Dual Parathyroid Pathology; A Common Failure of Technetium-99 Sestamibi Scan for Preoperative Parathyroid Adenoma Localization

PHPT is present up to 0.1% of the general population, and it is clinically recognized in patients presenting with hypercalcemia or as a part of Multiple Endocrine Neoplasia (MEN) types I and II a. Although there have been sporadic reports of the coexistence of hyperparathyroidism and non-medullary thyroid carcinoma, concurrence of parathyroid adenoma and papillary thyroid carcinoma is rare. The cause of the association between thyroid disease and primary PHPT remains unclear [3]. The oncogenic effect of hypercalcemia on the thyroid gland has been assumed, and low-dose radiation therapy for the head and neck, especially in childhood and adolescence, is known to induce thyroid and parathyroid tumors [4]. Since the coexistence can complicate patient management via untreated hypercalcemia, unrecognized thyroid cancer and the necessity of re-operative neck surgery patients should be screened for both disease entities carefully. It is advisable to evaluate the thyroid gland prior to parathyroid gland operations. Although synchronous parathyroid and thyroid carcinomas are rare, they can coexist. It is important not only to do biochemical studies, including serum calcium and PTH concentrations but also to carefully interpret imaging studies as preoperative FNAB and ultrasound of the neck may be helpful to evaluate occult primary hyperparathyroidism, enabling surgery to be performed more aggressively and preventing a second operation that might increase morbidity and mortality.

The exact mechanism that is MIBI scan is less sensitive for dual parathyroid pathology or polyglandular pathology is uncertain, but there are certain factors that may determine MIBI uptake by parathyroid adenoma, most importantly, adenoma size, adenoma cellular function and system resolution which relies on adenoma size and MIBI uptake. Linero and co-workers showed that MIBI uptake by hyper functioning parathyroid adenoma in PHPH might be linked to a higher gland metabolism activity, probably related to cell proliferation [5]. Same author studied 46 patients with PHPT and confirmed that MIBI sensitivity is adenoma is high (91%) than parathyroid hyperplasia (67%) or double adenoma (50 %). No relation was found between biochemical or cytological parameter and scan results, weight and gland volume were significantly greater for adenoma (p.0014 and p.0004) respectively and statically significant difference between them were observed between glands with positive and negative scan [6]. Turgut B et al., suggested that MIBI scan is clearly superior to ultrasound a diagnostic tool and P-Glycoprotein (P-GP) expression, oxyphilic cell content and tumour volume may not have a main effect on MIBI scan result of parathyroid adenoma [7]. Sun and co-workers found that large parathyroid adenoma that express (P-GP) or the multi resistance related protein failed to accumulate MIBI [8]. Katz et al., found that MIBI scan failed to identify the presence of bilateral lesions in 13 patients out of 15 patients with multinodular lesions [9,10]. This fact indicates that in the era of the minimally invasive parathyroidectomy, preoperative MIBI imaging cannot be the sole basis on which the decision to perform limited cervical exploration.

In summary this case demonstrates coexistence of parathyroid adenoma and unrecognized thyroid cancer and the necessity to evaluate the thyroid gland prior to parathyroid gland surgery. Most importantly Tc-99m MIBI scans valuable in preoperative localization of parathyroid adenoma and less useful for detecting parathyroid hyperplasia. In recurrent or resistant hyperparathyroidism considering cross sectional imaging such as MRI with or without repeated Tc-99m MIBI scan is helpful in localizing parathyroid adenoma or hyperplasia.