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Elsy, Asiri, Osman, and Alghamdi: Origin and branching pattern of the iliohypogastric and ilioinguinal nerves and their exits in relation to the psoas major muscle: a cadaveric study
Original Article

Anat Cell Biol 2025;58(1):14-21.

Published online: 10 January 2025

DOI: https://doi.org/10.5115/acb.24.175

Origin and branching pattern of the iliohypogastric and ilioinguinal nerves and their exits in relation to the psoas major muscle: a cadaveric study

Bijo Elsy1, , Waad Hassan Mohammad Asiri1, Lina Eltag Sir Elkhatim Osman1, Mansour Abdullah Saeed Alghamdi1, 2

1Department of Anatomy, College of Medicine, King Khalid University, Abha, Saudi Arabia

2Genomics and Personalized Medicine Unit, The Center for Medical and Health Research, King Khalid University, Abha, Saudi Arabia

Corresponding author: Bijo Elsy, Department of Anatomy, College of Medicine, King Khalid University, Abha 62529, Saudi Arabia, E-mail: rite2bijo@gmail.com

Received 8 July 2024       Revised 22 October 2024       Accepted 21 November 2024

Copyright © 2025. Anatomy & Cell Biology

(open-access):

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

This study aims to determine the level of origin, branching pattern and exits of the iliohypogastric and ilioinguinal nerves in relation to the psoas major muscle. Additionally, this study confirms the presence and retroperitoneal courses of the double nerves. We dissected a total of 24 iliohypogastric and ilioinguinal nerves (6 male and 6 female cadavers). The origin, branching, and exits in relation to the psoas major muscle, the absence of these nerves or the presence of double nerves, and their retroperitoneal course were carefully examined. All the images were recorded by photographing. In this study, we mainly observed variations in exits, branching patterns, and their retroperitoneal course. The iliohypogastric nerve was absent in 2 cases (8.3%). In the type I pattern, in 1 case (4.2%), the common trunk descends anteriorly to the iliac vessels from the iliolumbar vessels. In 4 cases (16.7%), the double ilioinguinal nerve with different branch patterns and retroperitoneal courses was observed. In 1 single nerve case (4.2%), the ilioinguinal nerve descends anterior to the iliac vessels from the iliolumbar vessels. To our knowledge, the branching pattern of the double ilioinguinal nerves and their retroperitoneal course have not been reported in any available data. Sound knowledge of the variations in the origin, branches, and retroperitoneal course of the iliohypogastric and ilioinguinal nerves is very helpful for the improvement of peripheral nerve blocks and other various surgical procedures to avoid complications and nerve injuries.

Keywords: Iliohypogastric nerve, Ilioinguinal nerve, Iliolumbar vessels, Lumbar plexus, Psoas major

Introduction

Primaxial and abaxial are the two domains used in embryological classification. Each spinal nerve has primaxial muscle innervating, superficial extramural, and deep intramural branches. The muscles of the back and proximal body wall are included in the primaxial area, which is innervated by the primaxial muscle innervating branch of the dorsal rami of the spinal nerve. The abaxial muscles inside the body wall are innervated by the extramural branch of the ventral rami of the spinal nerve, whereas the abaxial muscles outside the wall are supplied by the intramural branch. The dorsal rami of the spinal nerve retain a segmental pattern, while the ventral rami branches contribute to the formation of the plexus [1-4].
The lumbar plexus is located within the substance of the psoas major muscle. The first lumbar ventral ramus is divided into the cranial and caudal branches. The cranial branch is thicker and bifurcates into the ilioinguinal and iliohypogatric nerves [5, 6]. The iliohypogastric and ilioinguinal nerves are the main sensory nerves that innervate the skin that borders the thigh and abdomen, and these nerves are included in the border nerves. In border nerve pain syndrome, burning neuropathic pain spreads from the lower abdomen to the inguinal region, the skin of the thigh below the medial end of the inguinal ligament, and the external genital area [7-9].
Anatomical variations in the level of origin, exits and branching patterns of the branches of the iliohypogastric and ilioinguinal nerves have been well documented in all available data [5, 6, 10, 11]. However, this study aims to determine what has not been reported in the literature, including the level of origin, branching pattern and exits, as well as the presence of any double nerves with their retroperitoneal course and the absence of any one of these nerves.
The iliohypogastric and ilioinguinal nerves can be damaged in surgical procedures in the lower abdominal region and in peripheral nerve blocks. Therefore, in-depth knowledge of the anatomical variations of these nerves reduces their injuries and complications in various surgical procedures.

