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CT-guided drainage of pelvic abscesses: The peranal transrectal approach
Clinical Radiology (1992) 45, 246 249
CT-Guided Drainage of Pelvic Abscesses: The Peranal Transrectal Approach D. J. LOMAS, A. K. DIXON, H. J. T H O M S O N * and D. ST J O H N COLLIER*
Departments of Radiology and *Surgery, Addenbrooke's Hospital and University of Cambridge, Cambridge Five patients with deep pelvic abscesses underwent computed tomography (CT)-guided catheter drainage using a transrectal approach. The use of an outer removable plastic sheath over the catheter to facilitate positioning and prevent inadvertent damage to the mucosal wall is described. This new approach using CT guidance is discussed and the alternative routes reviewed. Lomas, D.J., Dixon, A.K., Thomson, H.J. & St John Collier, D. (1992). Clinical Radiology 45, 246 249. CT-Guided Drainage of Pelvic Abscesses: The Peranal Transrectal Approach
Guided percutaneous catheter aspiration or drainage is now a widely accepted procedure in the management of abdominal and pelvic abscesses, particularly in postoperative patients in whom further surgery may be inadvisable. Guidance with imaging control allows precise positioning of a catheter or cannula after the planning of an optimal route to the collection. When draining abscesses, most workers select a route which avoids traversing bowel or solid organs and for abdominal collections this is usually straightforward. However, within the pelvis the bony walls and compact arrangement of the various structures (solid and fluid filled) restrict the available routes, particularly for collections in the perirectal and presacral areas. Such collections are usually extraperitoneal and therefore routes which avoid breaching the peritoneum are preferred. For these reasons some workers have continued to advocate formal surgical drainage, per rectum, for these 'deep' pelvic abscesses (Shapiro et al., 1989). Alternative guided approaches have been devised to overcome the problems of access, for example the transrectal, transvaginal and sciatic notch routes (Mauro et al., 1985; Nosher et al., 1986, 1987; Butch et al., 1986). As computed tomography (CT) is essentially a crosssectional or 'transaxial' imaging modality interventional techniques using CT guidance have tended to use predominantly transaxial routes which demonstrate the length of the cannula or catheter during insertion (Mueller et al., 1984). Ultrasound has the advantage of multiplanar views which, with endocavitary probes, allow the transrectal or transvaginal passage of a catheter to be observed in real time (Mauro et al., 1985; Nosher et al., 1986, 1987). However, there are few reports of draining pelvic abscesses using the transrectal or transvaginal routes monitored by CT, although some workers have advocated the technique (J_ R. Haaga, 1988, personal communication). We report a single technique allowing transrectal drainage of pelvic collections using CT guidance, and illustrate this with five cases.
Correspondence to: Dr Adrian K. Dixon, University Department of Radiology, Level 5, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2QQ.
METHODS Initial diagnostic images of the pelvis are obtained with the patient supine. Standard preparation with oral and rectal contrast medium is required to differentiate the collection from adjacent bowel. If the patient has not been imaged with CT on an earlier occasion intravenous contrast medium is also administered to identify vascular structures (Husband and Golding, 1983) and for potential abscess wall enhancement (Aronberg et al., 1978). Depending on the site of the abscess and the approach angle required for aspiration, the patient is placed prone or supine. The prone position is preferred because of better access to the perineum, however this is not practical in patients where marked posterior angulation of the cannula is required to enter the abscess_ The anus should be defined on the more caudal images; this allows an estimate of the distance from the anal margin to the ideal puncture site in the wall of the collection. A plastic cannula with a central metal trocar (e.g. Wallace 14 G) is selected which is long enough to reach the collection but leave the hub external to the patient. This is enclosed within a blunt-ended plastic sheath (e.g. a simple filling cannula) which has been slit along its length to allow later removal without disturbing the position of the cannula in the rectum (Fig. 1)_ Using a gloved finger, the protected cannula is inserted into the rectum by the distance calculated from the initial imaging. A sterile adhesive tape strip (e.g. Steristrip) attached to the cannula is useful as a simple distance marker. Contiguous images at the level of the collection will demonstrate the tip of the cannula and this is repositioned
Fig. 1 The drainage cannula and needle enclosed within a sterile plastic sheath whmh has been slit along its length to facilitate later removal.
