Focal Fatty Sparing Adjacent to the Gallbladder Fossa
Focal fatty sparing adjacent to the gallbladder fossa is a benign pseudolesion representing normal liver parenchyma that has been protected from fat deposition, typically due to aberrant venous blood flow from the gallbladder wall—this is not a tumor and requires no treatment. 1
What This Finding Represents
Focal fatty sparing occurs when an area of normal liver tissue remains unaffected in a background of diffuse hepatic steatosis (fatty liver). 1
This creates a hypoechoic (darker) area on ultrasound that can mimic a mass lesion, but it is actually normal liver tissue surrounded by fatty infiltration. 2
The gallbladder fossa is one of the most common locations for focal fatty sparing, occurring in approximately 67% of patients with fatty liver who have an intact gallbladder. 3
Why It Occurs at the Gallbladder
Efferent venous blood flow from the gallbladder wall directly supplies the adjacent liver parenchyma, and this blood flow pattern protects that area from fat accumulation. 4
Color Doppler studies demonstrate that 64% of patients with focal sparing at the gallbladder fossa show detectable venous blood flow from the gallbladder wall into the spared area, compared to only 5% in patients without focal sparing. 4
When the gallbladder has been surgically removed, focal sparing at this location drops dramatically to only 33% of patients, confirming the protective role of gallbladder blood supply. 3
The blood flow pattern is typically continuous venous flow (92% of cases) rather than pulsatile arterial flow. 4
Key Diagnostic Features
On imaging, focal fatty sparing has characteristic features that distinguish it from true mass lesions:
Geographic margins with no mass effect on surrounding vessels or structures 1
Isoenhancement throughout all vascular phases on contrast-enhanced ultrasound (CEUS), meaning it enhances identically to normal liver tissue 1
No distortion of intrahepatic vessels—blood vessels pass through the area undisturbed 1
The area appears hypoechoic (darker) on standard ultrasound only because it contrasts with the surrounding bright echogenic fatty liver. 2
Clinical Significance
This is a benign finding that mimics a tumor but requires no treatment or intervention. 1
Focal fatty sparing is listed among common pseudolesions that can mimic liver tumors, alongside focal fat deposition, vascular shunts, and transient perfusion abnormalities. 1
The typical location adjacent to the gallbladder fossa, combined with characteristic imaging features, allows confident diagnosis without biopsy. 1
Common Pitfalls to Avoid
Do not mistake focal fatty sparing for a hypovascular metastasis or other malignant lesion—the key differentiator is that focal sparing shows normal enhancement patterns on contrast imaging, while true lesions show abnormal enhancement. 1
If uncertainty exists, CEUS or MRI can definitively characterize the lesion by demonstrating normal vascular enhancement throughout all phases. 1
Focal fatty sparing can occur in other locations (porta hepatis, around the falciform ligament, near portal veins), but the gallbladder fossa location is highly characteristic and should raise suspicion for this benign entity. 1, 5
In patients who have undergone cholecystectomy, focal sparing at the gallbladder fossa becomes much less common, which can be a helpful historical clue. 3