INTRODUCTION

DESPITE MANY RECENT ADVANCES in the man-agement of infectious diseases, intra-ab-

dominal infection remains an important chal-lenge for the surgeon. These infections can stillcause substantial mortality and morbidity, es-pecially for some patient subgroups. Althoughantimicrobial therapy is important for pre-venting or managing abscesses, it cannot standalone. Prompt recognition, early localization,and effective drainage are essential for effectivetreatment of a patient with an intra-abdominal

abscess [1,2]. This article reviews imaging tech-niques that are used to aid in the diagnosis andlocalization of intra-abdominal abscess and dis-cusses appropriate antimicrobial therapy anddrainage techniques aimed at controlling theseinfections.

The abscess environment

The etiology of intra-abdominal abscessesvaries according to the source of the infectionand the status of the patient’s immune system.Many intra-abdominal abscesses are polymi-

SURGICAL INFECTIONSPremier IssueVolume 1, Number 1, 2000Mary Ann Liebert, Inc.

Diagnosis and Treatment of Intra-Abdominal Abscesses

KENNETH R. SIRINEK

ABSTRACT

Despite recent advances in the diagnosis and management of intra-abdominal abscesses, theseinfections still cause substantial morbidity and mortality. Low pH, large bacterial inocula,poor perfusion, the presence of hemoglobin, and large amounts of fibrin (which impedes an-tibiotic penetration) make the abscess a cloistered environment that is penetrated poorly bymany antimicrobial therapies. Therefore, management of these infections requires promptrecognition, early localization, and effective drainage, as well as appropriate antimicrobialuse. Although various imaging techniques, such as ultrasonography, gallium scans, and in-dium-labeled white-blood-cell scans, can be used for the diagnosis and localization of intra-abdominal abscesses, computer-assisted tomography is the most useful study. Once the di-agnosis is made and the abscess is localized, treatment should begin promptly. Percutaneousor open surgical drainage should be used. Broad-spectrum antibiotics should be given untilculture and sensitivity data are obtained. Once these data are obtained, a therapy with ap-propriate coverage that is likely to work in the abscess environment should be chosen. Per-cutaneous drainage is inappropriate for abscesses in the posterior subphrenic space or in theporta hepatis, for those among loops of small bowel, for suspected echinococcal cysts, and forabscesses containing necrotic or neoplastic tissues. Finally, surgeons need to be cognizant ofrisk factors, such as advanced age, obesity, complex abscesses, and high Acute Physiologyand Chronic Health Evaluation (APACHE) II or APACHE III scores, which correlate with pooroutcomes for these patients.

Department of Surgery, University of Texas Health Science Center at San Antonio, San Antonio, TX.

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crobial, although anaerobic gut organisms suchas Bacteroides often predominate [3–5]. The ab-scess environment often presents special chal-lenges for antimicrobial therapy [6]. Abscesseshave a low oxidation-reduction potential andlow pH as a consequence of limited vascular-ity and poor perfusion, anaerobic conditions,and dying tissue. High bacterial concentrationstend to depress oxygen-dependent phagocyto-sis and killing of bacteria by neutrophils andsuffuse the confined space with high concen-trations of b -lactamase enzymes. Antibioticpenetration into the abscess is limited not onlyby poor perfusion but also by mechanical bar-riers such as fibrin clots and the abscess wall[7–9]. Thus, treatment with antimicrobial ther-apy alone is usually insufficient to clear theseinfections—effective management requires ab-scess drainage.

DIAGNOSIS AND LOCALIZATION

Intra-abdominal infection should be sus-pected immediately in a patient who is at riskand who has the hallmark signs—tachycardia,tachypnea, leukocytosis, and cyclic or constanttemperature elevation characteristic of a sys-temic proinflammatory response [1]. The initialevaluation should include a history, physicalexamination, laboratory tests, plain roentgeno-grams of the chest and abdomen, and appro-priate cultures. The physical examinationshould not be omitted because a palpable massmay be found that indicates the presence of anabscess [10]. On plain films, one might find apleural effusion, atelectasis, elevated hemidi-aphragms, free intraperitoneal air, ileus, or dis-placed viscera. If a mass effect is identified ona plate the diagnostic challenge is to differen-tiate an abscess from a true cyst, biloma, loopsof bowel, lymphocele, or urinoma [11].

Diagnostic imaging systems can be helpfulin establishing the correct diagnosis. However,any imaging system has limitations that cangive rise to false-positive and/or false-negativeresults. For patients with an intra-abdominalabscess, such inaccuracies may lead to seriousconsequences—uncontrolled sepsis with its as-sociated high mortality (false negatives) or un-

necessary operations (false positives) in criti-cally ill patients. Therefore, it is important tochoose an imaging method that can identifyand localize an abscess effectively while ex-cluding the possibility that other lesions or col-lections may be present.