Materials and Methods

We dissected a total of 24 iliohypogastric and ilioinguinal nerves (6 male and 6 female cadavers) from the lumbar plexus. We carefully examined the level of origin, branching, and exit of these nerves in relation to the psoas major muscle. Furthermore, we observed their absence or presence of double nerves and their retroperitoneal course, which had not yet been reported in the available literature. Currently, sexual dimorphism is not considered because of the small sample size. All images were captured and documented through photography.
This study was carried out in the Department of Anatomy of King Khalid University, Abha, Saudi Arabia, and was approved by the Research Ethics Committee (ECM #2023-3325) of King Khalid University.

Results

Iliohypogastric nerve

In this study, the nerve originated in 18 cases (75.0%) of L1 and 4 cases (16.7%) from L2. We observed its absence in 2 cases (8.3%). In 4 cases (16.7%), this nerve has the lateral cutaneous and anterior abdominal muscular branches (Fig. 1). In all 24 cases, we have not seen any genital branches, and 20 cases (83.3%) do not have terminal branches in the abdomen (Fig. 2). This time we focused only on the abdomen and did not trace its branches within the muscles of the abdominal wall. In 8 cases (33.3%), the type I pattern of origin and its division at various levels between the exit and entrance points in the transversus abdominis muscle were observed (Figs. 3–5). In 1 type I case (4.2%), the common trunk descends anteriorly to the iliac vessels from the iliolumbar vessels (Fig. 5). In 16 cases (66.7%), the type II pattern was observed (Figs. 1, 2). In all 24 cases, this nerve emerges from the upper lateral border of the psoas major. In 2 cases (8.3%), the iliohypogastric nerve was very thin or smaller compared to the ilioinguinal nerve (Fig. 4). The origin, absence, and branches of the iliohypogastric nerve were calculated and presented in Table 1.

Ilioinguinal nerve

In 18 cases (75.0%), the nerve originated in L1, 5 cases (20.8%) from L2, and 1 case (4.2%) from L3, along with the lateral femoral cutaneous nerve (Fig. 6). In 8 cases (33.3%), the ilioinguinal and iliohypogastric nerves originate from the common trunk. This common trunk divides into the iliohypogastric and ilioinguinal nerves at various levels (Figs. 3–5). In 1 case (4.2%), the common trunk descends anteriorly to the iliac vessels from the iliolumbar vessels (Fig. 5). In 21 cases (87.5%), the ilioinguinal nerve exits from the lateral border of the psoas major muscle (Figs. 1, 2, 7), and in the other 3 cases (12.5%), it exits after piercing the psoas major muscle (Fig. 7).
In 8 cases (33.3%), including single and double nerves, there are terminal medial muscular and lateral cutaneous branches in the abdomen (Figs. 1, 7, 8), and the other 16 cases (66.7%) have no terminal branches in the abdomen (Fig. 2).
We found a single ilioinguinal nerve in 20 cases (83.3%), and in 1 case (4.2%), it descends anterior to the iliac vessels from the iliolumbar vessels (Fig. 9). Double ilioinguinal nerves were present in 4 cases (16.7%) (Figs. 7, 8). In 3 cases (12.5%), both ilioinguinal nerves originated at the L1 level. The second ilioinguinal nerve, in 1 case (4.2%), originated in L2.
In 2 cases (8.3%), the second ilioinguinal nerve descends onto the quadratus lumborum muscle and gives lateral cutaneous and medial muscular branches. The medial branch accompanies the first ilioinguinal nerve, and then both nerves together pierce the transversus abdominis muscle, and its lateral branch separately pierces the transversus abdominis muscle (Fig. 7). In the other 2 cases (8.3%), the first ilioinguinal nerve crosses the second ilioinguinal nerve in the lower part of the quadratus lumborum muscle. The first nerve has two branches: lateral cutaneous and medial muscular. The lateral branch accompanies the second ilioinguinal nerve, and these two nerves together pierce the transversus abdominis muscle. Just medial to it, the medial branch of the first ilioinguinal nerve pierces the transversus abdominis muscle (Fig. 8). The origin, branches, and presence of the double ilioinguinal nerve were calculated and presented in Table 2.

