Abdominal and groin hernias
Herniography showing a large right indirect inguinal hernia (arrow)
Hernias fall into two broad categories: large hernias that are clinically obvious but where an assessment of the abdominal wall is important to plan surgical repair, and suspected hernias where the clinical findings are not specific. Examples of this would be localised abdominal wall pain and the possibility of a second hernia in the contralateral groin.
CT is an excellent study of large parastomal and incisional hernias to show the size of the defect and the residual abdominal wall musculature. ultrasound can do this, but is often impeded by stoma bags and with large hernias it is difficult to measure accurately the size of the defect. If a hernia has become incarcerated, CT is the best examination to view its contents and assess bowel wall inflammation and viability.
Herniography(1) is an invasive procedure involving the intra-peritoneal injection of water soluble contrast, followed by screening in the erect or semi-erect position with coughing to look for filling of a hernial sac. It probably remains the gold standard for demonstrating the sac, but has been superseded by ultrasound for the routine examination of suspected groin hernias. Unusual hernias, such as obturator hernias, may be seen with herniography. Dynamic MRI has shown that levator ani hernia may be more common than suspected (2), but for most cases ultrasound is sufficient.
A key advantage of Ultrasonography is realtime imaging during stress - i.e. coughing or Valsalva, in both the supine and standing positions. It is possible to image groin hernia with MRI using fast sequences during Valsalva, but often coughing is needed to show small hernias, and the majority of hernias diagnosed on imaging are of course small, otherwise they would be clinically obvious.
During ultrasound of the groin the landmarks of the inguinal canal have to be identified and observed during stress manoeuvres, when small hernias will only be visible. Weakness of the posterior canal wall may also be observed in groin pain (3).
Unusual lesions, such a lipoma of the cord, may be found. The same principles are applied to examination of the abdominal wall to find small incisional hernias, or hernia at unusual sites, such as Spigelian hernia.
The visibility of any mesh inserted as part of the repair varies, but ultrasound is useful to exclude small post operative collections etc. in patients having pain after surgery.
Reference List
(1) Ekberg O. Inguinal herniography in adults: technique, normal anatomy, and diagnostic criteria for hernias. Radiology 1981; 138(1):31-36.
(2) Gearhart SL, Pannu HK, Cundiff GW, Buller JL, Bluemke DA, Kaufman HS. Perineal descent and levator ani hernia: a dynamic magnetic resonance imaging study. Dis Colon Rectum 2004; 47(8):1298-1304.
(3) Orchard JW, Read JW, Neophyton J, Garlick D. Groin pain associated with ultrasound finding of inguinal canal posterior wall deficiency in Australian Rules footballers. Br J Sports Med 1998; 32(2):134-139.