Localising Ectopic Parathyroid Adenomas: A Pictorial Review of 99mTc Sestamibi SPECT/CT

AIM: Localization of ectopic parathyroid adenomas is important in guiding surgical decisions with the aim of minimising post-operative morbidity. This pictorial review explores the role of 99mTc Sestamibi SPECT/CT imaging for localising these unusual sites and the subsequent surgical approach to these adenomas.

MATERIALS AND METHODS: We retrospectively reviewed 164 imaging studies of patients clinically suspected to have primary hyperparathyroidism and referred for localisation of adenomas between January 2010 and March 2013. All patients had 99mTc Sestamibi imaging with early and delayed SPECT/CT performed 20 minutes and 3 hours after the tracer injection respectively. SPECT/CT images were reconstructed to provide fused axial images as well as with volume rendering of the CT using recovery
software. All patients also underwent an ultrasound of the neck to confirm absence of adenomas in the usual location. The pre-operative imaging results were correlated with operative decisions and findings as well as histopathology.

RESULTS: In our series, 11 patients demonstrated an ectopic parathyroid adenoma which suggested an incidence of 6.7% of all patients referred for parathyroid imaging, lower than the 20-25% incidence rate reported in world literature. Ectopic locations demonstrated on SPECT/CT included the superior and anterior mediastinum (3 and 4 adenomas respectively), tracheoesophageal groove (3 adenomas) and retropharyngeal space (1 adenoma). Surgical plans required the addition of sternotomy in 2 patients. Surgical and histopathological findings confirmed the diagnosis of ectopic parathyroid adenoma in 8/ 9 patients. (2 patients are awaiting surgery).

CONCLUSION: SPECT/CT imaging provided accurate localisation of ectopic parathyroid adenomas and helped guide surgical approach in these patients.