Ultrasonography

Ultrasonography is a relatively sensitive anduseful tool for diagnosing an intra-abdominalabscess. Ultrasonography is noninvasive anddoes not require exposing patients to ionizingradiation. Because ultrasonography is portable,it can be brought to very ill patients who arenot easily transported [12]. However, becauseultrasonography is not fully automated, its ac-curacy is user-dependent [13]. It is less accu-rate than computed tomography (CT), less ca-pable of detecting small abscesses, and canmiss an infected focus in the retroperitonealarea [1]. The utility of ultrasonography may beaffected adversely by the size of the patient orthe presence of surgical wounds, dressings,drains, and ostomies that may prevent imag-ing of all areas of the abdomen and pelvis.Large amounts of bowel gas (e.g., ileus) can ob-scure underlying structures. Several studiesthat were undertaken to determine the sensi-tivity and specificity of ultrasonography for di-agnosing intra-abdominal sepsis are summa-rized in Table 1.

Computed tomography

Although ultrasound is somewhat useful,most surgeons rely on CT, which provides highanatomic resolution and has greater specificitythan does ultrasonography [13]. Compared toultrasonography, a CT scan allows better visu-alization of the retroperitoneum, lesser sac, andpelvis. Contrast enhancement may help to dif-ferentiate between a loop of intestine and afluid collection, but administration may be lim-ited by clinical factors (e.g., allergy or renal fail-ure for intravenous contrast, ileus for oral con-trast). Although the presence of debris,loculations, gas, and a contrast-enhanced rimsuggest the presence of an infection, a CT scancannot differentiate between sterile and in-fected fluid collections. A CT scan may not be

INTRA-ABDOMINAL ABSCESSES 33

an option for critically ill patients who are dif-ficult to transport to the area of the hospitalwhere the scanner is located or for those whoare morbidly obese and may not fit on thegantry [12]. However, portable CT scan equip-ment now allows the instrument to be broughtto the bedside. It remains to be determined ifthe image quality in portable CT scan equip-ment will be adequate for imaging the ab-domen. Studies examining the use of CT for in-tra-abdominal abscess are also summarized inTable 1.

Magnetic resonance imaging

Magnetic resonance imaging (MRI) has sev-eral limited advantages over CT scanning inpatients with intra-abdominal infection. MRIcan delineate better the extent of an abscess andthe presence of a capsule [14]. Compared toother imaging techniques, MRI will also clearlyshow the impact of an abscess on adjacentstructures, especially muscle and major blood

vessels. However, image quality is susceptibleto motion artifact, which cannot be avoidedwhen imaging the abdomen with MRI. More-over, it is cumbersome to take even a hemo-dynamically stable intensive care unit patientfor an MRI scan because nonferrous materialsare mandatory for clinical accouterments, suchas mechanical ventilators and infusion pumps.

Scintigraphy

Radioactive gallium (67Ga citrate) concen-trates in infected sites but is not very useful forlocalizing an intra-abdominal abscess becausethis substance accumulates in the intestine,liver, and spleen, causing a high backgroundof radiation [15]. In addition, gallium is con-centrated and excreted in feces, increasing thelikelihood of a false-positive interpretation.Moreover, scintigraphy delays diagnosis, be-cause 48 hours are generally required for studyresults and interpretation [13]. The literature ismixed regarding the sensitivity of this scan.

TABLE 1. STUDIES ASSESSIN G THE UTILITY OF ULTRASONOGRAPHY AND COMPUTED

TOMOGRAPHY FOR DIAGNOSIS OF INTRA-ABDOM INAL INFECTION

Patients Sensitivity Specificity AccuracyAuthor (year) (#) (%) (%) (%)

UltrasonographyTaylor et al. (1978) a 220 93.5 99.5 97Knochel, et al. (1980)b 123 82.5 94.5 90

(136 examinations)Butler, et al. (1987) c 21 — — 72Weldon, et al. (1995)d 50 71.5 87.5 —

Computed tomographyButler, et al. (1987) c 11 — — 82Haaga, et al. (1977) e 17 — — 91Knochel, et al. (1980)b 74 97.5 95.5 96

(80 studies)Wolverson, et al. (1979) f — 95.5 94.5 —

— 5 Not reported.aTaylor KJ, Wasson JF, De Graaf C, et al. Accuracy of grey-scale ultrasound diagnosis of abdominal and pelvic ab-

scesses in 220 patients. Lancet 1978;i:83–84.bRef. 20.cRef. 36.dWeldon MJ, Joseph AEA, French A, et al. Comparison of 99mTechnetium hexamethylpropylene-amine oxime la-

belled leucocyte with 111-Indium tropolonate labelled granulocyte scanning and ultrasound in the diagnosis of intra-ab-dominal abscess. Gut 1995;37:557– 564.

eHaaga JR, Alfidi RJ, Havrilla TR, et al. CT detection and aspiration of abdominal abscesses. Am J Roentgenol1977;128:465– 474.

fWolverson MK, Jagannadharao B, Sundaram M, et al. CT as a primary diagnostic method in evaluating intraabdom-inal abscess. Am J Roentgenol 1979;133:1089– 1095.