Discussion

The branches of the superficial extramural plexus that form the brachial and lumbar plexus, which innervate the girdle and limb muscles. While the deep intramural branch innervates the anterior abdominal wall muscles [1]. Developmental factors lead to variations and abnormalities in the branching patterns of the spinal nerve. Instances resulting from single gene mutations, such as those observed in experimental animals, are rarely seen in the human body [12]. The most mutated peripheral nerve is the lumbar plexus.
The iliohypogastric and ilioinguinal branches of the spinal nerves are highly variable in their innervation patterns [10, 13-15]. In the typical branch pattern, the L1 bifurcates into the extramural iliohypogastric and intramural ilioinguinal nerves [1, 5]. Sometimes, this nerve receives roots from the eleventh or twelfth thoracic nerve [16-18]. In this study, the nerve originated in 18 cases (75.0%) of L1 and 4 cases (16.7%) from L2. Other authors have reported that the origin of L1 was 62.5% to 96.5% [19-26] and 1.6% from L1–L2 [23].
We observed the absence of the nerve in 2 cases (8.3%), but the percentages of its absences reported were 1%, 2%, 6.6%, 13.34%, 20.6%, and 34.35% of the cases [22-24, 26-28], respectively. The iliohypogastric nerve exits from the upper lateral border of the psoas major muscle and crosses in front of the quadratus lumborum muscle. Above the iliac crest, it enters the transversus abdominis muscle [6, 29, 30].
In various studies [29-33] the iliohypogastric nerve was reported to have three terminal branches: the lateral cutaneous branch (iliac branch), the genital sensory branch, and the anterior abdominal muscular branch (hypogastric branch). But Bergman et al. [6] reported only the terminal lateral cutaneous and anterior cutaneous branches.
In this study, we observed 4 cases (16.7%) of lateral cutaneous and muscular branches. But in the 24 cases, we have not seen any genital branch, and 20 cases (83.3%) have not seen any terminal branches in the abdomen. The genital branch of the iliohypogastric nerve was absent in 12% of cases [33]. In 60% of cases [33-35], the distal parts of the iliohypogastric and ilioinguinal nerves joined to form a single genital branch. In all cases in our study, the iliohypogastric and ilioinguinal nerves run separately in the lower abdominal region. This time, we focused only on the abdominal branches and did not trace their branches within the muscles of the abdominal wall.
The type I pattern ranged from 5.8% to 53% and 47 to 94.2% of the type II or classic pattern were reported in other studies [13, 14, 21, 25, 27-29, 36-40]. The ilioinguinal and iliohypogastric nerves unite to form a common trunk in the type I pattern, which emerges from the lateral border of the psoas major muscle. he trunk then splits into the ilioinguinal and iliohypogastric nerves, either between the transversus abdominis and internal oblique muscles or behind the kidney [39]. But in the type II pattern, the iliohypogastric and ilioinguinal nerves emerge independently from the lateral border of the psoas major muscle.
In this study, 8 cases (33.3%) of type I and its division occurred at various levels between exit and entry points in the transversus abdominis muscle. In 1 case (4.2%), the common trunk descends anteriorly to the iliac vessels from the iliolumbar vessels. 16 cases (66.7%) of type II origin patterns were observed. In all 24 cases, this nerve emerges from the upper lateral border of the psoas major muscle.
