Intra-abdominal adhesions in ultrasound. Part I: The visceroperitoneal bordeline, anatomy and the method of examination.

It needs to be emphasized that ultrasonography is a primary test performed in order to evaluate the abdominal wall and structures located in their vicinity. It allows for the determination of the anatomy and lesions in this localization. Thorough knowledge concerning the ultrasound anatomy of the tested structures constitutes a basis of all diagnostic successes. Therefore, this part of the article is devoted to this subject matter. The possibility to diagnose intra-abdominal adhesions with ultrasound is underestimated and rarely used. The aim of this paper is to discuss and document the ultrasound anatomy of the posterior surface of the abdominal wall as well as to present techniques directed at the detection of adhesions, in particular the visceroperitoneal ones. The posterior surface of the abdominal wall constitutes an extensive tissue area of complex structure, with folds and ligaments surrounded by various amounts of the epiperitoneal fat. In some places, this tissue separates the components of the fascia and peritoneum complex. The ultrasound manifestation of this complex is two hyperechogenic lines placed parallelly to each other in the places where they are not separated by the accumulated adipose tissue. Another factor which separates the peritoneum from the viscera is of dynamic character. It is a so-called visceral slide induced by easy or deep breathing. Its size should not be lower than 1 cm and the deflections gradually and symmetrically diminish from the epigastric to hypogastric region. Last but not least, the evaluation of the reciprocal relation of the abdominal wall with viscera may be aided by rhythmical manual compressions on the abdominal wall (ballottement sign) performed below the applied ultrasound transducer. During this test, the size of the visceral slide in relation to the abdominal wall is observed. The maneuver is usually performed in uncooperative patients or those with shallow breath. The authors' own experiences indicate that the effectiveness of the test is increased when lower extremities are moderately bent. This relaxes the muscle tension in the anterior wall of the abdomen. To assess the condition of these structures, linear transducers with the frequency of 5-9 MHz prove the most appropriate. In obese patients, a convex transducer with the frequency of 3.5-5 MHz also may be used. The acoustic focus should be set on the borderline of the abdominal wall and viscera and in order to visualize the changes it might be helpful to use harmonic, compound and XRes imaging. When examining the abdominal wall, the cross and longitudinal sections should be made. The complete evaluation of the visceroperitoneal borderline includes nine segments - three in the epigastrium, three in the mid-abdomen and three in the hypogastrium.

The majority of ultrasonographers still share the belief that ultrasound (US) tests are of little usefulness in detecting intra-abdominal adhesions. Above all, this situation results from poor native literature on this matter(. This study has been started in order to popularize this topic and share new observations.

First of all, it needs to be emphasized that ultrasonography is a crucial test performed in order to evaluate the abdominal wall and structures located in their vicinity. It allows for the determination of the anatomy and lesions in this localization. The basis of all diagnostic successes is thorough knowledge concerning the ultrasound anatomy of the tested structures. Therefore, this part of the article is devoted to this subject matter.

On the posterior surface of the abdominal wall of, mainly, the umbilical region, two hyperechogenic lines placed parallelly to each other may be visualized by using linear, high-frequency transducers. They correspond to: the transverse abdominal fascia (the upper hyperechogenic line) and the parietal peritoneum (the lower hyperechogenic line) – fig. 1. Fig. 2 presents the same, but enlarged image. The topography becomes more complicated in the median line, when the transducer is moved from the umbilicus to the diaphragm. The relation of the fascia and peritoneum complex always changes here as a result of gradual cephalad thickening of the epiperitoneal fat which clearly separates these structures and surrounds the round ligament of the liver (fig. 3 A). In the right and left hypochondriac regions, below the diaphragm the described structures are also separated by the epiperitoneal fat layer, which either is less thick (fig. 3 B) or does not exist at all (fig. 3 C). The situation is even more complicated in the area of the umbilicus. It is difficult to select the presented image here since seven longitudinal, anatomical structures converge in this region (fig. 4). The median umbilical fold reaches the umbilical ring from the bottom along the median line and the symmetrical medial and lateral umbilical folds run from two oblique directions(. The omphalomesenteric remnant runs above the right lateral umbilical fold and is centered into the median part of the right iliac fossa. It is rarely detectable in US, though(. Finally, the round ligament of the liver reaches the umbilicus from the oblique superolateral side. Moreover, the epiperitoneal fat is also located between the umbilicus and retropubic space (Retzius’ space) stretching in the form of a triangular pyramid (fig. 5).

Fig. 1

The divided sonogram presents the right (P) and left (L) sides of the abdominal wall with two, barely visible, hyperechogenic lines of parallel course (marked with arrows), which correspond to the transverse fascia (upper line) and parietal peritoneum (lower line). T – viscera

Fig. 2

An enlarged image of the abdominal wall. The upper arrow shows the transverse fascia and the lower one – parietal peritoneum. T – viscera

Fig. 3 A

Divided sonogram. On the left – the middle epigastric region. The upper arrow shows the transverse fascia and the lower one – parietal peritoneum. Between the structures there is a thick layer of epiperitoneal fat (t). On the right side of the sonogram, above the middle part of the right liver lobe, the arrows point to a gradual separation of the transverse fascia from the parietal peritoneum by the epiperitoneal fat (t)

