# Abscess Drainage and Fluid Collections

## Introduction

Percutaneous image-guided drainage of abscesses and fluid collections is a cornerstone of interventional radiology and has largely replaced open surgical drainage for most intra-abdominal, pelvic, and thoracic collections. Understanding the indications, techniques, catheter selection, and management principles is essential for all radiology residents. Successful drainage requires appropriate patient selection, safe access planning, and diligent post-procedure catheter management.

## Indications

Indications for percutaneous drainage include **abscess** (infected fluid collection requiring drainage for source control), **biloma** (post-surgical or post-traumatic bile leak), **urinoma** (perinephric or pelvic urine collection), **lymphocele** (post-surgical lymphatic fluid collection, often after renal transplant or pelvic lymph node dissection), **hematoma** (organized or liquefied hematoma causing symptoms or superinfection), **empyema** (infected pleural effusion), and **pancreatic collections** (walled-off necrosis and pseudocyst).

## Contraindications

Contraindications include **lack of safe percutaneous access route**, **uncorrectable coagulopathy** (following SIR periprocedural guidelines), and **sterile, asymptomatic collections** not causing obstruction (which may be observed). Echinococcal cyst is a relative contraindication and requires pretreatment with albendazole if drainage is necessary.

## Imaging Guidance

**Ultrasound** is preferred for superficial collections, pleural effusions, and pelvic collections accessible via transabdominal or transrectal/transvaginal approach, offering real-time visualization. **CT** is preferred for deep abdominal and retroperitoneal collections, collections near bowel or vascular structures, and when ultrasound access is limited by body habitus or overlying gas. **Fluoroscopy** is a useful adjunct for wire and catheter manipulation, contrast injection (sinography/abscessography).

![CT-guided percutaneous drainage of a right lower quadrant appendiceal abscess showing catheter within the collection](ct-guided-abscess-drainage.png)

## Drainage Techniques

### Trocar Technique

In the trocar technique, the catheter is advanced directly into the collection over a stiffening cannula or stylet. This provides single-step entry and is faster but less controlled. It is best suited for large, superficial, easily accessible collections.

### Seldinger Technique

The Seldinger technique involves accessing the collection with a needle under image guidance, aspirating fluid to confirm appropriate position, advancing a guidewire through the needle into the collection, dilating the tract over the wire, and then advancing the drainage catheter over the wire. This approach is preferred for deep collections and when traversing sensitive structures near bowel or vessels.

### Tandem Technique

The tandem technique combines elements of both trocar and Seldinger approaches, with a needle placed adjacent to the trocar path for wire placement.

## Catheter Selection

**Pigtail catheters** are most commonly used, with the locking pigtail maintaining position within the collection. Sizes range from **8-14 French** for simple fluid to **12-16 French** for viscous material, necrotic debris, or empyema. Larger bore catheters (20-28 Fr) may be needed for organized collections or walled-off pancreatic necrosis. The **locking mechanism** (locking suture or pull-string) forms the pigtail and prevents dislodgement. Multiple sideholes along the distal segment facilitate drainage.

## Post-Procedure Management

### Catheter Care

The catheter should be **flushed** with 10 mL sterile saline every 8-12 hours to maintain patency. Daily **output volume** and character (purulent, serous, bilious) should be recorded. The catheter is secured to the skin with suture or an adhesive retention device.

### Criteria for Catheter Removal

Removal is appropriate when output falls below 10-20 mL per day, the patient shows clinical improvement (defervescence, normalizing WBC, symptom resolution), follow-up imaging shows resolution or near-resolution of the collection, and there is no evidence of fistulous communication on sinogram.

### Follow-up Imaging

A **sinogram/abscessogram** (injection of contrast through the drain under fluoroscopy) assesses cavity size and fistulous communication before removal. CT or ultrasound can assess the residual collection.

## Site-Specific Considerations

### Hepatic Abscess

**Pyogenic abscesses** are typically polymicrobial, often following biliary obstruction or a procedure. **Amebic abscesses** are usually in the right lobe, large and single; medical therapy (metronidazole) is tried first, with drainage if there is no response in 48-72 hours or if there is risk of rupture. A transpleural route is acceptable if necessary, though angling to avoid the pleural space when possible is preferred.

### Pelvic Abscess

The **transgluteal approach** (CT-guided) through the greater sciatic foramen avoids the sciatic nerve and gluteal vessels. The **transrectal or transvaginal approach** (ultrasound-guided) is used for deep presacral collections. An anterior transabdominal approach is used when a safe window is available.

### Pleural Empyema

| Empyema Stage | Characteristics | Management |
|---------------|----------------|------------|
| Stage I (Exudative) | Free-flowing fluid | Simple aspiration or small-bore catheter |
| Stage II (Fibrinopurulent) | Loculated, fibrinous debris | Catheter drainage +/- fibrinolytics (tPA + DNase) |
| Stage III (Organized) | Thick pleural peel, trapped lung | Surgical decortication |

Management is stage-dependent. The **exudative** stage (Stage I) requires simple aspiration or a small-bore catheter. The **fibrinopurulent** stage (Stage II) requires catheter drainage with or without intracavitary fibrinolytic therapy (tPA + DNase). The **organized** stage (Stage III) may require surgical decortication.

### Pancreatic Collections

**Acute peripancreatic fluid collections** are usually sterile and self-limited; drainage is performed only if infected. **Walled-off necrosis (WON)** requires a mature capsule (typically at least 4 weeks) and may need a large-bore catheter or surgical debridement. **Pseudocysts** have a thin wall and homogeneous fluid and can be drained percutaneously, endoscopically, or surgically.

![Fluoroscopic sinogram through a pelvic abscess drain demonstrating residual cavity without fistulous communication, confirming readiness for catheter removal](sinogram-pelvic-drain.png)

![Ultrasound-guided transvaginal drainage of a deep pelvic abscess using a pigtail catheter](transvaginal-pelvic-abscess-drainage.png)

## Key Clinical Pearls

Send fluid from **all** drained collections for Gram stain, culture, cell count, and fluid analysis (amylase, bilirubin, creatinine as clinically indicated). A sudden **decrease in output** may indicate catheter obstruction (flush or reposition) or resolution of the collection (confirm with imaging). **Multiloculated collections** may require multiple catheters or catheter repositioning for complete drainage. Do not remove a drain prematurely in the setting of an enteric fistula; prolonged drainage with nutritional support may allow fistula closure. **Clinical non-improvement** after 48-72 hours of drainage should prompt repeat imaging to evaluate for undrained loculations, catheter malposition, or alternative diagnosis.

## References

1. vanSonnenberg E, Wittich GR, Goodacre BW, et al. Percutaneous Abscess Drainage: Update. *World J Surg*. 2001;25(3):362-369.
2. Gervais DA, Brown SD, Connolly SA, et al. Percutaneous Imaging-Guided Abdominal and Pelvic Abscess Drainage in Children. *Radiographics*. 2004;24(3):737-754.
3. Rahman NM, Maskell NA, West A, et al. Intrapleural Use of Tissue Plasminogen Activator and DNase in Pleural Infection. *N Engl J Med*. 2011;365(6):518-526.
4. Banks PA, Bollen TL, Dervenis C, et al. Classification of Acute Pancreatitis -- 2012: Revision of the Atlanta Classification. *Gut*. 2013;62(1):102-111.