Causes of discordant or negative ultrasound of parathyroid glands in treatment naïve patients with primary hyperparathyroidism.

OBJECTIVES: To describe causes of discordant or negative parathyroid ultrasound and to assess factors influencing them.
MATERIALS AND METHODS: Retrospective review of patients who underwent parathyroidectomy between 2000 and 2012 was done. Imaging findings were compared with operative findings and pathology to identify discrepant (n=60; 32 negative, 28 incorrect) parathyroid ultrasounds.
RESULTS: Fifty (83.3%) patients had parathyroid adenoma, of which 10 (16.6%) were ectopic and three were double adenomas; 8 (13.3%) had multigland hyperplasia and two had parathyroid carcinoma. Discrepant reports were due to incorrect localisation in 8 (13.3%); difficulty in differentiating thyroid from parathyroid lesion in 12 (20%); large and small size in two and three patients, respectively; overcall in 5 (8.3%) and satisfaction of search in 7 (11.7%) patients. There was significant correlation between presence of multi-nodular goitre and incorrect reports (χ(2)=4.112, p=0.04). Experience of ultrasound operators performing initial and second look ultrasound was significantly different (p<0.0001). Second look ultrasound was concordant with surgical findings in 39(65%) patients; 21 (66%) patients with initially negative ultrasound and four out of five extra-mediastinal ectopic lesions. Ten patients with negative initial ultrasound had elongated parathyroid lesion. Scintigraphy was concordant in 44 (73.3%) patients and nine were ectopic.
CONCLUSION: Second look ultrasound performed by experienced operator for negative or discordant initial ultrasound of parathyroid is a useful strategy which will improve the accuracy of parathyroid ultrasound. Being able to differentiate thyroid from parathyroid lesion is a factor which will influence performance of parathyroid ultrasound.