10 - Ultrasonography of Normal Anatomy

Ultrasonography of Normal Anatomy #

Conventional surface Ultrasonography of the Normal Infantile Pylorus #

The sonographic appearance of infantile hypertrophic pyloric stenosis (IHPS) was first described by Teele and Smith (l977) (Chap. 23). Subsequently a number of authors investigated the sonographic features of the normal infantile pylorus.

In transverse section the normal pylorus presents as a hypoechoic ring with a central echogenic core, resembling a "doughnut" or "target" (Fig. 10.1). By comparing sonographic images with histological sections Blumhagen and Coombs (l98l) were able to show that the hypoechoic ring coresponded to the muscular layer in the wall, while the more echogenic central core was formed by the mucosal and submucosal layers, including the muscularis mucosae. On these views the overall diameter of the ring, as well as the thickness of the sonolucent muscular layer, could be measured. The width of the hypoechoic muscular layer in normal infants between the ages of 2 and 10 weeks, was found to be approximately 3.0 mm.

Fig. 10.1. Transverse ultrasonic section of normal pyloric ring showing "doughnut" (arrow). The hypoechoic ring is the muscular, and the inner echogenic core the mucosal/submucosal component of the ring

Strauss et al. (l98l), using a static gray-scale B-scan unit and subsequently a real-time unit with a 5MHz focused transducer, considered the infantile pylorus to be within normal limits if its overall diameter measured 1.5cm or less.

Longitudinal sections of the normal pylorus, on which the canal length can be measured, may also be obtained. In tracing the thin, hypoechoic muscular layer distally to the gastric outlet, Blumhagen and Noble (l983) found the "antral" muscular layer to vary from 1.5 to 3.0 mm in thickness in normal infants. Khamapirad and Athey (l983), using digital gray-scale static equipment and a 5MHz focused transducer, studied transverse and longitudinal sonographic images of the pylorus in 12 normal infants between the ages of one and 6 weeks. The normal pyloric ring was similar in appearance to the mass of IHPS but was less than 1.0cm in diameter.

In a control group of 24 normal infants ranging in age from 2 days to 32 weeks, Graif et al. (l984) found the mean and standard deviation for the transverse diameter to be 7.45 ± 2.2 mm. The mean single wall thickness was 2.3 mm with a standard deviation of ± 0.7 mm, while the mean length of the pylorus was 12.0 mm with a standard deviation of ± 3.7 mm.

Wilson and Vanhoutte (l984) measured what they called the true pyloric muscle length in l7 normal babies, and found the range to vary from 12.0 to 15.0 mm.

Stunden et al. (l986), in 88 normal infants under the age of 5 months, found the mean overall diameter of the pylorus to be 9.1 ± 1.1mm, the mean muscle thickness 1.6 ± 0.4 mm, and the mean canal length 8.3 ± 2.5 mm. These measurements were all obtained with the pylorus in its most contracted state. Additional information could be obtained when the pylorus was viewed in real-time. Normally the pyloric "canal" was seen to relax, allowing fluid to pass from stomach to duodenum. Some variation in overall diameter and muscle thickness did occur, probably representing alterations in muscle tone.

According to Stringer et al. (l986) the thickness of the inner echogenic layer, consisting of the mucosa, muscularis mucosae and submucosa, normally varies between 2.5 and 3.5 mm in infants.

Swischuk (l989) found the hypoechoic outer muscular layer to measure only 1.0 mm in normal infants. At times it was too thin to be measureable.

Discussion #

The anatomy of the pyloric ring may be determined accurately by means of non-ionizing, non-invasive sonography in normal human subjects. This has been done in a number of volunteers, in whom it was confirmed that the ring consists mainly of mucosal and submucosal tissues, surrounded by a relatively thin, peripheral muscular ring (Chap. 11). The relative paucity of muscular fibres in the pyloric ring suggests that it is unlikely to be a sphincter in the usually accepted sense of the word.

