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Duplication of the colon
Clin. Radiol. (1978)
29, 205-209
DUPLICATION OF THE COLON E. M. BASS
Department of Radiology, Groote Schuur Hospital, Observatory, Cape Town 7925, South Africa Colonic d u p l i c a t i o n is a rare congenital a b n o r m a l i t y t h a t can p r e s e n t diagnostic difficulties t o the radiologist. Three n e w cases are r e p o r t e d to illustrate t h e d i f f e r e n t t y p e s o f this a n o m a l y . A classification is p r e s e n t e d in w h i c h t h e c o n d i t i o n is divided i n t o t w o t y p e s : in t y p e I lesions t h e d u p l i c a t i o n is l i m i t e d t o the c o l o n and in t y p e II lesions t h e r e are associated d u p l i c a t i o n s o f t h e g e n i t o - u r i n a r y tract. The w i d e s p e c t r u m o f possible pathological, clinical and radiological features are reviewed.
INTRODUCTION AND MATERIAL D u p l i c a t i o n o f t h e c o l o n is an u n c o m m o n c o n g e n i t a l a n o m a l y usually diagnosed during i n f a n c y or early c h i l d h o o d . A l t h o u g h less c o m m o n t h a n small b o w e l d u p l i c a t i o n , K o t t r a and D o d d s ( 1 9 7 1 ) reviewed 50 r e p o r t e d cases and f o u n d a female p r e p o n d e r a n c e b u t n o a p p a r e n t racial n o r familial p r e d e l i c t i o n . Three new cases o f colonic d u p l i c a t i o n are r e p o r t e d t o illustrate the d i f f e r e n t t y p e s and range o f the condition. CASE R E P O R T S Case 1. - L. R., a full-term infant, was noted at birth to have no anal opening. A defunctioning colostomy was done and a distal loopogram revealed rectal agenesis. At the age of 1 year a definitive puU-through operation was satisfactorily performed and it was found that there was reduplication of the colon with a proximal communication in the transverse colon and the distal communication at the rectum. Subsequent barium enema showed both lumina to be of equal calibre (Fig. 2) but the duplicated lumen contained some hard faecal masses. Plain films of the abdomen showed lumbarisation of the first sacral segment and the symphysis pubis was fairly widely separated. A left fused (cake) kidney was shown on intravenous pyelogram and a large urethral diverticulum was present on voiding cystourethrography. Follow-up was uneventful apart fr0m a few episodes of faecal impaction, relieved by olive oil enemata. Case 2. - W. H., a female aged 6 years, was first admitted to an infectious diseases hospital suffering from severe measles complicated by bronchopneumonia. On examination, she was found to have two anal orifices. In line with each anal orifice were two complete, but separate vestibules, each consisting of a clitoris, labia minora and urethral and vaginal orifices. The mother had noted the paired genital and anal structures, but partly because of her own ignorance and because the child had been continent, had not sought medical aid. Barium was introduced into each anal opening (Fig. 3a, b) and the colon was found to be duplicated in its entire course with the proximal communication at the caecum. In addition, contrast examinations showed two separate bladders and urethras and two separate vaginas and cervices. No surgical treatment was contemplated and the child was discharged. Nine years later, the child complained of abdominal pain and was readmitted to hospital. The right anal
orifice was catheterised and contrast flowed to the caecum. Some air was introduced into the left anal opening and the two separate lumina, one filled with contrast and one with air, are shown in Fig. 4a. Barium then filled the duplicated colon and Fig. 4b shows both lurmna filled with contrast. The child had been well for the intervening 9 years and was fully continent for urine and faeces. Case 3. - D. L., a female aged 62 years, was referred for a barium enema because of rectal bleeding. On rectal examination she had fairly marked haemorthoids. Barium enema was normal, except for a wide-mouthed, large diverticular-like structure arising from the hepatic flexure (Fig. 5). The mucosa inside this structure was continuous with the colonic mucosa and active contraction was noted on fluoroscopy. The colon showed no evidence of diverticular disease and this structure was regarded as a small tubular communicating reduplication of the colon. CLASSIFICATION A classification s y s t e m for c o l o n duplication is s h o w n in Table 1 and Fig. 1. T y p e I d u p l i c a t i o n is
COLON DUPLICATIONS TYPE I A - C
TYPE I I A
TYPE II B
TYPE II C
VAGINAE
BLADDERS
Fig. 1 - Classification of colon duplications.
