What is the interpretation and management of adrenal nodules with intracellular lipid on MRI in a patient with a history of Bowen Disease?

Interpretation of Adrenal Nodules with Intracellular Lipid on MRI

The adrenal nodules in this patient are benign adenomas and do not require further imaging follow-up or intervention. The characteristic signal dropout on out-of-phase MRI images confirms the presence of intracellular lipid, which is diagnostic of benign adrenal adenomas 1.

MRI Findings and Interpretation

The MRI findings show:

• Two left adrenal nodules: a 2.5 cm medial nodule and an 11 mm lateral nodule
• Both nodules demonstrate marked signal dropout on out-of-phase images
• Enhancement similar to spleen
• T2 signal characteristics similar to spleen
• Normal right adrenal gland
• Incidental Bosniak 1 cyst in the right kidney (4.8 cm)
• No hepatic masses

Significance of Signal Dropout on Out-of-Phase Images

The presence of intracellular lipid detected by chemical shift MRI (in-phase and out-of-phase sequences) is highly specific for benign adrenal adenomas 1. This imaging technique exploits the different resonance frequencies of protons in water and fat to detect microscopic fat within adrenal lesions.

When microscopic fat is identified as a homogeneous signal intensity drop on MRI, these features are diagnostic of lipid-rich adenoma 1. The ONCO-RADS guidelines specifically categorize adrenal lesions showing signal dropout on opposed-phase T1-weighted images compared with in-phase images as category 2 (benign) lesions with low likelihood of cancer 1.

Management Recommendations

Based on the current guidelines:

1. No further imaging follow-up is required for these lesions as they are radiologically characterized as benign adenomas <4 cm 1.

2. No functional testing is required unless the patient has clinical symptoms or signs suggesting hormonal excess 1.

3. The incidental finding of a Bosniak 1 cyst in the right kidney is benign and requires no further evaluation.

Relevance of Bowen Disease History

The history of Bowen Disease (squamous cell carcinoma in situ of the skin) does not impact the management of these adrenal adenomas, as:

1. Bowen Disease is not known to metastasize to the adrenal glands
2. The MRI characteristics of these lesions are definitively benign
3. There is no established association between Bowen Disease and adrenal adenomas

Potential Pitfalls in Adrenal Imaging

While chemical shift MRI is highly accurate for diagnosing adenomas, be aware of these potential pitfalls:

• Heterogeneous signal intensity drop is a more controversial finding, as minute amounts of microscopic fat have been identified in pheochromocytomas, adrenocortical carcinomas, and some metastases 1
• Some lipid-poor adenomas may not demonstrate significant signal dropout and could be mischaracterized
• Approximately 1/3 of adrenal adenomas may not show typical imaging characteristics on other modalities like CT washout studies 1

In this case, the homogeneous signal dropout in both nodules is characteristic of benign adenomas, and no further evaluation or follow-up is necessary.