Pediatr Radiol (1990) 20:258-261
Pediatric Radiology 9 Springer-Verlag 1990
Ultrasound study of acute appendicitis in children with emphasis upon the diagnosis of retrocecal appendicitis* L. C e r e s 1, I. A l o n s o t, R L 6 p e z 1, G. P a r r a 1 a n d J. E c h e v e r r y 2 Departments of 1Pediatric Radiology and 2Pediatric Surgery, Hospital Materno Infantil, Mfilaga, Spain
Abstract. A c u t e appendicitis in children frequently presents equivocal clinical manifestations. D e l a y of the p r o p e r diagnosis and unnecessary laparotomies are c o m m o n . A b d o m i n a l ultrasound has p r o v e d to be useful in the diagnosis of acute appendicitis in adults. We have p e r f o r m e d a preoperative ultrasound study in 368 children with acute appendicitis. A m o n g them, 92 had a retrocecal appendicitis. U l t r a s o u n d established the correct diagnosis in 92.6% of patients, and in 94.5% of those with a retrocecal appendicitis. A t our institution an abdominal s o n o g r a p h y is p e r f o r m e d on any child with a doubtful clinical diagnosis of acute appendicitis, helping the surgeon to take the decision to p e r f o r m a laparotomy.
It is well k n o w n that acute appendicitis is the most c o m m o n indication of e m e r g e n c y abdominal surgery in children. A l t h o u g h the clinical presentation is typical in m o s t cases, about 30% of patients present confusing symptomatology, leading to delay of the p r o p e r diagnosis as well as to a rate as high as 2 0 - 2 5 % of unnecessary laparotomies [1-3]. Several imaging procedures have b e e n p r o p o s e d to improve diagnostic accuracy. Plain abdominal films are routinely taken in m o s t institutions [4]. B a r i u m examination m a y be of s o m e value [5, 6], and even CT has b e e n used to study complicated appendicitis [7, 8]. A b d o m i n a l s o n o g r a p h y has p r o v e d to be a very useful tool in the evaluation of acute a b d o m i n a l pain in adults and children [4, 9, 10], and has b e e n p r o p o s e d by severeal authors for the diagnosis of acute appendicitis [2, 3, 11-13]. A b d o m i nal U S is a very suitable technique to investigate children with acute a b d o m i n a l pathology, because it is non-invasive, quick and free of radiation. We present our experience with 368 children o p e r a t e d on for acute appendicitis w h o were e x a m i n e d with US prior to surgery.
368 of them prior to surgery. During a first period of 18 months we conducted a prospective study; all children with a clinical diagnosis of acute appendicitis established by the surgeon on duty were examined by US whenever a radiologist with experience in pediatric sonography was on call. During the following 18 months, studies were done mainly in doubtful cases. Meanwhile, all the radiologists at our Hospital were trained to perform these studies. In all patients, US findings were correlated with surgical and pathological reports. At the same time, a second group of children either suffering from acute abdominal pain of unclear ethiology, or with the clinical diagnosis of acute appendicitis, was also examined by US. In this group the sonographic study was normal, or established a diagnosis not previously suspected. None of these children were operated for acute appendicitis, and they are not included in this paper. All the examinations were performed using a 5 MHz autofocus sector transducer, which allows the study of both superficial and deep abdominal areas. The same systematic study was done on all patients. The study begins examining the right upper quadrant, and descending through the right flank toward the right iliac fossa and the pelvis. Following the technique described by Puylaert, a gentle compression with the transducer is applied, to displace the bowel loops [2]. This compression is extremely well tolerated by most children. The psoas muscle and the iliac vessels are the anatomical landmarks to identify the appendix, which usually is located between these structures and the abdominal wall (Fig. 1). A normal, non inflamed appendix is seldom visualized by US [3].
