CT sensitivity for adrenal adenoma according to lesion size

Abstract

PURPOSE: To retrospectively evaluate CT sensitivity for characterizing adrenal adenoma according to lesion size.

MATERIALS AND METHODS: Between January 2004 and November 2012, 140 patients with 140 histologically proven adenomas underwent preoperative adrenal CT protocols consisting of unenhanced CT, early enhanced CT, and delayed enhanced CT. Adenomas were divided into three size groups: small adenoma (n = 60), ≥ 1 to <2 cm; medium adenoma (n = 47), ≥ 2 to <3 cm; and large adenoma (n = 33), ≥ 3 cm. Adenoma was diagnosed when a lesion met one of the following criteria: (a) unenhanced CT attenuation value ≤ 10 HU, (b) absolute percentage washout ≥ 60%, or (c) relative percentage washout ≥ 40%. The standard reference was pathologic examination of an adrenalectomy specimen. Adenoma size, lesion attenuation value, or percentage washout was correlated with the Spearman's rank correlation. CT sensitivities were compared between size groups of adenomas with the Fisher's exact test.

RESULTS: As adenoma size increased, the lesion attenuation value (ρ = 0.324; P = 0.001) increased on unenhanced CT, and the absolute (ρ = -0.186; P = 0.028) or relative (ρ = -0.374; P < 0.001) percentage washout decreased on early and delayed enhanced CT. CT sensitivities were 100% (60/60) for small adenomas, 97.9% (46/47) for medium adenomas, and 66.7% (22/33) for large adenomas (P < 0.001).

CONCLUSIONS: Adrenal CT protocols misdiagnose a substantial number of large adenomas as non-adenomas because CT sensitivity for adenoma markedly decreases, when the lesion size is 3 cm or larger.