pheochromocytoma
PHEOCHROMOCYTOMA
Pheochromocytoma is a rare adrenal gland tumor that may precipitate life-threatening hypertension.
It can occur at any age but usually occurs during young to mid-adult life.
Majority of patients presents with ≥1 of the following hypertension resistant to standard antihypertensive treatment, hypertensive crisis with malignant hypertension, hypertensive encephalopathy, aortic dissection, or myocardial infarction and paroxysmal symptoms which suggest seizure disorder, anxiety attacks or hyperventilation.

Laboratory Tests

  • Evaluation using liquid chromatography w/ mass chromatography is preferred over laboratory methods
  • Blood for plasma metanephrine measurement should be obtained w/ patient in supine position, w/ subsequent extractions done in the same position

Plasma Metanephrine

  • Diagnostic test of choice
    • More suitable for high risk patients w/ a hereditary predisposition
    • Normal plasma levels excludes the diagnosis
    • Elevated plasma levels confirm the diagnosis
  • Clonidine suppression test
    • Maybe done when plasma total cathecholamines concentration is elevated but not diagnostic
    • May distinguish elevated norepinephrine levels secondary to sympathetic nerves vs true pheochromocytoma
    • Failure to suppress norepinephrine levels by 50% suggests pheochromocytoma
  • Glucagon stimulation test
    • Performed when plasma metanephrine levels are high but catecholamines are either normal or only moderately high
    • A 3-fold rise in norepinephrine levels in response to glucagon signify pheochromocytoma
    • Rarely used

Urine Biochemical Tests

  • Alternative for excluding pheochromocytoma
    • May be preferred in those at low risk for pheochromocytoma

Accuracy is improved if at least 2 of the following are measured from urine sample:

  • Unconjugated (free) catecholamines
    • Normal range: 590-885 nmol/24 hr (100-150 mcg/24 hr)
    • Diagnostic range: >1480 nmol/24 hr (>250 mcg/24 hr), or 2-fold elevation from normal level
    • Epinephrine should also be measured & may be high if multiple endocrine neoplastics (MEN) adrenal lesion is present
  • Metanephrine/Normetanephrine
    • Upper limit of normal range: 7 micromol/24 hr (1.3 mg/24 hr)
    • Diagnostic range: Normetanephrine (>900 mcg/24 hr); Metanephrine (>400 mcg/24 hr)

24-Hr Urine Sample

  • Analysis of urine sample should be done when patient is symptomatic eg hypertensive or during a crisis
  • Full 24-hr sample is preferred
  • CrCl should be measured to assess adequacy of collection
  • If possible, patient is at rest, not taking medication & no recent exposure to radiographic contrast media
  • Acidify & refrigerate urine during & after collection
  • Tests may need to be repeated during attacks to exclude diagnosis
    • Pharmacologic tests may be helpful in difficult cases

Imaging

  • Once patient is diagnosed tumor localization & search for possible metastases should be undertaken
    • Maybe adrenal or extra-adrenal (paraganglioma)
    • Patient can be prepared pharmacologically at the same time
  • CT scan & MRI are 1st-line diagnostic tools
    • Both provide localization & metastatic assessment
    • CT scan is preferred over MRI as 1st-line diagnostic tool for imaging of the thorax, abdomen & pelvic area
    • MRI is used best for detection of tumors in the skull base & neck, patients w/ contraindications for contrast dyes & radiation, & for patients w/ artifacts seen in CT

Anatomic Imaging

Magnetic Resonance Imaging

  • Identify intraadrenal lesions
  • Identify extraadrenal lesions in the abdomen
    • Look for von Hippel-Lindau disease neurofibromatosis or multiple endocrine neoplasia type 2 (MEN-II) if bilateral or extra-adrenal
  • Detect intracardiac, juxtacardiac, juxtavascular pheochromocytoma
    • Reduces cardiac and respiratory motion-induced artifacts
  • Initial evaluation for children, pregnant women or in cases of contrast allergy

CT Scan

  • Detects adrenal pheochromocytoma of ≥0.5-1 cm or metastatic pheochromocytoma of ≥1-2 cm
  • Extraadrenal tumors w/in the abdomen & pelvis (inital CT should visualize these areas); chest & neck
  • Spiral CT preferred for small thoracic tumors
  • CT w/ contrast can aggravate or precipitate crisis
    • Some consider CT as the most useful method to locate pheochromocytoma

Abdominal Aortography

  • May be used to identify extraadrenal tumors in the abdomen since they are usually supplied by a large aberrant artery
  • Alpha-adrenergic blockade must be completed before attempting aortography

Functional Imaging

Functional imaging techniques are not recommended as 1st-line procedures for localizing pheochromocytoma

Metaiodobenzylguanidine (MIBG) Scintigraphy

  • May use I131 and I123
    • I123 is superior to I131, but is not approved by USFDA
  • Useful in detecting recurrent or metastatic pheochromocytoma, tumors w/ fibrosis, extranodal tumors, tumors in unusual location or in areas w/ distorted anatomy
  • Indicated when abdominal imaging results are negative, or if found pheochromocytoma is >10 cm in diameter

Positron Emission Tomography (PET) Imaging

  • Advantages include low radiation exposure & superior spatial resolution
  • Imaging is carried out immediately
    • Unlikely delays in scintigraphy
  • Provides accurate information regarding the number & location of metastatic lesions
  • Preferred over MIBG scintigraphy for patients w/ known metastatic lesions
  • Limited availability among various centers
  • Procedure is expensive

Somatostatin Receptor Scintigraphy

  • Detects malignant/metastatic tumors better than primary/benign tumors
  • Low sensitivity
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