eMedicine Specialties > Radiology > Vascular/Interventional

Percutaneous Abscess Drainage

Author: Evan J Samett, MD, Consulting Staff, Department of Radiology, MacNeal Hospital
Contributor Information and Disclosures

Updated: Apr 3, 2006

Introduction

Over the last 20 years, percutaneous abscess drainage (PAD) has evolved from revolutionary to routine, replacing open surgical abscess drainage in all but the most difficult or inaccessible cases. It was originally believed that only patients with simple fluid collections were candidates for PAD; however, researchers have convincingly demonstrated that both septated and viscous fluid collections may be successfully treated percutaneously, particularly with the adjunctive use of lytic agents. The simpler the abscess, the more likely PAD will be rapidly successful.

An aggressive practical approach with relatively simple devices and techniques may yield a high success rate with few complications.

Abscess Definition

One definition of an abscess is a drainable, infected fluid collection. One dictum is "If it will not go through a catheter, it cannot be drained. If it is not infected it is not an abscess." Differentiating a phlegmon from an abscess can be difficult. A phlegmon may be defined as a vascularized infection that still has perfusion. Some nonsuppurate lymphadenitis may not demonstrate enhancement on imaging studies (eg, CT scanning, MRI, amplitude Doppler ultrasonography [US]), but other collections that do not show central enhancement suggest the presence of an abscess, hematoma, or necrosis.

A phlegmon is an undrainable infection. A viscous abscess without significant debris may be difficult to aspirate through a needle but should be drainable through catheters of appropriate caliber. Irrigation with saline or fibrinolytic agents may be necessary for successful drainage of an abscess with significant debris, blood, or viscous elements.

Imaging

Occasionally, an abscess is noted as an incidental finding on CT or US in a patient without clear stigmata of sepsis or systemic infection, such as in an older patient with failure to thrive. More often a diagnostic study is performed for a suspected abscess in a patient with clinical sepsis or infection syndrome (fever and leukocytosis). The patient usually has risk factors for abscess, such as recent surgery, infection, perforated viscous, or immunosuppression.

Serious local infection can be categorized by location, viscosity, complexity, contents, etiology, or surrounding structures. It can occur in solid organs (eg, liver, muscle), potential spaces (eg, pleural or peritoneal cavity), or in preexisting or physiologic fluid collections or organs (eg, gallbladder, urinary tracts).

CT and US

CT and US are excellent at identifying potential abscess areas. In the proper clinical setting, strong signs are a well-circumscribed fluid collection, thickened membranes or septations, gas bubbles, contrast enhancement, and debris. Weaker signs are nonloculated or thin-walled nonenhancing collections that have alternative pathophysiologic explanations, such as peritoneal or pleural fluid.

MRI

MR is most useful in identifying abscesses in the musculoskeletal system. Subtle infection from streptococci may cause erysipelas, which usually manifests as a spreading cellulitis. However, deeper infection in the fascia between the subcutaneous tissue and muscle or between muscle layers or at the periosteum also can be associated with streptococci and imaged well with short axis contrast-enhanced MR. MR is the best way to find intraosseous and subperiosteal abscesses associated with osteomyelitis. CT or US may be needed to determine if a process contains sufficient fluid elements to benefit from PAD.

Infected tissues

The spectrum of infected tissue ranges from infected viable organs with no significant degradation of physical integrity to total liquefactive necrosis. Main determinants of ease of drainage are viscosity and complexity (ie, septation, loculation, and debris). Viscosity ranges from that of near water to near solid. Abscess complexity ranges from unilocular to innumerable septations and loculations. Typical examples of complex viscous abscesses include infected pancreatic abscesses or infected retroperitoneal hematomas. These processes are challenging to treat percutaneously and may require multiple interventions over a prolonged recovery period.

Abscesses associated with a perforated bowel (high- and low-flow fistulas) are also challenging to treat. The presence of a low- or high-flow enteric fistula dramatically increases the expected duration of therapy. Successful treatment requires the understanding and cooperation of the patient and referring physician. Knowledge of abscess etiology occasionally may guide therapy. A patient with a history of ruptured viscus is at high risk for enteric organisms. Infection with Echinococcus species must be treated cautiously because of the risk of anaphylaxis.

