Posterior parahepatic cysts are an incidental finding of a small, isolated, nodular structure adjacent to the posterior segment of the right hepatic lobe.
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Pathology
Due to the benign imaging characteristics and stability on long-term imaging, no pathologic diagnosis of these lesions has been obtained.
Radiographic features
In most cases, there is a single cyst, occasionally several can occur. The cysts can range in size from 0.3 cm to 2.5 cm, long axis. Attenuation varies from 12-80 HU. Posterior parahepatic cysts do not enhance, are not FDG-avid, and appear cystic on MRI. They do not grow on follow-up imaging.
Most lesions occur at or above the level of the upper pole of the right kidney, consistently near the posterior segment of the right hepatic lobe, proximal to the right hemidiaphragm. Occasionally the lesions appear connected to the liver itself.
Differential diagnosis
Considerations include
-
diaphragmatic pseudotumor
- results from a slip or infolding of the right hemidiaphragm, and can simulate a nodule on axial imaging
- appears elongated on reformatted imaging, with imaging characteristics identical to the diaphragm
- diaphragmatic mesothelial cyst
- metastasis (e.g. melanoma, sarcoma)
- unlikely isolated finding without metastases elsewhere
- diminutive accessory right hepatic lobe 2
- likely under-recognized
- ectopic hepatic foci 2
- analogous to splenunculi
- endometriosis
- splenosis
- dropped gallstones
Practical points
Radiologists should be familiar with this entity and avoid unnecessary alarm and workup when posterior parahepatic cysts are encountered in routine practice. In the setting of a history of malignancy, a follow-up examination may be appropriate to ensure stability.
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