Material and method Between January 1986 and December 1988, 833 consecutive children, aged 2 to 14 years, were operated on with the clinicl diagnosis of acute appendicitis. An abdominal US study was performed in * Presented at the ESPR meeting in Dubin 1989. Selected for publication by an International Group of the ESPR
Fig. 1. The psoas and the iliac vessels are the anatomical landmarks to identify the appendix
L. Ceres et al.: US study of acute appendicitis in children
259
Fig.2. Acutely inflamed appendix; longitudinal image l~g.3. On cross section the appendix is visualized as a target. I = Iliac bone, Ps = psoas
Fig. 4. Gangrenous appendicitis. The appendix is enlarged, with irregular borders, and the mucosa tines are interrupted (arrowheads)
Results
quent finding is the presence of a paralytic ileus localized in the right lower quadrant. Bowel loops are seen filled with fluid, with sluggish or absent peristaltic waves. Occasionally, this fluid may be echogenic, or give the image of a fluid-fluid level, typical of a pus collection. A negative sonographic diagnosis was established in 26 patients (7%), based on the non visualization of the appendix or on the absence of any of the above described signs. Only 17 of them proved to be false negatives (4.7 %), while in the other 9 the appendix was normal according to the pathological report. There were also 10 cases (2.7%) with false positive diagnoses, but in one of them the appendix contained a carcinoid tumour. Ninety-two children had a retrocecal appendicitis. Ultrasound established the right diagnosis in 85, and in two cases the diagnosis was just "acute appendicitis". There were 5 false negatives (5.5%), and not a false positive among these patients.
Abdominal US established the correct diagnosis in 92.6% of patients. The sonographic findings agree with those described by most authors, and are summarized in Table 1. A combination of several findings in the same patients was rather frequent. The most common finding in children with acute appendicitis is an enlarged inflamed appendix, visualized on longitudinal imaging as a hypoechogenic tubular structure in continuity with the cecum and having a blind distal end. The mucosa is identified as two thin echogenic lines surrounding the lumen (Fig. 2). The echogenic aspect of the appendiceal lumen depends on the amount of fecal material contained in it. Contrary to bowel loops, the inflamed appendix lacks peristalsis, is rigid and is not easy to compress. On cross section the appendix resembles a target with a hypoechogenic external ring (Fig. 3). With the progression of the inflammatory reaction the appendiceal wall thickens, and becomes irregular. Where the echogenic lines of the mucosa are interrupted, it is a sign of gangrenous appendicitis (Fig.4), and where the tubular aspect of the appendix gradually disappears, it indicates periappendicitis. Appendicoliths are visualized as intra, luminal hyperechoic structures with a shadowing (Fig. 5). Only approximately 50% of appendicoliths identified by US were also seen on the plain film of the abdomen. The sonographic appearance of an appendix abscess is a complex mass. Sometimes we can recognise the appendix inside the mass, the omentum wrapping the appendix in the form of an echogenic band, and some bowel loops (Fig. 6). All cases with a sonographic diagnosis of appendiceal abscess were confirmed at laparotomy. Another fre-
Table 1. US findingsin children with acute appendicitis
% Of cases Enlarged appendix Irregular appendiceal borders Appendicoliths Appendiceal abscess Periappendiceal fluid Localized ileus
61.8 33 29.6 21.5 24.9 16.3
% Of retrocecal appendicitis 69.5 22.5 33.7 28.2 20 11
Discussion
The diagnosis of acute appendicitis by means of abdominal sonography has been demonstrated in several recent publications, mainly in adult patients [2, 3, 11-13]. The present study proves that US is also very accurate in the diagnosis of acute appendicitis in pediatric patients. Retrocecal appendicitis represents approximately 28% of our patients. These children usually come to the Hospital with symptoms lasting for at least 24 to 48 h, and with rather confusing clinical manifestations for the surgeon. Delay in the diagnosis is common in that group of patients, and as a result of this delay, perforation was found by laparotomy in 42% of retrocecal appendicitis, while it did occur only in 14% of patients with iliac appendicitis. The sonographic visualization of a retrocecal inflamed appendix was first reported by Claes at als in 1984 [14]. It has been surprising to us that the particular value of US in demonstrating a retrocecal appendicitis has not been emphasized in the literature, even in the largest series so far reported. A retrocecal appendicitis is, however, very easy to diagnose by US, because there are no bowel loops interposed between the appendix and the lateral wall of
260
L. Ceres et al.: US study of acute appendicitis in children
Fig.5. Cross section image of a retrocecal appendicitis with an appendicolith. The appendix is located between the cecum (C) and the transversus (T)