Viscosity and complexity

Viscosity and complexity are difficult to assess with imaging alone. Viscosity cannot be readily predicted unless debris or suspended bubbles are seen. Fine septations are easily missed on CT scans because of partial volume averaging on routine scans. For example, a patient had a large intrahepatic pseudocyst infected with fungus. CT demonstrated a simple cyst appearance, a sharply demarcated isodense unilocular collection. US demonstrated innumerable fine septations. The complex nonviscous abscess was successfully treated with PAD. A patient with sepsis syndrome had a minimally irregular unilocular abscess appearance on CT scans. US revealed a well-demarcated hyperechoic mass with central lucency, possibly a hemangioma or necrotic malignancy. The patient was later found to have a perirectal abscess as the source for infection.

Differentiating bowel from intra-abdominal fluid

Differentiating bowel from pathologic intra-abdominal fluid collections is important. This may be difficult in patients with scant body fat, postsurgical abdomen, or unopacified bowel loops. Multislice spiral CT imaging with GI preparation and intravenous contrast media are helpful tools. Thin-slice, coronal, or sagittal reformatted images may help the practitioner understand the anatomy. Delayed imaging with additional oral contrast preparation may be considered in challenging cases.

Risk Assessment: Patient Selection And Preprocedure Workup

PAD is generally a safe and effective treatment. The preprocedure evaluation assists procedure planning and risk assessment. Clinical factors increase or decrease complication risks. See Image 3 for an example of a preassessment form suitable for most invasive procedures.

Safe PAD depends on an intact clotting system. In some practices, coagulation abnormalities are sufficiently common that obtaining preprocedure international normalized ratio (INR), prothrombin time, and platelet counts is routine.

Bleeding risk depends on the etiology, the degree of coagulopathy, and the reversibility of coagulopathy. The risk is nominal as long as the prothrombin time or INR and platelet counts are stable after correction. The risk is increased if coagulopathy recurs quickly. Recurrent or irreversible coagulopathy is caused by synthetic failure (eg, liver or bone marrow) or consumption (eg, hypersplenism, disseminated intravascular coagulation).

A common practice is to correct recurrent coagulopathy for the duration of a procedure. A risk of delayed hemorrhage may be present if the coagulopathic state recurs in the early postprocedure period. Anecdotal reports describe of fatal bleeding more than 24 hours postprocedure in this situation. The extensive amount of transfusion required to achieve this level of protection is expensive and burdens blood bank resources. If a patient cannot be treated noninvasively, manage coagulopathy as follows:

• INR of 1.3-1.4: Perform examination with radiology attending approval or correct prior to procedure.
• INR of 1.4-2: Correct coagulopathy prior to examination and verify repeat INR at less than 1.3.
• INR greater than 2: Patients on warfarin may require 24 hours or more for correction of the INR. Patients with synthetic failure may be difficult to adequately correct. Patients with severe coagulopathy requiring procedures may require coagulation support after the procedure.

Treatment plan

CT scanning is an excellent modality to plan the PAD access path. Position, angle, and depth can be assessed along with the presence of intervening or adjacent vital structures (eg, bowel, lung, spleen, liver), which increase the overall risk of PAD. If abscess suspicion is high, and one must traverse intervening structures, then a Seldinger technique may be planned to confirm the presence of an abscess with a needle aspiration before dilating the tract for catheter placement. Ultrasonography may be used for large or superficial collections or for bedside procedures. Advantages with ultrasonography include real-time imaging of the needle and catheter path, reduced radiation, and the ability to perform the procedure in the interventional radiology suite in concert with conventional fluoroscopy.

Risk assessment helps determine if the treatment plan is appropriate and reasonable. Decisions are based upon the risk of complication, expectation of clinical benefit, overall prognosis, and availability of treatment alternatives. The more likely a fluid collection is infected, the more likely drainage will be clinically beneficial. One may be less aggressive with nonloculated fluid such as free ascites or pleural effusion. These collections may need a diagnostic aspiration prior to attempted catheter drainage.

WBC count with differential and vital signs helps determine the infection's seriousness. One should consider treatment alternatives when fluid collections are in proximity to vital structures, have a difficult access route, or are found in a severely coagulopathic patient. Neurologic and psychologic factors impact a patient's ability to tolerate the procedure without sedation and the risk of postprocedure catheter dislodgment.