206
CLINICAL RADIOLOGY
T a b l e 1 - Classification o f c o l o n d u p l i c a t i o n s
Type 1, (a) (b) (c)
(d)
Duplication limited to alimentary tract (frequently asyrnptomatic) Spherical Tubular Double-barrelled; one or more communications with colon (i) Limited to colon (ii) Associated ileal duplication Multiple duplications; combinations of (a), (b) and (c)
* Type 2. Colon duplication (usually double-barrelled) associated with duplications of urinary or genital tracts (frequently symptomatic). (a) Two separate perinealani. (b) Fistulae, i.e. distal portion of one or both duplicates having a fistulous connection with another hollow viscus. (c) Anorectal agenesis (imperforate anus): one or both rectums imperforate, in the pelvis, no fistula, *Modified from Smith (1969).
limited to the colon or rectum and is usually partial. Type II lesions often involve the entire colon and are associated with duplication of the lower urinary or Fig. 2 - Case 1. Barium enema examination showing barium genital tracts or both. Associated congenital anoma- filling duplicated colonic lumina (a and b). Note the impacted faecal masses in lumen (b). lies, involving other parts of the gastro-intestinal tr ac t, the genito-urinary and musculo-skeletal systems, are found with both types, but are more common with type II lesions. Type IIa lesions with two separate perineal ani are usually associated with mucosal lining similar to stomach, small bowel or double genitalia, and a double urethra and bladder. colon. These patients are usually continent, have no sympColon duplications m a y have a spherical, tubular toms and complaints are limited to the cosmetic or double-barrelled configuration and are usually disfiguration. Most type IIb lesions also have double located along the mesenteric border o f the colon. A genitalia and urinary tract duplication and symptoms patient with colonic triplication has been reported by are related to the fistula or obstruction from in- Gray (1940). As a rule, the duplicates share a adequate drainage. Surgery is usually successful in common mesentery, when present, and a common these cases. Type IIc cases usually.have single genitals, blood supply. The duplication may bulge into the but all have duplications of the lower urinary tract. colon lumen if it is restricted by encircling muscle. If These cases have symptoms o f obstruction and a communication exists, the duplication contains operative results are poor. According to this classifi- faeces whereas non-communicating duplications concation, Cases 1, 2 and 3 reported in this paper are rain clear, often mucoid fluid. Enzymatic secretions may cause ulceration and bleeding with resultant type llc, IIa and Ic lesions respectively. discolouration of the liquid contents. On histologic examination the outer wall o f the duplication has all the tissue layers of a normal colon. PATHOLOGICAL F E A T U R E S The common wall may vary from two mucosal layers True intestinal reduplications must be distin- with intervening connective tissue to two complete guished from enteric cysts and vitelline remnants attached colon walls. The mucosal layer is always (Smith, 1960) and have the following characteristics: alimentary in type, but may not correspond to that (a) an intimate attachment to some part of the of the adjacent bowel, e.g. gastric mucosa may be alimentary tract; (b) a smooth muscle coat; and (c) a present in rectal duplication.
DUPLICATION
OF THE COLON
207
Fig. 3 - Case 2. (a) Barium examination with separate catheterisation of each anal orifice. Note the air-filled duplicated lumen adjacent to the larger barium-filled lumen (arrows). (b) Barium has now flowed to the caecum in the larger lumen. Note the air-filled haustra adjacent to the transverse and ascending colons (arrows).
CLINICAL FEATURES
A palpable abdominal mass may be the presenting feature, especially in children. Ravitch (1953) described a case in which the duplication compressed the left ureter with resultant hydronephrosis. A carcinoma may arise in a duplicated colon (Heiberg et al., 1973), and alter the symptomatology. The clinical features of the above three cases vary. The duplication in the first case causes minor bouts of partial obstruction due to faecal impaction with resultant constipation, pain and distension. These episodes were never severe and were controlled by diet and enemata. Despite the complete duplication, the second case had no significant symptoms referable to the anomaly. The duplication in Case 3 was an incidental finding of no significance.