to the right iliac fossa, but also including the right upper quadrant and the right flank, in order not to miss a retrocecal appendicitis. T h e r e were no false positive studies in patients with retrocecal appendicitis, but in one case the sonographic diagnosis was "retrocecal appendicitis", and at laparotomy an acute gangrenous appendicitis in a high mobile cecum was found; in fact, the appendix was located in the right upper quadrant. We do not believe that this case should be considered as a true false positive. According to these results, US is highly specific for retrocecal appendicitis (100% specificity). Sensitivity is similar for retetrocecal appendicitis (94.5%) and for the total series (95.5%). Our results are slightly better than those previously reported [2, 3, 12] due probably to the fact that children are easier to explore by US than adults. The usefulness of abdominal US as a diagnostic test in patients with acute appendicitis has been recently questioned. Authors conclude that negative sonograms, even in small number, may increase the mortality rate of the whole group of patients, because delay in surgery increases the number of perforations [15-16]. A detailed discussion of those articles is beyond the scope of this paper. On a first review of our cases, the postoperative complication rate was not significantly different between the 233 children examined by US and the 340 who were not examined. Development of an abscess was the most common complication, affecting 43 patients (7.5%). Ultrasound was also used to diagnose and follow up these complications. As stated by Dr. Ravitch: "We seek a series of criteria ... that we will be safeguard from ever missing a case of acute appendicitis, and on the other hand, will not be accumulating a large specimen collection of normal appendices" [1]. The result of an US examination can be a very important additional criteria for the surgeon. A negative sonographic study, however, does not exclude acute appendicitis, and patients must be closely observed until the symptoms have completely subsided. If necessary, US studies should be repeated. In our experience, signs of appendiceal abscess, gangrenous appendicitis or appendicoliths are seldom missed by an expert sonographer. Furthermore, when a child with acute appendicitis is admitted to the Hospital after being treated elsewhere with antibio-
Fig.6. Appendiceal abscess. Complex mass (arrows) containing the appendix with a small fecalith, the omentum (E), and a bowel loop (I) Fi.g7. Retrocecal appendicitis with an abscess. A complex mass (arrowheads) containing some fecal material (*) is seen between the
cecum (C) and the transversus abdominis (T). There is free fluid on the right paracolic space (L) Fig.8. Thickened anterior pararenal space in a child with retrocecal appendicitis
the abdomen. The inflamed appendix is identified on cross section as a target image underneath the transversus abdominis muscle (Fig. 5), becoming a tubular structure on longitudinal imaging. The sonographic findings of retrocecal appendicitis are those described in iliac appendicitis, but the incidence of complex masses is greater in retrocecal appendicitis reflecting a higher incidence of perforation (Fig.7). We have also visualized in several children with retrocecal appendicitis a thickening and an increase in the echogenicity of the anterior pararenal space (Fig. 8); to our knowledge, this finding has only been described in children with acute pancreatitis [10]. Only in 5 patients with a retrocecal appendicitis were the US studies reported as normal. Reviewing these cases, in 4 instances the examinations were performed by young radiologists with little experience with this technique. We want to emphasize that as US is an operator-dependant technique, it is very important to perform a systemic routine examination as previously described; not limited
L. Ceres et al.: US study of acute appendicitis in children tics a n d / o r a n a l g e s i c s , his o r h e r s y m p t o m s b e c o m e s p e c i a l l y c o n f u s i n g . I n s e v e r a l s u c h cases, U S a d v i s e d t h e s u r g e o n to p e r f o r m a l a p a r o t o m y t h a t o t h e r w i s e w o u l d b e d e l a y e d . So, we d o n o t b e l i e v e t h a t t h e p r a c t i c e o f a b d o m i n a l U S in c h i l d r e n w i t h e q u i v o c a l clinical f i n d i n g s will exp o s e t h o s e p a t i e n t s to a h i g h e r risk. I n c o n c l u s i o n , t h e d i a g n o s i s of a c u t e a p p e n d i c i t i s c o n t i n u e s to b e b a s e d m a i n l y o n clinical f i n d i n g s , a n d t h e surg e o n s h o u l d b e r e s p o n s i b l e for a s s u m i n g t h e final d e c i s i o n r e g a r d i n g t h e i n d i c a t i o n for s u r g e r y in a child w i t h a c u t e a b d o m i n a l p a i n . U l t r a s o u n d is a n a c c u r a t e m e t h o d to est a b l i s h t h e c o r r e c t d i a g n o s i s in d o u b t f u l cases a v o i d i n g d e l a y o r u n n e c e s s a r y surgery. A t o u r i n s t i t u t i o n , t h e p r a c tice of a b d o m i n a l U S s t u d i e s in c h i l d r e n w i t h a c u t e a b d o m i n a l p a i n of u n c l e a r ethiology, t o g e t h e r w i t h close o b s e r v a t i o n o f t h e s e c h i l d r e n , has s i g n i f i c a n t l y d e c r e a s e d t h e incidence of negative appendicectomies.
