What is a left adrenal adenoma?

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Last updated: September 25, 2026 • View editorial policy

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What is a Left Adrenal Adenoma?

A left adrenal adenoma is a benign tumor arising from the adrenal cortex on the left side, representing the most common type of adrenal lesion, found in 1-2% of the general population and accounting for 80-85% of incidentally discovered adrenal masses. 1

Definition and Classification

An adrenal adenoma is specifically defined as:

  • A lesion originating from the adrenal gland measuring at least 1 cm in size 1
  • When ≥4 cm, it may be categorized as an adrenal "mass" rather than just a nodule 1
  • Most commonly discovered incidentally on imaging performed for unrelated reasons (termed an "adrenal incidentaloma") 1

Functional Status

Adrenal adenomas are classified by hormonal activity:

Nonfunctioning adenomas (70%): 1

  • No biochemical evidence of hormone excess
  • Completely asymptomatic
  • Discovered only through imaging

Functioning adenomas (30%): 1

  • Mild autonomous cortisol secretion (MACS) - most common functional type
  • Primary aldosteronism (PA) - less common
  • Cushing syndrome (CS) - least common

Among patients who undergo endocrine testing, the breakdown is approximately 69% nonfunctioning, 19% cortisol-producing, and 12% aldosterone-producing 1.

Clinical Significance

Prevalence and Detection

  • Overall population prevalence: 1-2% 1
  • Detection increases dramatically with age, reaching 3.2% in those over 65 years 1
  • Found on 4-10% of cross-sectional abdominal imaging 1
  • The incidence has increased 10-fold from 1995 to 2017, primarily due to improved imaging technology and widespread CT availability 1

Benign Nature

The vast majority of adrenal adenomas are benign, with one large cohort of 25,356 patients showing zero malignant lesions among adenomas 1. This is critical for patient counseling and management decisions.

Imaging Characteristics

CT Features (First-line imaging) 1, 2

Benign adenomas are definitively diagnosed when:

  • Non-contrast CT attenuation ≤10 Hounsfield Units (HU) - sensitivity 71%, specificity 98% 1
  • Homogeneous appearance
  • Well-circumscribed borders
  • 100% of malignant lesions have attenuation >10 HU 1

The low attenuation reflects intracellular lipid content, which is characteristic of benign adenomas and very rare in malignant lesions 1.

Size Considerations

  • <4 cm: Lower malignancy risk (7%) 1
  • 4-6 cm: 6% malignancy risk 1
  • >6 cm: >25% malignancy risk 1

Required Evaluation

Every adrenal incidentaloma, including left adrenal adenomas, requires two assessments: 1

  1. Imaging characterization to exclude malignancy
  2. Biochemical evaluation for hormone excess, even if asymptomatic 1

Mandatory Biochemical Screening 2

  • All patients: Screen for autonomous cortisol secretion (1 mg dexamethasone suppression test)
  • If hypertension or hypokalemia present: Screen for primary aldosteronism (aldosterone-to-renin ratio)
  • If attenuation >10 HU or symptoms of adrenergic excess: Screen for pheochromocytoma
  • Do NOT screen for pheochromocytoma if unenhanced CT shows <10 HU and no adrenergic symptoms 2

Special Populations Requiring Urgent Assessment

Patients <40 years old: 1

  • Higher risk of malignancy
  • Should undergo urgent MRI (preferred over CT)
  • Surgical resection should be considered even for radiologically benign-appearing lesions
  • Single follow-up study at 12 months may be considered for clearly benign lesions

Pregnant patients: 1

  • Same approach as young patients
  • MRI preferred to avoid radiation

Patients with extra-adrenal malignancy: 1

  • <30% of adrenal lesions are metastatic
  • Still evaluate for benign features first
  • Must screen for pheochromocytoma even if metastasis suspected (cannot reliably differentiate on imaging)

Key Clinical Pitfalls

  1. Never assume an adrenal mass is benign without proper imaging characterization - even small lesions require non-contrast CT to measure attenuation 1, 2

  2. Never skip biochemical evaluation - up to 30% of "incidental" adenomas are hormonally active, and patients may not have obvious symptoms 1

  3. Do not biopsy adrenal masses routinely - biopsy is not recommended for standard workup 2

  4. Multidisciplinary review is essential when imaging is not clearly benign, hormone hypersecretion is present, or surgery is considered 2

Management Implications

Surgery is NOT indicated for: 2

  • Asymptomatic, nonfunctioning unilateral adenomas with obvious benign imaging features (≤10 HU on non-contrast CT)
  • Small stable lesions without hormone excess

Surgery should be considered for: 2

  • Functioning adenomas with clinically significant hormone excess
  • Lesions with indeterminate or suspicious imaging features
  • Significant growth on surveillance imaging
  • Size >4 cm with concerning features (individualized based on patient age, comorbidities, and preferences)

References

1
Guideline

imaging of adrenal masses.

Endocrine practice : official journal of the American College of Endocrinology and the American Association of Clinical Endocrinologist, 2025

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This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.