Diagnostic Ultrasound - Abdomen and Pelvis

Adrenal Adenoma
TERMINOLOGY
Synonyms
• Adrenocortical adenoma
Definitions
• Extremely common, benign tumor of adrenal cortex
IMAGING
General Features
• Best diagnostic clue
○ Small, well-circumscribed, homogeneous adrenal mass
• Location
○ Can be bilateral (10%)
• Size
○ Varies from 2-5 cm
○ Smaller lesions are seen with Conn syndrome, usually < 2
cm (20% < 1 cm)
• Morphology
○ Typically small, round, or oval, smoothly marginated, and
homogeneous
○ Size is particularly important: Smaller adrenal lesions
tend to be benign; > 4 cm more likely malignant
– Size stability over 12 months supports benignity
Ultrasonographic Findings
• Nonspecific sonographic appearance
• Well-circumscribed, solid, oval-shaped mass, typically < 3 cm
• Usually homogeneous and hypoechoic
○ Or slightly heterogeneous with mixed echogenicity
• Atypically can appear more heterogeneous
○ Possibly with hemorrhage/necrosis or calcification (rare)
○ Necrosis is seldomseen in small adenoma
CT Findings
• Usually small (< 3 cm) and homogeneous
• Smoothly marginated and well defined
• Atypical features: Large size (> 3 cm), hemorrhage, cystic
degeneration, calcification
• NECT: CT characteristics depend on lipid content
○ Lipid-rich adenomas (70-90%): Attenuation < 10 HU is
characteristic and diagnostic
○ Lipid-poor adenoma (10-30%): Variable attenuation from
10-30 HU or higher, more nonspecific appearance
○ May see glandular atrophy bilaterally in setting of
Cushing syndrome
• CECT: Avid enhancement with rapid de-enhancement
○ Characteristic pattern of lesion washout when
comparing enhancement on portal venous phase to
attenuation at 10 min post injection: > 60% absolute
percent washout
– (Lesion attenuation on enhanced CT - lesion
attenuation on delayed CT) / (lesion attenuation on
enhanced CT - lesion attenuation on unenhanced CT) x
100%
– Diagnostic for adenoma
– Independent of lipid content
MR Findings
• T1WI: Chemical shift MR can confirm presence of
intracellular lipid
○ Shows signal dropout on out-of-phase imaging
– Compare lesion to spleen or muscle (SI of liver may be
affected by lipid deposition)
○ Diagnostic for adrenal adenomas containing lipid
• T1WI C+: No established dynamic enhancement
characteristics for MR
Nuclear Medicine Findings
• PET/CT
○ No increased uptake of FDG
○ Useful in differentiating from malignant lesions (↑
uptake)
Angiographic Findings
• Adrenal venography: Adrenal vein sampling in setting of
Conn syndrome
○ Can distinguish unilateral vs. bilateral aldosterone
secretion
○ Higher aldosterone:cortisol ratio than peripheral sample
= abnormal
Imaging Recommendations
• Best imaging tool
○ NECT and CECT or MR
• Protocol advice
○ Full adrenal mass CT protocol should include NECT and
CECT (with 10 min delayed phase)
– Check attenuation on NECT before contrast
administration to eliminate unnecessary imaging
– Use thin sections (3 mm) to better assess small lesions
○ Chemical shift MR can also be used to characterize
indeterminate adrenal nodules with attenuation of 10-
30 HU
○ CECT with 10 min delayed-phase imaging should be used
to characterize indeterminate adrenal nodules with CT
attenuation > 30 HU
• Recommendations for evaluating nonspecific incidental
adrenal nodules (ACR)
○ ≤ 1 cm can be ignored
○ 1-4 cm needs further evaluation or follow-up to establish
stability
○ ≥ 4 cm should undergo biopsy or PET
DIFFERENTIAL DIAGNOSIS
Adrenal Metastases
• Unilateral or bilateral; more often hypoechoic than
echogenic
• ± necrosis or hemorrhage
• Usually known to have malignancy elsewhere, although
adenoma is still more common even in setting of known
cancer
• NECT: Metastases can mimic lipid-poor adenoma
• CECT: Shows prolonged washout pattern, < 60% on 10 min
delayed phase
Adrenal Lymphoma
• Unilateral or bilateral masses
• Usually secondary spread to adrenal with evidence of
lymphoma elsewhere
• Unilateral primary lymphoma (non-Hodgkin) rare
Diagnoses: Adrenal Gland
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