criterion was used to define intra- operative cure.

The postoperative values of serum calcium and PTH were recorded at specific times (i.e. direct post- operative [<24 hours of surgery], 3 months after surgery and at their final follow-up at 6 months).

 

Results: 77.3% of patients were female with median age of 57 years. The overall sensitivity [95%-CI] per diagnostic tool was 60% for US scan, 87% for CT scan, and 33% for Sestamibi (overall p<0.05). In 17 (22.7%) patients, CT was the only modality which correctly identified abnormal glands.

Eight patients (10.7%) in whom none of the imaging modalities was correct had bilateral neck exploration, in two of them (25.0%) the adenoma was in an ectopic location and five (62.5%) had multiglandular disease.

The combined sensitivities for multimodality imaging were also calculated. The standard combination of US and Sestamibi resulted in a sensitivity of 65%, this was statistically less than the sensitivity for CT alone (p<0.001). The combination of US and CT resulted in a sensitivity of 88%, this was not statistically significantly different from that of CT alone (p>0.99). Sestamibi was not helpful in patients with negative combined US and CT scans.

 

Discussion and conclusion: Several factors influenced imaging sensitivity in this study; the first factor was the weight and size of parathyroid adenoma. The sensitivity of CT for localizing abnormal parathyroid glands weighing <1.0g was 81%, significantly better than that of US (54%; p=0.002) or US & Sestamibi (62%; p=0.04). Combining the results of US & CT in patients with smaller glands did not lead to an increase in the sensitivity compared with CT alone (p>0.99).

The second important factor was ectopic parathyroid adenoma. The sensitivity for CT alone was 82% which was statistically better than US (50%; p=0.039) and combined US & Sestamibi (57%; p=0.07). However, combining US&CT led to increased accuracy of 86%; p=0.016).

The diagnosis of multiglandular disease seemed to be the most difficult, the sensitivity for US & Sestamibi was of 40% and the accuracy rate for combined US&CT was statistically similar at 50%.

The combination of US and CT was able to correctly identify the location of parathyroid adenoma in 88% of patients, with a relatively better diagnostic accuracy for smaller and ectopic adenomas.

This finding suggests that a change of current paradigm of performing US and Sestamibi is desirable and US & CT should be considered as a first-line imaging modality in patients with PHPT considered for surgery.