Radiological anatomy of the colon in children.
Dosed hydrostatic barium enema.
Department of Pediatric Radiology of 1st city Hospital, Minsk, Belarus.
State Geriatric Center, Netanya, Israel.
Levin M, MD, PhD, DSc, radiologist.
Amnon ve-Tamar, 1/2, Netanya, 42202, Israel.
The purpose of this work was to offer the accurate method of X-ray examination of the rectum and colon.
Material and method. We analyze the results of X-ray investigation of the colon in 65 children of different ages, in which the pathology of the colon and anorectum was not detected.The hydrostatic dosage barium enema standardized by hydrostatic pressure, the capacity of the colon in each case with correction of the projection magnification was produced in them.
Results. The true width of the rectum, the different parts of the colon and anal canal length in different age groups were determined. Method for analysis of X-ray data was proposed.
Conclusion. Dosed hydrostatic barium enema is an accurate method for estimating the magnitude of the rectum and colon, as well as the state of the puborectalis muscles. It can be used for scientific analysis of the functional constipation and anorectal malformation.
In the 21st century, X-ray study of the colon has been used much less frequently than before, while other methods (manometry, ultrasound, scintigraphy, study with radiopaque markers, defecograpgy, CT and MRI) began to play important role in the diagnostic process. However, barium enema is a main method in the determination of the rectal and colon dimensions in Hirschsprung's disease, anorectal anomalies and functional constipation. The bowel management program entails daily treatments with adjustments of medications and doses based on clinical response and abdominal X-ray findings . In most cases assessment of the colon is empirical, because it is impossible to determined precisely about the expansion of any parts of the colon without knowing of their normal limits. Meunier et al in 1984 proposed to measure the width of the rectum on the basis of the recto-pelvic ratio (RPR). The RPR was obtained by dividing the diameter of the rectal width by the diameter of the linea transversa (T) of the pelvis . The mean RPR in patients with fecal impaction was 0.68 (range 0.32-0.83). The rectal width in control was 0.52 with upper limit of 0.61 . This method has not found practical application, as the normal and pathological indicators overlap.
Gladman M.A. et al, who examined adults patients, concluded that the maximum limit of normal width of the rectum is 6.3 cm [4,5]. The width of the rectum increases with age as a result of increasing of the pelvic size and the diameter of stool accumulating in the rectum. This means that the maximum size of the rectum correspond to the maximum size of the stool. It is enough to draw a circle with a diameter of 6.3 cm, to ensure that such a diameter of stool may not be the norm for an undersized girl of 18 years, or even for a man of high growth.
The purpose of this work was to offer the most accurate method of X-ray examination of the rectum and colon.
Material. In the years 1980-1983 in the Belarusian center of pediatric surgery 589 studies of the colon were produced. This was the period when the barium enema has been the standard method for the diagnosis of acute (acute appendicitis) and chronic abdominal pain, anemia, and for localization of space-occupying lesions in the abdominal cavity. Sixty five studies of the total number of patients were selected where the barium enema by our proposed procedure was carried out. In them on the basis of clinical, manometric studies and/or rectoscopy no diseases of the rectum and colon were found.
Method. The study was conducted by the dosage hydrostatic barium enema [17,18]. In infants the bowel filling was made from a rubber bulb. In other cases a barium was introduced from the synthetic graded bag. The bottom of this bag at the beginning of the study was located 40 cm above the deck of the table. A barium was introduced into the colon up to the reflux into the terminal ileum. The difference of barium volume in the bag before and after the colon filling corresponds to the colon volume. The radiopaque restrictor (marker) is strung on the tip of the enema. It is in contact with the anus during the study. At least two radiographs (AP and lateral) have been made after the filling of the colon. On direct radiograph the widths of the different parts of the colon are measured (Figure 1). On a lateral radiograph were measured the maximum width of the vertical portion of the rectum, as well as interval not containing contrast medium between the rectum and a contrast marker on the posterior contour of the tip (Figure 2).
Figure 1. Direct radiography of the abdomen and scheme to it.
The locations of the measurements of the different parts of the colon are marked: (a) the height of the cecum; widest part of each section were measured: (b) - cecum, (c) - ascending colon, (d) - transverse colon (e) - descending colon, (f) - sigmoid colon.
Figure 2. X-ray imaging of the anal canal in the lateral projection (A) and scheme to it (B).
А. A child 11 years. The axis of the anal canal (AC) is shifted forward with respect to the axis of the rectum. Black arrow – rectal width, white arrow – anal canal length.
B. The scheme: OK - axis of vertical branch of the rectum; NM - axis of horizontal branch of the rectum; AC - axis of anal canal; P - pubis; PRM – puborectalis muscle, P – pubis, R - radiopaque marker near the anus.