Consider medical and surgical treatment alternatives. For example, if an abscess is small and close to or in the spine, the drainage procedure could spread the infection to the cerebrospinal fluid (CSF) and spinal cord. These infections may benefit from an initial trial of IV antibiotics.

A risk/benefit categorization can be adapted from angioplasty guidelines for all invasive procedures. This uses an ordinal scale from 1-4 (the higher the number, the less ideal the procedure).

• Category 1: Proposed treatment or procedure is the procedure of choice. A high technical success rate is expected and generally results in complete relief of symptoms or normalization of abnormal clinical conditions or provides diagnostic clinical information.
• Category 2: Lesions or processes are well suited for the proposed treatment or procedure. A high technical success rate is expected and generally results in complete relief or significant improvement or provides relevant clinical information. This includes lesions and processes that are treated with adjunctive surgery or other modalities.
• Category 3: Lesions or processes are amenable to proposed treatment or procedure. A moderate technical success rate is expected. Because of disease severity, type or location, or procedure risk, there is a moderate expectation of obtaining long-term benefit or relevant clinical information. The procedure may be indicated because of other patient risk factors or because of the lack of alternative treatment options.
• Category 4: The procedure has limited utility because of a low technical success rate, high risk, or poor long-term benefit. The patient has extensive, possibly co-morbid disease. The procedure may be indicated in high-risk situations when no treatment alternative is available.

Marginal procedures (categories 3 and 4) require close interdisciplinary consultation. Serious clinical conditions warrant an aggressive approach with an attendant increase in risk. Potentially helpful procedures must be differentiated from those with a low expectation of durable clinical benefit. Difficult PAD procedures generally are well tolerated if performed with a minimum of needle passes. Solid organ, even intrasplenic, abscess may be drained. Consider drainage of a high-probability abscess in a salvageable patient with coagulopathy.

Pad Technique

The PAD technique depends on case specifics and personal preference. Consider location of the fluid collection and the likelihood that it is infected as well as the patient's overall condition.

The optimum access route is determined by the following:

• Shortest pathway
• Easiest angulation or localization
• Avoidance of intervening or adjacent structures - Bowel (peritonitis risk), vital organs (bleeding risk, especially spleen), and sterile pleural effusions (secondary empyema risk)
• Most convenient catheter location for patient
• For a solid organ abscess (eg, liver), access path should traverse a small amount of normal organ to reduce the risk of peritoneal spillage and bleeding

Bowel transgression is of concern, particularly the colon. One may traverse bowel when the alternatives have a higher risk-benefit ratio. Bowel transgression is generally tolerated when multiple needle punctures are avoided, and the catheter is left in for at least 2 weeks to create a mature tract. Referring/surgical service should be aware of the increased PAD risk in these situations. One should avoid aspiration of "low-probability" collections through the colon.

PAD is performed using standard aseptic technique and local lidocaine anesthesia. Begin with a diagnostic aspiration, followed by catheter placement if fluid is purulent. Alternatively, a trocar technique may be used. Simple abscesses smaller than 5 cm in diameter may be treated with aspiration (and lavage) alone.

Localization techniques

The localization technique is influenced by individual and institutional preference. Any modality may be used to assist needle placement. Prior to ready availability of CT fluoroscopy, patient assessment may be performed with CT scanning, with the PAD procedure performed with US localization. Conventional fluoroscopy can be used as an adjunct to US. US guidance allows real-time imaging and does not involve radiation exposure. CT fluoroscopy is increasingly available and facilitates "one-stop-shopping." The diagnostic CT and PAD may now be performed readily in one setting.

Large abscesses are amenable to "point-and-shoot" US localization. Manipulate the transducer to determine the puncture site, angle, depth, and margin for error. Mark the site by indenting the skin with the hub end of a needle. Entry is memorized, a one-blade-diameter skin incision made with a No 11 scalpel, and the needle placed without further imaging. Real-time US may be used for small, deep, or otherwise difficult access. A HiLiter needle (Inrad) may assist real-time guidance. In addition, US guidance hardware and software may make a difficult access much easier for those operators less experienced at free-hand sonographic guidance.