References #

  1. Blumhagen JD, Coombs JB. Ultrasound in the diagnosis of hypertrophic pyloric stenosis. J Clin Ultrasound l98l, 9, 289-292.
  2. Blumhagen JD, Noble HGS. Muscle thickness in hypertrophic pyloric stenosis: sonographic determination. Amer J Roentg l983, 140, 221-223.
  3. Graif M, Itzchak Y, Avigad I. et al. The pylorus in infancy: overall sonographic asssessment. Pediatr Radiol l984, 14, 14-17.
  4. Khamapirad T, Athey PA. Ultrasound diagnosis of hypertrophic pyloric stenosis. J Pediatr l983, 102, 23-26.
  5. Strauss S, Itzchak Y, Manor A, et al. Sonography of hypertrophic pyloric stenosis. Amer J Roentg l98l, 135, 1057-1058.
  6. Stringer DA, Daneman A, Brunelle F, et al. Sonography of the normal and abnormal stomach (excluding hypertrophic pyloric stenosis) in children. J Ultrasound Med l986, 5, 183-188.
  7. Stunden RJ, Le Quensne GW, Little KET. The improved ultrasound diagnosis of hypertrophic pyloric stenosis. Pediatr Radiol l986, 16, 200-205.
  8. Swischuk LE. Imaging of the Newborn, Infant and Young Child. Williams and Wilkins, Baltimore, 3rd ed l989, pp 394-413.
  9. Teele RL, Smith EH. Ultrasound in the diagnosis of idiopathic hypertrophic pyloric stenosis. New Engl J Med l977, 296, 1149-1150.
  10. Wilson DA, Vanhoutte JJ. The reliable sonographic diagnosis of hypertrophic pyloric stenosis. J Clin Ultrasound l984, 12, 201-204

Endoscopic Ultrasonography of the Layer Structure of the Gastric Walls #

B-mode and real-time ultrasonography is a well-established and valuable diagnostic procedure in the examination of various intra-abdominal conditions. However, factors such as obesity, alimentary gas and ribs may limit the resolution and field of view in conventional surface echography. Hisanaga et al (l980) developed a sonographic scanner which could be introduced into the lumen of the stomach; as the gastric walls are quite thin, adjacent organs such as the pancreas could be observed from within the gastric lumen.

Strohm et al. (l980) and DiMagno et al. (l980) were the first to incorporate an ultrasonic probe into the tip of an endoscope, thereby eliminating most of the barriers of conventional surface sonography and allowing endoscopic ultrasonic scanning (EUS) of internal organs in the vicinity of the oesophagus, stomach and duodenum. Initially Strohm et al. (l980) reported their experiences with a prototype radial scanning ultrasonic endoscope, and DiMagno et al. (l980) introduced a prototype of a linear arrayed ultrasonic endoscope. Later Strohm (l984) pointed out that better resolution was achieved with high frequency transducers which allowed successful visualization of the pancreas, liver, gall bladder and spleen in many cases. Using a high frequency transducer of 7.5 MHz, Nakazawa et al. (l984) called endoscopic ultrasonography a diagnostic tool of great value in gastroenterology.

Caletti et al. (l984 a) showed that the wall structure of the stomach could be studied by endoscopic ultrasonography and that the different layers could be identified. This was not possible with either conventional abdominal sonography or endoscopy alone. The gastric walls were best explored when the stomach was distended and filled with 300 to 500ml de-aired water. To facilitate distension and avoid peristaltic contractions, 2.0 ml propantheline bromide or 1.0 mg glucagon was administered intravenously. Initially 4 layers of different echogenicity were discerned. From within outwards these were: firstly, an echogenic layer considered to correspond to the mucosa and submucosa; secondly, a hypoechoic layer probably corresponding to the muscularis externa; thirdly, an echogenic layer indicating the serosa, and fourthly a hypoechoic layer due to the periserosal fat. The "antral" wall was thicker than that of the body of the stomach. A peristaltic contraction also caused wall thickening; this could mimic infiltration of the wall, e.g. by carcinoma, and was the reason for distending the lumen and paralyzing the walls by appropriate premedication.

At present there is substantial agreement that 4 and often 5 different layers can be identified in the gastric wall by means of endoscopic ultrasonography (Caletti et al. l984 b, l986; Aibe et al. l986; Bolondi et al. l986). From within outwards these are:

  1. a thin hyperechoic layer, corresponding to the mucosa
  2. a thin hypoechoic layer, the muscularis mucosae
  3. a wide hyperechoic layer, the submucosa
  4. a thin hypoechoic layer, the muscularis externa
  5. a thin hyperechoic layer, the serosa

Aibe et al. (l986) compared endoscopic ultrasonic images of the wall with histological sections of resected specimens. It was found that the first and second layers sometimes merged in the antral wall, together representing the mucosal epithelium, the lamina propria and the muscularis mucosae. Occasionally an extra thin layer was discernible in both the second and fourth layers. In the pyloric region of the stomach the fourth layer, i.e. the muscularis externa, was relatively thicker and the third layer, the submucosa, relatively thinner than in other parts of the stomach.

