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Everything you need to know about Computed Tomography (CT) & CT Scanning


Adrenal adenoma

  • most common adrenal tumor and may occur in up to 9% of patients (post mortum data)
  • increased incidence in patients with diabetes or hypertension
  • most adenomas have a high proportion of intracellular lipid and so are of low CT attenuation
  • up to 30% of adenomas do not contain intracellular lipid
  • normal adrenal cortex secretes cortisol, aldosterone, and androgens
  • normal adrenal medulla secretes epinephrine and norepinephrine
  • most adrenal adenomas are normally functioning glands although adenomas can be a cause of adrenal hyperfunction
  • 15-25% of cases of Cushing’s syndrome are due to adrenal masses, most commonly adenomas
  • adrenal adenomas account for up to 80% of cases of primary aldosteronism. These lesions are small with over 20% being less than 1 cm in size
  • up to 10% of cases bilateral
  • CT is now the study of choice to diagnosis an incidental adrenal adenoma

CT Findings

  • on noncontrast CT adenomas are typically of low CT attenuation (<10HU) and are easily recognized
  • usually 2-4 cm in size and usually round or oval in shape
  • following infusion of iodinated contrast adenomas may enhance but will de-enhance relatively quickly.
  • washout of an adenoma at 10 minutes post injection is over 50% and is diagnostic of a adenoma and no follow-up necessary
  • calcification is rare
  • lipid poor adenomas (noncontrast value of >10HU) have a washout pattern similar to lipid rich adenomas

MR Findings

  • signal typically low on T2 weighted images
  • chemical shift imaging can be done to identify fat within the lesion as signal intensity is decreased relative to normal tissue

PET Findings

  • preliminary reports show that malignant masses have increased FDG uptake while adenomas have no increased uptake

Imaging Recommendations

  • CT is the study of choice and if an adenoma is considered non-contrast scans are usually suffiecient (attenuation value <10 HU). If IV contrast is given (typical incidental finding) and lesion is less than 37 HU at 15 minutes psot injection it is still considered benign. If it is denser than 37 HU then delayed scans are done to look for washout. Using a washout value of 40% results in a sensitivity of 96% and a specificity of near 100% for diagnosis of an adenoma.
  • CT scanning of the adrenal gland is done with 3 mm thick sections at 3 mm intervals (or less)

Differential Diagnosis

  • adrenal metastases
  • primary adrenal carcinoma
  • ganglioneuroma
  • metastases
  • myelolioma
  • unilateral hemorrhage
  • pheochromcytoma

Presentation

  • most adrenal adenomas are detected as incidental findings on CT or MR scans
  • adrenal adenomas can be hyperfunctioning and are detected as part of a workup for Cushings syndrome, primary aldosteronism and Conn syndrome

Natural History

  • adrenal adenomas tend to remain stable is size and once diagnosed no follow up is necessary
  • adrenal adenomas have no increased malignant potential treatment
  • when imaging is unsuccessful a biopsy can be done which has low complication rate and a high degree of accuracy (up to 96% in one series)
  • if an adenoma is diagnosed by CT (based on noncontrast or contrast CT with washout( then no follow up is necessary
  • if adenoma is hyperfunctioning it is removed via laprascopic procedure

References

  1. Imaging of Adrenal Incidentalomas: Current Status
    Dunnick NR, Korobkin M
    AJR 2002;179:559-568
  2. Spectrum of CT Findings in nonmalignant disease of the adrenal gland
    Kawashima A, Sandler CM , Fishman EK et al.
    RadioGraphics 1998;18:393-412
  3. CT Time attenuation curves of adrenal adenomas and nonadenomas
    Korobkin M, Brodeur FJ, Francis IR et al.
    AJR 1998;170:747-752
© 1999-2020 Elliot K. Fishman, MD, FACR. All rights reserved.