Case Report: The Fifth Liver Lobe; A Hybrid Left‐Sided Anatomical Variation of Accessory Liver Lobes

Abstract

Accessory liver lobes (ALL) are supernumerary lobes in the liver. Although their origin is not completely understood, they appear to be due to a congenital anomaly caused by hyperplasia, trauma, and/or surgery. Two types of accessory lobes are documented in the literature: continuous and ectopic accessory lobes, differing in that the ectopic lobe is anatomically separate from the normal liver as opposed to the continuous subtype. Although rare, several reports exist with Riedel’s Liver Lobe being among the most well‐known. In these cases, the ALL is normally continuous with the right side of the liver and exists as either a sessile or pedunculate attachment. In our case, a rare ALL was found on the left lobe during a routine dissection of a male cadaver. However, structurally it is different from both continuous and ectopic ALL in that it is not joined to the liver via a connecting stalk nor is completely separate. Rather, this variant, a 7.5cm long ‐ 7.0cm wide‐2cm tall ALL displays a ligamentous attachment alongside the lateral edge of the left lobe. Most cases of ALL are asymptomatic and discovered incidentally. In imaging studies, ALL may be confused with tumors leading to misdiagnosis and errors in treatment. Although infrequent, there are reports of complications of ALL including infarction, hemorrhage, biliary atresia, and gallbladder torsion. Hypotheses for the embryological process of an ALL include heteroplastic embryological development as well as increased intraabdominal tension. Awareness of this variant will help decrease risk of iatrogenic injury in suspected ALL cases.