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Sensitivity has been reported as low as 59%[16], although a large-scale review showed gal-lium to have high sensitivity and specificity[17]. In one study of 50 patients, gallium wasfound to have a 63% sensitivity and 94% speci-ficity [18]. Another study showed a sensitivityand a specificity of more than 90% for galium[19].

Indium (111In)-labeled leukocytes are gener-ally more accurate than gallium in labeling sitesof inflammation. Still, the liver and spleen nor-

mally accumulate these cells in high concen-trations, leading to high background radiationand consequent difficulty in detecting an up-per-abdominal abscess [15]. Labeled leuko-cytes are not as sensitive as a CT scan in iden-tifying an intra-abdominal abscess. A studycomparing labeled leukocytes, CT scan, andultrasonography found a sensitivity of 86% forlabeled leukocytes, 82% for ultrasonography,and 98% for CT [20]. Tumor uptake can alsobe a problem. However, the use of labeled

A

B

FIG. 1. Computed tomography scan showing subhepatic abscess noted 10 days after laparoscopic appendectomyfor perforated appendicitis. The abscess (A) before and (B) after percutaneous drainage.

INTRA-ABDOMINAL ABSCESSES 35

cells has some advantages. Although ultra-sonography and CT cannot differentiate be-tween infected and noninfected fluid collec-tions, labeled leukocytes only accumulate insites of active infection or inflammation [15].Use of indium-labeled leukocytes has the ad-ditional advantage of allowing identificationof extra-abdominal infections [15], which arenot uncommon in patients with signs andsymptoms suggesting an intra-abdominalprocess. For pyrexia of unknown origin, a se-ries of 166 labeled white-blood-cell studiesfound a sensitivity of 60% and a specificity of70% [21].

TREATMENT

Effective management of intra-abdominalabscesses requires both appropriate antibiotictherapy and surgical drainage.

Choice of antibiotic

Initial therapy should consist of broad-spec-trum antibiotics until culture and antibioticsensitivity results are available. Because thepathogens are frequently similar to those in-volved in secondary peritonitis, it is rational todirect initial therapy against Bacteroides fragilis

TABLE 2. PERCUTANEOUS VS SURGICAL DRAINAGE OF INTRA-ABDOMINAL ABSCESSES

Type of Number Success rateStudy (year) treatment treated (%) Mortality (%)

Johnson, et al. (1981) a PD 27 89 11.5SD 43 70 21.5

Halasz and van Sonnenberg (1983)b PD 11 — 9.5SD 19 — 16.5

Aeder, et al. (1983) c PD 13 69 23.5SD 32 — 37.5

Brolin, et al. (1984)d PD 24 92 0.5SD 24 88 13.5

Glass and Cohn. (1984)e PD 15 47 —SD 44 88 —

Lurie, et al. (1987) f PD 29 80 17.5SD 60 81 17.5

Olak, et al. (1986)g PD 27 70 11.5SD 27 85 7.5

Malangoni, et al. (1990)h PD 18 61 11.5SD 30 53 27.5

Hemming, et al. (1991) i PD 42 93 12.5SD 41 — 14.5

Levison and Zeigler (1991) j PD 45 47 29.5SD 46 54 28.5

PD 5 percutaneous drainage (overall success rate 71.3%, mortality rate 14.8%); SD 5 surgical drainage (overall suc-cess rate 71.2%, mortality rate 20.5%); — 5 Not reported or indeterminate.

aJohnson WC, Gerzof SG, Robbins AH, Nabseth DC. Treatment of abdominal abscesses: Comparative evaluation ofoperative drainage versus percutaneous catheter drainage guided by computed tomography or ultrasound. Ann Surg1981;194:510– 520.

bHalasz NA, van Sonnenberg E. Drainage of intraabdominal abscesses: Tactics and choices. Am J Surg1983;146:112– 115.

cRef. 35.dRef. 32.eGlass CA, Cohn I Jr. Drainage of intraabdominal abscesses: A comparison of surgical and computerized tomography

guided catheter drainage. Am J Surg 1984;147:315– 317.fRef. 1.gOlak J, Christou NV, Stein LA, et al. Operative vs percutaneous drainage of intra-abdominal abscesses: Comparison

of morbidity and mortality. Arch Surg 1986;121:141– 146.hRef. 38.iRef. 31.jRef. 34.

