Clin. Radiol. (1978) 29, 553-560 P L A I N F I L M A N A L Y S I S IN SIGMOID V O L V U L U S W. S. YOUNG, H. E. ENGELBRECHT and A. STOKER From the Departments of Radiology, University of Natal and Edendale Hospital Pietermaritzburg The plain film findings in a series of 40 proven cases of sigmoid volvulus have been analysed. Approximately one-third of the cases were considered to be diagnostically difficult, with marked distension of the proximal colon. The difficulty was sometimes compounded by gas-filled loops of small bowel, excess fluid in the sigmoid loop, superimposition of the limbs of the sigmoid loop, a low lying transverse colon and by radiographic shortcomings. The essential radiological exercise in the plain film diagnosis of sigmoid volvulus lies in the identification of the walls of the enlarged sigmoid loop. The loop was characterised in the great majority of cases by an ahaustral margin, an apex below the left hemidiaphragm and above the level of D10, an inferior convergence lying to the left of the midline at the level of the upper sacral segments and by a contained air : fluid ratio in excess of 2 : 1. The radiographic appearance of the medial walls of the sigmoid loop is not specific to sigmoid volvulus. The peripheral walls of the loop may be obscured by proximally dilated colon, particularly when there is radiographic overpenetration. The inferior convergence of the limbs of the sigmoid loop, although usually identified in retrospect, are frequently inconspicuous. The smooth margin of the radiolucent sigmoid loop projecting beyond the haustrated proximal colon in the flanks and particularly in the right upper quadrant, was found to be of considerable diagnostic aid in those cases where the greater part of the sigmoid loop was obscured by proximal colonic distension.
There is an increased incidence of sigmoid volvulus in certain groups of the population, notably the geriatric and mentally defective, where constipation appears to be the common factor. It is also well recognised that the condition has a geographical distribution and is related to a high cereal intake (Scott, 1965). For the formation of volvulus the intestine must be able to rotate around its base, which is usually narrow. The sigmoid colon is provided with a freely mobile mesentery, the pelvic mesocolon, which connects the limbs of the loop and is attached to the left lower posterior abdominal wall over an angulated line. Any shortening of this line of attachment will close the limbs of the loop and predispose to volvulus. A bulky sigmoid colon stretches its mesentery, and narrows its base. The lateral part of the posterior attachment of the mesentery is frequently deficient, producing an abnormally wide lower left paracolic gutter. The sigmoid loop on its shortened base usually undergoes 180-540 degrees of clockwise or anticlockwise torsion. Secondary axial torsion of the pelvirectal junction ensues to cause complete intestinal obstruction. The sigmoid loop undergoes progressive distension with gas and to a lesser extent 41
with liquid faeces. Varying degrees of proximal colonic and occasionally small intestinal, distension ensues. Recurrent partial obstruction in the sigmoid colon leads to hypertrophy of its muscular wall and blood vessels, an anatomical adaptation which can be life saving by delaying gangrene in an established sigmoid volvulus (Grave, 1976). This 'thick-walled' variety of sigmoid volvulus is well recognised in Africa (Davey, 1968) and contrasts with the 'thin-walled' type seen more commonly in elderly Caucasians, where gangrene may develop at an early stage. The radiological findings in sigmoid volvulus essentially comprise the demonstration of an air and fluid distended sigmoid loop on plain radiographs of the abdomen and at barium enema, a characteristic obstruction just proximal to the rectosigmoid junction. Plain radiographs of the abdomen may show the sigmoid colon as a large, gas-filled ahaustral loop arising from the pelvis and often extending to the diaphragm. Its appearance has been likened to 'a bent inner tube' (Essenson and Ginzberg, 1949) (Fig. 1). The convergence of three white lines, representing the walls of the loop into the left iliac
554
CLINICAL
RADIOLOGY
obstruction at or proximal to the rectosigmoid junction (Fig. 2). In those cases where the barium transverses the point o f obstruction a characteristic spiralling of the mucosal folds may be shown. This was originally described as 'a screw-like torsion of the mucous folds of the colonic relief' (Ligat and Overend, 1933).
MATERIALS AND METHODS
Fig. 1 - 'Bent inner t u b e ' appearance. Flank (white arrow) and pelvic (black arrow) overlap.
The purpose of this paper is to examine and document the plain film findings in a series of 40 proven cases of sigmoid volvulus and to analyse in particular the less obviously diagnostic radiographs with the intention of prospectively increasing the diagnostic accuracy in the more difficult case. Supine and erect radiographs were available in all cases. The patients were all Africans and their ages ranged from 14 to 76 years with a mean of 41. The male : female ratio was approximately 7 : 1. |n none of the cases was there operative evidence of sigmoid or caecal perforation and in only five was the sigmoid colon gangrenous. The cases were divided into two main categories: the one in which the plain film diagnosis of sigmoid volvulus was considered to be easy and the other in which the diagnosis was considered to be relatively difficult. Criteria pertaining to the dimension, disposition, outline and content of the sigmoid loops were recorded as was the proximal colonic and small intestinal gaseous content. This data is shown in Table 1. RESULTS
Fig. 2
'Bird of prey' sign at barium enema.
