September 24, 2017
Biochemical Investigation of a Pituitary Incidentaloma Minimize

Investigation of a pituitary incidentaloma

Indication

The advent of high quality pituitary imaging has led to the recognition of unsuspected pituitary tumours. This is not surprising since autopsy studies have shown that 10-20% normal individuals have pituitary microadenomas.  Unsuspected macroadenomas are not silent and therefore it is considered unlikely that there is a progression from micro-to macroadenoma.  The most likely tumours (>80%) are prolactinomas and non-functioning tumours. Other tumours, aneurysms and inflammations may also present as a tumour on imaging.

Contraindication

Principle

  1. Screening tests for prolactinoma
  2. Screening tests for cortisol hypersecretion by 24 h UFC and low dose dexamethasone suppression test.
  3. Screening for excess growth hormone
  4. Random measurement of gonadotropins, TFTs and alpha subunit.

Side effects

Preparation

The patient should be fasted for the glucose tolerance test.

Requirements

  1. 24 hour urine containers
  2. 1 mg dexamethasone
  3. 75 g anhydrous glucose in approximately 400 mL cold water or 388 mL Lucozade ® is given. If the glucose solution is given, it should be chilled to improve palatability.
  4. 5 fluoride oxalate tubes for glucose & 5 Li heparin blood tube (for prolactin, growth hormone)

Procedure

Day 1:

24 hour urine collection for cortisol
perform glucose tolerance test
take blood sample for prolactin with the last growth hormone sample

Day 2:

 

Day 3:

The patient takes 1 mg Dexamethasone orally between 2200-2400 and the following morning at 0900h a blood sample (3 mL plain blood) is taken for plasma cortisol.

Interpretation

see individual tests

Sensitivity and Specificity

see individual tests

References

  • Molitch ME. Evaluation and treatment of the patient with a pituitary incidentaloma. J Clin Endocrinol Metab 1995;80:3-6.
  

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