Riedel's lobe is a tongue-like, inferior projection of the right hepatic lobe beyond the level of the most inferior costal cartilage on cross-sectional images 1. It is not considered a true accessory lobe of the liver but an anatomical variant of the right lobe of the liver 3.
Riedel's lobe has an incidence of ~17.5% (range 3.3-31%) and is more frequently found in females 2-3 with a M:F of approximately 1:3 4.
Riedel's lobe is an important variant to be aware of because it can simulate a mass and has even lead to laparotomy 2 and pathology (e.g. malignancy or even torsion) can occur 4 and cause symptoms low in the pelvis.
It was originally reported in 1888 by Riedel in seven female patients who had palpable masses in the right hypochondrium, which were subsequently confirmed at surgery 2.