MRI of the Brain for Secondary Adrenal Insufficiency
MRI of the sella turcica (pituitary-focused imaging) is usually appropriate and recommended for all patients with confirmed secondary adrenal insufficiency to identify structural causes such as pituitary adenomas, hypophysitis, infiltrative disease, or other hypothalamic-pituitary pathology. 1, 2
Diagnostic Rationale
Secondary adrenal insufficiency results from ACTH deficiency due to pituitary or hypothalamic dysfunction, making imaging of the hypothalamic-pituitary axis essential for determining the underlying etiology. 1
When MRI is Indicated
MRI of the sella should be performed once the biochemical diagnosis of secondary adrenal insufficiency is confirmed through hormonal testing showing:
- Low or inappropriately normal cortisol with low or inappropriately normal ACTH 1, 2
- Failed response to ACTH stimulation testing 3, 4
The American College of Radiology specifically recommends that MRI sella without and with IV contrast, or MRI sella without IV contrast, is usually appropriate for initial imaging of adults with suspected or known hypofunctioning pituitary gland (hypopituitarism). 1 The addition of IV contrast is preferred for optimal assessment of pituitary lesions, though noncontrast MRI also provides diagnostic detail. 1
What MRI Can Identify
MRI is superior to other imaging modalities because of its excellent soft-tissue characterization of the hypothalamic-pituitary axis and parasellar regions. 1 Key findings that may be detected include:
- Pituitary adenomas (including microadenomas that may be occult without contrast) 1
- Hypophysitis (inflammatory pituitary disease) 2
- Infiltrative diseases (sarcoidosis, hemochromatosis, histiocytosis) 2
- Empty sella syndrome (complete or partial absence of pituitary tissue) 3
- Pituitary apoplexy (hemorrhage or infarction) 1, 3
- Hypoplastic adenohypophysis with or without visible pituitary stalk 3
- Suprasellar masses or other structural abnormalities 3
Clinical Context Matters
While MRI is recommended for establishing etiology, some cases of isolated secondary adrenal insufficiency may show completely normal pituitary anatomy on MRI. 5, 3 In a study evaluating patients with isolated ACTH deficiency, all three cases demonstrated normal pituitary anatomy despite confirmed secondary adrenal insufficiency. 3 This highlights that:
- A normal MRI does not rule out secondary adrenal insufficiency 5, 3
- The diagnosis is primarily biochemical, not radiological 1, 2
- MRI serves to identify treatable structural causes rather than confirm the diagnosis 1, 2
Important Caveats
Never delay treatment of suspected acute adrenal insufficiency to obtain imaging. 1 If a patient presents with clinical features suggesting adrenal crisis (hypotension, hyponatremia, hypoglycemia), immediate treatment with IV hydrocortisone 100 mg should be initiated before any diagnostic procedures. 1, 2
The diagnostic workup sequence should be:
- Confirm biochemical diagnosis with paired cortisol and ACTH measurements 1, 2
- Initiate appropriate glucocorticoid replacement 1, 2
- Obtain MRI of the sella to determine etiology 1, 2
Special Populations
In patients with traumatic brain injury, imaging may reveal edema or hemorrhage within the hypothalamic-pituitary axis that correlates with secondary adrenal failure. 6 These patients should undergo both hormonal testing and neuroimaging as part of their evaluation. 6
For patients with panhypopituitarism (deficiency of multiple pituitary hormones including ACTH), MRI is particularly important as it guides decisions about surgical intervention for macroadenomas causing mass effect. 2
Bottom Line
Yes, MRI of the brain (specifically the sella turcica with pituitary protocol) is required for proper evaluation of secondary adrenal insufficiency to identify the underlying structural cause and guide appropriate management, though it should never delay emergency treatment and a normal MRI does not exclude the diagnosis. 1, 2