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CT-GU1DED TRANSRECTAL ABSCESS DRAINAGE
if necessary so that it lies adjacent to the wall of the collection_ F r o m the images the appropriate angle of entry into the collection can be assessed. With the hub of the cannula held firmly the protective sheath is withd r a w n . The cannula is then angled and advanced into the collection. Pus usually escapes under pressure; a specimen is saved for microbiology. The central metal needle is removed and, using a Seldinger guide-wire exchange technique and dilators, the cannula m a y be exchanged for a larger pigtail catheter (e.g. van Sonnenberg 8.3 or 12 F). The abscess is then aspirated as completely as possible_ The catheter may 'be left to drain freely or regularly aspirated. External to the rectum the catheter can he attached to the skin with adhesive plaster or sutured (e.g. to the proximal thigh). It is currently impractical to fix the catheter firmly to the rectal wall; indeed the catheter tip is likely to be expelled during defaecation.
(a)
CASE R E P O R T S Case 1 (Fig. 2). A 23-year-old foreign student presented with fever and suprapubic pain 2 weeks following appendicectomy, at which a perforated appendix had been excised and a small adjacent collection drained. On readmission he was pyrexial with a leucocytosis of 22 x 109/ litre and experienced pelvic tenderness on both abdominal and rectal examination. CT demonstrated an 8 cm pelvic collection which was drained transrectally using a van Sonnenberg 12 F catheter. Pus (550 ml) was aspirated from which both Haemophilus influenzae and anaerobic organisms were cultured. The catheter tip was expelled at 24 h. Despite oral antibiotic therapy the collection reaccumulated and a further drainage procedure was carried out 1 week later, when the catheter was firmly sutured to the skin of the upper thigh. On this occasion a further 500 ml of pus was obtained. Intravenous antibiotics (gentamicin, lnetronidazole and benzyl penicillin) were administered for 4 days followed by oral benzyl penicillin and metronidazole. Review ultrasound 3 days after the second procedure demonstrated satisfactory resolution, and the catheter was removed. He remained well and returned to his native country 1 week later; further follow up was impractical. Case 2. A 20-year-old man presented with a 2 day history of lower abdominal pain and vomiting. Marked pelvic tenderness was elicited on rectal examination and CT revealed a 9 cm diameter collection between the bladder and rectum. This collection extended to a further small collection around a calcified appendicolith in the right iliac fossa. intravenous antibiotic therapy with metronidazole, gentamicin and ampicillin was instituted and the collection was drained transrectally with an 8.3 F van Sonnenberg catheter, producing 270 ml of pus flora which Escherichia coli and Streptococcus viridans were cultured. The catheter was expelled at 12 h. He became pyrexial again at 72 h when CT showed a residual but smaller collection. Accordingly a further drainage with an 8.3 F catheter was performed and 120 ml of pus aspirated. He subsequently became apyrexial and was discharged on oral antibiotic therapy. He experienced mild pelvic discomfort 3 weeks later when CT demonstrated a very small (2 cm diameter) collection which was managed with further oral antibiotic therapy. Clinical and ultrasound follow up have been satisfactory. An elective appendicectomy is planned. Cases 3, 4 and 5. The next three patients all underwent restorative proctocolectomy, with ileal reservoir formation (Parks' pouch (Everett, 1989)) for chronic syrup tomatic ulcerative colitis. Two of these patients subsequently developed pelvic pain and became pyrexial with a leucocytosis (14 and 11.4 x 109/litre respectively). Indium labelled white cell imaging demonstrated probable pelvic collections. In the first of these two patients (Case 3, a 34-year-old woman) CT demonstrated a 5 × 3 cm collection (Fig. 3a) posterior to the ileal pouch, from which 25 ml of pus was drained via a 8 F van Sonnenberg catheter introduced transrectally (Figs 3b and c). Anaerobic streptococci were cultured from the pus. One week later CT demonstrated almost complete resolution and she remains well 3 months later. In the second patient (Case 4, a 26year-old woman) CT demonstrated a l0 x 5 cm pelvic collection from which 65 ml was aspirated transrectally via an 8 F catheter. This was removed at 48 h. Repeat CT 1 week later demonstrated that this initial deep collection had resolved but that there was a new unrelated 3 cm diameter midline pelvic collection adjacent to the anterior abdominal wall incision. This was drained via a standard anterior percutaneous
(b)
(c) Fig. 2 - A series of images from Case. 1. (a) The CT appearances 1 week after the initial procedure. There is still a large pelvic abscess with some air within anteriorly (probably introduced at the time of the first drainage). The close relation to loops of gut again render an anterior abdominal wall approach difficult. (b) Prone therapeutic CT, somewhat more caudal. This shows the catheter in situ in the centre of the collection. The air is now in the superior portion of the collection. Note the distortion of the rectum (arrow). (c) After drainage to dryness, the collection is much smaller. The rectum has already assumed a much more normal shape.
