Focal Thickening at the Gallbladder Fundus: Adenomyomatosis
Focal thickening at the gallbladder fundus is most likely adenomyomatosis, which characteristically presents with this localized pattern and can be differentiated from other causes by identifying Rokitansky-Aschoff sinuses on imaging.
Key Diagnostic Features
The fundal location is particularly suggestive of adenomyomatosis rather than diffuse inflammatory processes. When evaluating focal fundal thickening, the presence of Rokitansky-Aschoff sinuses (intramural diverticula appearing as small cystic spaces) is pathognomonic for adenomyomatosis 1.
CT Imaging Characteristics
On CT, adenomyomatosis demonstrates specific features that distinguish it from localized chronic cholecystitis 2:
Findings favoring adenomyomatosis:
- Oval contour of the thickened area
- Inner layer enhancement pattern
- Intralesional cystic areas (representing Rokitansky-Aschoff sinuses)
- Absence of adjacent gallbladder wall thickening
Findings favoring chronic cholecystitis:
- Flat contour
- Adjacent gallbladder wall thickening extending beyond the focal area
Importantly, wall thickness, enhancement grade, enhancement pattern, and presence of stones do not reliably differentiate between these entities 2.
Advanced Imaging Considerations
High-frequency contrast-enhanced ultrasound (HF-CEUS) demonstrates superior diagnostic accuracy (87.5% overall) compared to conventional ultrasound (56.2%) 3. In adenomyomatosis, nonenhanced Rokitansky-Aschoff sinuses are clearly visualized in 83.3% of cases 3.
Critical Pitfall: Excluding Malignancy
While adenomyomatosis is the most likely diagnosis for focal fundal thickening, gallbladder cancer must be excluded, particularly given that 62% of suspicious gallbladder wall thickening cases in one tertiary center proved malignant 4.
Red flags suggesting malignancy rather than adenomyomatosis:
- Arterial phase inhomogeneous hyperenhancement
- Venous phase hypoenhancement
- Disruption of gallbladder wall layer structure
- Loss of the normal two-layered wall pattern 3, 1
The preservation of wall layering and identification of Rokitansky-Aschoff sinuses are the most reliable imaging clues for confirming benign adenomyomatosis 1.
Clinical Algorithm
When encountering focal fundal gallbladder thickening:
- First-line imaging: Ultrasound remains the initial test of choice 5
- Look specifically for: Rokitansky-Aschoff sinuses (small cystic spaces within the wall)
- If equivocal: Proceed to CT with IV contrast or high-frequency contrast-enhanced ultrasound
- Assess for malignancy features: Wall layer disruption, irregular enhancement, or associated mass
- Consider surgical resection if malignancy cannot be confidently excluded, given the high malignant transformation rate in suspicious cases 4
The diagnosis of fundal adenomyomatosis can be made confidently when characteristic Rokitansky-Aschoff sinuses are identified with preserved wall architecture and no features suggesting malignancy 2, 3, 1.