Figure 4a. Myelolipoma in a 72-year-old woman with a history of metastatic endometrial carcinoma. Axial (a–c) and coronal (d–f) CT (a, d), PET (b, e), and fused PET-CT (c, f) images show a left adrenal mass (arrow). At CT, the mass measured 7.6 x 5.6 cm and was seen to contain macroscopic fat (internal attenuation of –32 HU), a finding that is most consistent with a myelolipoma. However, a collision tumor (coexistent myelolipoma and metastasis) was difficult to fully exclude with CT alone. Fused PET-CT images revealed no evidence of significantly increased FDG uptake in the left adrenal gland to suggest the presence of malignancy. The majority of myelolipomas are not FDG avid. Certain rare cases of increased avidity have been reported when adenomatous and hematopoietic elements predominate. In patients with a history of malignancy, fusion PET-CT is helpful in recognizing myelolipoma and excluding concomitant metastatic adrenal involvement (collision tumors).