approach using an 8 F catheter. Her pyrexia resolved and she remains well 6 months later. The third patient (Case 5, a man of 50 years) also developed a 5 cm collection in the pre-sacral space following restorative proctocolectomy. However, his post-operative course was particularly complicated and on three occasions over 5 months a pelvic collection was drained using a transrectal approach with CT guidance. Appropriate antibiotic therapy for the cultured organisms (E. coli, Bacteroides, and Group F streptococci) was given. The CT examinations and subsequent barium studies revealed no evidence of a fistula communicating with the bowel. Ultimately because of persisting pain and rectal irritation the ileal pouch was excised and an ileostomy fashioned. At surgery a small abscess cavity was found and also excised, although no infective focus was reported.
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(a)
(b)
(c) Fig. 3 A series of images from Case 3. (a) Diagnostic CT showing an abscess (arrow) in the pre-sacral space, posterior to the pouch formed by rectoplasty. There is an air-fired level in the pouch; dilute contrast medium was instilled per rectum before this study. (b) Therapeutic CT. Needle, cannula and invisible sheath in position in pouch immediately caudal to the level shown in (a). The protective sheath was then removed as this was considered a suitable site for puncture of the posteriorly and cranially situated abscess using appropriate angulation. Pus was aspirated at puncture. Guide-wire exchange to an 8 F pigtail catheter; 25 ml pus aspirated via catheter. (c) Pigtail catheter in collapsed abscess cavity at the end of procedure.
DISCUSSION Pelvic abscesses may arise secondary to bowel or gynaecological surgery, as well as following pelvic inflammatory disease, Crohn's disease, appendicitis or more generalized peritonitis (Finne, 1980; Casola et al., 1987; Pan and Shirkoda, 1987). In addition, when a 'neorectum' (Parks' pouch (Everett, 1989)) has been constructed from terminal ileum following colectomy for ulcerative colitis, and pouch-anal anastomosis carried out, leakage from the ileo-anal anastomosis may lead to abscess formation deep in the pelvis.
The traditional surgical treatment of pelvic abscesses, which usually requires general anaesthesia, is drainage by a transrectal (or occasionally transvaginal) approach (Storer, 1984). After needle aspiration through the rectal wall to confirm the diagnosis and site the rectal wall is incised, the opening widened with a finger to allow loculi to be broken down, and a drain o r trocar catheter (Nivatvongs, 1986) inserted. Daily digital examination per rectum of the abscess opening is performed during the following week to ensure continuing free drainage. This is likely to contribute to the low recurrence rate of approximately 10% given in the limited series reported in the surgical literature (Finne, 1980). This surgical approach is usually possible only when there is a large mature fluctuant pelvic collection which has walled off from adjacent viscera and is easily palpable per rectum. In two of our patients (Cases 3 and 5) the collections were not easily palpable, making this type of surgical approach difficult. Percutaneous drainage of infected pelvic collections is now an established procedure providing an alternative to formal surgical drainage. The choice as to which route to employ often depends as much on local expertise and availability of equipment as on perceived risk. The complication rate is low for all routes and the numbers in published series are rarely large enough to allow truly valid comparisons of morbidity and mortality rates (Mueller et al., 1984). Studies of guided biopsies confirm the overall low complication rate of similar techniques (Welch et al., 1990). Potential risks of percutaneous aspiration or drainage include missing the collection, incomplete drainage and damage or perforation of adjacent structures (bladder, bowel, vessels, nerves, etc.). With experience the procedures are relatively quick to perform and can be carried out during a routine imaging list (Lomas and Dixon, 1990). The choice of imaging technique also depends on personal experience, although clearly some approaches are biased to one modality (e.g. sciatic notch approach with CT). CT provides a comprehensive view of the pelvis and is not restricted in obese patients or by the presence of copious bowel gas. Ultrasound, although providing a limited view, allows multiplanar orientation and true real-time demonstration of insertion of the drainage device. Endovaginal and endorectal probes provide detailed images of 'deep' pelvic collections and potentially of catheter placement. The portability of ultrasound allows procedures to be performed at the bedside (e.g. in the Intensive