Method of the analysis radiographs. The area between the marker (anus) and the rectum, which does not contain a contrast agent is equal to the anal canal length measured by the manometric method. Consequently, this is a zone of the anal canal contraction. We present in the table only the results of measuring the width of the rectum and anal canal length, which are necessary for the analysis of radiographs in patients with constipation (table).
In order to compare the different studies as well as studies of the same patient at different ages, we calculate the constant (C), which is the integral characteristic of the colon value. It is calculated using the following formula:
V× R × к
C = -------------
Where: C – constant, V – colon volume (ml);
R – rectal width (cm);
к – projection distortion factor, which is the ratio of the true width of the marker to its image on the radiograph;
h – patient height (cm).
In newborns with a high intestinal obstruction the colon width was the same on all extent. The true width is equal to 0.7 cm. In infants with normal digestive tract the width of the colon ranged from 1 to 1.5 cm with no significant differences between its parts. With the growth of the child occurs an expansion of all parts, always with the same ratio between them. Sigmoid colon is always the narrower part. The descending colon is somewhat broader of the sigmoid colon. The cecum and ascending colon are the widest sections. The rectum and transverse colon width take an intermediate position (Fig. 3).
Figure 3. Scheme of expansion of the different parts of the colon and rectum in different age groups:
1-sigmoid colon; 2-descending colon; 3- rectum; 4 - transverse colon; 5 - cecum; 6 - ascending colon.
The loop of the sigmoid colon is always located in the pelvis. The dome of the cecum in infants has a symmetric semi-oval shape. In older age groups, sometimes a deformation of the dome appears. Appendix in 80% of infants was filled, but in other age groups, only in 39% of cases. Haustration of the colon from 4 years appears, at first in the right half of the colon, and then in the left.
The rectum in babies looks rectilinear. Its axis practically coincides with the axis of the anal canal (Figure 4). With age, the bending of the rectum forward at the level of S-5 is formed (see Figure 2). Consequently, the rectum is actually represented by two parts: vertical and horizontal.
Between the horizontal part of the rectum and the anal canal an acute (anorectal) angle is formed. In children with a normal physique the retro-reсtal space, i.e., the interval between the posterior wall of the rectum and the anterior surface of the sacrum increases from 0.1 cm in the first year of life, up to 0.5 cm in the older age group.
Figure 4. The lateral radiograph of the 4 months baby.
The anal canal is a direct continuation of the rectum. The penetration of contrast agent into the top of the anal canal in front of the enema tip determined while the posterior wall is pressed tightly to the tip.
The length of the rentgen negative space between the rectum and the marker around the anus was 1.7 cm in newborns, and increased up to 3.9 cm in older children. During the barium enema a barium penetration in the upper part of the anal canal in front of the enema tip is observed. At this time, the posterior wall of the anal canal at this level is tightly pressed against the tip. This pattern continued less than one minute and then the barium disappeared from the anal canal. Such a situation arose during barium enema from one to three times. Capacity, i.e. the volume of the colon, increased from 562 +/- 38 ml in children of the first year of life up to 1050 +/- 32 ml in older children. Integral characteristic quantities of the colon (C) are in the range 19-31.
In most cases, the magnitude of the colon evaluated empirically based on previous experience. However, it is impossible to determine precisely about the expansion of any parts of the colon without knowing of their normal limits. For example in the article of Woody and co-workers on a direct radiography of the abdomen, which is cited as an example of the norm, a significant extension and elongation of the sigmoid colon is defined. It is wider than the descending colon and extends beyond the pelvis .
Meunier et al in 1984 proposed to measure the width of the rectum on the basis of recto-pelvic ratio (RPR). The RPR was obtained by dividing the diameter of the rectal width by the diameter of the linea transversa (T) of the pelvis (figure 5) .
Figure 5. Determination of the RPR. The maximal pelvis diameter (linea transversa – T) and the rectum diameter (R) at this level are shown .
The mean RPR in patients with fecal impaction was 0.68 (range 0.32-0.83). The rectal width in control was 0.52 with upper limit of 0.61 . This method has not found practical application, as the normal and pathological indicators overlap. There are limitations of this method due to two reasons. First, standardization by minimal volume of barium is incorrect. When rectum is empty, it is in the contracted state due to the tonus of its wall. The introduction of 10 ml of barium, regardless of age to a greater extent reflects the tone of the rectum and sigmoid colon, than their size. Secondly, it should be remembered that the rectum is the straight bowel only in dogs. In humans, it is the most curved section. It makes the S-bends in two projections. On the direct image different segments of the rectum overlap. Measure the normal rectal width can be only on the lateral image.
