|ESSR 2019 / P-0019|
|A practical guide to identify the major sensory nerves of the groin on ultrasound|
Imaging findings OR Procedure Details
Nerve identification using the appropriate landmarks on ultrasound;
1.Ilioinguinal and iliohypogastric nerves.
-Originating from the TH12-L1 nerve roots, both nerves run subperitoneally until they pierce the abdominal wall muscles, at a level superior to the anterior superior iliac spine (ASIS). At this point, the nerves can be picked up on ultrasound.
-Landmarks: starting on the ASIS, a linear high frequency probe is placed in a transverse plane medial to it and shifted 3 to 5 cm superior. The muscle bellies of the internal oblique abdominal muscle (IO) is recognized lying superficial to the transverse abdominal muscle (TA) . Between these layers, splitting of the fascia is visualized and the IH nerve is usually seen running medially to the II nerve in this plane ( Fig. 1 ).
-Infiltration: using an in-plane approach, the needle is inserted laterally aiming to the fascial plane between the IO and TA.
2. Genitofemoral nerve.
-Originating from the L1-L2 nerve roots, the nerve runs superficial to the psoas muscle and splits into a femoral and a genital branch above the inguinal ligament. The genital branch enters the inguinal canal through the deep inguinal ring, lateral to the inferior epigastric artery (IEA).
-Landmarks: The inguinal ligament stretches between the ASIS and the pubic tubercle. A linear high frequency probe is placed parallel to the inguinal ligament and shifted upwards along the external iliac artery (EIA) lying deep to the ligament. The IEA emerges from the EIA superficially, running medially towards de deep portion of the rectus abdominis muscle. The genital branch sits lateral to the IEA origin ( Fig. 2 ).
-Infiltration: using an in-plane approach, the needle is inserted laterally pointing to the lateral side of the IEA origin.
3. Obturator nerve.
-Originating from L2-L4 nerve roots, the nerve pierces the psoas muscle, runs through the obturator foramen and splits into an anterior and posterior branch. The branches are separated by the adductor brevis (AB) muscle at the level of the thigh.
-Landmarks: a linear high frequency probe is placed in a transverse plane on the pectineus muscle covering the medial part of the superior ramus of the pubic bone. The probe is shifted downwards, revealing the adductor muscles, the adductor longus (AL) lying superficial to the adductor brevis muscle and the deeper adductor magnus muscle (AM). The anterior and the posterior branches are located in the fascial plane superficial and deep to the AB respectively ( Fig. 3 ).
-Infiltration: using an in-plane approach, the needle is inserted laterally pointing towards the anterior branch in the fascial plane between AL and AB. Tilting the needle point deeper towards the fascial plane between AB and AM allows reaching the posterior branch.
4. Pudendal nerve.
-Originating from the S2-S4 nerve roots, the nerve travels distally and posteriorly to exit the pelvis through the greater sciatic notch. It then runs between the sacrotuberous (STL) and sacrospinous (SSL) ligaments at the level of the ischial spine (IS) with the internal pudendal artery (IPA) on the lateral side of it. This is the point to pick up the nerve on ultrasound, although it runs further distally into Alcock’s canal.
-Landmarks:: a linear high frequency probe (or low frequency curved array probe in the obese) is placed in a transverse plane on the ischial tuberosity and shifted upwards to reveal the STL as a moderate hyperechoic line superior to it. The IS is the bright hyperechoic straight line, continuous with the posterior acetabulum, lateral to the moderate hyperechoic SSL. At this position, color Doppler locates the IPA pulsations. The pudendal nerve sits medial to the artery ( Fig. 4 ).
-Infiltration: using an in-plane approach, the needle is inserted medially and directed towards the medial aspect of the IPA.
Thematically related posters
ESSR 2019 / P-0138
US of the common peroneal nerve and ITS two terminal branches: how to do it; a detailed didattic approach