Care Unit) with a minimum of disruption for the patient. While it might have been possible to drain the large collections related to appendiceal problems (Cases 1 and 2) with ultrasound monitoring, it is debatable whether the smaller pre-sacral collections (Cases 3, 4 and 5) could have been managed in this way. An anterior percutaneous approach is well suited to superficial collections close to the anterior abdominal wall. With 'deeper' collections careful manipulation is necessary to achieve accurate catheter placement and avoid deflection of the cannula during insertion. Ideally the bladder should be avoided and thus an empty bladder may appear to be advantageous; however, this may allow the interposition of bowel loops and make the route equally hazardous. Anterolateral approaches parallel to the iliac wings are useful for avoiding intervening bowel, but care must be taken to avoid vessels (e.g_ the inferior
CT-GUIDED TRANSRECTAL ABSCESS DRAINAGE
epigastric artery). Despite these manoeuvres some collections will remain inaccessible via an anterior approach unless one is prepared to traverse bowel or bladder. The advantages of an anterior approach include convenience for the operator and relative comfort for the patient; Catheters can be easily secured to the anterior abdominal wall. A posterolateral percutaneous approach via the sciatic notch has been described using CT guidance (Butch et al_, 1986). This allows drainage of perirectal and pre-sacral collections that are inaccessible via the anterior route. There is a theoretical risk of damage (Jaques and Mauro, 1986) to the structures traversing the sciatic notch (gluteal vessels, sciatic nerve, etc.) but in the reported series so far no serious complications have been encountered. However, this may be a painful procedure and temporary paraesthesiae can occur, presumably caused by trauma to branches of the sacral plexus during the initial needle insertion. Catheter fixation to the skin in the gluteal region is straightforward, although in a relatively uncomfortable position for the patient. Transvaginal and transrectal routes allow a relatively painless approach to perirectal and pre-sacral collections. The short distances involved allow for good catheter control and reduce the risk of misplacement during insertion. With a catheter left in situ there is a theoretical risk of reverse infection and adequate fixation of the catheter may be difficult to achieve even when sutured to the thigh. The short length of catheter within the soft and relatively mobile rectum prevents the catheter tip being firmly secured. The use of an 'anchored' catheter (Cope, 1988) might avoid this problem. Even if the catheters block or dislodge they may create a track into the rectum allowing subsequent free drainage. To increase the probability of forming a track as large a catheter as possible should be used (the small size catheters used in Cases ! and 2 may have contributed to the reformation of the collection). This parallels the traditional surgical technique of incising a large pelvic abscess and allowing free drainage per rectum. Leaving a catheter traversing the vaginal or anal orifice is slightly uncomfortable for the patient but usually well tolerated. In our limited experience three out of five of these 'deep' pelvic collections have been associated with complex bowel reconstruction surgery and, although repeat drainages proved necessary in three patients, only one subsequently required formal surgery. We consider that when presented with the clinical problem of a pelvic abscess that cannot be easily approached percutaneously using an anterior approach, the peranal transrectal route using CT guidance provides a simple and effective alternative.
249
Acknowledgements. We would like to thank the various clinicians responsible for these patients, in particular M r W. G. Everett. The contribution of the nurses and radiographers is also appreciated.
REFERENCES Aronberg, D J, Stanley, R J, Levitt, R G & Sagel, SS (1978). Evaluation of abdominal abscesses with computed tomography. Journal of Computer Assisted Tomography, 2, 184 187. Butch, R J, Mueller, PR, Ferrucci, JT Jr, Wittenberg, J, Simeone, JF, White, EM et al. (1986). Drainage of pelvic abscesses through the greater sciatic foramen. Radiology, 158, 487 491. Casola, G, van Sonnenberg, E, Neff, CN, Saba, RM, Withers, C & Emarine, CW (1987). Abscesses in Crohn's disease: percutaneous drainage. Radiology, 163, 19-22. Cope, C (1988). Percutaneous subhepatic cholecystostomy with a removable anchor. American Journal of Roentgenology, 151, 1129 1133. Everett, WG (1989). Experience of restorative protocolectomy with ileal reservoir. British Journal of Surgery, 76, 77 81. Finne, CO (1980). Transrectal drainage of pelvic abscess. Dtseases of the Colon