Use an 18-gauge, 15-cm Trocar needle (DTN-18-15.0, Cook) with an 8.5F general-purpose locking pigtail catheter (ULT8.5-38-25-P-6S-CLM-RH, Cook). A 21- to 22-gauge needle or 12-14F drainage catheter are not usually required for safety, efficacy, or fluid dynamics. When indicated, use the Accustick (Boston Scientific) needle or Neff Percutaneous Access set (NPAS-100-RB-NT, Cook). Larger-diameter drainage catheters are available from various vendors. Exceptions include viscous fluids and collections of necrotic tissue such as pancreatic infections or some empyemas.

Needle choice

• Typical abscess fluid is readily aspirated through an 18-gauge needle, which has approximately one-twentieth the resistance to fluid flow of a 21- to 22-gauge needle.
• Viscous or debris-laden fluid is more likely to cause a false-negative aspirate with a 21-gauge needle as only clear supernatant may return through the needle.
• An 18-gauge needle is easier to control and image and accepts a 0.038-inch guidewire. Neff and Accustick sets first require a 0.018-inch mandrel wire followed by a coaxial dilator.
• The 18-gauge needle costs less than the Neff access set.
• There is no clinically significant difference in needle trauma between the 18 and 22-gauge needles when a catheter is placed through the same tract. (This has been demonstrated for arteriotomy.)
• The 21-gauge needle may be used to minimize trauma for a challenging localization, low-probability fluid collection, or personal preference.

Drainage catheter size and the needle aspiration test

The drainage catheter's effectiveness is determined chiefly by its inner diameter and kink resistance. Determine the catheter choice with the needle aspiration test (NAT). If the fluid can be easily aspirated (1 mL in 1 second) by a 10-mL syringe through an 18-gauge needle, then the abscess is drained with the 8.5F catheter. Gobien and Park's published data support this approach. The catheter (8.5F) may be used for 3-6 months.

Most abscess fluid should pass the NAT. Viscous or debris-laden fluid requires larger diameter catheters: 10-14F for complex abscesses and 24-30F for severe pancreatic necrosis. If no significant fluid can be aspirated, consider biopsy. Viscous collections require larger diameter catheters and more aggressive flushing. Septations may be disrupted with a guidewire maceration technique once initial drainage subsides. Multiple catheters may be required. Some authors have had success using thrombolytic agents (urokinase, tissue plasminogen activator [t-PA]) for complex abscesses. Thrombolytics may disrupt fibrin and bacterial cell structures.

Supplies

For the trocar technique, all that is required is a trocar-type drainage catheter, drainage bag, and a minor procedure tray containing preparations, local anesthesia, a scalpel, and draping material. For the Seldinger technique, additional supplies include a guidewire and fascial dilators. Heavy-duty guidewire and hydrophilic dilators with Coons taper (Cook) may be helpful. Careful attention must be paid to securing the PAD catheter.

The most common post-PAD problem is inadvertent catheter dislodgement. The author has had good results using 2 adhesive-type catheter securing devices used in tandem. The author places a [] as the catheter leaves the skin and a [] closer to the catheter hub if room is available. Place all extrathoracic drainage catheters to gravity drainage or bulb suction. The author has had good results with the Tru-Close system (Uresil), which comes either with or without a built-in suction bellows. Consider a Pleur-Evac–type device for intrapleural collections to prevent tension pneumothorax. The catheter is flushed at least once per nursing shift with 10-20 mL of normal saline. Adjust the volume and frequency of catheter flush based on cavity size, drainage quality, and quantity.

Manage patients cooperatively

Management of the patient with an abscess drainage catheter is best performed in a cooperative fashion with referring and surgical services. The quality and quantity of drainage is monitored along with signs of patient recovery. Clinical follow-up care may be augmented with CT, US, fluoroscopy, and plain film contrast studies if the infection is not resolving. Additional catheter manipulation or placement is based on these results.

Simple abscess treatment usually is complete within 1-2 weeks. A complex abscess or enteric fistula may require weeks to months. Over the course of therapy, catheters may need to be revised, replaced, or repositioned. There are different approaches to post-PAD catheter management. Some prefer to remove the catheter as soon as drainage diminishes below 10 mL/shift. The author prefers to keep the catheter in until the cavity begins to close. Depending on the case, treatment is complete within a matter of days to weeks. Patients usually receive concurrent antibiotic therapy.