fossa has been emphasised as a useful diagnostic aid (Frimman-Dahl, 1974). The erect film may show the upper, gas-filled part of the sigmoid loop as a large inverted 'U" with a fluid level in each limb. Barium enema examination demonstrates a tapered
The greater part of the sigmoid loop could be readily identified in 26 cases (group 1). The radiographs o f the other 14 cases were difficult to interpret (group 2). In 13 of these the sigmoid loop was difficult to identify. In the remaining case the sigmoid colon was unusually small for the condition and the radiographs might have been interpreted as showing a simple rectosigmoid obstruction. The sigmoid loop walls where visualised were ahaustral in 36 cases, but in three cases a small section o f the peripheral wall measuring approximately 3 - 6 cm showed haustration. In one case none of the peripheral wall could be identified. The medial walls of the sigmoid loop were commonly approximated to form a thick white line (summation line) (Fig. 3, 4a). Less frequently the medial walls overlapped each other to show a central black band (Fig. 5). In some cases a combination of
PLAIN FILM ANALYSIS
IN S I G M O I D
VOLVULUS
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There is an increased incidence of sigmoid volvulus in certain groups of the population, notably the geriatric and mentally defective, where constipation appears to be the common factor. It is also well recognised that the condition has a geographical distribution and is related to a high cereal intake (Scott, 1965). For the formation of volvulus the intestine must be able to rotate around its base, which is usually narrow. The sigmoid colon is provided with a freely mobile mesentery, the pelvic mesocolon, which connects the limbs of the loop and is attached to the left lower posterior abdominal wall over an angulated line. Any shortening of this line of attachment will close the limbs of the loop and predispose to volvulus. A bulky sigmoid colon stretches its mesentery, and narrows its base. The lateral part of the posterior attachment of the mesentery is frequently deficient, producing an abnormally wide lower left paracolic gutter. The sigmoid loop on its shortened base usually undergoes 180-540 degrees of clockwise or anticlockwise torsion. Secondary axial torsion of the pelvirectal junction ensues to cause complete intestinal obstruction. The sigmoid loop undergoes progressive distension with gas and to a lesser extent 41
with liquid faeces. Varying degrees of proximal colonic and occasionally small intestinal, distension ensues. Recurrent partial obstruction in the sigmoid colon leads to hypertrophy of its muscular wall and blood vessels, an anatomical adaptation which can be life saving by delaying gangrene in an established sigmoid volvulus (Grave, 1976). This 'thick-walled' variety of sigmoid volvulus is well recognised in Africa (Davey, 1968) and contrasts with the 'thin-walled' type seen more commonly in elderly Caucasians, where gangrene may develop at an early stage. The radiological findings in sigmoid volvulus essentially comprise the demonstration of an air and fluid distended sigmoid loop on plain radiographs of the abdomen and at barium enema, a characteristic obstruction just proximal to the rectosigmoid junction. Plain radiographs of the abdomen may show the sigmoid colon as a large, gas-filled ahaustral loop arising from the pelvis and often extending to the diaphragm. Its appearance has been likened to 'a bent inner tube' (Essenson and Ginzberg, 1949) (Fig. 1). The convergence of three white lines, representing the walls of the loop into the left iliac
554
CLINICAL
RADIOLOGY
obstruction at or proximal to the rectosigmoid junction (Fig. 2). In those cases where the barium transverses the point o f obstruction a characteristic spiralling of the mucosal folds may be shown. This was originally described as 'a screw-like torsion of the mucous folds of the colonic relief' (Ligat and Overend, 1933).
MATERIALS AND METHODS
Fig. 1 - 'Bent inner t u b e ' appearance. Flank (white arrow) and pelvic (black arrow) overlap.
The purpose of this paper is to examine and document the plain film findings in a series of 40 proven cases of sigmoid volvulus and to analyse in particular the less obviously diagnostic radiographs with the intention of prospectively increasing the diagnostic accuracy in the more difficult case. Supine and erect radiographs were available in all cases. The patients were all Africans and their ages ranged from 14 to 76 years with a mean of 41. The male : female ratio was approximately 7 : 1. |n none of the cases was there operative evidence of sigmoid or caecal perforation and in only five was the sigmoid colon gangrenous. The cases were divided into two main categories: the one in which the plain film diagnosis of sigmoid volvulus was considered to be easy and the other in which the diagnosis was considered to be relatively difficult. Criteria pertaining to the dimension, disposition, outline and content of the sigmoid loops were recorded as was the proximal colonic and small intestinal gaseous content. This data is shown in Table 1. RESULTS
Fig. 2
'Bird of prey' sign at barium enema.
fossa has been emphasised as a useful diagnostic aid (Frimman-Dahl, 1974). The erect film may show the upper, gas-filled part of the sigmoid loop as a large inverted 'U" with a fluid level in each limb. Barium enema examination demonstrates a tapered
The greater part of the sigmoid loop could be readily identified in 26 cases (group 1). The radiographs o f the other 14 cases were difficult to interpret (group 2). In 13 of these the sigmoid loop was difficult to identify. In the remaining case the sigmoid colon was unusually small for the condition and the radiographs might have been interpreted as showing a simple rectosigmoid obstruction. The sigmoid loop walls where visualised were ahaustral in 36 cases, but in three cases a small section o f the peripheral wall measuring approximately 3 - 6 cm showed haustration. In one case none of the peripheral wall could be identified. The medial walls of the sigmoid loop were commonly approximated to form a thick white line (summation line) (Fig. 3, 4a). Less frequently the medial walls overlapped each other to show a central black band (Fig. 5). In some cases a combination of
PLAIN FILM ANALYSIS
IN S I G M O I D
VOLVULUS
+
~
+
+ +
+
+ + + + + + + + + + + + + + + + + + + + + + + + + + + +
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