References
1. Ravitch MM (1982) Appendicitis. Review article. Pediatrics 70: 414 2. Puylaert JBC (1986) Acute appendicitis: US evaluation using graded compression. Radiology 158:355 3. Abu-Yousef MM, B leicher J J, Maher JW, et al (1987) High resolution sonography of acute appendicitis. A JR 149:53 4. Simeone JF, Novelline RA, Ferrucci JT, et al (1985) Comparison of sonography and plain films in evaluation of the acute abdomen. AJR 144:44 5. Schisgall RM (1983) Use of the barium swallow in the diagnosis of acute appendicitis. Am J Surg 146:663
261 6. Jona JZ, Belin RP, Selke AC (1980) Barium enema as a diagnostic aid in children with abdominal pain. Surg Gynecol Obstet 144: 351 7. Gale ME, Birnbaum S, Gerzof SG, et al (1985) CT appearance of appendicitis and its local complications. J Comput Assist Tomogr 9:34 8. Feldberg MAM, Hendriks MJ, van Waes PFGM (1985) Computed tomography in complicated acute appendicitis. Gastrointest Radio110: 289 9. Mendelson RM, Lindsell DRM (1987) Ultrasound examination of the pediatric "acute abdomen": preliminary fingings. Br J Radio160: 414 10. Ceres L, Alonso I (1989) Ecografia de las Urgendas abdomihales en pediatria. Monografias de Diagnostico por Imagen. 7: 119 1I. Parulekar SG (1983) Ultrasonic findings in disease of the appendix. J Ultrasound Med 2:59 12. Takada T, Yasuda H, Uchiyama K, et al (1986) Ultrasonographic diagnosis of acute appendicitis in surgical indication. Int Surg 71: 9 13. Puylaert JBC (1987) Graded compression ultrasound in acute disease of the right lower quadrant. Semin Ultrasound CT and MR 8:385 14. Claes H, Reygaerts D, Leemans J, et al (1984) Ultrasonic visualization of the acute inflamed retrocecal appendix: a report of 4 cases. J Beige Radio167: 333 15. Rosenquist JC (1988) The usefulness of diagnostic tests. A JR 150:1189 16. Hillman BJ (1988) The value of imaging technology to patients health A JR 150:1191 Dr. L. Ceres Servicio de Radiologia Pediatrica Hospital Materno Infantil Arroyo de los Angeles E-29011 M~laga Spain
Literature in pediatric radiology (continued from p. 252) Journal of Bone and Joint Surgery Americml Volume (Boston)
Fractures in patients who have myelomeningocele. Lock, T.R., Aronson, D.D. (Aronson, D. D., Dept. of Orthop. Surg., Wayne State Univ. School of Med., Hutzel Hosp., 4707 St. Antoine, Detroit, MI 48201,USA) 71-A, 1153 (1989) Ewing sarcoma in a phalanx of an infant's finger. Strege, D.W. et al. (Dept. of Orthop. Surg., Univ. Med. Center, 1325South Grand Blvd., St.Louis, MO 63104, USA) 71-A, 1262 (1989) Pseudarthrosis of the radius after fracture through normal bone in a child who had neurofibromatosis. Kaempffe, E A., Gillespie, R. (Dept. of Orthop. Surg., State Univ., School of Med., 462 Grider St., Buffalo, NY 14215, USA) 71-A, i419 (1989) Treatment of dislocation of the hip, detected in early childhood, based on magnetic resonance imaging. Bos, C.EA. et al. (Univ. Hosp., Rijnsburgerweg 10, NL 2333AA Leiden, The Netherlands) 7J-A, 1523 (1989) Journal of Computer Assisted Tomography (New York)
