Case 10
History:
36 year old female with left adrenal mass seen on an outside chest CT scan
Findings:
In and out of phase MR images of the upper abdomen showing a left adrenal mass demonstrating diffuse signal loss on the out of phase sequences consistent with a lipid rich adenoma.
Diagnosis:
Left adrenal adenoma
Discussion:
Adrenal gland adenomas account for 1.4 to 8.7% of postmortem examinations, depending on the criteria used. The adrenal glands are a common site of metastasis, particularly from lung carcinoma. Approximately 70% of the adenomas have intracellular lipid, while 30% do not. Lipid-rich adrenal adenomas contain intracytoplasmic lipid, which accounts for their low attenuation on unenhanced CT and their loss of signal on opposed-phase chemical shift MRI. Chemical shift imaging relies on the different resonance frequency rates of water and lipid molecules. To perform chemical shift images, two breath-hold T1-weighted sequences are performed. At short echo time 2.2 msec at 1.5 T water and lipid molecule are out of phase while at 4.4 msec TE they are inphase. These numbers change at 3T. In the case of lipid rich adenomas, a signal drop-off is demonstrated on out-of-phase images secondary to the intra-voxel signal cancellation of the lipid and water protons. With the chemical shift technique, the sensitivity and specificity ranges from 81 to 100% and 94 to 100%, respectively. In general, metastases and carcinomas contain larger amounts of fluid than adenomas and thus appear bright on T2-weighted images. However, there is significant overlap.
References:
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- Blake MA, Kalra MK, Sweeney AT, et al. Distinguishing benign from malignant adrenal masses: multi-detector row CT protocol with 10-minute delay. Radiology 2006;238 : 578–585.
- Caoili EM, Korobkin M, Francis IR, et al. Adrenal masses: characterization with combined unenhanced and delayed enhanced CT. Radiology 2002;222 : 629–633.