Minor forms of colonic duplication are often asymptomatic and may remain unrecognised unless associated with other congenital anomalies. Symptomatology is usually related to obstruction with resultant constipation, distension and pain. The cause of the obstruction varies. Non-communicating lesions (types Ia and Ib) often enlarge due to retained secretions and compress the adjacent bowel. Type I lesions projecting into the lumen may cause intussusception (Gross et al., 1952). Type II lesions become distended when the distal anomaly prevents adequate emptying. Gastrointestinal bleeding may result from ulceration due to enzymatic secretions. In addition, stretching of mesenteric vessels around the duplication may cause ischaemia (Gross et al., 1952) with RADIOLOGICAL FEATURES resultant blood loss. Pain may result from overdistension and obThe roentgen features depend on the size, shape, struction; rarely the proteolytic enzymes in the extent and location of the duplication. Small duplisecretions may cause inflammation. cations often show no abnormal roentgen findings.
208
CLINICAL R A D I O L O G Y
Fig. 4 - Case 2. (a) Nine years later. Barium-filled colon with air-containing haustra seen superior to the transverse colon. (b) Both lumina are now filled with barium.
Fig. 5 - C a s e 3. Diverticular structure arising from hepatic flexure. Note the continuous mucosal lining with adjacent colon.
Plain abdominal films may show a non-specific soft tissue mass. Calcification within a duplication is rare (Weber and Dixon, 1946). Large or small bowel obstruction is present when the duplication significantly compresses the adjacent bowel lumen. Communicating duplications may be seen as a gas-filled structure in close apposition to the bowel with an air-fluid level often on the erect film. Associated congenital anomalies of the lumbar spine or sacrum may be evident. The diagnosis is usually made by barium examinations. The colon or rectum is frequently displaced or compressed by an adjacent mass. Communicating lesions usually show an irregular duplicate lumen and discrete ulcers may be seen if gastric mucosa is present. Unsuspected double-barrelled lesions may be recognised by air-containing haustral markings adjacent to the barium-filled colon; these later fill with barium through the communication. Complete duplications with separate perineal or ectopic anal openings are easily recognised by introducing barium through both openings. A small bowel series may show associated anomalies especially ileal duplication, malrotation or a Meckel's diverticulum. Intravenous pyelography or cystography may demonstrate a double bladder or urethra.
DUPLICATION OF THE COLON Differentiation from mesenteric cysts or l y m p h cysts may be difficult on roentgenographic studies although these have a thinner wall and less tendency to significantly compress the adjacent bowel. Colon duplications in adults may simulate a carcinoma (Reilly et al., 1968), while in infants the resultant obstruction, constipation and abdominal distension must be distinguished from Hirschsprung's disease.
CONCLUSIONS Knowledge of the varied clinical and roentgenographic features of colon duplication helps the radiologists in diagnosis and to suggest appropriate additional studies where indicated. A confident roentgenographic diagnosis may spare an asymptomatic patient an unnecessary exploratory laparotomy. Complete radiologicai evaluation o f such cases must include examinations o f the colon, small bowel, lumbar spine, pelvis and genito-urinary tract. Unless the duplications are obstructed or show other significant symptoms, the management is conservative. Duplications of tlie lower genito-urinary
209
tract are usually consistent with fertility and good health and surgery is reserved for those patients who are symptomatically or cosmetically disturbed, REFERENCES Gray, A. W. (1940). Triplication of large intestine. Archives of Pathology, 30, 1215-1222. Gross, R. E., Holcomb, G. W. & Farber, S. (1952). Duplications of alimentary tract. Paediatrics, 9,449 468. Heiberg, M. L., Marshall, K. G. & Himal, H. S. (1973). Carcinoma arising in a duplicated colon. Case report and review of literature. British Journal o f Surgery, 60, 981-982. Kottra, J. J. & Dodds, W_ J. (1971). Duplication of the large bowel. Radiology, 113, 310-315. Ravitch, M. M. (1953). Hind-gut duplication-doub!ing of colon and genito-urinary tracts. Annals o f Surgery, 137, 588-601. Smith, E. D. (1969). Duplication of anus and genitourinary tract. Surgery, 6~;, 909-921. Smith, J. R. (1960). Accessory enteric formations: classification and nomenclature. Archives o f Diseases of Childhood, 30, 87-89. Weber, H. M. & Dixon, C. F. (1946). Duplication of entire large intestine (colon duplex): report of case. American Journal of Roentgenology and Radiation Therapy, 56, 319-324.
