What labs should be checked for a patient with a pituitary lesion on Magnetic Resonance Imaging (MRI)?

Laboratory Tests for Pituitary Lesions on MRI

For patients with pituitary lesions identified on MRI, a comprehensive hormonal evaluation should include anterior and posterior pituitary function tests to assess for both hypersecretion and hypopituitarism, as up to 85% of patients with nonfunctioning pituitary adenomas have at least one hormonal deficiency. 1, 2

Anterior Pituitary Function Tests

Hypersecretion Assessment

• Prolactin

  • Essential for all pituitary lesions
  • Distinguishes prolactinomas (typically >200 ng/mL) from stalk effect (typically <100 ng/mL)
  • Present in 25-65% of nonfunctioning adenomas 2

• Growth Hormone (GH)/IGF-1

  • For suspected acromegaly or gigantism
  • IGF-1 is the preferred screening test

• ACTH/Cortisol

  • 24-hour urinary free cortisol or overnight dexamethasone suppression test for suspected Cushing's disease

• TSH/Free T4

  • For suspected TSH-secreting adenoma (rare)

Hypopituitarism Assessment

• Growth Hormone Axis

  • IGF-1 levels (most commonly deficient axis, 61-100% of cases) 2
  • Consider GH stimulation testing if clinically indicated

• Gonadal Axis

  • Males: Total testosterone, LH, FSH
  • Females: Estradiol, LH, FSH
  • Deficient in 36-95% of patients with pituitary lesions 2

• Adrenal Axis

  • Morning cortisol
  • ACTH stimulation test if morning cortisol is borderline
  • Deficient in 17-62% of patients 2

• Thyroid Axis

  • Free T4 and TSH
  • Deficient in 8-81% of patients 2

Posterior Pituitary Function Tests

• Serum sodium
• Serum and urine osmolality
• Water deprivation test (if diabetes insipidus is suspected)

Additional Considerations

Timing of Laboratory Testing

• Perform laboratory testing before surgical intervention
• For incidental findings, complete hormonal evaluation is recommended regardless of lesion size 3

Special Clinical Scenarios

• Empty Sella Syndrome

  • Up to 40% of patients may have at least one hormone deficiency 4
  • Complete anterior pituitary hormone assessment is necessary

• Pituitary Apoplexy

  • Urgent assessment of adrenal and thyroid function is critical
  • Complete hormone panel should follow acute management

Pitfalls to Avoid

1. Missing stalk effect hyperprolactinemia

   • Mild elevation of prolactin (typically <100 ng/mL) can occur due to compression of the pituitary stalk
   • Don't misdiagnose as prolactinoma

2. Overlooking partial hypopituitarism

   • Even with normal screening tests, stimulation testing may be needed if clinical suspicion is high

3. Ignoring diabetes insipidus

   • Particularly important in lesions affecting the hypothalamus or pituitary stalk

4. Failing to recognize hypopituitarism in emergency settings

   • Adrenal insufficiency can be life-threatening and requires immediate treatment

Follow-up Laboratory Testing

• For non-functioning pituitary adenomas not requiring immediate surgery:

  • Repeat hormonal evaluation at 6 months and yearly thereafter 3
  • More frequent testing if clinical symptoms develop

• Post-surgical evaluation:

  • Complete hormonal assessment 4-6 weeks after surgery
  • Regular follow-up testing based on clinical status

The American College of Radiology recommends MRI with and without contrast as the preferred imaging modality for initial evaluation and follow-up of pituitary lesions, with laboratory testing guided by the radiographic findings and clinical presentation 1.