The continued advance of imagings (Fluoroscopy,ultrasound and computed tomography) for guidance, atraumatic catheter introduction techniques and effective antibiotics have combined to allow the development of effective drainage of abdominal abscess. By 1978, S.G. Gerzof was advocating percutaneous catheter drainage as a routine treatment of choice for abscess, and by 1979 was beginning to challenge the results of operative drainage. Because of the promising result alternative to surgery - less traumatic, low cost and avoiding major operation including general anesthesia , percutaneous drainage has now been acknowledged to be "one of the great advances in operation in the past 20 years"

    Abscesses are well-defined fluid masses composed of necrotic debris, leukocytes, bacteria , and fluid exudate. The abscess wall is usually a well-defined structures composed of fibrin, inflammatory cells and dilated blood vessels, which act as a physiologic and mechanical barrier to contain the infection. The current methods for detecting intraabdominal abscess are conventional radiographic studies with or without contrast media , radionuclide scanning ,ultrasound(US), computed tomography (CT) and (rarely) magnetic resonance imaging (MRI). An early diagnosis is very important in the successful treatment of abdominal abscess . US ,being safe, easy, quick, and inexpensive , is often used as the initial screening procedure. US can be severely compromised by overlying intestinal gas ,intervening bony structures, obesity and other technical limitations. In such circumstances , CT is preferred as the initial screening method. CT also permits the thorough and systemic evaluation of the abdominal cavity.

    None of the CT and ultrasound signs are specific for abscess. This is particularly true in the postoperative abdomen, where a variety of intraabdominal and retroperitoneal fluid collections must be considered. Because the variety of fluid collections such as biloma, urinoma, lymphocele, pseudocyst..etc cannot be distinguished from one another , and because of the importance of correct diagnosis for instituting proper therapy, definitive diagnosis should be made by needle aspiration.

    Because of the availability of accurate detection and guidance methods such as US and CT, percutaneous abscess drainage by catheter techniques has become popular in the past 15-20 years. Percutaneous drainage maintains the integrity of the abscess wall as a barrier preventing dissemination of sepsis. It is very important for interventional radiologist to introduce a drainage catheter for decompression and evacuation of pus as gently and atraumatically as possible.

CHOICE OF IMAGING GUIDANCE SYSTEM

    Percutaneous drainage of fluid collections and abscesses is done under imaging guidance following many of the technical principles. Imaging guidance is used to insert a needle into the collection. The needle must not traverse bowel or vital organs in most cases. However there are exceptions to this rule such as collections in that organs or collections at porta hepatis, which are sometimes drained via a transhepatic route, and infected or noninfected collections in the lesser sac such as pancreatic absess or pseudocyst, which may be drained by a transgastric approach.

    In Thailand , Fluoroscopy, ultrasound and CT are usually available and can be used for guided puncture and aspiration or guidance in percutaneous drainage.

Advantages of Fluoroscopy:
    - Real-time monitoring of guide wire and catheter manipulation : prevent inadvertent guide wire or catheter withdrawal

Disadvantages of Fluoroscopy:
    - Very poor contrast resolution when compared to ultrasound or CT
    - Provide only two-dimension anatomic display.

( Fluoroscopic imaging yields realtime monitoring for catheter manipulation and identification of collection space by contrast injection )

(US image shows abscess cavity and realtime monitoring of needle insertion )

Disadvantages of Ultrasound:
    - An abscess cannot be distinguished from other types of abdominal fluid collection by US criteria alone.
    - Bowel gas and bone interposed between the transducer and the collection may degrade the US image sufficiently to make safe access planning impossible.
    - Limited applicability in postoperative patients with surgical dressings and/or draining wounds

Advantages of CT:
    - Excellent three-dimension localization of fluid collection for drainage so it provides the best demonstration of the relationship of the target to surrounding structures such as bowel, bone, blood vessels, and lung.
    - Excellent contrast resolution, which can be further enhanced by use of intravenous and oral contrast media.
    - Ability to define the location of a needle tip within a fluid collection allows small collection to be aspirated and/or drained with a high degree of accuracy and low risk for complications.
    - Can be performed in postoperative patients with overlying wounds, stomas and dressings.
    - CT guidance is helpful in draining deep abdominal-pelvic abscesses or approaching those collections with narrow access windows. Fluid collection in close proximity to major blood vessels, bowel, or lung should be drained with CT guided puncture.

