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IMAGING OF INCIDENTAL ADRENAL
LESIONS:
PRINCIPLES, TECHNIQUES AND
ALGORITHMS
Giles W.L. Boland
Massachusetts General Hospital
Harvard Medical School
Objectives
• Comprehensive overview of adrenal
imaging
• Basic principles
• Techniques (CT, MRI, PET/CT)
• Algorithms
Why characterize lesions?
• Most adrenal lesions detected by CT
• 2-7% of CT’s depending on age
• Almost always benign in the non-oncology
patient
• Song et al. 973 patients without cancer none had malignant masses (AJR 2008)
• Further characterization needed in a
patient with cancer - up to 50% lesions
metastatic
Which is metastatic?
LUNG CANCER
No adrenal metastases
Primary lesion can be surgically removed
and curative therapy performed
LUNG CANCER
Adrenal metastasis
Lung lesion now inoperable and palliative
therapy performed
Principles
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Why it’s important to characterize lesions
Macroscopic features
Serial Imaging
Lipid sensitive techniques (CT and MRI)
Physiologic techniques (CT washouts)
Functional techniques (PET and PET/CT)
Principles: lesion morphology
Size
lesions > 4 cm tend to be metastases or
carcinoma
Lesion morphology
Shape
irregular shape often malignant (but not always)
Lesion morphology
Lesion heterogeneity
inhomogeneous - often malignant
homogeneous - indeterminate
Change in lesion size
• Use cheapest radiological test:
“the old film” - prior CT
• No change: adenoma
• Increase in size: metastasis
2001
1996
Metastatic disease
2008
2009
Serial imaging - lymphoma
2005
2007
2008
Serial imaging - hematoma
2007
2008
Morphologic features
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Usually not helpful
Better tests needed to avoid biopsy
Needs high specificity
Sensitivity less important but adequate
Ideally serial imaging not required
LESION CHARACTERIZATION
• Test devised to confidently diagnose
adenomas
• Reduces # of percutaneous biopsies
• Curative therapy for primary tumor
possible
TEST SPECIFICITY: ADENOMA
• SPECIFICITY needs to be close to 100%
• Non-specific: curative surgery will be
performed for primary malignant lesion
when adrenal metastases is present
TEST SENSITIVITY: ADENOMA
• SENSITIVITY less crucial
• Lesion remains indeterminate and
therefore biopsy/MRI performed and
adenoma confirmed
Lipid sensitive techniques
• Based on lipid content of detected lesion
• Abundant intracytoplasmic fat in adrenal
cortex (both functioning and nonfunctioning adenomas) - cholesterol, fatty
acids neutral fat
• Metastases lipid poor
• CT and MRI
Macroscopic fat - myelolipoma
Lipid sensitive techniques
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70% adenomas lipid-rich
30% lipid-poor lesions
All metastases are lipid-poor
Lipid-poor adenomas and mets are
therefore indeterminate
• These lesions require further
characterization (follow-up, washouts,
PET, biopsy)
Lipid sensitive CT
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Non-contrast CT
Place ROI on lesion
Lee et al 1991
38 adenomas:
-2.2 HU
28 metastases: 29 HU
HU
0
2
4
8
Sensitivity
41
47
55
65
Specificity
100
100
99
98.5
10
71
98
12
18
73
86
97
88
Boland et al. AJR 1998
Region of interest
38 HU
46 HU
6 HU
MRI
• Chemical Shift Imaging
• Fat protons precess < water
• Equal proportion within voxel = zero
signal
• Detects same tissue as CT (i.e. fat)
• In theory offers no advantages
• Longer test
• Less availability
Lipid-Rich Adenoma
In-phase
Out-of-phase
Lipid-poor metastasis
In-phase
Out-of-phase
Chemical shift – voxel water/fat ratio
CT
In-phase
Out-of-phase
Contrast-enhanced CT
• Adrenals enhance
• Metastases tend to enhance to a higher
HU than adenomas
• HU measurements meaningless on
dynamic study
• Too much cross-over of HU values
between benign and malignant lesions
Perfusion Imaging: CT Washouts
• Adenomas washout faster than
metastases
• Even lipid poor adenomas washout faster
• Delayed CT
• Ratio of enhanced to delayed HU
• Disrupt busy CT schedule
• Better for patient in one sitting
Korobkin AJR 1998
• Relative % washout
• Absolute % washout
• Rule of thumb
• Adenomas washout > 40% (> 60%
absolute)
• Non-adenomas < 40% (> 60% absolute)
Washout
• Absolute: Enhanced - Delayed
x 100%
Enhanced - Unenhanced
• Relative:
Enhanced - Delayed
Enhanced
x 100%
Lipid Poor Adenomas:
Caoili et al. Radiology 2002
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127 adenomas: 39 non-adenomas
22 lipid poor
Adrenal protocol
Characterize 19/22 masses as benign
124/127 adenomas characterized by CT
Other masses had additional features to
suggest adenoma
Blake et al. Radiology 2005
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MDCT
122 masses
10 minute delay
RPW threshold 38%
100/98% sensitivity/specificity
All malignant lesions RPW < 40%
Metabolic Imaging
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PET
Metabolically hyperactive cells trap FDG
Used since early 1990’s
Now in favor due to PET/CT
How useful?
Metastasis
Visual, SUV and SUR
• RSNA 2008 (Jagtiani et al)
• Meta-analysis 15 reports
• 878 adrenal lesions (457 benign and 421
malignant lesions) in 763 patients
• 10 PET stand-alone, 5 PET/CT scanners
• Visual as effective as SUR/SUV
Uptake < liver = benign
Uptake = liver = benign
Uptake slightly > liver
= indeterminate
Uptake >> liver = malignant
Adrenal algorithm
• Non contrast CT:
< 10 HU
> 10 HU
STOP
Washouts
• Washouts: Absolute:
> 60%
< 60%
> 40%
< 40%
Adenoma
Mets
Adenoma
Mets
Relative:
• 10 versus 15 minutes delays?
Best Test
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PET/CT
Combines functional PET with anatomy
Even better with washouts
Multiple reports
> 95% accuracy
Which test?
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No test has a monopoly
Non-contrast CT effective for adenoma
CT washouts with CT protocol
Can stop there
Will be some indeterminate lesions
Suspicious lesions
PET/CT increasingly common
Few lesions will need biopsy
THANK YOU!
Radiology 2008;249:756-77
Incidental Adrenal Lesions:
Principles, Techniques, and Algorithms for Imaging
Characterization