Abdominal wall ultrasound

Layers of the abdominal wall as seen on high frequency ultrasound. Fat (F); external oblique muscle (EO); internal oblique muscle (IO); transversus abdominis muscle (TA);  rectus abdominis (RA); peritoneum (arrow); aponeurosis of external oblique (white arrowhead) and anterior part of the aponeurosis of internal oblique contributing to the rectus sheath (black arrowhead).

External oblique muscle

The outermost muscular layer of the lateral abdominal wall is made up from the external oblique muscles.  These two muscles arise from the outer parts of the lower 7 to 8 ribs on either side and extends anteroinferiorly to the anterior aspect of the iliac crests, pubic tubercle and to the linea alba in the midline. Towards the midline the muscle forms an aponeurosis.

Note that the direction of the fibres of the external oblique muscle (EO) can be appreciated using CT. Also labelled, rectus abdominis (RA); linea semilunaris (white arrowhead); linea alba (black arrowhead) and spermatic cord (arrow).

Inguinal ligament

At its most inferior aspect the aponeurosis of external oblique folds back on itself to form the inguinal ligament and inguinal canal. This is an important component of the anterior abdominal wall since it contains two potential openings for the development of hernias. The first opening is the deep inguinal ring traditionally described as lying immediately lateral to the inferior epigastric artery, though in several studies(1,2,3) this has been shown to be variable. The second opening is the superficial inguinal ring located just superolateral to the pubic tubercle.

The location of the inguinal ligament.

Oblique coronal reconstruction demonstrating the inguinal ligament (white arrowheads); the pubic tubercle (black arrowhead) and the anterior superior iliac spine (open arrowhead).


1. Conaghan P, Hassanally D, Griffin M, Ingham Clark C. Where exactly is the deep inguinal ring in patients with inguinal hernias? Surg Radiol Anat. 2004;26(3):198-201.

2. Andrews BT, Burnand KG, Ferrar D. Putting a finger on the deep inguinal ring. J R Coll Surg Edinb. 1996;41(2):90-92.

3. Sanjay P, Reid TD, Bowrey DJ, Woodward A. Defining the position of deep inguinal ring in patients with indirect inguinal hernias. Surg Radiol Anat. 2006;28(2):121-124.

Internal oblique muscle

The origin of this muscle is inferiorly and therefore the fibres run superiorly and anteriorly in contrast to those of external oblique. The origin is from the anterior aspect of the iliac crest, lateral aspect of the inguinal ligament and thoracolumbar fascia. The insertion is at the linea alba, the pubis and the lower three ribs.

Axial CT image demonstrating the internal oblique muscle (arrow) and its aponeurosis (arrowhead) which splits to cover rectus abdominis anteriorly and posteriorly.

Transversus abdominis muscle

This lies deep to the muscles mentioned previously. Fibres run from the lower 6 ribs and the thoracolumbar fascia to the linea alba. The inferior fibres run to insert at the pubis with the internal oblique muscle.

Transversus abdominis muscle (TA); the transversus abdominis plane (arrowhead); internal oblique (IO); and external oblique (EO).The transversus abdominis plane is important in the anaethetisation of the abdominal wall post operatively since this is the plane through which the the intercostal and subcostal nerves pass. The associated arteries and veins follow the same course as the nerves. Inferiorly, the iliohypogastric and ilioinguinal nerves travel in this plane, but pass through internal oblique and the external oblique aponeurosis anteriorly.

Rectus sheath

This surrounds the rectus abdominis muscle on either side which arises from the pubic symphysis and pubic crest and inserts at the xiphoid process and 5th, 6th and 7th costal cartilages. Also, within the sheath are, amongst other vessels, the inferior epigastric vessels. The anterior margin of the sheath is formed by the external oblique aponeurosis and  the anterior part of the internal oblique aponeurosis. The posterior margin is formed from the posterior part of the internal oblique aponeurosis and the transversus abdominis aponeurosis. The posterior layer ends at the arcuate line or linea semicircularis equidistant from the pubic symphysis and umbilicus.  Additionally, the sheath ends superiorly at the superior insertions of the contributing muscles. The linea semilunaris indicates the most lateral extent of the rectus abdominis.

