ACR Incidental Adrenal mass management

{
  "applicability": {
    "use_for": "Incidentally detected adrenal mass on CT or MRI in an asymptomatic adult (age >=18 years) imaged for a reason unrelated to possible adrenal disease.",
    "bilateral_rule": "Assess each adrenal lesion separately.",
    "generally_do_not_pursue": "Short-axis size <1 cm unless clinical circumstances warrant evaluation.",
    "do_not_apply_when": [
      "symptoms_or_signs_are_attributable_to_adrenal_disease",
      "the_mass_is_not_incidental",
      "workup_cannot_change_management_due_to_comorbidity_or_limited_life_expectancy"
    ]
  },
  "categories": [
    {
      "outcome_code": "macroscopic-fat",
      "role": "specific_benign_subtype",
      "defining_feature": "macroscopic_fat_consistent_with_myelolipoma"
    },
    {
      "outcome_code": "benign-features",
      "role": "leave_alone_endpoint",
      "defining_features": [
        "unenhanced_CT_<=10_HU",
        "chemical_shift_signal_loss_relative_to_spleen",
        "no_enhancement_cyst_or_hemorrhage",
        "benign_calcification"
      ]
    },
    {
      "outcome_code": "prior-malignancy",
      "role": "clinical_context_branch",
      "defining_feature": "known_cancer_and_no_diagnostic_benign_feature"
    },
    {
      "outcome_code": "large-mass",
      "role": "size_branch_without_cancer",
      "defining_feature": "isolated_indeterminate_mass_>=4_cm"
    },
    {
      "outcome_code": "indeterminate",
      "role": "characterization_or_follow_up_branch",
      "defining_feature": "no_diagnostic_benign_feature_and_not_resolved_by_precedence_rules"
    }
  ],
  "category_precedence": [
    "If macroscopic fat is present, use macroscopic-fat as the specific benign endpoint.",
    "Otherwise, diagnostic benign imaging features route to benign-features regardless of size.",
    "For a non-benign mass, known malignancy routes to prior-malignancy before the no-cancer size branches.",
    "Without cancer history, an indeterminate isolated mass >=4 cm routes to large-mass; smaller masses route to indeterminate."
  ],
  "diagnostic_definitions": {
    "lipid_rich_adenoma": {
      "unenhanced_CT_HU": "<=10",
      "endpoint": "benign-features"
    },
    "chemical_shift_adenoma": {
      "finding": "signal_loss_relative_to_spleen_between_in_phase_and_opposed_phase",
      "endpoint": "benign-features"
    },
    "no_enhancement": {
      "formula": "postcontrast_HU - precontrast_HU",
      "threshold": "<10_HU_change",
      "interpretation": "cyst_or_hemorrhage",
      "endpoint": "benign-features"
    },
    "macroscopic_fat": {
      "interpretation": "myelolipoma",
      "endpoint": "macroscopic-fat"
    },
    "absolute_percentage_washout": {
      "formula": "100 * (enhanced_HU - 15_min_delayed_HU) / (enhanced_HU - unenhanced_HU)",
      "adenoma_threshold": ">=60_percent"
    },
    "relative_percentage_washout": {
      "formula": "100 * (enhanced_HU - 15_min_delayed_HU) / enhanced_HU",
      "use_when": "unenhanced_value_unavailable",
      "adenoma_threshold": ">=40_percent"
    },
    "isolated": "No other metastatic disease identified."
  },
  "branches": [
    {
      "id": "prior_stability",
      "condition": "stable_for_>=1_year",
      "action": "benign_no_additional_imaging",
      "outcome_code": "benign-features"
    },
    {
      "id": "no_cancer_1_to_2_cm",
      "condition": "indeterminate_1_to_2_cm_no_prior_imaging_no_cancer_history",
      "action": "consider_adrenal_CT_follow_up_at_12_months_for_stability",
      "outcome_code": "indeterminate"
    },
    {
      "id": "no_cancer_>2_to_<4_cm",
      "condition": "indeterminate_>2_to_<4_cm_no_prior_imaging_no_cancer_history",
      "action": "dedicated_adrenal_CT_at_detection",
      "outcome_code": "indeterminate"
    },
    {
      "id": "still_indeterminate_after_protocol",
      "condition": "APW_<60_percent_and_RPW_<40_percent_or_otherwise_uncharacterized",
      "action": "imaging_follow_up_biopsy_PET_CT_or_resection_according_to_clinical_scenario",
      "outcome_code": "indeterminate"
    },
    {
      "id": "new_or_enlarging_no_cancer",
      "condition": "new_or_enlarging_indeterminate_mass_without_cancer_history",
      "action": "biochemical_evaluation_then_follow_up_adrenal_CT_or_resection_according_to_growth_and_context",
      "outcome_code": "indeterminate"
    },
    {
      "id": "isolated_>=4_cm_no_cancer",
      "condition": "isolated_indeterminate_mass_>=4_cm_without_cancer_history",
      "action": "consider_resection_without_biopsy_for_possible_adrenocortical_carcinoma",
      "outcome_code": "large-mass"
    },
    {
      "id": "known_cancer_1_to_<4_cm",
      "condition": "indeterminate_mass_1_to_<4_cm_known_cancer_no_prior_stability",
      "action": "dedicated_adrenal_CT_without_and_with_contrast",
      "outcome_code": "prior-malignancy"
    },
    {
      "id": "known_cancer_escalation",
      "condition": "new_enlarging_necrotic_still_indeterminate_or_>=4_cm_in_oncology_patient",
      "action": "consider_FDG_PET_CT_or_image_guided_biopsy_for_presumed_metastasis",
      "outcome_code": "prior-malignancy"
    }
  ],
  "safety": [
    "Consider biochemical assays for functional status for most incidental adrenal masses.",
    "Exclude pheochromocytoma before biopsy or resection; obtain plasma metanephrines when it is suspected.",
    "Imaging characterization does not determine whether an adenoma is hyperfunctioning.",
    "Contrast-enhanced CT alone cannot reliably distinguish an adenoma from metastasis in a patient with cancer; use the dedicated pathway."
  ],
  "required_inputs": [
    "adult_and_asymptomatic_status",
    "short_axis_size_cm",
    "unenhanced_HU_or_reason_unavailable",
    "enhancement_or_washout_when_available",
    "macroscopic_fat_or_other_benign_features",
    "prior_imaging_and_stability",
    "known_malignancy",
    "other_metastatic_disease",
    "clinical_functional_signs"
  ],
  "missing_input_behavior": [
    "Do not select a definitive branch without cancer history, size and benign-feature status; return the missing inputs.",
    "Do not calculate washout when a required attenuation value or the 15-minute delay is absent.",
    "Do not recommend biopsy without the pheochromocytoma safety warning."
  ],
  "version_context": {
    "implemented_system": "ACR Incidental Findings Committee adrenal white paper, 2017",
    "current_adjacent_document": "ACR Appropriateness Criteria Adrenal Mass Evaluation, 2021",
    "rule": "Keep the 2017 IFC algorithm version explicit; do not silently substitute a different society guideline or the adjacent ACR procedure-appropriateness document."
  },
  "source_locator": "Mayo-Smith et al., JACR 2017;14:1038-1044, Fig. 1; pp.4-6 for applicability, size branches, washout formulas, PET/CT, biopsy and endocrine evaluation. ACR Appropriateness Criteria Adrenal Mass Evaluation (2021) reviewed for version context."
}