Usefulness of semi-quantitative analysis in 123I metaiodobenzylguanidine SPECT/CT for the differentiation of pheochromocytoma and cortical adenoma

Abstract

Objective: ¹²³I metaiodobenzylguanidine (MIBG) scintigraphy is a useful tool for the diagnosis of pheochromocytomas (PHEOs), but some PHEOs are difficult to differentiate from cortical adenoma (CA) or normal adrenal uptake by visual evaluation alone. A new semi-quantitative analysis using ¹²³I MIBG SPECT/CT is thus expected. Herein, we introduce the tumor-to-liver count ratio (T/L) and the tumor-to-muscle count ratio (T/M).

Methods: We examined the cases of 21 patients with PHEOs (10 males, 11 females; age 24-80, median 61 years) and 23 patients with CA (15 males and 8 females, age 30-78, median 58 years). The visual scoring based on ¹²³I MIBG planar images (planar score) and SPECT images (SPECT score) was used as the conventional evaluation. Using ¹²³I MIBG SPECT/CT findings, we calculated the semi-quantitative values of the count ratio using the maximum or mean count of the tumor and the liver or muscle as the reference organ (T/L_max, T/L_mean, T/M_max and T/M_mean). Each evaluation of the PHEOs and CAs was compared, and the diagnosing performance was evaluated based on an ROC analysis.

Results: The area under curve (AUC) values were as follows: the planar score, 0.833; SPECT score, 0.813; T/L_max, 0.986; T/L_mean, 0.975; T/M_max, 0.955; and T/M_mean, 0.933. The AUC for T/M_max was significantly higher than those of the planar score, and SPECT score by ROC analysis (p < 0.01 each).

Conclusion: The semi-quantitative value of ¹²³I MIBG SPECT/CT is more useful than the conventional visual evaluation for differentiating PHEOs from CAs.

Keywords: 123I MIBG; Adrenal cortical adenoma; Adrenal tumor; Pheochromocytoma; SPECT/CT.