How should an incidentally discovered cystic lesion in the left adrenal gland/upper pole of the kidney on MRI performed for back pain be evaluated and managed?

Evaluation and Management of Incidental Cystic Adrenal/Upper Kidney Lesion

This incidental cystic lesion requires both imaging characterization with non-contrast CT and comprehensive hormonal evaluation to exclude functional tumors and malignancy, regardless of its benign appearance.

Immediate Next Steps

1. Imaging Characterization

Since the MRI has already been performed, you need to determine if this is truly an adrenal lesion or a renal cyst. The first critical step is obtaining a dedicated non-contrast CT scan to measure Hounsfield units (HU) and definitively localize the lesion 1.

• If HU <10: Confirms benign lipid-rich adenoma
• If HU >10: Requires second-line imaging with either washout CT or chemical shift MRI 1

Important caveat: The location description "left adrenal gland/upper kidney" suggests diagnostic uncertainty. Adrenal cysts can be difficult to distinguish from upper pole renal cysts, and misdiagnosis occurs even with advanced imaging 2. The MRI report should clarify whether this originates from adrenal tissue or kidney, as management differs significantly.

2. Mandatory Hormonal Evaluation

All patients with adrenal incidentalomas require biochemical screening, even if imaging suggests a simple cyst 1. This is non-negotiable because:

• Functional tumors (including pheochromocytomas) can appear cystic
• Imaging alone cannot exclude hormone excess
• Missing a pheochromocytoma has life-threatening consequences

Required tests:

• 1 mg dexamethasone suppression test (preferred screening for autonomous cortisol secretion) 1
• If hypertension or hypokalemia present: Aldosterone-to-renin ratio 1
• If HU >10 on CT or any symptoms of catecholamine excess: Plasma or 24-hour urinary metanephrines 1

Critical pitfall: Do NOT skip pheochromocytoma screening just because it looks cystic—approximately one-third of pheochromocytomas can have cystic features or washout characteristics mimicking adenomas 1.

Size-Based Management Algorithm

If Lesion is <4 cm and Hormonally Inactive:

No further follow-up imaging or functional testing is required if the lesion demonstrates clearly benign features (simple cyst characteristics, macroscopic fat, or HU <10) 1.

If Lesion is ≥4 cm (Even if Benign-Appearing):

Repeat imaging in 6-12 months is mandatory 1, 3. The 4 cm threshold is critical because:

• Malignancy risk increases from 7% to 34% above 4 cm 4
• Lesions >6 cm carry >25% malignancy risk 4
• Large cysts warrant surveillance even if hormonally inactive

On follow-up imaging:

• Growth >5 mm/year: Consider adrenalectomy after repeating functional work-up 1
• Growth <3 mm/year: No further imaging needed 1

If Lesion Remains Indeterminate After Full Work-up:

Use shared decision-making: either repeat imaging in 3-6 months versus surgical resection 1. Given the 2025 guidelines emphasize that indeterminate lesions should be discussed at multidisciplinary conferences 4, consider referral to endocrinology and surgical consultation 4, 1.

Special Considerations for Cystic Lesions

Adrenal cysts represent 4-22% of adrenal incidentalomas and are usually benign 1. However:

• Pseudocysts (most common surgical type) can result from prior hemorrhage and may decrease in size over time 4
• Endothelial cysts are more common in autopsy series and can enlarge over years 5
• Cystic degeneration can occur in pheochromocytomas and adrenocortical carcinomas 6, 3

Management of confirmed simple adrenal cysts:

• Lesions >5-6 cm, symptomatic lesions, or those with concerning features warrant surgical excision 3, 5, 7
• Conservative management acceptable for small, asymptomatic, hormonally inactive cysts 8, 3

Critical Pitfalls to Avoid

1. Don't assume "cystic = benign": Malignant lesions can have cystic components 6, 9

2. Don't biopsy without excluding pheochromocytoma first: Biopsy is rarely indicated and risks tumor seeding in adrenocortical carcinoma 1

3. Don't confuse adrenal-renal fusion or ectopic adrenal tissue with renal masses: These can mimic renal cell carcinoma 10, 2

4. Don't rely solely on washout CT: One-third of adenomas don't wash out appropriately, and one-third of pheochromocytomas falsely appear benign 1

Recommended Approach for Your Patient

1. Review the MRI images with radiology to confirm whether this is adrenal or renal in origin
2. Order non-contrast CT if not already done to measure HU
3. Obtain hormonal screening (at minimum: 1 mg dexamethasone suppression test)
4. Measure lesion size to determine if ≥4 cm threshold met
5. Consider multidisciplinary review if any atypical features present 4, 1

The most recent 2025 Endocrine Practice guidelines emphasize that even stable lesions require hormone exclusion, as some functional tumors (particularly pheochromocytomas) remain stable in size 4.