Emergence and distribution of the ilioinguinal nerve in the inguinal region: applications to the ilioinguinal anaesthetic block (about 100 dissections).

The variations in the emergence and distribution of the ilioinguinal nerve are the cause of the failures of the ilioinguinal block and the difficulties at interpreting the ilioinguinal nerve syndrome. In order to identify its variations and set reliable anatomical landmarks for performing the ilioinguinal block, we dissected 100 inguinal regions of 51 adult corpses. The nerve was absent in seven cases and double in one case. The ilioinguinal nerve emerged from the internal oblique muscle, passing at 1 +/- 0.8 cm of the inguinal ligament and 3.33 +/- 2 cm of the ventral cranial iliac spine. It appeared behind the inguinal ligament and/or the ventral cranial iliac spine in 19 cases and presented a common trunk with the iliohypogastric nerve in 13 cases. In 47 cases, the nerve appeared in the form of a single trunk. Sixteen modes of division and eight types of predominantly anterior scrotal topographic distribution could be noted. These results show the high variability of the emergence and the sensory distribution of the ilioinguinal nerve. They enable us to propose techniques for ilioinguinal block performance using more accurate anatomical landmarks formed by the inguinal ligament and the ventral cranial iliac spine and a better diagnostic approach of ilioinguinal neuropathies.