Pad Pitfalls And Device Properties

A variety of guidewires are available for PAD with different properties and prices. Guidewires should meet the following specifications:

• Stiff enough to guide dilators and catheter into abscess
• Not too stiff to prevent easy coiling of wire shaft within abscess
• Floppy tipped enough to encourage wire to coil within the abscess and not perforate the abscess wall
• Short enough to make use convenient

These requirements usually are satisfied by a 0.038-inch-outside-diameter 145-cm "heavy-duty" stainless steel wire such as the Coons Interventional wire (THSF-38-145-COONS, Cook). Its shaft stiffness is between that of a standard angiographic wire and an Amplatz Extra/Super Stiff (Cook/Boston Scientific). It has a long floppy tip and costs less than $20.

Guidewire stiffness depends on construction, material, and diameter. Stainless steel is cheaper and stiffer than Nitinol but does not have Nitinol's kink resistance. Wire stiffness is related by the fourth power of radius. A guidewire's stiffness is derived from the inner mandrel, not the outer wire coiling. Most rigid guidewires are constructed as a solid mandrel with a thin outer coating. Stainless steel Lunderquist Exchange wire (Cook) and the newer nitinol-based Nitrix (EV3) are examples.

Maintain guidewire access

It is critical to never lose guidewire access during any portion of a drainage procedure. When access is lost, re-entry may be difficult because of spontaneous decompression of the abscess or difficulties in imaging from disruption of the region. An advantage of the Accustick system is that it retains the 0.018-inch wire as the 0.038-inch wire is passed. If the larger wire becomes dislodged, then the smaller wire can be used for reaccess.

The author uses Teflon dilators with a Coons modification where the tip tapers over a 5-cm length rather than the standard 1 cm. Coons modification allows the author to use only even-size French dilators. The author always overdilates to the next even dilator size to ease catheter passage.

When encountering difficulty passing the dilator or catheter, check the skin incision first. There may be a remaining strand of subcutaneous connective tissue or the incision may be too small. The easiest way to assess this is to gently pull back on the dilator or catheter (without losing guidewire access). If the skin tents up as the catheter is withdrawn, enlarge the incision and reattempt passage. Hydrophilic coated dilators are now available (Cook) that greatly ease dilator passage. They use similar technology to the popular hydrophilic guidewires and are only slippery when wet.

Resistance to dilator or catheter

When there is resistance to passing the dilator or catheter, the assembly may kink under the skin. This is best determined with fluoroscopy. When it occurs, gently withdraw the wire and catheter as a unit to undo the kink. Try to readvance slowly. Have an assistant hold the guidewire straight to prevent buckling or accidental withdrawal. Buttress the tissues with a free hand, hold the catheter close to the skin, and advance the catheter or dilator in short firm strokes. This increases the radius of curvature (reduces buckling) and increases the effective rigidity of the unit.

If this fails, either the catheter/dilator or guidewire must be exchanged. If there is sufficient catheter or dilator in the abscess, then the wire may be exchanged for a more rigid or Nitinol variety. If not, the dilator or catheter may be exchanged for a hydrophilic 5F dilator, whereupon a stiffer wire may be exchanged. Occasionally, either the tract must be balloon dilated or an alternate access route chosen. These issues occur more frequently in scarred areas, such as in patients who have had multiple nephrostomy procedures.

Drainage catheters

Commercial drainage catheters come in a wide variety of sizes and materials. Factors to evaluate are cost, comfort, flexibility, ease of tracking (ability to follow guidewire), kink resistance, inner diameter, side-hole diameter, durability, tip configuration, securing mechanism, and catheter coating.

Most drainage catheters are placed with an inner-stiffening cannula using an over-the-guidewire technique. There is usually an option to use a traditional metal cannula or a newer flexible plastic cannula. When using the metal cannula, the catheter-cannula combination is advanced as a unit until the abscess is entered. The cannula is unlocked from the catheter. The catheter is deployed much as an IV catheter: the cannula is held steady while the catheter is advanced into the abscess. The disadvantage of the metal cannula is that the catheter is more likely to kink once it is disconnected from the cannula. The author prefers to use a flexible plastic cannula that remains connected to the drainage catheter until the final position is achieved. Once the catheter is in place, remove the cannula.