Compared to the ilioinguinal nerve, 2 cases (8.3%) of thinner and smaller iliohypogastric nerves were observed. Usually, the iliohypogastric nerve is larger than the ilioinguinal nerve, and occasionally these nerves are reciprocal in size [6, 41, 42].
An intramural branch of the L1 spinal nerve innervates the internal oblique muscles and the transversus abdominis muscles. It ends as a sensory nerve that travels to the skin surrounding the genital region of the abaxial domain [1]. The ilioinguinal nerve originated from different roots T12 to L3 [26, 43, 44]. We observed 18 (75.0%) cases that originated from L1. Similar origins were observed [6, 19, 22, 45-47], ranging from 51.5% to 86.5% of the cases. In our study, there were 5 cases (20.8%) of L2, but other authors reported 1.66% and 2% [22, 24]. This nerve is derived from L2 and L3 in 1.3%, 1.5%, and 10% [44, 21, 26] of reported cases. However, in the current study, this nerve originated in L3 in 1 case (4.2%), along with the lateral femoral cutaneous nerve.
Usually, the ilioinguinal nerve exits from the lateral border of the psoas major muscle [5, 48]. The same exits were found in 21 cases (87.5%) in our study. In the other 3 cases (12.5%), it exits after piercing the psoas major muscle; the same exit was reported by Bergman et al. [6]. In 1 case (4.2%), the common trunk of the nerve descends anterior to the iliac vessels from the iliolumbar vessels. But in another 1 case (4.2%), the single ilioinguinal nerve descends anterior to the iliac vessels from the iliolumbar vessels.
The ilioinguinal nerve gives a lateral cutaneous (iliac branch), muscular, and occasional communicating branches. The communicating branch that may connect with the iliohypogastric or lateral femoral cutaneous nerve [5, 6, 48]. In this study, 16 cases (66.7%) of the nerves have no terminal branches in the abdomen, and in 8 cases (33.3%), single and double nerves, have medial muscular and lateral cutaneous terminal branches in the abdomen, but no communicating branches.
We observed single ilioinguinal nerves in 20 cases (83.3%) and double ilioinguinal nerves in 4 cases (16.7%). But in some studies, 2% and 3.3% cases of double ilioinguinal nerves were observed [23, 24, 47]. In all 3 cases (12.5%), these nerves originated at the level of L1. The second ilioinguinal nerve, in 1 case (4.2%), originated in L2. In our study, we have not seen any absence of the ilioinguinal nerve.
In all 4 cases (16.7%), these nerves run obliquely and parallel to each other, crossing the quadratus lumborum muscle. In 2 cases (8.3%), in the lower part of the quadratus lumborum muscle, the first ilioinguinal nerve crosses the second ilioinguinal nerve. The first nerve has two branches: lateral cutaneous and medial muscular. The lateral cutaneous branch accompanies the second ilioinguinal nerve, which does not have branches, and these two nerves together pierce the transversus abdominis muscle. Just medial to it, the medial muscular branch of the first ilioinguinal nerve pierces the transversus abdominis muscle. In the other 2 cases (8.3%), the second ilioinguinal nerve descends on the quadratus lumborum muscle, and then it gives lateral cutaneous and medial muscular branches.
The first ilioinguinal nerve, which has no branches, accompanies the medial muscular branch, and then both nerves together pierce the transversus abdominis muscle. The lateral branch of the second ilioinguinal nerve independently pierces the transverse abdominis muscle.