29, 205-209
DUPLICATION OF THE COLON E. M. BASS
Department of Radiology, Groote Schuur Hospital, Observatory, Cape Town 7925, South Africa Colonic d u p l i c a t i o n is a rare congenital a b n o r m a l i t y t h a t can p r e s e n t diagnostic difficulties t o the radiologist. Three n e w cases are r e p o r t e d to illustrate t h e d i f f e r e n t t y p e s o f this a n o m a l y . A classification is p r e s e n t e d in w h i c h t h e c o n d i t i o n is divided i n t o t w o t y p e s : in t y p e I lesions t h e d u p l i c a t i o n is l i m i t e d t o the c o l o n and in t y p e II lesions t h e r e are associated d u p l i c a t i o n s o f t h e g e n i t o - u r i n a r y tract. The w i d e s p e c t r u m o f possible pathological, clinical and radiological features are reviewed.
INTRODUCTION AND MATERIAL D u p l i c a t i o n o f t h e c o l o n is an u n c o m m o n c o n g e n i t a l a n o m a l y usually diagnosed during i n f a n c y or early c h i l d h o o d . A l t h o u g h less c o m m o n t h a n small b o w e l d u p l i c a t i o n , K o t t r a and D o d d s ( 1 9 7 1 ) reviewed 50 r e p o r t e d cases and f o u n d a female p r e p o n d e r a n c e b u t n o a p p a r e n t racial n o r familial p r e d e l i c t i o n . Three new cases o f colonic d u p l i c a t i o n are r e p o r t e d t o illustrate the d i f f e r e n t t y p e s and range o f the condition. CASE R E P O R T S Case 1. - L. R., a full-term infant, was noted at birth to have no anal opening. A defunctioning colostomy was done and a distal loopogram revealed rectal agenesis. At the age of 1 year a definitive puU-through operation was satisfactorily performed and it was found that there was reduplication of the colon with a proximal communication in the transverse colon and the distal communication at the rectum. Subsequent barium enema showed both lumina to be of equal calibre (Fig. 2) but the duplicated lumen contained some hard faecal masses. Plain films of the abdomen showed lumbarisation of the first sacral segment and the symphysis pubis was fairly widely separated. A left fused (cake) kidney was shown on intravenous pyelogram and a large urethral diverticulum was present on voiding cystourethrography. Follow-up was uneventful apart fr0m a few episodes of faecal impaction, relieved by olive oil enemata. Case 2. - W. H., a female aged 6 years, was first admitted to an infectious diseases hospital suffering from severe measles complicated by bronchopneumonia. On examination, she was found to have two anal orifices. In line with each anal orifice were two complete, but separate vestibules, each consisting of a clitoris, labia minora and urethral and vaginal orifices. The mother had noted the paired genital and anal structures, but partly because of her own ignorance and because the child had been continent, had not sought medical aid. Barium was introduced into each anal opening (Fig. 3a, b) and the colon was found to be duplicated in its entire course with the proximal communication at the caecum. In addition, contrast examinations showed two separate bladders and urethras and two separate vaginas and cervices. No surgical treatment was contemplated and the child was discharged. Nine years later, the child complained of abdominal pain and was readmitted to hospital. The right anal
orifice was catheterised and contrast flowed to the caecum. Some air was introduced into the left anal opening and the two separate lumina, one filled with contrast and one with air, are shown in Fig. 4a. Barium then filled the duplicated colon and Fig. 4b shows both lurmna filled with contrast. The child had been well for the intervening 9 years and was fully continent for urine and faeces. Case 3. - D. L., a female aged 62 years, was referred for a barium enema because of rectal bleeding. On rectal examination she had fairly marked haemorthoids. Barium enema was normal, except for a wide-mouthed, large diverticular-like structure arising from the hepatic flexure (Fig. 5). The mucosa inside this structure was continuous with the colonic mucosa and active contraction was noted on fluoroscopy. The colon showed no evidence of diverticular disease and this structure was regarded as a small tubular communicating reduplication of the colon. CLASSIFICATION A classification s y s t e m for c o l o n duplication is s h o w n in Table 1 and Fig. 1. T y p e I d u p l i c a t i o n is
COLON DUPLICATIONS TYPE I A - C
TYPE I I A
TYPE II B
TYPE II C
VAGINAE
BLADDERS
Fig. 1 - Classification of colon duplications.