Displacement of the quadrigeminal plate in tumors of the fourth ventricle: MR appearance. Nemoto, Y. et al. (Dept. of Rad. and Neurosurg., Univ. School of Med., 1-5-7 Asahimachi, Abenoku, Osaka 545, Japan) 13, 769 (1989) MR findings on primitive neuroectodermal tumors. Figueroa, R.E. et at. (Dept. of Rad., Med. College, 1120 15th St., Augusta, GA 30912, USA) 13, 773 (1989) Rapid three-dimensional display of the cerebral ventricles from noncontrast CT scans. Naidich, T.R et al. (Dept. of Rad., Baptist Hosp., 8900 North Kendall Dr., Miami, FL 33176-2197,USA) 13,779 (1989) Tuberous sclerosis: increased MR detection using gradient echo techniques. Berns, D. H. et al. (Dept. of Rad., Univ. Hosp., Case Western Reserve Univ.,2074 Abington Rd, Cleveland, OH 44106, USA) 13, 896 (1989)
Evaluation of craniosynostosis with three-dimensional CT imaging.Parisi, M. et al. (Finch, I.J., Dept. of Rad., Santa Clara Valley Med. Center, 751 S. Bascom Ave., San Jose, CA 95128,USA) 13,1006 (1989) Hemangioendothefioma of bone: CT findings. Merine, D., Fishman, E.K. (Fishman, E. K., The Russell H. Morgan Dept. of Rad. and Rad. Science, John Hopkins Med. Inst., Baltimore, MD 21205, USA) 13,1098 (1989) Journal of Neurosurgery (Baltimore)
Syringomyelia extending to the basaI ganglia. Okada, S. et al. (Dept. of Neurosurg., Prefectural Univ. of Med., Kawaramachi-Hirokoji, Kamigyoku, Kyoto 602, Japan) 71, 616 (1989) Intracerebral myiasis from Hypoderma boris larva in a child. Kalelioglu, M. et at. (Aktiirk, E, Kaxadeniz Teknik Univ. Tip Fakultesi, Norosirurii AnabilimDali, Trabzon, Turkey) 71, 929 (1989) Eosinophilic granuloma of the cervicothoracic junction. Sweasey,T_A., Dausin; R.C. (Univ. Med. Center, 1500East Med. Center Dr., Ann Arbor, M148109-0338, USA) 71, 942 (1989) Journal of Nuclear Medicine (New York)
Regional brain blood flow in congenital dysphasia: studies with technetium99m HM-PAO SPECT. Denays, R. et al. (Dept. of Neurol., Saint-Pierre Hosp., 322 Rue Haute~B-1000 BruxelIes, Belgium) 30,1825 (1989) Journal of Pediatrics (St. Louis)
Chiari type I malformation in children. Dure, L.S. et al. (Percy, A.K., Dept. of Ped., Baylor College of Med., One Baylor Plaza, Itoustom TX 77030, USA) 115, 573 (1989) (continued on p. 276)
Pediatric Radiology 9 Springer-Verlag 1990
Ultrasound study of acute appendicitis in children with emphasis upon the diagnosis of retrocecal appendicitis* L. C e r e s 1, I. A l o n s o t, R L 6 p e z 1, G. P a r r a 1 a n d J. E c h e v e r r y 2 Departments of 1Pediatric Radiology and 2Pediatric Surgery, Hospital Materno Infantil, Mfilaga, Spain
Abstract. A c u t e appendicitis in children frequently presents equivocal clinical manifestations. D e l a y of the p r o p e r diagnosis and unnecessary laparotomies are c o m m o n . A b d o m i n a l ultrasound has p r o v e d to be useful in the diagnosis of acute appendicitis in adults. We have p e r f o r m e d a preoperative ultrasound study in 368 children with acute appendicitis. A m o n g them, 92 had a retrocecal appendicitis. U l t r a s o u n d established the correct diagnosis in 92.6% of patients, and in 94.5% of those with a retrocecal appendicitis. A t our institution an abdominal s o n o g r a p h y is p e r f o r m e d on any child with a doubtful clinical diagnosis of acute appendicitis, helping the surgeon to take the decision to p e r f o r m a laparotomy.