A midline transverse section US view of the linea alba (arrow) and the rectus abdominis muscles on either side (RA), the anterior (black arrowhead) and posterior (white arrowhead) components of the rectus sheath are shown

Inferior epigastric artery

The inferior epigastric artery is an important artery of the abdominal wall and arises from the external iliac artery and passes up via the transversalis fascia to the arcuate line where is pierces the rectus abdominis. Superiorly the rectus abdominis is supplied by the superior epigastric artery, a continuation of the internal thoracic artery.

Imaging of these arteries is frequently performed prior to breast reconstruction. Previously more common transverse rectus abdominis myocutaneous (TRAM) flaps are being replaced by deep inferior epigastric artery (DIEA) or deep inferior epigastric artery perforator (DIEP) flaps due to lower complications associated, especially with the latter1-3. Preoperative evaluation by angiography has been shown to reduce the time of surgery and may have an effect on complications4.

CT angiography is now the preferred method of imaging the inferior epigastric vessels, superior to US when used preoperatively in breast reconstruction5, but with the disadvantage of ionizing radiation. Despite a possible dose as low as 6mSv6 using CT, MR is being investigated to assess the inferior epigastric vessels7.

Three images of the inferior epigastric arteries are shown above.

1. Coronal MIP demonstrating the normal course of the inferior epigastric arteries.

2. Thick slab axial MIP image demonstrating the deep inferior epigastric artery perforator branches.

3. The inferior epigastric vessels (colour) within the rectus abdominis.


1. MINQIANG X, LANHUA M, JIE L, DALI M, JINGUO L. The value of multidetector-row CT angiography for pre-operative planning of breast reconstruction with deep inferior epigastric arterial perforator flaps. Br J Radiol. 2009:29140440.

2. Ghattaura A, Henton J, Jallali N, et al. One hundred cases of abdominal-based free flaps in breast reconstruction. The impact of preoperative computed tomographic angiography. Journal of Plastic, Reconstructive & Aesthetic Surgery. In Press, Corrected Proof. Available at: http://www.sciencedirect.com/science/article/B7XNJ-4XR60NK-1/2/d1466f93a91f8e3ce93543fa49f27d61 [Accessed March 27, 2010].

3. Phillips TJ, Stella DL, Rozen WM, Ashton M, Taylor GI. Abdominal Wall CT Angiography: A Detailed Account of a Newly Established Preoperative Imaging Technique1. Radiology. 2008;249(1):32-44.

4. Smit JM, Dimopoulou A, Liss AG, et al. Preoperative CT angiography reduces surgery time in perforator flap reconstruction. Journal of Plastic, Reconstructive & Aesthetic Surgery. 2009;62(9):1112-1117.

5. Rozen WM, Phillips TJ, Ashton MW, et al. Preoperative imaging for DIEA perforator flaps: a comparative study of computed tomographic angiography and Doppler ultrasound. Plast. Reconstr. Surg. 2008;121(1):9-16.

6. Rozen WM, Whitaker IS, Stella DL, et al. The radiation exposure of Computed Tomographic Angiography (CTA) in DIEP flap planning: low dose but high impact. Journal of Plastic, Reconstructive & Aesthetic Surgery. 2009;62(12):e654-e655.

7. Neil-Dwyer J, Ludman C, Schaverien M, McCulley S, Perks A. Magnetic resonance angiography in preoperative planning of deep inferior epigastric artery perforator flaps. Journal of Plastic, Reconstructive & Aesthetic Surgery. 2009;62(12):1661-1665.

Abdominal wall MR

MR anatomy of the abdominal wall demonstrating the three flat muscles (short arrow); the linea semilunaris (open arrow); rectus abdominis (black arrowhead); the linea alba (open arrowhead); the epigastric vessels (long arrow); the quadratus lumborum muscle (black arrow) and the erector spinae (white arrowhead).