( CT guided image shows needle entering the collection in the abdomen which is very close to the transverse colon )

Disadvantages of CT
    - Guide wire and catheter manipulation cannot be monitored as easily with CT as they can with real-time fluoroscopy.
    - Access to the patient may be limited by the CT gantry
    - Patients must be brought to the CT room.

    Our preference is to used a combination of either ultrasound or CT guidance for guided puncture and aspiration then fluoroscopic guidance for guide wire and catheter manipulation.

DRAINAGE METHODS

    Percuteneous drainage usually has five steps : detection of the collection , route planning , diagnostic aspiration, catheter selection and insertion and catheter management.

    Once a suspected abscess is detected on the imagings, a safe percutaneous access route must be planned. The best access route is the shortest, safest tract. However, oblique approaches are often necessary to avoid nearby vital structures. Three parameters should be determined to define the drainage route : the cutaneous entry site, the center of the abscess and the distance and angle between them. Once this route is defined, the interventional radiologist should attemp to follow it as closely as possible with the aspiration needle.

    Diagnostic aspiration is usually needed to confirm infection within a collection. We generally performed with a 22-gauge needle. This is particularly helpful when the collection is in a difficult location which is sometime requiring a needle tract through normal structures. Passage of the needle through bowel should be avoided to prevent bacterial contamination of a potentially sterile collection. Small abscesses may not require catheter drainage and can be treated by simple aspiration and systemic antibiotic. Complete aspiration may not be possible with a skinny needle , and a larger needle ( 20 to 18 gauge ) might be needed. Usually, a large needle can simply be inserted in tandem alongside a fine needle.

    Drainage catheter selection is dependent on the character of the fluid. Thin serous collections are drained with 8 to 10 French size ,commercial available, multiple side-holes pigtail catheters. Thicker materials require large bore catheters with sump ports. Loculated collections may require several separate catheters for satisfactory drainage.

    In Bhumibol Adulyadej Royal Thai Air Force Hospital, we usually use the commercial available multiple side-holes pigtail catheters. Eventhough there is an internal retention device within the drainage catheters, we usually prefer two or three 2-0 silk sutures carefully tied to the skin. These sutures can prevent accidentally forceful traction which may avulse the wall of the abscess and cause serious hemorrhage or wide dissemination of pus.

( Another type of drainage catheter )

( Location and mechanism of the sump hole and drain holes at distal part of a sump catheter)

    Another type of drainage catheter is a Robnel catheter which is mainly used in the patients with economic problem. It is the cheapest catheter , usually used for catheterization of urinary bladder. Having only two side holes and no internal locking -device causing easily dislodgement are the main disadvantages of the catheter. However dislodgement of the catheter can be prevented easily by silk sutures tied to the skin.

( A hole should be made at the tip of a Robnel catheter for a guide wire passing through during insertion )

    In percutaneous drainage, the two major techniques are Trocar technique and modefied Seldinger technique.

    Trocar technique is usually performed in case of superficial and large collections with a wide access window. This technique is similar to the placement of a chest tube. The catheter is mounted on a sharp metal introducer, and the entire system is pushed through the frontal wall of the collection. The catheter is then advanced off the metal stiffner and into the cavity. The catheter is finally left in place for continuous drainage.

( Trocar diagram )

    Modified Seldinger technique, performing in Bhumibol Adulyadej Hospital, is usually the same as the procedure described in the Cope method. A small needle ( usually a 21-22 gauge needle) is used to puncture a collection. Once the collection has been entered with the needle, a small stiff ,0.018-inch guide wire is inserted and the needle is removed. A curve,6.3 French sized,Teflon dilator is introduced over this 0.018-inch guide wire. The 0.018-inch guide wire is then removed when there is back flow of pus through this dilator. The dilator also has a side hole in the inside of the curve through which a tight-J 0.038-inch guide wire will exit. Subsequently dilators and large catheter can be introduced over this guide wire. This method is atraumatic and allowing replacement of a small (0.018-inch) guide wire with a large (0.038-inch) guide wire with only one puncture.

( Seldinger diagram )

Catheter management

    The fluid collection is aspirated as completely as possible after the catheter has been placed. The major therapeutic effect of percutaneous abscess drainage occurs at this time. Following complete evacuation, gentle saline irrigation is performed until the drainage is clear. Following complete irrigation, the area is reimaged ( by US or CT) to be certain that no residual collections remain. If additional collections are seen, the catheter should be repositioined ,or additional catheters should be placed immediately.