It is well k n o w n that acute appendicitis is the most c o m m o n indication of e m e r g e n c y abdominal surgery in children. A l t h o u g h the clinical presentation is typical in m o s t cases, about 30% of patients present confusing symptomatology, leading to delay of the p r o p e r diagnosis as well as to a rate as high as 2 0 - 2 5 % of unnecessary laparotomies [1-3]. Several imaging procedures have b e e n p r o p o s e d to improve diagnostic accuracy. Plain abdominal films are routinely taken in m o s t institutions [4]. B a r i u m examination m a y be of s o m e value [5, 6], and even CT has b e e n used to study complicated appendicitis [7, 8]. A b d o m i n a l s o n o g r a p h y has p r o v e d to be a very useful tool in the evaluation of acute a b d o m i n a l pain in adults and children [4, 9, 10], and has b e e n p r o p o s e d by severeal authors for the diagnosis of acute appendicitis [2, 3, 11-13]. A b d o m i nal U S is a very suitable technique to investigate children with acute a b d o m i n a l pathology, because it is non-invasive, quick and free of radiation. We present our experience with 368 children o p e r a t e d on for acute appendicitis w h o were e x a m i n e d with US prior to surgery.
368 of them prior to surgery. During a first period of 18 months we conducted a prospective study; all children with a clinical diagnosis of acute appendicitis established by the surgeon on duty were examined by US whenever a radiologist with experience in pediatric sonography was on call. During the following 18 months, studies were done mainly in doubtful cases. Meanwhile, all the radiologists at our Hospital were trained to perform these studies. In all patients, US findings were correlated with surgical and pathological reports. At the same time, a second group of children either suffering from acute abdominal pain of unclear ethiology, or with the clinical diagnosis of acute appendicitis, was also examined by US. In this group the sonographic study was normal, or established a diagnosis not previously suspected. None of these children were operated for acute appendicitis, and they are not included in this paper. All the examinations were performed using a 5 MHz autofocus sector transducer, which allows the study of both superficial and deep abdominal areas. The same systematic study was done on all patients. The study begins examining the right upper quadrant, and descending through the right flank toward the right iliac fossa and the pelvis. Following the technique described by Puylaert, a gentle compression with the transducer is applied, to displace the bowel loops [2]. This compression is extremely well tolerated by most children. The psoas muscle and the iliac vessels are the anatomical landmarks to identify the appendix, which usually is located between these structures and the abdominal wall (Fig. 1). A normal, non inflamed appendix is seldom visualized by US [3].
Material and method Between January 1986 and December 1988, 833 consecutive children, aged 2 to 14 years, were operated on with the clinicl diagnosis of acute appendicitis. An abdominal US study was performed in * Presented at the ESPR meeting in Dubin 1989. Selected for publication by an International Group of the ESPR
Fig. 1. The psoas and the iliac vessels are the anatomical landmarks to identify the appendix
L. Ceres et al.: US study of acute appendicitis in children
259
Fig.2. Acutely inflamed appendix; longitudinal image l~g.3. On cross section the appendix is visualized as a target. I = Iliac bone, Ps = psoas
Fig. 4. Gangrenous appendicitis. The appendix is enlarged, with irregular borders, and the mucosa tines are interrupted (arrowheads)
Results
quent finding is the presence of a paralytic ileus localized in the right lower quadrant. Bowel loops are seen filled with fluid, with sluggish or absent peristaltic waves. Occasionally, this fluid may be echogenic, or give the image of a fluid-fluid level, typical of a pus collection. A negative sonographic diagnosis was established in 26 patients (7%), based on the non visualization of the appendix or on the absence of any of the above described signs. Only 17 of them proved to be false negatives (4.7 %), while in the other 9 the appendix was normal according to the pathological report. There were also 10 cases (2.7%) with false positive diagnoses, but in one of them the appendix contained a carcinoid tumour. Ninety-two children had a retrocecal appendicitis. Ultrasound established the right diagnosis in 85, and in two cases the diagnosis was just "acute appendicitis". There were 5 false negatives (5.5%), and not a false positive among these patients.
