Diagnostic Ultrasound - Abdomen and Pelvis

Renal Angiomyolipoma
TERMINOLOGY
Abbreviations
• Angiomyolipoma (AML)
IMAGING
General Features
• Best diagnostic clue
○ Discrete intrarenal mass containing macroscopic fat
• Location
○ Renal cortex
• Size
○ Few mm to very large
• Heterogeneous group of benign neoplasms with varying
pathologic, radiologic, and clinical characteristics
• Triphasic AML: Composed of varying amounts of
dysmorphic blood vessels, smooth muscle, and mature
adipose tissue; can be classified radiologically into "classic"
and "fat-poor" subtypes
○ Classic AML: Contains fat detectable by imaging
○ Fat-poor AML ("AML with minimal fat"): Insufficient
amount of fat to be detected by conventional CT or MR
imaging; divided into 3 categories
– Hyperattenuating AML: Abundant smooth muscle
component; average size 3 cm
– Isoattenuating AML: Interspersed fat within smooth
muscle; shows chemical shift suppression mimicking
clear cell renal cell carcinoma (RCC)
– AML with epithelial cysts: Extremely rare; cystic
components and few, if any, fat cells
• Epithelioid AML: Extremely rare subtype
Ultrasonographic Findings
• Grayscale ultrasound
○ Echogenicity depends on amount of fat
○ Classic AML: Renal lesion of similar echogenicity to renal
sinus fat
– Small < 3 cm: Round, well-marginated, hyperechoic
renal cortical lesion
– Larger: More lobulated and exophytic
– Acoustic shadowing in 21-33% of AML (not in RCC)
– Hypoechoic rim and intratumoral cysts suggest RCC
○ Hemorrhage in perinephric space and retroperitoneum
from tumor rupture
• Color Doppler
○ Tortuous dilated vessels, aneurysms
CT Findings
• NECT
○ Classic AML: Contains fat measuring < -10 HU
– Appearance depends on proportion of fat, blood
vessel, and smooth muscle components
– Region of interest measurements of thin sections or
histogram analysis may be needed to detect fat
□ Hemorrhage may obscure fat
○ Fat-poor AML
– Hyperattenuating AML: High attenuation on CT
– Isoattenuating AML: Isoattenuation to renal tissue
○ Calcification very rare in AML, suggests RCC
• CECT
○ Varied enhancement pattern based on amount of fat
and vascular components
○ Extension of tumor into inferior vena cava (IVC) is rare
• CTA
○ Aneurysmal renal vessels may be seen
MR Findings
• T1WI
○ Classic AML: Hyperintense with signal loss on fat
suppression
• T2WI
○ Classic AML: Isointense to fat, suppress with fat
suppression
○ Fat-poor AML: Hypointense, do not suppress with fat
suppression
• T1WI C+
○ Variable enhancement
• Chemical shift
○ India ink artifact at border of mass indicates AML;
however, signal loss throughout mass (that does not
suppress with fat suppression) could represent clear cell
RCC or AML
Angiographic Findings
• Vascular tumor with long tortuous arteries and aneurysms,
active bleeding rarely seen
• Current role is for embolization of bleeding AML or for
prophylaxis in larger AML at risk of bleeding
Imaging Recommendations
• Best imaging tool
○ CT/MR more specific than US
○ Ultrasound may be used for screening and monitoring of
AML, depending on body habitus
• Protocol advice
○ Echogenic masses detected by ultrasound should be
further evaluated with CT or MR to confirm presence of
fat
○ Consider fat-poor AML if solid, enhancing mass is
hypointense on T2WI
DIFFERENTIAL DIAGNOSIS
Renal Cell Carcinoma
• May be echogenic on US but rarely contains fat
○ Fat typically associated with coarse calcification while
AML are very rarely calcified
• RCC may engulf renal sinus fat
• Ablated RCC may be replaced by fat, history and prior
imaging are essential
• After acute hemorrhage, RCC or AML may be
indistinguishable if no fat is detected
Perirenal Liposarcoma
• Large exophytic AML may resemble retroperitoneal
liposarcoma
• Smooth compression of kidney & extension beyond
perirenal space favor liposarcoma
• Identification of enlarged/bridging renal vessels and
aneurysms favor AML
• Beak of renal tissue around fatty mass or small cortical
defect at interface of mass with kidney favor AML
Diagnoses: Urinary Tract
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