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and the Enterobacteriaceae [22]. The antimicro-bial regimen can be selectively revised once thecausative pathogens have been identified inculture [6].

Several antimicrobial regimens have beenused to treat patients with an intra-abdominalabscess. Previously, the most commonly usedtherapy was an aminoglycoside combinedwith either clindamycin or metronidazole [23].More recently, imipenem/cilastatin is amongmany drugs that have proved to be effectivefor this clinical problem [24]. However, basedon in vitro studies, imipenem and aminogly-cosides seem to lose some efficacy against B.fragilis at a reduced pH [25]. Piperacillin/tazobactam, as monotherapy, is also effectivefor treating patients with an intra-abdominalabscess because of the coverage of anaerobesin addition to broad gram-positive and gram-negative coverage [23,26]. Piperacillin/tazo-bactam also penetrates well into abdominal tissues [27] and works well at a low pH [28,29].

Drainage: open surgical vs. percutaneous

Two general approaches can be taken for ab-scess drainage: open surgical and percutaneoustechniques. Percutaneous drainage can beguided by CT or ultrasonography (Fig. 1). CT-assisted drainage has the advantage of high-quality imaging of abscesses and of surround-ing tissues; ultrasound offers dynamic imagingduring the puncture process, which may be im-portant for small abscesses that move duringbreathing [30]. In addition, preoperative per-cutaneous drainage of diverticular abscessesmay allow a patient to undergo just one surgi-cal procedure (subsequent sigmoid resectionwith primary anastomosis) rather than twoduring the same hospitalization [31].

While the relative success rates of percuta-neous and open surgical drainage are quitesimilar (Table 2), not all abscesses should bedrained by the less invasive percutaneousroute [32–34]. CT-assisted percutaneousdrainage has been recommended when thereare no more than two abscess cavities or loca-tions and when the drainage route does not tra-verse the bowel. Also, percutaneous drainage

is recommended for uncontaminated organsand spaces (peritoneal or pleural) and whenthere is an absence of a source of continuouscontamination [30,35]. Open surgical drainagemay appear to have a higher mortality rate(Table 2), but selection bias is always presentin nonrandomized trials of therapy for intra-abdominal infection.

Risk factors for complications

Most published analyses of risk factors havebeen performed retrospectively. Reviewingthese retrospective studies is difficult becausemost were conducted in patients who were notstratified by risk factors. Still, several importantrisk factors can be identified for morbidity andmortality. The number of surgical proceduresappears to influence risk: A 30% mortality ratehas been reported for patients who were un-dergoing multiple exploratory celiotomies forinfections (e.g., tertiary peritonitis) [36]. Deathsin patients with liver abscesses were related todelay in diagnosis, gram-negative sepsis at pre-sentation, and biliary origin of the abscess [37].Fry, et al. found that age greater than 50 years,multiple organ failure, a lesser sac abscess, sub-hepatic abscess, a blood culture that was posi-tive for the presence of infection, and recurrent,persistent, or multiple abscesses were each as-sociated with a fatal outcome [10]. Hemming,et al., in a review of 83 patients, found that highAcute Physiology and Chronic Health Evalua-tion (APACHE) II scores indicated an increasedrisk for the development of complications.APACHE II scores were significantly higher inthe nonsurvivors and in subjects who devel-oped complications in both treatment groups.There was, however, no significant differencein morbidity or mortality for patients treatedby percutaneous vs open surgical drainage[31]. Patients with complex abscesses (e.g.,multiple loculations, inaccessible locations) arealso at increased risk for complications [38]. Fi-nally, obesity is a complicating factor that im-pedes diagnosis as well as increasing morbid-ity [39].

Future studies should consider risk factorswhen comparing treatments for intra-abdomi-nal abscesses. In addition, continued refine-

INTRA-ABDOMINAL ABSCESSES 37

ment of imaging technology and greater un-derstanding of the abscess microenvironmentshould help surgeons to manage patients withintra-abdominal abscess appropriately.

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ment of abdominal abscesses. Am Surg 1984;50:102–108.

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Address reprint requests to:Kenneth R. Sirinek, MD, PhD

Department of SurgeryUniversity of Texas Health Science Center at

San Antonio7703 Floyd Curl Drive

San Antonio, TX 78284-7842

E-mail: sirinek@uthscsa.edu