Seeing that the muscularis mucosae and the serosa are only a few micrometers thick, Bolondi et al. (l986) thought it was unlikely that they could produce such echographically evident layers; the acoustic reflection caused by interfaces created by different anatomical layers should also be taken into account. It was thought that any echogenic band should correspond not only to a distinct anatomical layer, but also to an interface between tissues of differing acoustic impedance. Accordingly Bolondi et al. (l986) postulated that the first layer was partially generated by ultrasound reflection at the interface between intraluminal fluid and the mucosa, while the fifth layer indicated the serosa/fluid reflection.

In pathological conditions the extension of lesions into the various layers of the gastric wall may be precisely determined by means of endoscopic ultrasonography. In patients with gastric ulceration of the "antrum", Strohm and Classen (l986) demonstrated considerable thickening of the wall and especially of the submucosa and muscularis externa. Benign gastric submucosal tumors could readily be localized between the different layers and could be distinguished from malignant processes. In cases of gastric carcinoma Aibe et al. (l986) showed that it was possible to determine whether the lesion was limited to the mucosa (as in early gastric carcinoma) or whether it had spread into the other layers of the wall. In many cases the depth of tumor invasion could be determined precisely (Ohashi et al. l989).

Discussion #

According to direct viewing by endoscopic ultrasonography, the “antral” wall is thicker than that of the body of the stomach; a peristaltic contraction also causes wall thickening.
The method may perhaps be utilized to investigate contractions of the pyloric sphincteric cylinder in subjects in whom the walls have not been paralyzed. As far as we are aware such an investigation has not yet been reported.

References #

  1. Aibe T, Fuji T, Okita K, et al. A fundamental study of normal layer structure of the gastrointestinal wall visualized by endoscopic ultrasonography. Scand J Gastroenterol l986, 21, Suppl 123, 6-15.
  2. Bolondi L, Caletti G, Casanova P, et al. Problems and variations in the interpretation of the ultrasound feature of the normal upper and lower GI tract wall. Scand J Gastroenterol l986, 21, Suppl 123, 16-26.
  3. Caletti G, Bolondi L, Labo G. Anatomical aspects in ultrasonic endoscopy of the stomach. Scand J Gastroenterol l984 (a), l9, Suppl 94, 34-42.
  4. Caletti G, Bolondi L, Labo G. Ultrasonic endoscopy: the gastrointestinal wall. Scand J Gastroenterol l984 (b), l9, Suppl 102, 5-8.
  5. Caletti G, Bolondi L, Zani L, et al. Technique of endoscopic ultrasonography investigation: esophagus, stomach and duodenum. Scand J Gastroenterol l986, 21, Suppl 123, 1-5.
  6. DiMagno EP, Baxton JL, Regan PT, et al. Ultrasonic endoscope. Lancet l980, l, 629-631.
  7. Hisanaga K, Hisanaga A, Nagata K, et al. High speed rotating scanner for transgastric sonography. Amer J Roentg l980, 135, 627-629.
  8. Nakazawa S, Sugiyama H, Kimoto E, et al. Specifications of endoscopic ultrasonography. Scand J Gastroenterol l984, l9, Suppl 94, 1-6.
  9. Ohashi S, Nakazawa S, Yoshino J. Endoscopic ultrasonography in the assessment of invasive gastric cancer. Scand J Gastroenterol l989, 24, 1039-1048.
  10. Strohm WD, Phillip J, Classen M, et al. Ultrasonic tomography by means of an ultrasonic fiberendoscope. Endoscopy l980, 12, 241-244.
  11. Strohm WD. Limits of conventional abdominal sonography and features of endoscopic sonography. Scand J Gastroenterol l984, l9, Suppl 94, 7-12.
  12. Strohm WD, Classen M. Benign lesions of the upper gastrointestinal tract by means of endoscopic ultrasonography. Scand J Gastroenterol l986, 21, Suppl 123, 41-46.
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