Gladman M.A. et al, who examined adults patients, concluded that the maximum limit of normal width of the rectum is 6.3 cm [4,5]. The width of the rectum increases with age as a result of the increasing the pelvic size and diameter of the stool accumulating in the rectum. This means that the maximum size of the rectum correspond to the maximum size of the stool. It is enough to draw a circle with a diameter of 6.3 cm, to ensure that such a diameter of stool may not be the norm. These authors filled of the rectum with barium of volume to 500 m under minimal pressure. During introduction of 500 ml under minimal pressure, the width of the rectum on the radiograph in patients with megareсtum will more reflect the tone of the rectum, than the true diameter, since a contrast medium is unable to stretch of the rectum to its maximum size, and will be distributed into the left part of the colon. Analysis of these papers indicates that the authors did not take into account the increase in the projection, significance of which depends on the distance from the object being studied (rectum) to the cassette. The greater the patient's pelvis, the more it will increase relative to the norm. At full and large people on the lateral radiograph the rectal size can be 2-fold greater than in reality (figure 6).
Figure 6. The enlargement of the rectal image on the X-ray depending on the width of the pelvis (Scheme).
Green line – the real rectal width; red line – its image in small pelvis; blue line – its image in large pelvis.
Dosed hydrostatic barium enema deprived drawbacks described above. It is standardized by the hydrostatic pressure, on the volume of the colon in each case and the real sizes of all parameters. It differs from the standard method of investigation only by the presence of the contrast marker near the anus and the radiometric analysis of the radiographs. It has never been used in healthy patients to determine normal values. In 1980-1983 barium enema was used for diagnosis of various diseases of the abdominal cavity, including the acute and chronic appendicitis. For this purpose the cecum and the appendix were filled with the barium [6-9].
The distance between the marker around the anus and rectum ranged from 2.21 ± 0.15 cm in the first year of life up to 3.43 ± 0.10 cm over the age of 10 years. The length of this interval is equal to the length of the anal canal, according to the manometric studies (1.67 ± 0.34 cm in neonates), (1-3 cm in infants), (3.03 ± 0.52 in more than one year) , 3.5 cm in adults ( 2.5-4.2) . Since, this area, performs the retention function, as the anal canal,and it has full equality on the length, we have every reason to believe that the distance between the rectum and the marker near the anus represents a contracted anal canal and its length is equal to the length of the anal canal.
We measured the pressure in the anal canal during the filling of the colon with a barium. On the lateral view sometimes a barium penetration from the rectum into the upper part of the anal canal in front of the enema tip was observed. At this time, the posterior wall of the anal canal was pressed against the enema tip (Fig. 4). This phenomenon is accompanied by a decrease in pressure in the anal canal. This situation lasted less than one minute, after which the barium which penetrated into the anal canal, was squeezed back into the rectum, and this by a rise in anal pressure to basal level was accompanied . It is known that "PRM (puborectalis muscle) contributes to the squeeze pressure in the proximal part of the anal canal and EAS to the distal anal canal. PRM squeeze-related increase in anal canal pressure might be important in the anal continence mechanism" . The peak pressure of the IAS is seen at a level of 1.6 cm from the anal verge, which corresponds to the peak relaxation pressure. The EAS is the only muscular structure located from 0.5 cm to 1 cm from the anal verge. Finally, the posterior superior location of the PRM from 2.4 cm to 4.0 cm from the anal canal . Thus, the X-ray picture of the penetration of barium only to the upper part of the anal canal in front of the enema tip is the radiological equivalent of the reсtoanal inhibitory reflex - relaxation of the IAS and contraction of the PRM and EAS.
The proposed method of the barium enema makes it possible to estimate with mathematical precision the magnitude of the rectum and colon. The megarectum determines if the true width of the rectum on the lateral radiograph larger than the maximal size of norm for this age. Megacolon determined by a constant, if it exceeds 31. It has been possible to differentiate megacolon varying degrees depending on the constant (C):1st degree - (C = 31- 45); 2nd degree - (C = 45-60) and 3rd degree - C> 60. For the first time on the radiographs the length of the anal canal has been measured, allowing to determine the state of the puborectalis muscle: hypertrophy, weakness or complete failure, in patients with functional constipations and anorectal malformations [15,12]. And it is very important, as puboreсtalis muscle plays a main role in the fecal retention [16-18].
Dosed hydrostatic barium enema is an accurate method for estimating the magnitude of the rectum and colon, as well as the state of the puborectalis muscles. It can be used for scientific analysis of the diseases associated with megareсtum and megacolon.
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