Types of inferior mesenteric artery: a proposal for a new classification

The inferior mesenteric artery (IMA) is the third main branch of the abdominal aorta and arises at the level of L3, supplying the large intestine from the distal transverse colon to the upper part of the anal canal. The aim of this study was to characterise the course and morphology of the terminal branches of the IMA, and also creating a new IMA classification, which seems to be necessary for clinicians performing surgery in this area.

The anatomical variations in the branching patterns of the IMA were examined in 40 cadavers fixed in a 10% formalin solution. Morphometric measurements were then obtained twice by two researchers.

Due to the proposed classification system, type I characterised by a common trunk preceding bifurcation into sigmoidal branches and the superior rectal artery after giving left colic artery (LCA) occurred in 57.5% of cases, type II, trifurcation type, in 25%, type III with the superior rectal arteries originating firstly from the IMA in 5%, type IV with the ascending lumbar artery in 10% of cases and type V, a novelty, in 2.5%. The origin of IMA was observed at the level of L2/L3 in 22.5% of cases, at L3 in 25% of cases, at L3/L4 in 15% of cases, at L4 in 35% of cases and at the level of L5 in 2.5% of cases. More than one third (38.1%) of total cases with additional arteries and rapidly bifurcating branches occurred in types III, IV, and V. In women, only the IMA and LCA were significantly narrower than in men. Only the diameter of the IMA correlated with the diameter of the superior rectal artery.

The IMA is characterised by high morphological variability. The introduction of a new, structured, anatomical classification seems necessary for all clinicians.