Figure 6a. Hyperattenuating, septated benign cyst in an 84-year-old man with mild renal insufficiency. (a) Unenhanced CT scan shows a 4-cm-diameter lesion with high attenuation (68 HU). (b) Contrast-enhanced CT scan shows no significant enhancement (70 HU). (c) Longitudinal sonogram shows that the lesion is cystic and has one delicate septation (arrow). Although this lesion meets the criteria for a benign hyperattenuating cyst, some recommend follow-up of all hyperattenuating lesions larger than 3 cm in diameter (6).