Craniopharyngioma laboratory tests
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Patients with craniopharyngioma may have abnormal pituitary hormone levels, which is suggestive of disruption of hormone production due to pressure effects on the pituitary gland. The hypothalamic-pituitary axis hormones, namely growth hormone, thyroid hormone, luteinising and follicle stimulating hormone should be measured together with cortisol levels and an assessment of serum and urine osmolality. In addition, an estimate of bone age and, for young females, ovarian ultrasonography is useful. Ideally, any abnormalities should be corrected pre-operatively but, at the very least, low cortisol levels and diabetes insipidus should be treated prior to a surgical procedure.
Laboratory Findings
- The following hormones should be checked in patients who are being suspected of having craniopharyngioma.
- Serum Growth hormone
- Serum Leutinizing hormone
- Serum Follicle stimulating hormone
- Serum Prolactin
- Serum Thyroid stimulating hormone
- Serum ACTH
- Morning serum cortisol
Metyrapone test
- The rationale for the administration of metyrapone is that it blocks 11-beta-hydroxylase (CYP11B1), the enzyme that catalyzes the conversion of 11-deoxycortisol to cortisol, resulting in a reduction in cortisol secretion.
- The ensuing fall in serum cortisol should, if the hypothalamic-pituitary-adrenal axis is normal, cause an increase in ACTH secretion and therefore an increase in adrenal steroidogenesis up to and including 11-deoxycortisol.
Cosyntropin stimulation test
- The rationale for the administration of cosyntropin (ACTH) is that the adrenal glands atrophy when they have not been stimulated for a prolonged period; as a result, they do not secrete cortisol normally in response to a bolus dose of ACTH.
- The test is usually performed by administering 0.25 mg (25 units) of cosyntropin (synthetic ACTH 1-24) intramuscularly or intravenously and measuring serum cortisol 60 minutes later.
- A serum cortisol concentration of ≥18 mcg/dL (497 nmol/L) is considered a normal response.
Insulin-induced hypoglycemia test
- The rationale for this test is that hypoglycemia induced by insulin administration is a sufficient stress to stimulate ACTH and therefore cortisol secretion.
- The test is performed by administering 0.1 unit of insulin per kg of body weight and measuring serum glucose and cortisol before and 15, 30, 60, 90, and 120 minutes after the injection.
- In normal subjects, serum cortisol increases to ≥18 mcg/dL (498 nmol/L) if the serum glucose falls to <50 mg/dL (2.8 mmol/L).
- Besides the hormonal level the following lab test are commonly done in cases of craniopharyngioma.