In cost-containment environments, the author has used a custom 35-cm, 7.1F polyethylene pigtail catheter (Cook). The P7.1-38 series catheter has a 0.062-inch inner lumen and is adequate for most abscess fluids. The catheter is easy to track and has good kink resistance. It is durable enough to use for approximately 2 weeks. It does not have a locking-pigtail suture, which is a minor disadvantage. Its low cost makes it ideal for short-term drainage procedures in cooperative patients or as a bridging catheter in a patient who will undergo multiple treatment stages. This catheter does not have a locking pigtail, and extra care is needed when securing it to avoid accidental dislodgement.

Many drainage catheters come with the option of being deployed as a trocar by putting in an inner stylet. The author uses the trocar technique only for percutaneous cholecystostomy procedures that require a catheter with a small locking loop to facilitate the catheter traversing the often leatherlike gallbladder wall.

Pad Complications And Medical Legal Pitfalls

PAD complications

Significant PAD complications are rare. One significant complication at the author's institution occurred in a patient with a pancreatic region abscess when the catheter entered the duodenum. Although the patient did well clinically, the high volume of gastric juice drainage prompted surgery. Given the location of the patient's original abscess, this complication was not unexpected.

Successful PAD depends upon the initial placement of the drainage device and it remaining in place for the duration of treatment. The greatest complication risk for all catheter placement procedures is catheter dislodgment. No ideal fixation device or technique is available. Locking sutures on drainage catheters may not reduce the incidence of catheter dislodgment but are indicated for maintaining a catheter in a cavity removed from the access, such as a transhepatic cholecystostomy or a transrectal pelvic abscess drainage. Torque generated by a patient rolling over in bed overcomes any catheter fixation system. A catheter fixator is merely a catheter position reminder.

The author has had some success using 2 catheter fixation devices in tandem. Even this aggressive approach will not prevent all catheter dislodgments. Debilitated, confused, and uncooperative patients are at risk. Patients often do well in a home setting with well-motivated caregivers.

Educate the patient as well as clinical nursing and physician staff to carefully monitor the catheter for possible dislodgment. Catheter dislodgment is reflected in a change in the length of catheter visible outside of the patient. When this is noticed, secure the catheter to the skin and obtain radiographs for comparison with the baseline study. Catheter dislodgment may be noticed only when the catheter is leaking (coiled under the bandage) or on the floor. Replacement catheters may be placed along the existing tract if detected early enough (usually <8 h) using a 5F dilator, contrast, and hydrophilic guidewire.

Medical legal pitfalls

James in Kadir (1991) describes basic medicolegal principals that apply to all invasive radiology. Invasive radiology lawsuits are usually related to procedure complications rather than misdiagnosis. Complaints stem from 5 general principles.

• The procedure was not indicated. It is usually alleged that a less invasive or less risky procedure could have been performed. When appropriate there should be chart documentation of the indication of the procedure performed (vs alternative approaches) by the radiologist and referring physician.
• Failure to obtain informed consent. The physician must provide the patient with a general understanding of the procedure, its risks and hazards, and the medically acceptable alternatives. Consent for all potential procedures must be obtained in advance before a patient receives sedation-analgesia. For underage or incompetent patients, the responsible consenting person must be known. The physician must recognize when a patient is withdrawing consent during a procedure and comply.
• Failure to perform the procedure in a reasonable manner and deviation from the standard of care. The radiologist should have documentation of adequate training, including a logbook of procedures, successes, and complications. There should be documentation of adequate training and CME for new procedures and technology.
• Failure to promptly recognize and react to a complication. Satisfactory and unsatisfactory results of procedures must be promptly and adequately noted in the chart. Follow-up care should be documented.
• Failure to adequately treat the complication according to an adequate standard of care. The radiologist must be familiar with the recognition and treatment of contrast reactions. Basic life support and/or advanced cardiac life support certification should be kept current. There should be documentation of consultations obtained (eg, surgical) in the treatment of complications.

Multimedia

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Media file 1: StatLock catheter securement device for a drainage catheter. This may be used in conjunction with PercuStay for added protection from catheter dislodgement.

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Media file 2: Dress normally. Secure the catheter and/or drainage bag tubing to skin further down to help prevent catheter dislodgment.

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Media file 3: Radiology procedure preassessment form.

Keywords

PAD, CT/US-guided drainage, abscess drainage

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