Preoperative localization of parathyroid adenomas with technetium-99m methoxyisobutylisonitrile imaging: relationship...

In addition to tumor size, it has been suggested that P-glycoprotein (P-gp) expression and/or oxyphilic cell content in parathyroid adenomas has an important influence on the results of technetium 99m methoxyisobutylisonitrile (Tc-99m MIBI) parathyroid imaging.

In this study, we compared the results of MIBI parathyroid imaging and immunohistochemical analysis (IHA) of P-gp expression, oxyphilic cell content, and tumoral tissue volume in parathyroid adenomas. We also evaluated the relationship between MIBI and ultrasound (US) results, operation findings, serum biochemical values.

Forty (40) patients (36 female and 4 male; mean age, 53.2 +/- 8.16 years) with hyperparathyroidism who had undergone surgery were included in this study. Preoperatively, "double phase" parathyroid scintigraphy with Tc-99m MIBI (including imaging of the neck and mediastinum) was performed in all patients. Thirty-two (32) of the patients had also neck US. Serum parathormon (PTH), calcium (Ca), phosphorus (P), and alkaline phosphatase (ALP) levels were measured preoperatively. In resected parathyroid tissues, P-gp expression and percentage of oxyphilic cell content were analyzed with IHA in 34 patients.

Three (3) of the resected parathyroid tissues were hyperplastic parathyroid tissue, whereas 31 of the tissues were parathyroid adenoma (mean volume, 1.99 +/- 1.93 mL). In Tc-99m MIBI parathyroid scintigraphy, 70% of the parathyroid adenoma/hyperplastic parathyroid tissue was detected in correct localization; at US, this rate was 46.8%. According to the resected parathyroid tissue localization at surgery, sensitivity, accuracy, positive predictive value, and prevalence in scintigraphy were 82.3%, 70%, 82.3%, and 85%, respectively. Those were 60%, 46.8%, 68.2%, and 78.1% for US, respectively. No significant correlation and no concordance was found between MIBI and US results (kappa, -0.103, r = -0.11; p: 0.53). Interestingly, significant correlation was found between tumoral volume and ALP level (r = 0.42; p = 0.010) and between PTH and ALP levels (r = 0.72; p < 0.001). Significant correlation was also found between patient age and tumoral volume (r =-0.37; p = 0.02) and between PTH and serum Ca levels (r = 0.32; p = 0.04). In 23 of 34 patients in whom histopathological examination was done MIBI was positive and in 13 of these patients (56.5%), P-gp expression was positive. When the histopathological results and MIBI results were compared, there was no significant correlation and concordance between P-gp expression (kappa = 0.09, r = 0.10; p = 0.54), oxyphilic cell content (r = -0.17; p = 0.33), and tumoral tissue volume (r = -0.14; p = 0.38). In 12 of 19 patients (63%) who had parathyroid tissue < 1 mL and in 15 of 24 patients (62.5%) who had oxyphilic cell content < 10%, lesions were also detected correctly with MIBI scintigraphy.

Present study results suggest that MIBI scintigraphy was clearly superior to US as a diagnostic tool. However, P-gp expression, oxyphilic cell content, and tumoral volume may have not a main effect on MIBI parathyroid scintigraphy results in parathyroid adenoma.