In Reply Dr O’Neil and colleagues question the use of PET/CT imaging with 18F-FDG in a patient with a large adrenal mass with irregular margins when a suspicion for malignancy was high.
The main roles of PET/CT imaging with 18F-FDG in the evaluation of adrenal masses are to further characterize an adrenal mass, especially its likelihood for malignancy; complete preoperative staging; provide information for patient follow-up; and provide prognostic information.
Few studies have evaluated the value of contrast-enhanced adrenal CT in nononcologic patients, and most data lack robustness.1 Rather, its role has been to distinguish adrenocortical adenomas from adrenal metastases in patients with cancer. In a prospective study including adrenal masses in nononcologic patients, in the subgroup of masses with unenhanced CT density of 10 Hounsfield units or greater, imaging had a sensitivity of 90% and specificity of 50% for relative washout (optimal threshold value, ≤23%) and a sensitivity of 91% and specificity of 40% for absolute washout (optimal threshold value, ≤47%).2 For such masses with abnormal relative or absolute washout values and diameters of 4 cm or greater, the risk of malignancy was estimated to be 32%. We agree with O’Neil and colleagues that the presence of irregular margins and a central hypodense area increase the risk of malignancy. However, some other nonmalignant diagnoses are also possible, such as atypical adenomas, ganglioneuromas, and schwannomas. The use of PET/CT imaging with 18F-FDG enables a shift from a diagnostic adrenalectomy to tailored surgery based on an accurate preoperative diagnosis.
The presence of metastatic disease usually contraindicates surgical removal of an adrenocortical carcinoma. Therefore, the exclusion of distant metastases is essential for optimal management. Although PET/CT imaging with 18F-FDG can be less sensitive than conventional imaging for small lung or liver metastases, it has an overall greater specificity and therefore can be an important complementary imaging modality. In certain cases, PET/CT imaging with 18F-FDG also can reveal occult metastases.
Thus, we recommend that nononcologic patients with large or indeterminate adrenal masses be evaluated with PET/CT imaging using 18F-FDG. However, unlike oncologic situations,3 the effect on management remains to be demonstrated.
PET/CT imaging with 18F-FDG is more specific than conventional imaging in the follow-up of adrenocortical carcinoma.4 However, lesion detection is widely dependent on the uptake ratio between tumor and adjacent healthy tissues. However, the uptake pattern of adrenocortical carcinoma is variable and ranges from 1.4 to 20.2 In the patient presented in the Clinical Challenge, the high uptake of 18F-FDG would be valuable in classifying doubtful images during follow-up.
Although the 18F-FDG uptake ratio does not seem to be correlated with the secretory profile or Weiss score of adrenocortical carcinomas, some quantitative metabolic parameters were found to be associated with a worse prognosis and could therefore be helpful for guiding therapies.5
We think that the addition of PET/CT imaging with 18F-FDG in some adrenal masses, as described in our Clinical Challenge, can be cost-effective, guiding the decision about whether and how to operate on a patient with an adrenal mass, especially if the mass is large or indeterminate.
Footnotes
Conflict of Interest Disclosures: The authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest and none were reported.
References
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