Figure 1: T2 Coronal image demonstrates mixed high and low signal intensity mass in the region of the right adrenal gland corresponding to subacute hemorrhage within the right adrenal gland.
Figure 2 and Figure 3: Paired T1 in- and out-of-phase images demonstrate a mixed low and high signal intensity mass replacing the right adrenal gland compatible with subacute adrenal hematoma. There is no significant signal loss within the mass which would be suggestive of microscropic fat seen in lipid-rich adrenal adenomas.
Figure 4: T1 fat-suppressed image demonstrates no significant signal loss within the mass to suggest the presence of macroscopic fat.
Adrenal hemorrhage 肾上腺出血
Adrenal hematoma is in the differential diagnosis for an adrenal mass.
Causes of adrenal hemorrhage include stress, trauma, bleeding diathesis, neonatal stress and adrenal tumor.
Subtraction imaging is a helpful MRI tool for evaluating the presence of enhancement within a mass.
As discussed above, adrenal hemorrhage can occur due to a variety of reasons. It can vary in size, shape and appearance depending on the amount of hemorrhage, whether it is gradual or acute, whether there have been repeated episodes of hemorrhage and the ability of the patient to achieve hemostasis. Clinically, patients may experience upper abdominal, back or flank pain and show clinical and laboratory signs of massive blood loss. Adrenal insufficiency is an uncommon consequence, but can occur in the setting of bilateral adrenal hemorrhage.
Major objectives of imaging tests include both diagnosing the presence and amount of adrenal hemorrhage as well as determining whether or not there is an underlying adrenal mass responsible for the hemorrhage.
Adrenal hemorrhage is well-characterized on CT, usually appearing as a round or ovoid mass. Stranding of the periadrenal fat may be an associated finding. The density of the hematoma varies with age. In the acute and subacute stages, the hematoma is usually hyperdense, measuring between 50-90 HU. The hematoma will gradually decrease in size and density over time, and chronically may evolve into a pseudocyst, often with a calcified rim.
The appearance of adrenal hemorrhage will also vary with time on MRI. In the acute stage (less than 7 days after onset), hypo- or isointense signal will be present on T1 weighted images and T2 weighted sequences will demonstrate marked hypointensity. Subacute hemorrhage (7 days to 7 weeks) will be bright on both T1 and T2 weighted sequences due to the presence of extracellular methemoglobin. With chronic hemorrhage (seven weeks or older) a low signal rim will be seen on both T1 and T2 weighted sequences due to hemosiderin deposition and fibrous capsule formation.
Subtraction is an excellent tool in evaluating for enhancement within a lesion. If there is high signal present on the unenhanced T1 weighted sequences, it will be “subtracted”, so that any signal seen on the subtracted image must represent enhancement. Subtraction imaging has a well-established role for evaluating breast and renal masses on MRI and is also widely used in MR angiography.