and Rectum, 23, 293 297. Husband, JE & Golding, SJ (1983). The role of computed tomography guided needle biopsy in an oncology service. Clinical Radtology, 34, 255 260. Jaques, PF & Mauro, M (1986). Drainage of pelvic abscesses through the greater sciatic foramen. Letter. Radiology, 160, 278-279. Lomas, OJ & Dixon, AK (1990). The duration of interventional procedures using CT guidance. Journal oflnterventional Radiology, 1, 13-15. Mauro, MA, Jacques, PF, Mandell, VS & Mandel, SR (1985). Pelvic abscess drainage by the transrectal catheter approach in men. American Journal of Roentgenology, 144, 477-479. Mueller, PR, van Sonnenberg, E & Ferrucci, JT Jr (1984). Percutaneous drainage of 250 abdominal abscesses and fluid collections. Radiology, 151,337 347. Nwatvongs, S (1986). Low pelvic abscesses. A technique of drainage using a small trocar catheter. American Journal of Surgery, lfil, 409411. Nosher, JL, Needell, GS, Amorosa, JK & Krasna, IH (1986). Transrectal pelvic abscess drainage with sonographic guidance. American Journal of Roentgenology, 146, 1047 1048. Nosher, JL, Winchman, H K & Needell, GS (1987). Transvaginal pelvic abscess drainage with US guidance. Radiology, 165, 872 873. Pan, G & Shirkoda, A (1987). Pelvic exenteration: role of CT in followup. Radiology, 164, 665-670. Shapiro, MP, Elan Gale M & Gerzof, SG (1989). CT of appendicitis: diagnosis and treatment. Radiologic Clinics of North America, 27, 753 762. Storer, EH ([984). Peritonitis and intraabdominal abscesses. In: Principles of Surgery 4th edn. eds. Shwartz, SI, Shires, GT, Spencer, FC & Storer, EH. pp. 1415-1416. McGraw Hill, New York. Welch, T,I, Sheedy II, PF, Johnson, CD, Johnson, M & Stephens, DH (1990). CT-guided biopsy: prospective analysis of I000 procedures. Radiology, 171,493 496.
CT-Guided Drainage of Pelvic Abscesses: The Peranal Transrectal Approach D. J. LOMAS, A. K. DIXON, H. J. T H O M S O N * and D. ST J O H N COLLIER*
Departments of Radiology and *Surgery, Addenbrooke's Hospital and University of Cambridge, Cambridge Five patients with deep pelvic abscesses underwent computed tomography (CT)-guided catheter drainage using a transrectal approach. The use of an outer removable plastic sheath over the catheter to facilitate positioning and prevent inadvertent damage to the mucosal wall is described. This new approach using CT guidance is discussed and the alternative routes reviewed. Lomas, D.J., Dixon, A.K., Thomson, H.J. & St John Collier, D. (1992). Clinical Radiology 45, 246 249. CT-Guided Drainage of Pelvic Abscesses: The Peranal Transrectal Approach
Guided percutaneous catheter aspiration or drainage is now a widely accepted procedure in the management of abdominal and pelvic abscesses, particularly in postoperative patients in whom further surgery may be inadvisable. Guidance with imaging control allows precise positioning of a catheter or cannula after the planning of an optimal route to the collection. When draining abscesses, most workers select a route which avoids traversing bowel or solid organs and for abdominal collections this is usually straightforward. However, within the pelvis the bony walls and compact arrangement of the various structures (solid and fluid filled) restrict the available routes, particularly for collections in the perirectal and presacral areas. Such collections are usually extraperitoneal and therefore routes which avoid breaching the peritoneum are preferred. For these reasons some workers have continued to advocate formal surgical drainage, per rectum, for these 'deep' pelvic abscesses (Shapiro et al., 1989). Alternative guided approaches have been devised to overcome the problems of access, for example the transrectal, transvaginal and sciatic notch routes (Mauro et al., 1985; Nosher et al., 1986, 1987; Butch et al., 1986). As computed tomography (CT) is essentially a crosssectional or 'transaxial' imaging modality interventional techniques using CT guidance have tended to use predominantly transaxial routes which demonstrate the length of the cannula or catheter during insertion (Mueller et al., 1984). Ultrasound has the advantage of multiplanar views which, with endocavitary probes, allow the transrectal or transvaginal passage of a catheter to be observed in real time (Mauro et al., 1985; Nosher et al., 1986, 1987). However, there are few reports of draining pelvic abscesses using the transrectal or transvaginal routes monitored by CT, although some workers have advocated the technique (J_ R. Haaga, 1988, personal communication). We report a single technique allowing transrectal drainage of pelvic collections using CT guidance, and illustrate this with five cases.
Correspondence to: Dr Adrian K. Dixon, University Department of Radiology, Level 5, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2QQ.
