|ECR 2019 / C-3464||
|Dynamic ultrasound of abdominal wall hernias|
Findings and procedure details
US is a technique with known limitations and highly dependent on the operator expertise. To accurately diagnose and give relevant information about an abdominal wall hernia, the radiologist must be aware of some key aspects:
1 - KNOW YOUR ANATOMY:
An understanding of abdominal wall and inguinal region anatomy is essential to a accurate sonographic diagnosis. The inferior epigastric artery (Fig. 2) at its origin is a critical anatomic landmark in differentiating indirect from direct inguinal hernias [1,5,6]. The inferior epigastric artery can usually be identified sonographically along the midposterior surface of the rectus abdominis muscle at a level about half way between the umbilicus and pubic symphysis while scanning in a transverse plane, it can then be traced inferiorly and laterally to its origin from the external iliac artery (Fig 3).
Indirect inguinal (Fig. 2)
Lateral to the inferior epigastric artery and superior to the inguinal ligament (into the inguinal canal). Indirect inguinal hernias can have 2 different appearances: sliding and nonsliding types. The sliding type has a relatively wide neck in comparison to the fundus, it is usually reducible and is more likely to contain bowel and other intraperitoneal contents (Videos 1 and 2). The nonsliding type has a relatively narrower neck, usually contain only fat tissue, are nonreducible, and are more difficult to diagnose sonographically than are sliding types (Fig. 4).
Located medial to the inferior epigastric artery and superior to the inguinal ligament (Hesselbach's triangle) (Fig. 2). It can be difficult to assess the relationship of the hernia neck to the inferior epigastric vessels (Video 3). An helpful tip is to evaluate the relationship of the hernia sac to the spermatic cord. Indirect inguinal hernias tend to lie along the anterior and lateral aspect of the spermatic cord, whereas direct inguinal hernia sacs tend to lie medial and posterior to the cord. Bulging of the conjoined tendon during Valsalva maneuver (posterior inguinal wall deficiency), is usually a precursor of a direct inguinal hernia [1,6,7].
Arise within the femoral canal (Fig. 5), located inferior to the inguinal ligament, lateral to the lacunar ligament, and usually medial to the femoral vein. The saphenofemoral junction, similar to the origin of the inferior epigastric artery for inguinal hernias, is the key landmark for identifying the femoral canal. Most contain only fat, and femoral hernias that contain bowel are almost always nonreducible and frequently strangulated as well [1,8].
Occurs along the linea semilunaris (the lateral border of the rectus abdominis), usually just superior to the inferior epigastric artery, at the end of the semilunar line where the spigelian fascia is penetrated and weakened by the inferior epigastric vessels [1,5,6]. In some cases, the spigelian fascia, like the linea alba, can become diastatic and widen. Because spigelian hernias pass through multiple layers of tendons, aponeuroses and fascias, projections of the hernia may also extend intraparietally between the layers of lateral muscles (transverse abdominis, internal oblique, external oblique) (Fig. 6).
Umbilical and paraumbilical hernias
Umbilical hernias usually occurs in children through a weak umbilical scar [1,9]. Paraumbilical hernia occurs through the linea alba just above the umbilicus or, less commonly, just below the umbilicus.
Between the xiphoid process and the umbilicus. Narrow neck in comparison to the size of the fundus and are thus usually not reducible  (Fig. 7).
2 - KNOW THE CLINIC AND THE PATIENT:
More than often, a few short clinical questions of the patient’s history give invaluable information.
The most common symptoms of a hernia include a swelling in the groin, heavy feeling in the abdomen, and discomfort in the abdomen regions, especially when coughing, lifting or bending over
Risk factors for developing an abdominal wall hernia include: advanced age; family history; chronic cough; chronic constipation; male gender; obesity; pregnancy; premature birth and low birth weight; previous abdominal surgery; previous inguinal hernia or hernia repair [1,4].
Signs and symptoms of a strangulated hernia include: nausea, vomiting or both; fever; sudden pain that quickly intensifies; a hernia bulge with recent color or temperature changes; constipation [1,5].
3 - KNOW THE TECHNIQUE:
A high-frequency linear transducer is usually preferred, at least a 7-MHz transducer. Using a 50-mm-long transducer is optimal because its larger field of view allows us to identify landmarks better ( virtual convex display can also be helpful). Only in very obese patients is a lower-frequency transducer necessary, usually a curved array [6,9].
The patient is initially scanned in the supine position and then examined in the upright position. Upright scanning is particularly important for evaluation of a femoral hernia [1,5,6,9]. Images are also routinely obtained during a particular position or maneuver that patients associate with their hernias.
Dynamic maneuvers include Valsalva maneuver, compression maneuver, and upright positioning. Dynamic maneuvers can cause the contents within a hernia to move, making them more conspicuous (Video 4). Hernias that appear to contain only fat during quiet respiration may be shown to contain bowel during the Valsalva maneuver [1,5].