Abdominal US established the correct diagnosis in 92.6% of patients. The sonographic findings agree with those described by most authors, and are summarized in Table 1. A combination of several findings in the same patients was rather frequent. The most common finding in children with acute appendicitis is an enlarged inflamed appendix, visualized on longitudinal imaging as a hypoechogenic tubular structure in continuity with the cecum and having a blind distal end. The mucosa is identified as two thin echogenic lines surrounding the lumen (Fig. 2). The echogenic aspect of the appendiceal lumen depends on the amount of fecal material contained in it. Contrary to bowel loops, the inflamed appendix lacks peristalsis, is rigid and is not easy to compress. On cross section the appendix resembles a target with a hypoechogenic external ring (Fig. 3). With the progression of the inflammatory reaction the appendiceal wall thickens, and becomes irregular. Where the echogenic lines of the mucosa are interrupted, it is a sign of gangrenous appendicitis (Fig.4), and where the tubular aspect of the appendix gradually disappears, it indicates periappendicitis. Appendicoliths are visualized as intra, luminal hyperechoic structures with a shadowing (Fig. 5). Only approximately 50% of appendicoliths identified by US were also seen on the plain film of the abdomen. The sonographic appearance of an appendix abscess is a complex mass. Sometimes we can recognise the appendix inside the mass, the omentum wrapping the appendix in the form of an echogenic band, and some bowel loops (Fig. 6). All cases with a sonographic diagnosis of appendiceal abscess were confirmed at laparotomy. Another fre-
Table 1. US findingsin children with acute appendicitis
% Of cases Enlarged appendix Irregular appendiceal borders Appendicoliths Appendiceal abscess Periappendiceal fluid Localized ileus
61.8 33 29.6 21.5 24.9 16.3
% Of retrocecal appendicitis 69.5 22.5 33.7 28.2 20 11
Discussion
The diagnosis of acute appendicitis by means of abdominal sonography has been demonstrated in several recent publications, mainly in adult patients [2, 3, 11-13]. The present study proves that US is also very accurate in the diagnosis of acute appendicitis in pediatric patients. Retrocecal appendicitis represents approximately 28% of our patients. These children usually come to the Hospital with symptoms lasting for at least 24 to 48 h, and with rather confusing clinical manifestations for the surgeon. Delay in the diagnosis is common in that group of patients, and as a result of this delay, perforation was found by laparotomy in 42% of retrocecal appendicitis, while it did occur only in 14% of patients with iliac appendicitis. The sonographic visualization of a retrocecal inflamed appendix was first reported by Claes at als in 1984 [14]. It has been surprising to us that the particular value of US in demonstrating a retrocecal appendicitis has not been emphasized in the literature, even in the largest series so far reported. A retrocecal appendicitis is, however, very easy to diagnose by US, because there are no bowel loops interposed between the appendix and the lateral wall of
260
L. Ceres et al.: US study of acute appendicitis in children
Fig.5. Cross section image of a retrocecal appendicitis with an appendicolith. The appendix is located between the cecum (C) and the transversus (T)
to the right iliac fossa, but also including the right upper quadrant and the right flank, in order not to miss a retrocecal appendicitis. T h e r e were no false positive studies in patients with retrocecal appendicitis, but in one case the sonographic diagnosis was "retrocecal appendicitis", and at laparotomy an acute gangrenous appendicitis in a high mobile cecum was found; in fact, the appendix was located in the right upper quadrant. We do not believe that this case should be considered as a true false positive. According to these results, US is highly specific for retrocecal appendicitis (100% specificity). Sensitivity is similar for retetrocecal appendicitis (94.5%) and for the total series (95.5%). Our results are slightly better than those previously reported [2, 3, 12] due probably to the fact that children are easier to explore by US than adults. The usefulness of abdominal US as a diagnostic test in patients with acute appendicitis has been recently questioned. Authors conclude that negative sonograms, even in small