METHODS Initial diagnostic images of the pelvis are obtained with the patient supine. Standard preparation with oral and rectal contrast medium is required to differentiate the collection from adjacent bowel. If the patient has not been imaged with CT on an earlier occasion intravenous contrast medium is also administered to identify vascular structures (Husband and Golding, 1983) and for potential abscess wall enhancement (Aronberg et al., 1978). Depending on the site of the abscess and the approach angle required for aspiration, the patient is placed prone or supine. The prone position is preferred because of better access to the perineum, however this is not practical in patients where marked posterior angulation of the cannula is required to enter the abscess_ The anus should be defined on the more caudal images; this allows an estimate of the distance from the anal margin to the ideal puncture site in the wall of the collection. A plastic cannula with a central metal trocar (e.g. Wallace 14 G) is selected which is long enough to reach the collection but leave the hub external to the patient. This is enclosed within a blunt-ended plastic sheath (e.g. a simple filling cannula) which has been slit along its length to allow later removal without disturbing the position of the cannula in the rectum (Fig. 1)_ Using a gloved finger, the protected cannula is inserted into the rectum by the distance calculated from the initial imaging. A sterile adhesive tape strip (e.g. Steristrip) attached to the cannula is useful as a simple distance marker. Contiguous images at the level of the collection will demonstrate the tip of the cannula and this is repositioned
Fig. 1 The drainage cannula and needle enclosed within a sterile plastic sheath whmh has been slit along its length to facilitate later removal.
247
CT-GU1DED TRANSRECTAL ABSCESS DRAINAGE
if necessary so that it lies adjacent to the wall of the collection_ F r o m the images the appropriate angle of entry into the collection can be assessed. With the hub of the cannula held firmly the protective sheath is withd r a w n . The cannula is then angled and advanced into the collection. Pus usually escapes under pressure; a specimen is saved for microbiology. The central metal needle is removed and, using a Seldinger guide-wire exchange technique and dilators, the cannula m a y be exchanged for a larger pigtail catheter (e.g. van Sonnenberg 8.3 or 12 F). The abscess is then aspirated as completely as possible_ The catheter may 'be left to drain freely or regularly aspirated. External to the rectum the catheter can he attached to the skin with adhesive plaster or sutured (e.g. to the proximal thigh). It is currently impractical to fix the catheter firmly to the rectal wall; indeed the catheter tip is likely to be expelled during defaecation.
(a)
CASE R E P O R T S Case 1 (Fig. 2). A 23-year-old foreign student presented with fever and suprapubic pain 2 weeks following appendicectomy, at which a perforated appendix had been excised and a small adjacent collection drained. On readmission he was pyrexial with a leucocytosis of 22 x 109/ litre and experienced pelvic tenderness on both abdominal and rectal examination. CT demonstrated an 8 cm pelvic collection which was drained transrectally using a van Sonnenberg 12 F catheter. Pus (550 ml) was aspirated from which both Haemophilus influenzae and anaerobic organisms were cultured. The catheter tip was expelled at 24 h. Despite oral antibiotic therapy the collection reaccumulated and a further drainage procedure was carried out 1 week later, when the catheter was firmly sutured to the skin of the upper thigh. On this occasion a further 500 ml of pus was obtained. Intravenous antibiotics (gentamicin, lnetronidazole and benzyl penicillin) were administered for 4 days followed by oral benzyl penicillin and metronidazole. Review ultrasound 3 days after the second procedure demonstrated satisfactory resolution, and the catheter was removed. He remained well and returned to his native country 1 week later; further follow up was impractical. Case 2. A 20-year-old man presented with a 2 day history of lower abdominal pain and vomiting. Marked pelvic tenderness was elicited on rectal examination and CT revealed a 9 cm diameter collection between the bladder and rectum. This collection extended to a further small collection around a calcified appendicolith in the right iliac fossa. intravenous antibiotic therapy with metronidazole, gentamicin and ampicillin was instituted and the collection was drained transrectally with an 8.3 F van Sonnenberg catheter, producing 270 ml of pus flora which Escherichia coli and Streptococcus viridans were cultured. The