The Valsalva maneuver is most easily achieved by asking the patient to seal their lips around the back of their hand and blowing. Compression is essential to assess reducibility and tenderness. Care must be taken not to apply too much compression with the probe because it may prevent herniation from occurring. Some patients state that the symptoms are only present in the upright position, this being particularly important in groin hernias. Delayed imaging in the upright position may be helpful in demonstrating the peritoneal fluid filling the hernial sac .
Do not forget the correlation with clinical aspects, as a very painful examination should raise a flag to the possibility of a complicated hernia.
Middle line hernias:
Identify the rectus abdominis, trying to display both medial margins in the ultrasound image (Fig. 8).
Depending if it is above or below the umbilicus, start in the epigastric region or umbilical region, respectively, and move slowly the transducer inferiorly along the linea alba (Fig. 9).
Repeat with the patient straining or performing the Valsalva maneuver.
If a hernia is identified, measure the neck and assess its reducibility by asking the patient to relax the abdominal muscles and gently applying compression with the transducer.
The patient may be examined in the standing position if the initial examination fails to reveal the hernia.
Begin at the level of the umbilicus in the lateral margin of the rectus abdominis (the linea semilunaris) in the transverse plane (Fig. 10).
Move slowly the transducer inferiorly along the linea semilunaris- spigelian hernia occurs just superior to the epigastric artery that usually can be identified as it passes deep in relation to the lateral border of the rectus abdominis muscle.
Perform the dynamic evaluation as explained in points 3 to 5 of Middle line hernias examination.
Indirect Inguinal Hernia:
The transducer is positioned where the inferior epigastric artery originates from the external iliac artery, it is rotated obliquely so that the medial aspect is inferior, along the long axis of the inguinal ligament (Fig. 11).
With the transducer positioned longitudinal to the inguinal canal and visualizing the inferior epigastric artery at its origin, an indirect inguinal hernia can be seen laterally to the inferior epigastric artery.
The herniated tissue then turns medially anterior to the inferior epigastric artery traversing the inguinal canal. An indirect inguinal hernia may enter the scrotum in a man (inguino-scrotal hernia).
Perform the dynamic evaluation as explained in points 3 to 5 of Middle line hernias examination.
Direct Inguinal Hernia:
The transducer is placed longitudinal to the inguinal canal and anterior to the inferior epigastric artery origin.
The transducer is moved medially to Hesselbach's triangle (Fig. 12).
Perform the dynamic evaluation as explained in points 3 to 5 of Middle line hernias examination. With the Valsalva maneuver, this hernia will protrude directly anteriorly toward the transducer.
The transducer is moved inferior to the inguinal ligament, and the area medial to the femoral vein is evaluated for femoral hernia (Fig. 13).
Perform the dynamic evaluation as explained in points 3 to 5 of Middle line hernias examination. Upright scanning is particularly important for evaluation of a femoral hernia. During the Valsalva maneuver, the femoral vein will normally dilate and should be differentiated from a femoral hernia.
4 - KNOW THE PITFALLS AND ANATOMICAL VARIATIONS:
Hernias that contain only fat are nearly isoechoic with surrounding tissues, and therefore, they are relatively inconspicuous.
Divarication (or diastasis) of the rectus abdominis muscles can be confused with a midline hernia (Fig. 14).
Surgical displacement or atrophy of the anterior abdominal wall muscles may allow an intra-abdominal visceras to be more easily palpable and present clinically as a possible hernia .
Also, a recently incised muscle that has not healed completely may present as a focal bulge whereas focal spasm in an abdominal wall muscle may present as a painful transient mass [1,9].
An epigastric hernia may be simulated by the xiphoid process [1,5,9].
Enlarged lymph nodes may be present in the inguinal region, being easily palpable and present clinically as a painful mass and possible hernia.
A saphenous varix can be confused clinically with a femoral hernia, particularly if it is thrombosed .
Focal collections after surgery (hematoma, abscess) or exuberant scars can clinically simulate an anterior abdominal wall incisional hernia [1,5,9]. Dynamic maneuvers can help differentiating these from an incisional hernia.
5 - REPORT WITH QUALITY:
The report should contain:
The presence or absence of a hernia
Precise location (side, type of hernia)
The specific dynamic components of the examination
The information about hernias reducibility is fairly important, as irreducible hernias may progress to become obstructed or strangulated [1,8] (Video 5). Obstructed hernias contain bowel loops that have become mechanically obstructed. Strangulated hernias are ischemic from physical constriction of their blood supply. Hernias that have relatively broad necks in comparison to their fundi rarely become obstructed or strangulated. In strangulated hernias, the lymphatics and veins become obstructed long before arterial flow decreases and arterial blood flow can still get into the strangulated hernia despite the venous and lymphatic outflow being interrupted [1,5].
The imaging signs that suggest complication of hernias are:
increased echogenicity of fat within the hernia sac (Fig. 15)
free fluid in the sac (Fig. 15)
fluid within the loops herniated (Fig. 15)
bowel wall thickening (Fig. 15)
abnormalities in Doppler flow in an intestinal loop, its mesenterium or omentum
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