Figure 4b. APA. (a) Unenhanced CT scan obtained in a 30-year-old woman with primary aldosteronism shows a 5-cm low-attenuation (– 16 HU) right adrenal mass (arrow), a finding that is in keeping with an APA. The left adrenal gland is normal (arrowhead). (b) T1-weighted MR image obtained in a 45-year-old woman with primary aldosteronism shows an APA of the medial limb of the right adrenal gland (arrow). The lateral limb of the right adrenal gland and the left adrenal gland (arrowhead) appear normal. Both patients underwent surgery, with postoperative histologic analysis leading to the diagnosis of APA.