Imaging of endocrine organs (to assess structure) - parathyroid sestamibi

Role

Sestamibi scintigraphy is the standard functional imaging technique for localising a hyperfunctioning parathyroid gland (adenoma or hyperplasia) in confirmed primary hyperparathyroidism before surgical parathyroidectomy - exploiting differential tracer retention in hyperactive parathyroid tissue compared with normal thyroid/parathyroid tissue
Performed routinely as part of pre-operative planning once biochemical diagnosis of primary hyperparathyroidism is confirmed and surgery is being considered

Technetium-99m sestamibi is taken up by both thyroid and parathyroid tissue but washes out more slowly from hyperfunctioning parathyroid tissue (which has higher mitochondrial content/metabolic activity) - delayed imaging (after initial uptake) exploits this differential washout to identify the abnormal gland against the background of normally clearing thyroid tissue

Sensitivity is highest for a single parathyroid adenoma (the most common cause of primary hyperparathyroidism) and lower for multi-gland hyperplasia or smaller adenomas - a negative or equivocal scan does not exclude the diagnosis (which remains biochemical) and should prompt consideration of a complementary imaging modality (ultrasound, 4D-CT) rather than abandoning surgical planning
Often combined with neck ultrasound for complementary anatomical localisation, since the two modalities have different strengths and combining them improves overall localisation accuracy

Positive, concordant localisation on sestamibi (and complementary imaging) supports a minimally invasive, focused parathyroidectomy targeting the identified gland, rather than a more extensive bilateral neck exploration
Discordant or negative imaging generally prompts bilateral neck exploration by an experienced surgeon, or additional imaging before proceeding

Primary hyperparathyroidism (the primary indication), multi-gland hyperplasia (lower sestamibi sensitivity than single adenoma), minimally invasive vs bilateral parathyroidectomy decision-making, intraoperative PTH monitoring (confirms successful removal of hyperfunctioning tissue during surgery)

Sestamibi scanning is a pre-operative localisation tool, not a diagnostic test for primary hyperparathyroidism - the diagnosis itself remains biochemical (elevated calcium with inappropriately normal/elevated PTH), and a negative or equivocal scan in a biochemically confirmed case should prompt further localisation imaging rather than reconsideration of the underlying diagnosis

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