206
CLINICAL RADIOLOGY
T a b l e 1 - Classification o f c o l o n d u p l i c a t i o n s
Type 1, (a) (b) (c)
(d)
Duplication limited to alimentary tract (frequently asyrnptomatic) Spherical Tubular Double-barrelled; one or more communications with colon (i) Limited to colon (ii) Associated ileal duplication Multiple duplications; combinations of (a), (b) and (c)
* Type 2. Colon duplication (usually double-barrelled) associated with duplications of urinary or genital tracts (frequently symptomatic). (a) Two separate perinealani. (b) Fistulae, i.e. distal portion of one or both duplicates having a fistulous connection with another hollow viscus. (c) Anorectal agenesis (imperforate anus): one or both rectums imperforate, in the pelvis, no fistula, *Modified from Smith (1969).
limited to the colon or rectum and is usually partial. Type II lesions often involve the entire colon and are associated with duplication of the lower urinary or Fig. 2 - Case 1. Barium enema examination showing barium genital tracts or both. Associated congenital anoma- filling duplicated colonic lumina (a and b). Note the impacted faecal masses in lumen (b). lies, involving other parts of the gastro-intestinal tr ac t, the genito-urinary and musculo-skeletal systems, are found with both types, but are more common with type II lesions. Type IIa lesions with two separate perineal ani are usually associated with mucosal lining similar to stomach, small bowel or double genitalia, and a double urethra and bladder. colon. These patients are usually continent, have no sympColon duplications m a y have a spherical, tubular toms and complaints are limited to the cosmetic or double-barrelled configuration and are usually disfiguration. Most type IIb lesions also have double located along the mesenteric border o f the colon. A genitalia and urinary tract duplication and symptoms patient with colonic triplication has been reported by are related to the fistula or obstruction from in- Gray (1940). As a rule, the duplicates share a adequate drainage. Surgery is usually successful in common mesentery, when present, and a common these cases. Type IIc cases usually.have single genitals, blood supply. The duplication may bulge into the but all have duplications of the lower urinary tract. colon lumen if it is restricted by encircling muscle. If These cases have symptoms o f obstruction and a communication exists, the duplication contains operative results are poor. According to this classifi- faeces whereas non-communicating duplications concation, Cases 1, 2 and 3 reported in this paper are rain clear, often mucoid fluid. Enzymatic secretions may cause ulceration and bleeding with resultant type llc, IIa and Ic lesions respectively. discolouration of the liquid contents. On histologic examination the outer wall o f the duplication has all the tissue layers of a normal colon. PATHOLOGICAL F E A T U R E S The common wall may vary from two mucosal layers True intestinal reduplications must be distin- with intervening connective tissue to two complete guished from enteric cysts and vitelline remnants attached colon walls. The mucosal layer is always (Smith, 1960) and have the following characteristics: alimentary in type, but may not correspond to that (a) an intimate attachment to some part of the of the adjacent bowel, e.g. gastric mucosa may be alimentary tract; (b) a smooth muscle coat; and (c) a present in rectal duplication.
DUPLICATION
OF THE COLON
207
Fig. 3 - Case 2. (a) Barium examination with separate catheterisation of each anal orifice. Note the air-filled duplicated lumen adjacent to the larger barium-filled lumen (arrows). (b) Barium has now flowed to the caecum in the larger lumen. Note the air-filled haustra adjacent to the transverse and ascending colons (arrows).
CLINICAL FEATURES
A palpable abdominal mass may be the presenting feature, especially in children. Ravitch (1953) described a case in which the duplication compressed the left ureter with resultant hydronephrosis. A carcinoma may arise in a duplicated colon (Heiberg et al., 1973), and alter the symptomatology. The clinical features of the above three cases vary. The duplication in the first case causes minor bouts of partial obstruction due to faecal impaction with resultant constipation, pain and distension. These episodes were never severe and were controlled by diet and enemata. Despite the complete duplication, the second case had no significant symptoms referable to the anomaly. The duplication in Case 3 was an incidental finding of no significance.
