Adrenal adenoma

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[edit] Discussion of Adrenal adenoma

  • Adrenal adenoma is a common tumor, with a prevalence of 3% in autopsy series.
  • As the majority of lesions are small and nonfunctional, most adenomas are incidental findings.
  • Hyperfunctional adenomas also occur and are responsible for endocrine disorders such as Cushing syndrome and Conn syndrome.
  • Lipid-rich adenomas (approximately 80% of adenomas) are easily identified at both CT and MR imaging.

[edit] Imaging Findings for Adrenal adenoma

[edit] CT

[edit] Unenchanced CT

  • Adrenal adenomas appear as small (<3 cm), well-defined homogeneous masses that are typically hypoattenuating relative to the liver.
  • At an attenuation value of less than 0 HU at unenhanced CT, the diagnosis of an adenoma can be made with 100% confidence; however, this threshold has only 47% sensitivity.
  • At cutoff of 18 HU, a diagnosis of adenoma was made with 100% specificity and 85% sensitivity, compared to the specificity:sensitivity ratio of 68%:100% with a more conservative cutoff of 10 HU.
  • A rational approach advocated by some authorities is to choose the CT number threshold on the basis of the patient’s risk for metastatic disease. For example, a threshold of 10 HU could be applied to older patients or to those with known primary malignancies. A threshold of 18 HU could be applied to younger patients without underlying cancer.

[edit] Enhanced CT

  • Lipid-poor adenomas are more difficult to diagnose because the CT numbers increase and approach those of soft tissue.
  • Contrast-enhanced imaging with 10-minute-delayed CT scans may be helpful in these cases.
    • By using a threshold of 30 HU, the sensitivity and specificity for delayed contrast-enhanced CT in the characterization of benign disease are 80% and 100%, respectively.
    • A relative percentage washout of more than 50% in the delayed study represents a sensitivity and specificity of 98% and 100%, respectively, for the detection of adenoma.

[edit] MR

  • Chemical shift MR imaging can be used for further characterization when CT results are indeterminate.
  • Because of the high sensitivity of chemical shift MR imaging to minute amounts of intravoxel fat, MR imaging demonstrates signal intensity loss on opposed-phase images in the majority of adenomas, with a sensitivity of 89% for lesions with an attenuation of 10–30 HU and 100% for lesions with an attenuation of 10–20 HU with a maintained specificity of 100%.

[edit] Images

Patient #1: Adrenal adenoma was suspect on CT on confirmed on MRI

[edit] See Also

[edit] External Links

[edit] References for Adrenal adenoma