Fig. 3 B

The parasagittal section of the peripheral fragment of the right liver lobe. The arrows indicate the place of the separation of the fascia – peritoneum complex by the epiperitoneal fat (t). Markings: msz – external oblique muscle, msw – internal oblique muscle, mp – transverse muscle, W – liver

Fig. 3 C

The parasagittal section in a location similar to the one presented in fig. 3 B, but in a slim patient. The arrows point to the close contact of the fascia – peritoneum complex components which forms one hyperechogenic line as a result of the lack of the epiperitoneal fat. Markings: msz – external oblique muscle, msw – internal oblique muscle, mp – transverse muscle, W – liver

Fig. 4

The umblilicus (P) is presented in two sections. The anatomic structures presented in the previous figures are not distinguished easily in this location

Fig. 5

The two sections of the hypogastric region present the epiperitoneal fat (t) which separated the components of the fascia – peritoneum complex (upper arrows – the transverse fascia, lower arrows – the parietal peritoneum)

The arrangement of folds and ligaments surrounded by the epiperitoneal fat, which is described above, is presented in fig. 6. The quantity of the fat varies in individual persons. The aforementioned fat separates the transverse abdominal fascia from the parietal peritoneum. One needs to be cautious not to mistake the transverse tendinous intersections, which run through the upper fragments of the bellies of the rectus abdominis muscle, for a scar. There are three intersections in each muscle usually reaching the level of the umbilicus (fig. 7). A tendinous intersection in the lower part of these bellies is a rare variant. Despite being only briefly discussed in medical literature(, the anatomical data presented above, according to the authors of this article, significantly influence the identification of visceroperitoneal adhesions and avoidance of errors.

Fig. 6

The arrangement of the epiperitoneal fat which separates the fascia – peritoneum complex on the posterior surface of the abdominal wall. Markings: 1 – median umbilical fold, 2 – medial umbilical fold, 3 – lateral umbilical folds, 4 – omphalomesenteric remnant, 5 – round ligament, P – urinary bladder

Fig. 7

The cross section of the abdominal wall at the level of the tendinous intersection in the rectus abdominis muscle (bigger arrow pointed downwards). The smaller arrows indicate the fascia – peritoneum complex

Another way of separating the abdominal wall from the intra-abdominal contents is a so-called visceral slide. It is a cephalocaudal movement of viscera, induced by easy or deep respiration, which gradually diminishes from the region of the epigastrium to the hypogastrium (with the transducer applied longitudinally). The deflections on both sides of the median line should be the same. At easy breathing, the size of the visceral movement ranges from 1 to 2 cm. Deep respiration, however, increases the deflections to even 5 cm (fig. 8). Some examiners evaluate the mobility of the viscera with the transducer applied transversely. In normal conditions, the visceral shift should not be lower than 1 cm. Last but not least, the evaluation of the reciprocal relation of the abdominal wall with viscera may be aided by rhythmical manual compressions on the abdominal wall (ballottement sign) performed below the applied US transducer. During this test, the size of the visceral slide in relation to the abdominal wall is observed. The maneuver is usually performed in uncooperative patients or those with shallow breath. The authors’ own experiences indicate that the effectiveness of the test is increased when lower extremities are moderately bent. This relaxes the muscle tension in the anterior wall of the abdomen.

Fig. 8

The divided sonogram presents a normal viscera slide – 15 mm (arrows), which is induced by easy respiration

To assess the condition of these structures, long, linear transducers with the frequency of 5–9 MHz prove the most appropriate. In obese patients, a convex transducer with the frequency of 3.5–5 MHz may also be used. The acoustic focus should be set on the borderline of the abdominal wall and viscera and in order to visualize the changes it might be helpful to use harmonic, compound and XRes imaging. So as to thoroughly evaluate the condition of the abdominal wall, one needs to examine all the regions of the epigastrium (right hypochondriac, epigastric, left hypochondriac), mid-abdomen (right lateral, umbilical, left lateral) and hypogastrium (right iliac, hypogastric, left iliac) – in total, nine segments of the abdominal wall( when scanning in a sagittal plane. Furthermore, one should always bear in mind that the scars after surgical incisions as well as the sites where surgical instruments were inserted (including the umbilicus) must be examined.

The aforementioned hyperechogenic lines and the size of the visceral slide at easy and maximum deep respiration are subject to evaluation. The slide in both tests should not be lower than 1 cm. The said examination parameters must be compared in both sides of the abdomen. By using a shortened examination, one assesses only the area of the postoperative scars and the condition of the abdominal wall in a similar location on the other side. In case of doubts or difficulties in interpreting the images, the aforementioned ballottement sign may be used(. By using the described technique, one assesses the extensiveness of detected adhesions in relation to the abdominal wall (mapping) – sonotopogram.

Conclusion

The posterior surface of the abdominal wall constitute an extensive tissue area of complex structure, which is connected with the presence of folds and ligaments surrounded by various amounts of the epiperitoneal fat. This tissue separates the components of the fascia and peritoneum complex. Another factor which separates the peritoneum from the viscera is a so-called visceral slide induced by easy or deep breathing. Its size should not be lower than 1 cm. To assess the condition of these structures, linear transducers with the frequency of 5–9 MHz prove the most appropriate. The complete evaluation of the visceroperitoneal borderline encompasses nine segments of the anterior abdominal wall.