Minor forms of colonic duplication are often asymptomatic and may remain unrecognised unless associated with other congenital anomalies. Symptomatology is usually related to obstruction with resultant constipation, distension and pain. The cause of the obstruction varies. Non-communicating lesions (types Ia and Ib) often enlarge due to retained secretions and compress the adjacent bowel. Type I lesions projecting into the lumen may cause intussusception (Gross et al., 1952). Type II lesions become distended when the distal anomaly prevents adequate emptying. Gastrointestinal bleeding may result from ulceration due to enzymatic secretions. In addition, stretching of mesenteric vessels around the duplication may cause ischaemia (Gross et al., 1952) with RADIOLOGICAL FEATURES resultant blood loss. Pain may result from overdistension and obThe roentgen features depend on the size, shape, struction; rarely the proteolytic enzymes in the extent and location of the duplication. Small duplisecretions may cause inflammation. cations often show no abnormal roentgen findings.
208
CLINICAL R A D I O L O G Y
Fig. 4 - Case 2. (a) Nine years later. Barium-filled colon with air-containing haustra seen superior to the transverse colon. (b) Both lumina are now filled with barium.
Fig. 5 - C a s e 3. Diverticular structure arising from hepatic flexure. Note the continuous mucosal lining with adjacent colon.
Plain abdominal films may show a non-specific soft tissue mass. Calcification within a duplication is rare (Weber and Dixon, 1946). Large or small bowel obstruction is present when the duplication significantly compresses the adjacent bowel lumen. Communicating duplications may be seen as a gas-filled structure in close apposition to the bowel with an air-fluid level often on the erect film. Associated congenital anomalies of the lumbar spine or sacrum may be evident. The diagnosis is usually made by barium examinations. The colon or rectum is frequently displaced or compressed by an adjacent mass. Communicating lesions usually show an irregular duplicate lumen and discrete ulcers may be seen if gastric mucosa is present. Unsuspected double-barrelled lesions may be recognised by air-containing haustral markings adjacent to the barium-filled colon; these later fill with barium through the communication. Complete duplications with separate perineal or ectopic anal openings are easily recognised by introducing barium through both openings. A small bowel series may show associated anomalies especially ileal duplication, malrotation or a Meckel's diverticulum. Intravenous pyelography or cystography may demonstrate a double bladder or urethra.
DUPLICATION OF THE COLON Differentiation from mesenteric cysts or l y m p h cysts may be difficult on roentgenographic studies although these have a thinner wall and less tendency to significantly compress the adjacent bowel. Colon duplications in adults may simulate a carcinoma (Reilly et al., 1968), while in infants the resultant obstruction, constipation and abdominal distension must be distinguished from Hirschsprung's disease.
CONCLUSIONS Knowledge of the varied clinical and roentgenographic features of colon duplication helps the radiologists in diagnosis and to suggest appropriate additional studies where indicated. A confident roentgenographic diagnosis may spare an asymptomatic patient an unnecessary exploratory laparotomy. Complete radiologicai evaluation o f such cases must include examinations o f the colon, small bowel, lumbar spine, pelvis and genito-urinary tract. Unless the duplications are obstructed or show other significant symptoms, the management is conservative. Duplications of tlie lower genito-urinary
209
tract are usually consistent with fertility and good health and surgery is reserved for those patients who are symptomatically or cosmetically disturbed, REFERENCES Gray, A. W. (1940). Triplication of large intestine. Archives of Pathology, 30, 1215-1222. Gross, R. E., Holcomb, G. W. & Farber, S. (1952). Duplications of alimentary tract. Paediatrics, 9,449 468. Heiberg, M. L., Marshall, K. G. & Himal, H. S. (1973). Carcinoma arising in a duplicated colon. Case report and review of literature. British Journal o f Surgery, 60, 981-982. Kottra, J. J. & Dodds, W_ J. (1971). Duplication of the large bowel. Radiology, 113, 310-315. Ravitch, M. M. (1953). Hind-gut duplication-doub!ing of colon and genito-urinary tracts. Annals o f Surgery, 137, 588-601. Smith, E. D. (1969). Duplication of anus and genitourinary tract. Surgery, 6~;, 909-921. Smith, J. R. (1960). Accessory enteric formations: classification and nomenclature. Archives o f Diseases of Childhood, 30, 87-89. Weber, H. M. & Dixon, C. F. (1946). Duplication of entire large intestine (colon duplex): report of case. American Journal of Roentgenology and Radiation Therapy, 56, 319-324.