The imaging of incidentalomas
CMAJ 1998;158:472
See response from: T.C. Ooi.
In the editorial "Adrenal incidentalomas: incidental in detection, not significance" (CMAJ 1997;157[7]:903-4 [full text/résumé]), Dr. Teik Chye Ooi states that radiologists may dismiss these adrenal masses as "benign and inactive" and indeed that
they often suggest that "no further investigation is required."
We feel that the radiologist's imaging interpretation should be
used to direct further workup where applicable.
Extensive recent research on the imaging of adrenal adenomas has
looked specifically at not only "shape, contour, margins, [and]
signal intensity," as mentioned by Ooi, but also CT densitometry
and chemical-shift imaging using MRI.1,2 In our practice, needle biopsy of adrenal masses is rarely needed. The specificity of CT and MRI is greater than 95% in the differentiation of benign and malignant adrenal tumours. We agree with Ooi's assertion that differentiating a functioning tumour from a nonfunctioning one is not part of the imaging interpretation and therefore concur that biochemical workup is appropriate for adrenal incidentalomas.
Ooi suggests that expertise in interpretation of CT and MRI is
often lacking. We submit that "the standard of practice" for the
radiologist is to understand the image interpretation of adrenal
incidentalomas and to know when densitometry and chemical-shift
imaging would be appropriate. The cost-effectiveness of these
procedures should be weighed against the cost of biopsy, surgical
excision and the treatment of potential complications of adrenal
biopsy, which occur in 1% to 11% of cases.3
We believe that teamwork should be used in the workup of an
adrenal incidentaloma. The clinical aspects would include the
history, a physical examination and appropriate biochemical
tests. In the absence of any clinical abnormalities, further
imaging should be based on the imaging that led to the discovery
of the lesion. For example, if the abnormality was first
discovered by CT performed without intravenous administration of
contrast agent, the lesion's size, contour, shape and, most
important, density can be analysed from the CT images. If the
lesion is small (less than 3 cm in diameter) and has an
attenuation of less than 0 Hounsfield units (HU), no further
workup is necessary. If the lesion is small and the attenuation
is between 0 and 18 HU, a follow-up examination might be helpful.
Even for lesions for which the threshold of 18 HU is used, the
specificity of diagnosing the lesion as benign is reportedly up
to 100%.4
Indeterminate lesions may benefit from MRI, including chemical-
shift imaging for the assessment of subtle intracytoplasmic
lipid, which commonly occurs in benign adenomas. If MRI is
unavailable, then follow-up imaging after an appropriate interval
is reasonable. In rare circumstances biopsy may be required.
Daniel C. Rappaport, MD
Naeem Merchant, MD
Department of Medical Imaging
The Toronto Hospital
Toronto, Ont.
dcrapp@playfair.utoronto.ca
References
- Szolar DH, Kammerhuber F. Quantitative CT evaluation of
adrenal gland masses: a step forward in the differentiation
between adenomas and nonadenomas. Radiology
1997;202:517-21.
- Outwater EK, Siegelman ES, Radecki PD, et al. Distinction
between benign and malignant adrenal masses: value of T1-weighted
chemical-shift MR imaging. AJR 1995;165:579-83.
- Welch TJ, Sheedy PF 2nd, Stephens DH, Johnson CM, Swensen SJ.
Percutaneous adrenal biopsy: review of a 10-year experience.
Radiology 1994;193:341-4.
- Korobkin M, Brodeur FJ, Yutzy GG, et al. Differentiation of
adrenal adenomas from nonadenomas using CT attenuation values.
AJR 1996;166:531-6.
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