catheter was expelled at 12 h. He became pyrexial again at 72 h when CT showed a residual but smaller collection. Accordingly a further drainage with an 8.3 F catheter was performed and 120 ml of pus aspirated. He subsequently became apyrexial and was discharged on oral antibiotic therapy. He experienced mild pelvic discomfort 3 weeks later when CT demonstrated a very small (2 cm diameter) collection which was managed with further oral antibiotic therapy. Clinical and ultrasound follow up have been satisfactory. An elective appendicectomy is planned. Cases 3, 4 and 5. The next three patients all underwent restorative proctocolectomy, with ileal reservoir formation (Parks' pouch (Everett, 1989)) for chronic syrup tomatic ulcerative colitis. Two of these patients subsequently developed pelvic pain and became pyrexial with a leucocytosis (14 and 11.4 x 109/litre respectively). Indium labelled white cell imaging demonstrated probable pelvic collections. In the first of these two patients (Case 3, a 34-year-old woman) CT demonstrated a 5 × 3 cm collection (Fig. 3a) posterior to the ileal pouch, from which 25 ml of pus was drained via a 8 F van Sonnenberg catheter introduced transrectally (Figs 3b and c). Anaerobic streptococci were cultured from the pus. One week later CT demonstrated almost complete resolution and she remains well 3 months later. In the second patient (Case 4, a 26year-old woman) CT demonstrated a l0 x 5 cm pelvic collection from which 65 ml was aspirated transrectally via an 8 F catheter. This was removed at 48 h. Repeat CT 1 week later demonstrated that this initial deep collection had resolved but that there was a new unrelated 3 cm diameter midline pelvic collection adjacent to the anterior abdominal wall incision. This was drained via a standard anterior percutaneous
(b)
(c) Fig. 2 - A series of images from Case. 1. (a) The CT appearances 1 week after the initial procedure. There is still a large pelvic abscess with some air within anteriorly (probably introduced at the time of the first drainage). The close relation to loops of gut again render an anterior abdominal wall approach difficult. (b) Prone therapeutic CT, somewhat more caudal. This shows the catheter in situ in the centre of the collection. The air is now in the superior portion of the collection. Note the distortion of the rectum (arrow). (c) After drainage to dryness, the collection is much smaller. The rectum has already assumed a much more normal shape.
approach using an 8 F catheter. Her pyrexia resolved and she remains well 6 months later. The third patient (Case 5, a man of 50 years) also developed a 5 cm collection in the pre-sacral space following restorative proctocolectomy. However, his post-operative course was particularly complicated and on three occasions over 5 months a pelvic collection was drained using a transrectal approach with CT guidance. Appropriate antibiotic therapy for the cultured organisms (E. coli, Bacteroides, and Group F streptococci) was given. The CT examinations and subsequent barium studies revealed no evidence of a fistula communicating with the bowel. Ultimately because of persisting pain and rectal irritation the ileal pouch was excised and an ileostomy fashioned. At surgery a small abscess cavity was found and also excised, although no infective focus was reported.
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CLINICAL RADIOLOGY
(a)
(b)
(c) Fig. 3 A series of images from Case 3. (a) Diagnostic CT showing an abscess (arrow) in the pre-sacral space, posterior to the pouch formed by rectoplasty. There is an air-fired level in the pouch; dilute contrast medium was instilled per rectum before this study. (b) Therapeutic CT. Needle, cannula and invisible sheath in position in pouch immediately caudal to the level shown in (a). The protective sheath was then removed as this was considered a suitable site for puncture of the posteriorly and cranially situated abscess using appropriate angulation. Pus was aspirated at puncture. Guide-wire exchange to an 8 F pigtail catheter; 25 ml pus aspirated via catheter. (c) Pigtail catheter in collapsed abscess cavity at the end of procedure.
DISCUSSION Pelvic abscesses may arise secondary to bowel or gynaecological surgery, as well as following pelvic inflammatory disease, Crohn's disease, appendicitis or more generalized peritonitis (Finne, 1980; Casola et al., 1987; Pan and Shirkoda, 1987). In addition, when a 'neorectum' (Parks' pouch (Everett, 1989)) has been constructed from terminal ileum following colectomy for ulcerative colitis, and pouch-anal anastomosis carried out, leakage from the ileo-anal anastomosis may lead to abscess formation deep in the pelvis.