number, may increase the mortality rate of the whole group of patients, because delay in surgery increases the number of perforations [15-16]. A detailed discussion of those articles is beyond the scope of this paper. On a first review of our cases, the postoperative complication rate was not significantly different between the 233 children examined by US and the 340 who were not examined. Development of an abscess was the most common complication, affecting 43 patients (7.5%). Ultrasound was also used to diagnose and follow up these complications. As stated by Dr. Ravitch: "We seek a series of criteria ... that we will be safeguard from ever missing a case of acute appendicitis, and on the other hand, will not be accumulating a large specimen collection of normal appendices" [1]. The result of an US examination can be a very important additional criteria for the surgeon. A negative sonographic study, however, does not exclude acute appendicitis, and patients must be closely observed until the symptoms have completely subsided. If necessary, US studies should be repeated. In our experience, signs of appendiceal abscess, gangrenous appendicitis or appendicoliths are seldom missed by an expert sonographer. Furthermore, when a child with acute appendicitis is admitted to the Hospital after being treated elsewhere with antibio-
Fig.6. Appendiceal abscess. Complex mass (arrows) containing the appendix with a small fecalith, the omentum (E), and a bowel loop (I) Fi.g7. Retrocecal appendicitis with an abscess. A complex mass (arrowheads) containing some fecal material (*) is seen between the
cecum (C) and the transversus abdominis (T). There is free fluid on the right paracolic space (L) Fig.8. Thickened anterior pararenal space in a child with retrocecal appendicitis
the abdomen. The inflamed appendix is identified on cross section as a target image underneath the transversus abdominis muscle (Fig. 5), becoming a tubular structure on longitudinal imaging. The sonographic findings of retrocecal appendicitis are those described in iliac appendicitis, but the incidence of complex masses is greater in retrocecal appendicitis reflecting a higher incidence of perforation (Fig.7). We have also visualized in several children with retrocecal appendicitis a thickening and an increase in the echogenicity of the anterior pararenal space (Fig. 8); to our knowledge, this finding has only been described in children with acute pancreatitis [10]. Only in 5 patients with a retrocecal appendicitis were the US studies reported as normal. Reviewing these cases, in 4 instances the examinations were performed by young radiologists with little experience with this technique. We want to emphasize that as US is an operator-dependant technique, it is very important to perform a systemic routine examination as previously described; not limited
L. Ceres et al.: US study of acute appendicitis in children tics a n d / o r a n a l g e s i c s , his o r h e r s y m p t o m s b e c o m e s p e c i a l l y c o n f u s i n g . I n s e v e r a l s u c h cases, U S a d v i s e d t h e s u r g e o n to p e r f o r m a l a p a r o t o m y t h a t o t h e r w i s e w o u l d b e d e l a y e d . So, we d o n o t b e l i e v e t h a t t h e p r a c t i c e o f a b d o m i n a l U S in c h i l d r e n w i t h e q u i v o c a l clinical f i n d i n g s will exp o s e t h o s e p a t i e n t s to a h i g h e r risk. I n c o n c l u s i o n , t h e d i a g n o s i s of a c u t e a p p e n d i c i t i s c o n t i n u e s to b e b a s e d m a i n l y o n clinical f i n d i n g s , a n d t h e surg e o n s h o u l d b e r e s p o n s i b l e for a s s u m i n g t h e final d e c i s i o n r e g a r d i n g t h e i n d i c a t i o n for s u r g e r y in a child w i t h a c u t e a b d o m i n a l p a i n . U l t r a s o u n d is a n a c c u r a t e m e t h o d to est a b l i s h t h e c o r r e c t d i a g n o s i s in d o u b t f u l cases a v o i d i n g d e l a y o r u n n e c e s s a r y surgery. A t o u r i n s t i t u t i o n , t h e p r a c tice of a b d o m i n a l U S s t u d i e s in c h i l d r e n w i t h a c u t e a b d o m i n a l p a i n of u n c l e a r ethiology, t o g e t h e r w i t h close o b s e r v a t i o n o f t h e s e c h i l d r e n , has s i g n i f i c a n t l y d e c r e a s e d t h e incidence of negative appendicectomies.
References
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