Evaluation of MRI and SPECT Fusion Software to Localize Parathyroid Adenomas

While a successful neck exploration for PHP is primarily dependent on the experience of the surgeon, there are currently several localizing studies available to increase success. Although the necessity of localizing studies pre-operatively for first time neck explorations is still under debate, there is no question of their importance for persistent or recurrent PHP that requires re-operation. Localizing studies in these patients have been clearly shown to reduce operating time, avoid unnecessary dissection, reduce morbidity, and improve success rate.

Several modalities have been employed for localization such as ultrasound (US), computed tomography (CT), and magnetic resonance imaging (MRI). The sensitivity of ultrasound for the preoperative detection of parathyroid adenomas has been reported to be 65-90% (1). There are however, limitations to US. Because of the sonolucent appearance of parathyroid adenomas, it is impossible to distinguish an ectopic cervical parathyroid adenoma from a pathologic lymph node. Furthermore, mediastinal parathyroid adenomas are difficult, if not impossible to visualize due to acoustic shadowing from the sternum and clavicles (2). Also, this method is very operator-dependent. MRI has a slightly higher sensitivity of 62.5-94% while CT has a poor sensitivity of only 40-44% (1).

We are using dual-phase single photon emission tomography (SPECT) imaging with technetium 99m sestamibi and visual thyroid subtraction with technetium 99m as pertechnetate. This method can achieve sensitivities of 68-95% and specificities of 75-100% (1). SPECT imaging is dependent on the differential washout of sestamibi between normal thyroid tissue and abnormal parathyroid tissue. Theoretically, sestamibi will washout of normal thyroid tissue much more quickly than it will from abnormal parathyroid tissue. Therefore, SPECT imaging is usually performed immediately and then at 90 and 180 minutes after sestamibi injection. SPECT imaging, however, has several limitations, not the least of which is its inability to provide discrete anatomic detail.

In addition, we will use a control group of patients who have parathyroid adenomas but who have not yet had surgery to test the efficacy of our fusion software.

Our goal is to acquire MRI and SPECT imaging with fiducial markers and utilize fusion software to create a detailed anatomic map of the neck for more accurate localization of the lesion.