The traditional surgical treatment of pelvic abscesses, which usually requires general anaesthesia, is drainage by a transrectal (or occasionally transvaginal) approach (Storer, 1984). After needle aspiration through the rectal wall to confirm the diagnosis and site the rectal wall is incised, the opening widened with a finger to allow loculi to be broken down, and a drain o r trocar catheter (Nivatvongs, 1986) inserted. Daily digital examination per rectum of the abscess opening is performed during the following week to ensure continuing free drainage. This is likely to contribute to the low recurrence rate of approximately 10% given in the limited series reported in the surgical literature (Finne, 1980). This surgical approach is usually possible only when there is a large mature fluctuant pelvic collection which has walled off from adjacent viscera and is easily palpable per rectum. In two of our patients (Cases 3 and 5) the collections were not easily palpable, making this type of surgical approach difficult. Percutaneous drainage of infected pelvic collections is now an established procedure providing an alternative to formal surgical drainage. The choice as to which route to employ often depends as much on local expertise and availability of equipment as on perceived risk. The complication rate is low for all routes and the numbers in published series are rarely large enough to allow truly valid comparisons of morbidity and mortality rates (Mueller et al., 1984). Studies of guided biopsies confirm the overall low complication rate of similar techniques (Welch et al., 1990). Potential risks of percutaneous aspiration or drainage include missing the collection, incomplete drainage and damage or perforation of adjacent structures (bladder, bowel, vessels, nerves, etc.). With experience the procedures are relatively quick to perform and can be carried out during a routine imaging list (Lomas and Dixon, 1990). The choice of imaging technique also depends on personal experience, although clearly some approaches are biased to one modality (e.g. sciatic notch approach with CT). CT provides a comprehensive view of the pelvis and is not restricted in obese patients or by the presence of copious bowel gas. Ultrasound, although providing a limited view, allows multiplanar orientation and true real-time demonstration of insertion of the drainage device. Endovaginal and endorectal probes provide detailed images of 'deep' pelvic collections and potentially of catheter placement. The portability of ultrasound allows procedures to be performed at the bedside (e.g. in the Intensive Care Unit) with a minimum of disruption for the patient. While it might have been possible to drain the large collections related to appendiceal problems (Cases 1 and 2) with ultrasound monitoring, it is debatable whether the smaller pre-sacral collections (Cases 3, 4 and 5) could have been managed in this way. An anterior percutaneous approach is well suited to superficial collections close to the anterior abdominal wall. With 'deeper' collections careful manipulation is necessary to achieve accurate catheter placement and avoid deflection of the cannula during insertion. Ideally the bladder should be avoided and thus an empty bladder may appear to be advantageous; however, this may allow the interposition of bowel loops and make the route equally hazardous. Anterolateral approaches parallel to the iliac wings are useful for avoiding intervening bowel, but care must be taken to avoid vessels (e.g_ the inferior
CT-GUIDED TRANSRECTAL ABSCESS DRAINAGE
epigastric artery). Despite these manoeuvres some collections will remain inaccessible via an anterior approach unless one is prepared to traverse bowel or bladder. The advantages of an anterior approach include convenience for the operator and relative comfort for the patient; Catheters can be easily secured to the anterior abdominal wall. A posterolateral percutaneous approach via the sciatic notch has been described using CT guidance (Butch et al_, 1986). This allows drainage of perirectal and pre-sacral collections that are inaccessible via the anterior route. There is a theoretical risk of damage (Jaques and Mauro, 1986) to the structures traversing the sciatic notch (gluteal vessels, sciatic nerve, etc.) but in the reported series so far no serious complications have been encountered. However, this may be a painful procedure and temporary paraesthesiae can occur, presumably caused by trauma to branches of the sacral plexus during the initial needle insertion. Catheter fixation to the skin in the gluteal region is straightforward, although in a relatively uncomfortable position for the patient. Transvaginal and transrectal routes allow a relatively painless approach to perirectal and pre-sacral collections. The short distances involved allow for good catheter control and reduce the risk of misplacement during insertion. With a catheter left in situ there is a theoretical risk of reverse infection and adequate fixation of the catheter may be difficult to achieve even when sutured to the thigh. The short length of catheter within the soft and relatively mobile rectum prevents the catheter tip being firmly secured. The use of an 'anchored' catheter (Cope, 1988) might avoid this problem. Even if the catheters block or dislodge they may create a track into the rectum allowing subsequent free drainage. To increase the probability of forming a track as large a catheter as possible should be used (the small size catheters used in Cases ! and 2 may have contributed to the reformation of the collection). This parallels the traditional surgical technique of incising a large pelvic abscess and allowing free drainage per rectum. Leaving a catheter traversing the vaginal or anal orifice is slightly uncomfortable for the patient but usually well tolerated. In our limited experience three out of five of these 'deep' pelvic collections have been associated with complex bowel reconstruction surgery and, although repeat drainages proved necessary in three patients, only one subsequently required formal surgery. We consider that when presented with the clinical problem of a pelvic abscess that cannot be easily approached percutaneously using an anterior approach, the peranal transrectal route using CT guidance provides a simple and effective alternative.
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Acknowledgements. We would like to thank the various clinicians responsible for these patients, in particular M r W. G. Everett. The contribution of the nurses and radiographers is also appreciated.
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