What is the management for a patient with an adrenal mass, where MRI findings suggest a possible abscess but cannot rule out malignancy?

Management of Adrenal Mass with MRI Suggesting Abscess but Cannot Rule Out Malignancy

When MRI suggests an adrenal abscess but cannot definitively exclude malignancy, proceed with immediate hormonal evaluation, obtain dedicated non-contrast CT to measure Hounsfield units, and pursue multidisciplinary discussion regarding either CT-guided aspiration/drainage with culture (if abscess is most likely) or surgical resection (if malignancy cannot be excluded based on imaging characteristics and size). 1, 2

Immediate Diagnostic Steps

Hormonal Evaluation (Mandatory First Step)

• Obtain complete hormonal workup before any invasive procedure to exclude pheochromocytoma, as biopsy or drainage of an undiagnosed pheochromocytoma can precipitate hypertensive crisis 3, 2
• Required tests include:
  • Plasma free metanephrines or 24-hour urinary fractionated metanephrines 3, 4
  • 1 mg overnight dexamethasone suppression test (cortisol should be ≤50 nmol/L or ≤1.8 µg/dL) 5
  • Aldosterone-to-renin ratio if hypertension or hypokalemia present 4

Imaging Characterization

• Obtain dedicated non-contrast CT of the adrenal mass to measure density in Hounsfield Units (HU), as this is the essential first step to differentiate benign from potentially malignant lesions 2, 5
• If the mass measures <10 HU, it represents a benign lipid-rich adenoma regardless of other imaging features 2, 5
• If the mass measures >10 HU, proceed to contrast-enhanced CT with washout protocol (absolute washout ≥60% or relative washout ≥40% suggests benign pathology) 2, 4
• Masses with HU >20 and inhomogeneous appearance have sufficiently high malignancy risk that surgery becomes the usual management choice 5

Size-Based Risk Stratification

Masses <4 cm

• If HU ≤10 and homogeneous: benign adenoma, no further imaging needed 2, 5
• If indeterminate imaging: shared decision-making regarding repeat imaging in 3-6 months versus immediate surgery 1, 2

Masses ≥4 cm

• All masses ≥4 cm require either surgical resection or very close surveillance, even if radiologically benign, due to higher malignancy risk with larger size 2, 4, 5
• Masses >5 cm should be removed due to substantially elevated malignancy risk 2

Management Algorithm Based on Clinical Scenario

If Abscess is Most Likely (Based on Clinical Context)

• Consider CT-guided aspiration and drainage with culture if:
  • Patient has fever, leukocytosis, or recent bacteremia (particularly Staphylococcus aureus) 6
  • Imaging shows rim enhancement, fluid density, or other features typical of abscess 6
  • Mass is <4 cm with HU >10 but clinical picture strongly suggests infection 7, 6
• Only proceed with aspiration after biochemical exclusion of pheochromocytoma 3, 2

If Malignancy Cannot Be Excluded

• Surgical resection is indicated when:
  • Mass is >4 cm with inhomogeneous appearance or HU >20 5
  • Mass shows growth >5 mm/year on follow-up imaging 4
  • Patient has history of extra-adrenal malignancy (though isolated adrenal metastasis as true incidentaloma is extremely rare) 8
• Discuss in multidisciplinary expert meeting before proceeding 1, 5

If Imaging Remains Indeterminate After CT

• Repeat imaging in 3-6 months is reasonable for masses <4 cm with equivocal features 1, 4
• PET-CT can be useful in patients with history of malignancy (particularly lung cancer, colon cancer, lymphoma, or neuroendocrine tumors, where metastases typically show SUV >4) 1, 2
• Chemical shift MRI is an alternative second-line test, particularly for younger patients or when radiation exposure is a concern 1, 4

Critical Pitfalls to Avoid

• Never perform adrenal biopsy without first excluding pheochromocytoma biochemically, as this can cause life-threatening hypertensive crisis 3, 2
• Do not routinely biopsy suspected primary adrenal malignancy due to risk of tumor seeding and dissemination 1, 2
• Biopsy should only be considered when suspicion of primary adrenal malignancy is remote and pathology would directly influence management (such as suspected metastatic disease from known extra-adrenal primary) 1, 8
• Do not assume bilateral lesions represent metastatic disease—bilateral adenomas are common, especially in older patients 4

Follow-Up if Not Surgically Removed

• For masses with benign imaging characteristics (<10 HU, <4 cm): no further imaging required 2, 5
• For masses ≥4 cm even if radiologically benign: repeat imaging in 6-12 months 2, 4
• For indeterminate masses under surveillance: repeat imaging in 3-6 months initially 1, 4
• Growth <3 mm/year requires no further action; growth >5 mm/year warrants consideration for adrenalectomy after repeating hormonal workup 4