ppgl-initial-imaging-modality-selection

name	ppgl-initial-imaging-modality-selection
description	Selects the first-line imaging modality to localize a PPGL tumor after biochemical confirmation. Common triggers are 'Biochemical tests confirm PPGL, need to localize tumor,' 'Planning surgical approach requires anatomical localization,' and 'Positive screening test warrants imaging for tumor localization.'

Initial PPGL Imaging Modality Selection for Tumor Localization

STEP 1 — Gather Information

Collect biochemical test results (fractionated metanephrines/catecholamines ≥3× ULN), clinical presentation (symptoms, hypertension), suspected tumor location based on biochemistry (noradrenaline dominance suggests extra-adrenal/PGL), patient age, pregnancy status, renal function, availability of CT, MRI, 123I-MIBG scintigraphy, and 18F-FDG PET, and any contraindications (iodine allergy, claustrophobia, implanted devices). Proceed to step 2.

STEP 2 — Rule In / Rule Out

Is there a need to avoid ionizing radiation (pregnancy, pediatric patient, or requirement for frequent follow‑up imaging)? If yes, proceed to step 4 for MRI selection; if no, proceed to step 3.

STEP 3 — Classify or Stratify

Is anatomic detail required for surgical planning (e.g., assessing tumor size, exact location, relationship to vessels/organs, or differentiating adrenal vs extra‑adrenal)? If yes, proceed to step 4 for CT/MRI selection; if no, proceed to step 4 for functional imaging selection.

STEP 4 — Decide

• If MRI was chosen in step 2: order contrast‑enhanced MRI of the abdomen/pelvis (or dedicated head/neck MRI if skull‑base PGL suspected).
• If CT/MRI was chosen in step 3:
  • If no contraindication to iodinated contrast and renal function adequate, order contrast‑enhanced CT of the abdomen/pelvis (adrenal protocol).
  • If contrast contraindicated or renal insufficiency, order MRI instead.
• If functional imaging was chosen in step 3:
  • If 123I‑MIBG scintigraphy is available and thyroid blockade can be administered, order 123I‑MIBG whole‑body scan.
  • Otherwise, order 18F‑FDG PET/CT (particularly if SDHx pathogenic variant suspected).
  Schedule the study and inform the patient of preparation requirements.

Clinical Guardrails / Mimics / Pitfalls

Do not rely on functional imaging alone for anatomic localization needed for surgery; do not perform CT with iod contrast in pregnancy without obstetric clearance; do not omit thyroid blockade before 123I‑MIBG to avoid thyroid uptake and medullary thyroid cancer confounders; do not interpret 18F‑FDG PET uptake in the neck/supraclavicular areas without considering brown adipose tissue; do not use MRI if patient has non‑MRI‑compatible implants or severe claustrophobia; do not delay imaging after biochemical confirmation as timely localization guides preoperative α‑blocker titration.

Concrete Clinical Example

A 45‑year‑old man with paroxysmal hypertension, headaches, and palpitations has plasma‑free metanephrines 4× ULN, confirming PPGL. He is non‑pregnant, with normal renal function, and requires anatomic detail for laparoscopic adrenalectomy. Step 1: gathers data. Step 2: no radiation avoidance need. Step 3: anatomic detail required. Step 4: orders contrast‑enhanced CT abdomen/pelvis. Imaging shows a 3.2 cm right adrenal lesion with early arterial enhancement and washout, guiding surgical planning.

Source: Japan Endocrine Society Clinical Practice Guideline for the Diagnosis and Management of Pheochromocytoma and Paraganglioma 2025, Japan Endocrine Society, 2025, doi:10.1507/endocrj.EJ25-0165