Background: Mechanisms that are responsible for positive 99mTc-MIBI uptake in parathyroid glands are not clearly understood, some authors suggest there is a correlation between 99mTc MIBI accumulation and oxyphil cell content or parathyroid gland volume. The aim of our work was to assess the relationship between the pathological structure of parathyroids, their volume, oxyphil cell content and parathyroid 99mTc-MIBI retention.
Material and methods: A total of 62 hyperfunctioning parathyroid glands in 46 patients were retrospectively analyzed. Preoperative 99mTc-MIBI scintigraphy was performed according to the double-phase and subtraction protocol. After surgery all glands were evaluated histologically, oxyphil cell content was assessed and volume of each excised gland was calculated.
Results: Scintigraphy was positive in 41 of 62 parathyroid glands (66%). The median volume of positive glands was larger than that of negative glands (1.33 ml vs 0.7 ml, p = 0.015). Of the parathyroid lesions, there were 14 (22.6%) cases of nodular hyperplasia, 23 (37.1%) cases of diffuse hyperplasia, and 25 (40.3%) cases of adenomas. A high (≥ 25%) oxyphil cell content was found in 16 glands (25.8%) and a low ( < 25%) oxyphil cell content in 46 (74.2%) glands. Histopathology of parathyroid glands was related to the scintigraphy result (p = 0.002), but not to the 99mTc-MIBI uptake pattern (p = 0.868). The overall result of scintigraphy was not related to the oxyphil cell content (p = 0.797). 99mTc-MIBI uptake pattern wasn't related to the oxyphil cell content (p = 0.833). In general, parathyroid lesions with low oxyphil cell content were larger than parathyroid glands with high oxyphil cell content (1.33 ml vs 0.5 ml, respectively; p = 0.01). The median volume of parathyroids containing a high number of oxyphil cells and having a prolonged 99mTc-MIBI retention was larger than those without prolonged 99mTc-MIBI retention (1.62 ml vs 0.3 ml, respectively; p = 0.008). The median volume of parathyroids with low oxyphil cells content and showing prolonged 99mTc-MIBI retention was larger than those without prolonged 99mTc-MIBI retention (1.95 ml vs 1.07 ml, respectively; p = 0.014).
Conclusions: Our findings suggest that a positive scintigraphy result depends on parathyroid histopathology and gland volume and does not depend on the presence of oxyphil cells. Prolonged 99mTc-retention is not related to the parathyroid gland histopathology and the presence of oxyphil cells but to the gland volume.
Keywords: 99mTc-MIBI; oxyphil cells; parathyroid adenoma; parathyroid hyperplasia; parathyroid scintigraphy; parathyroid volume.