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, though several cysts may be present. The cysts can range in size from 0.3 cm to 2.5 cm in the long axis. Attenuation varies from 12-80 HU. Posterior parahepatic cysts do not enhance, are not FDG-avid, and appear cystic on MRI. They should 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 and proximal to the right hemidiaphragm. Occasionally, the lesions may appear attached to the liver itself.
Differential diagnosis
Considerations include
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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
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metastasis (e.g. melanoma, sarcoma)
unlikely isolated finding without metastases elsewhere
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diminutive accessory right hepatic lobe 2
likely underrecognized
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ectopic hepatic foci 2
analogous to splenunculi
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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