    The percutaneous catheter is most often left to closed-system, gravity drainage. If a sump catheter s been used, it should be connected to low suction. The utility of daily irrigation of catheters is debatable. In Bhumibol Adulyadej Hospital, we do not irrigate the catheter as long as the purulent material is draining. We usually irrigate catheters when there is clinical suspicious of occlusion of the drainage catheters. Irrigation of the abscess cavity is advocated as a method of lowering the viscosity and inducing better drainage, but vigorous irrigation may produce septicemia. Specific antibiotic coverage should be continued for the duration of treatment. The guidelines for catheter removal take into account several factors, including the following : Decrease in the amount of drainage per day to about less than 10 cc/day, Change in the appearance of the draining material from purulent to clear, No significant amount of residual content or no detectable collection in the follow up imagings, and improvement in the patient's symptoms ( especially fever ). Multiloculated collections are difficult to treat without surgical intervention. J.R. Haaga recommended filling the cavities with urokinase to dissolve the septa if they are composed predominately of fibrin. However, if the septa have become fibrotic, fibrinolytic agents will have little effect.

RESULTS

    Catheter drainage is highly successful for simple fluid collections and abscesses without fistulous connection to bowel. Success in cases of fistulae is variable, requires placement of the catheter tip into the fistula, and is usually depend on the underlying disease. Fistulae due to malignancy or inflammatory bowel disease do poorly. Nevertheless, catheter drainage is still useful in such patients in order to avoid the morbidity and mortality of emergency surgery, and allow time to improve the metabolic and nutritional status of the patient prior to definitive therapy

( Plain film of the abdomen shows right perinephric air from perinephric abscess)

( Plain film of the abdomen 2 weeks after percutaneous drainage)

    Percutaneous abscess drainage compares favorably with surgical therapy in terms of overall clincal success, duration of drainge and recurrent rate. Success raes ranging from 80-90 percent are widely reported for percutaneous drainage. The principal causes of failure ,reported in the literatures, are the followings : presence of necrotic material, multiloculated abscesses not suitable for percutaneous drainage, tumor with central necrosis simulating abscess, viscuos pus that could not drained adequately, persistent fistulae from gastrointestinal tract , diffused microabscesses, and contamination by C. albicans or other opportunistic agents.

    We can apply percutaneous drainage techniqe especially modified Seldinger technique for drainage of fluid in many organ such as percutaneous nephrostomy (PCN) for urinary drainage or percutaneous transhepatic biliary drainage (PTBD) for biliary drainage. The details of these topics will not include in this discussion.

COMPLICATIONS

    The nature of complications depends on a number of variable factors including extent and anatomic location of the abscess, the route of percutaneous drainage , the imaging modality and technique used , the skill of the radiologist, and the underlying clinical condition of the patient. Several series described low complication rates for percutaneous abscess drainage , with quoted rates between 0 and10 percent. Minor complications include bacteremia at the time of catheter placement, superficial skin infection, and minor bleeding. Major complications are massive hemorrhage, bowel injury, septicemia and disseminated intravascular coagulation. The major complications occur in less than 5 percent of cases and result in death in less than 1 percent. Finally , inadequate catheter care once the patient has left the radiology suite may lead to kinking, blockage or dislodgement of the catheter.

    Most complications can be avoided by careful consideration of the nature of the collection ( ie, unilocular vs multilocular), the anatomic location of the abscess, the image guidance system employed, the method and route of catheter drainage, the underlying condition of the patient, appropiate explanation of the procedure to the patient, adequate anesthesia and vigilant postprocedural catheter care.

CONCLUSION

    Percutaneous imaging-guided treatment of abdominal abscess has been considered as the most important progress in abdominal surgery in the past decade. It is the reasonable initial treatment for abdominal abscesses. The extremely favorable results are related to the high diagnostic accuracy of ultrasound and CT, which facilitate complete delineation of the collection, guided operations and also monitoring the results as well as complications.
Percutaneous drainage is a very successful technique that is the cornerstone of many interventional radiology procedures. Its widespread acceptance is an excellent example of the revolutionary changes made by interventional radiology on the current practice of medicine.