Intoduction

^99m Tc-sestamibi parathyroid scintigraphy is a means of functional imagery allowing the exploration of the hyperparathyroidy. We report through this work the case of a patient presenting a residual hypercalcemy after subtotal parathyroidectomy and at which the double-phase planar scintigraphy using ^99m Tc-sestamibi allowed the description of a mediastinum ectopic hearth.

Case report

A 50 year old women had a subtotal parathyroidectomy for biological hyperparathyroidy and presented with the persistence of a residual hypercalcemy. The computed tomography and resonance magnetic nuclear imagery were inconclusive sight the post-operative fibrosis.

Parathyroid scintigraphy of the neck and upper thorax and/or mediastinum was performed 20 minutes and 2 hours after injection of 740 MBq of technetium 99m-sestamibi. To this end we used a gamma-camera with large field provided with pin-hole and parallel-hole collimators (high résoluion-low energy) intended for mediastinal exploration.

The 20 ^th minute scan showed uptake in a normal appearing thyroid gland as well as uptake in one ovoid area in the upper mediastinum. The 2 ^nd hour image showed wash out of activity from the thyroid and persistence of activity in the upper mediastinum (Figure.1).

Figure 1

Figure 1 : Tc-Sestamibi parathyroid planar scintigraphy : the 20 minute scan showed uptake in a normal appearing thyroid gland as well as uptake in a heart of the right upper mediastinum .The 2 hour image showed wash out of activity from the thyroid and persistence of activity in the upper mediastinum (arrow).

A focused surgical resection was carried out. Pathologic examination of the surgical specimen revealed parathyroid adenoma tissue. The evolution was marked by a clear clinical improvement and a normalisation of the rate of parathormone.

Discussion

A successful parathyroidectomy depends on the identification and the resection of the whole of parathyroids in hyperactivity. During several decades, one did not have recourse to the preoperative imagery before a first surgery. A bilateral, long and meticulous exploration cervical, allowed the cure from 90 to 95% of patients [₁]. The two main reasons of the failure of the surgery are: ectopic glands (retro-oesophagium, mediastinum like that is the case in our patient, intra-thyroid gland, in the sheath of the carotid artery) and multiple parathyroid pathology not detected [₂]. The reintervention is often associated on a dramatic reduction of the rate of success and an increase in the surgical complications. The imagery is consequently imperative before one second intervention [₃,₄]. ^99m Tc-sestamibi parathyroid scintigraphy is currently regarded as the most significant technique of the imagery among patients reached of primary hyperparathyroidism [₅,₆]. Whatever the protocol used, the ^99m Tc- sestamibi parathyroid scintigraphy meets generally the need for detection of ectopic glands [₇]. When the preoperative imagery indicates a well defined ectopic hearth, suggesting a solitary adenoma, the surgeon can currently choose a surgery focused rather than a bilateral exploration like that was carried out in our patient.

Conclusion

Double-phase planar scintigraphy using ^99m Tc-sestamibi is a means of functional imagery contributing to the exploration of hyperparathyroidism. Its sensitivity is significantly higher than the other means of morphological imagery particularly when it acts a second surgical intervention. Its interest seems more considerable for the exploration of ectopic adenoma and to improve the success of surgery.