Conclusion

This present study observed a rare retroperitoneal course and branching pattern in the double ilioinguinal nerves. Iliohypogastric and ilioinguinal nerves may be damaged during surgical procedures in the lower abdominal region and in peripheral nerve blocks. Therefore, a detailed knowledge of the anatomical variations of these nerves, especially the retroperitoneal courses of the double ilioinguinal nerves, provides important information for the basic and clinical sciences and thereby reduces their injuries and complications in peripheral nerve blocks and surgical procedures.

Acknowledgements

We sincerely thank the Department of Anatomy, College of Medicine, at King Khalid University in Abha, Saudi Arabia, for all forms of help.

Notes

Author Contributions

Conceptualization: BE. Data acquisition: BE, WHMA, LESEO. Data analysis or interpretation: BE, WHMA. Drafting of the manuscript: BE, MASA. Critical revision of the manuscript: BE, LESEO, MASA. Approval of the final version of the manuscript: all authors.

Conflicts of Interest

No potential conflict of interest relevant to this article was reported.

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Fig. 1
Representative images show the type II pattern. The iliohypogastric nerve (IH) gives lateral cutaneous (a) and anterior abdominal muscular (b) branches. The ilioinguinal nerve (II) gives terminal medial muscular (1) and lateral cutaneous (2) branches. Both nerves exit from the lateral border of the psoas major muscle (PM). QL, quadratus lumborum muscle.
acb-58-1-14-f1.tif
Fig. 2
Representative images show the type II pattern. The iliohypogastric nerve (IH) and the ilioinguinal nerve (II) exit from the lateral border of the psoas major muscle (PM) and there are absences of terminal abdominal branches in both nerves. PMI, psoas minor muscle; QL, quadratus lumborum muscle.
acb-58-1-14-f2.tif
Fig. 3
Representative images show the type I pattern. CT, common trunk; IH, iliohypogastric nerve; II, ilioinguinal nerve; PM, psoas major muscle; PMI, psoas minor muscle; QL, quadratus lumborum muscle.
acb-58-1-14-f3.tif
Fig. 4
Representative images show the type I pattern. CT, common trunk; IH, iliohypogastric nerve; II, ilioinguinal nerve; PM, psoas major muscle; QL, quadratus lumborum muscle; IV, iliac vessels from iliolumbar vessels.
acb-58-1-14-f4.tif
Fig. 5
Representative images show the type I pattern. Common trunk (CT) descends anteriorly to the iliac vessels (IV) from iliolumbar vessels. IH, iliohypogastric nerve; II, ilioinguinal nerve; PM, psoas major muscle; PMI, psoas minor muscle; QL, quadratus lumborum muscle.
acb-58-1-14-f5.tif
Fig. 6
Representative images show that the ilioinguinal nerve (II) originates from L3 along with the lateral femoral cutaneous (LFC) nerve. IH, iliohypogastric nerve; PM, psoas major muscle; QL, quadratus lumborum muscle.
acb-58-1-14-f6.tif
Fig. 7
Representative images show the double ilioinguinal nerve. II 1, the first ilioinguinal nerve exits through the psoas major muscle (PM); II 2, the second ilioinguinal nerve exits the lateral border of PM with terminal medial muscular (1) and lateral cutaneous (2) branches; IH, iliohypogastric nerve; PMI, psoas minor muscle; QL, quadratus lumborum muscle.
acb-58-1-14-f7.tif
Fig. 8
Representative images show the double ilioinguinal nerve. II 1, first ilioinguinal nerve with medial muscular (A) and lateral cutaneous (B) terminal branches; II 2, second ilioinguinal nerve; IH, iliohypogastric nerve; QL, quadratus lumborum muscle.
acb-58-1-14-f8.tif
Fig. 9
Representative images show that the ilioinguinal nerve (II) descends anteriorly to the iliac vessels (IV) from iliolumbar vessels. PM, psoas major muscle; QL, quadratus lumborum muscle.
acb-58-1-14-f9.tif
Table 1
Incidence of variation in the origin, absence, and branches of the iliohypogastric nerve (n=24)
Iliohypogastric nerve Number of cases
Origin
L1
L2		 18 (75.0)
4 (16.7)
Absent 2 (8.3)
Two terminal branches 4 (16.7)
Absences of two terminal branches 20 (83.3)
With three terminal branches 0 (0)

Values are presented as number (%).

Table 2
Incidence of variation in the origin, branches, and presence of the double ilioinguinal nerve (n=24)
Ilioinguinal nerve Number of cases
Origin
L1
L2
L3		 18 (75.0)
5 (20.8)
1 (4.2)
Absent 0 (0)
Single 20 (83.3)
Double 4 (16.7)
Two terminal branches 8 (33.3)
Absences of two terminal branches 16 (66.7)
Three Terminal branches 0 (0)

Values are presented as number (%).

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