Interventional Radiology Imaging

Failing Abscess Drain After Colectomy: Why Is Catheter Upsizing the Next Step?

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Failing Abscess Drain After Colectomy: Why Is Catheter Upsizing the Next Step?

A 68-year-old man is back in the emergency department. Two months ago, he underwent a left hemicolectomy for colon carcinoma, a procedure complicated by a post-operative abscess. An interventional radiologist placed a percutaneous drain two weeks ago, and he was discharged on antibiotics. Today, he presents with recurrent abdominal pain and a low-grade fever. His drain output has been minimal, around 25 cc per day, and a new CT scan shows the abscess is unchanged in size. You are managing his care and must decide the next best step for this failing drainage. The American College of Radiology (ACR) finds that in this specific clinical context, the procedure of **Catheter upsizing** is *Usually appropriate*. This article details the clinical workflow for this exact scenario.

Who Fits This Clinical Scenario for a Failing Abscess Drain?

This guidance applies to a specific patient population: those with a known intra-abdominal abscess that has already been treated with percutaneous drain placement but is failing to resolve. The key inclusion criteria are:

  • A history of a previously placed percutaneous drain for an infected fluid collection (e.g., a post-surgical abscess).
  • Clinical signs of persistent or worsening infection, such as fever, leukocytosis, or abdominal pain, despite ongoing antibiotic therapy.
  • Objective evidence of treatment failure, specifically low or decreasing drain output in the face of a collection that remains stable or is increasing in size on follow-up imaging (typically CT).

It is critical to distinguish this situation from other related but distinct clinical problems. This workflow does not apply to:

  • Patients with a new, undiagnosed, and undrained fluid collection. A patient presenting for the first time with right lower quadrant pain and fever, for instance, requires a diagnostic workup to confirm the presence and nature of an abscess before any drainage is considered.
  • Patients with sterile or non-infected collections. A stable, walled-off fluid collection following pancreatitis in an afebrile patient, for example, is managed differently and may not require intervention at all.
  • Patients whose drain was intentionally removed. If a drain was removed because the collection was thought to be resolved, a recurrence of symptoms would trigger a new diagnostic evaluation, not necessarily an assumption of drain failure.

What Are the Potential Causes for a Non-Resolving Drained Abscess?

When a drained abscess fails to improve, the differential diagnosis centers on why the current treatment is insufficient. The primary goal of the next intervention is to identify and correct the underlying mechanical or biological issue.

Inadequate Drainage due to Catheter Issues
This is the most common and immediate consideration. The existing catheter may be malfunctioning for several reasons. It could be too small in diameter to effectively drain thick, viscous purulent material. It might be occluded by debris, fibrin, or a blood clot. The catheter could also be kinked or malpositioned, with its side holes no longer situated within the main abscess cavity. Low drain output despite a persistent large collection on CT is the classic sign pointing toward a mechanical catheter problem.

Complex or Multiloculated Abscess
The initial drain may only be accessing one compartment of a larger, multiloculated (septated) abscess. The persistent fever and pain are driven by the undrained, walled-off pockets of infection. The initial CT may have underestimated the collection’s complexity, or septations may have formed over time. The drain is functioning correctly for the space it’s in, but it cannot reach the entire infected volume.

Viscous Purulent Material
Some abscesses, particularly those with certain bacterial strains or significant necrotic debris, contain extremely thick pus that cannot be evacuated through a standard-sized (e.g., 8-10 French) catheter. Even if the catheter is perfectly positioned, the physical properties of the fluid prevent effective drainage, necessitating a more aggressive approach to either liquefy the contents or provide a larger conduit for removal.

Enteric Fistula or Ongoing Leak
Less commonly, but critically important in a post-colectomy patient, the abscess may be fed by an ongoing leak from a surgical anastomosis or an unrecognized bowel injury. In this case, the drain is removing fluid, but the source of contamination continues to replenish the collection. This turns a simple drainage problem into a more complex surgical or interventional challenge, and failure to recognize it leads to prolonged morbidity.

Why Is Catheter Upsizing the Recommended Next Step for This Presentation?

In the setting of a non-resolving abscess with an indwelling drain, the ACR designates **Catheter upsizing** as a *Usually appropriate* intervention. This procedure, performed by an interventional radiologist, directly addresses the most probable causes of treatment failure in a minimally invasive fashion.

The procedure involves accessing the existing drain tract. Under fluoroscopic guidance, a wire is passed through the current catheter into the abscess cavity. The old catheter is removed over the wire, and a new, larger-bore catheter (e.g., upsizing from a 10 French to a 14 or 16 French) is placed over the wire into the same position. During this exchange, the interventionalist can perform a “drain check” or “abscessogram” by injecting contrast into the cavity. This diagnostic step is invaluable; it can confirm proper catheter positioning, delineate the full extent and complexity of the cavity, identify previously unseen septations, and crucially, reveal any communication with the bowel that would indicate a fistula.

This single procedure can be both diagnostic and therapeutic. If the issue was a small or clogged catheter, the larger drain immediately improves drainage. If the abscessogram reveals complexity, it guides further management, such as placing a second drain into an undrained loculation.

Why Alternatives Are Rated Lower

  • Continued antibiotics and drainage (no change in care) is rated as *May be appropriate* but is a passive approach. Given the patient’s persistent symptoms and lack of imaging improvement, continuing the failing strategy is unlikely to succeed and risks clinical deterioration.
  • Open surgical drainage is also rated as *May be appropriate* but represents a significant escalation in care. Subjecting a post-operative, infected patient to another major laparotomy carries substantial morbidity and mortality. It is generally reserved for cases where percutaneous methods have failed or are not feasible.

Another procedure, **Intracavitary thrombolytic therapy and drainage**, is also rated *Usually appropriate*. This involves instilling a thrombolytic agent like tissue plasminogen activator (tPA) into the cavity to break down viscous fluid and septations. It is often performed in conjunction with or as an alternative to catheter upsizing, depending on the abscess characteristics and institutional preference.

What’s Next After Catheter Upsizing? Downstream Workflow

The management path following the procedure depends directly on the intraprocedural findings and the patient’s clinical response.

If the Procedure is Successful and Symptoms Resolve:
If a simple catheter upsize resolves a blockage and leads to increased drain output and rapid clinical improvement (defervescence, pain reduction, normalizing white blood cell count), the patient can be managed with continued drainage and antibiotics. The drain is typically removed once output is minimal (<10-20 cc/day) and a follow-up CT confirms resolution of the collection.

If an Enteric Fistula is Identified:
The discovery of a fistula during the abscessogram is a critical finding that changes management. The patient will require bowel rest, nutritional support (often total parenteral nutrition), and potentially further intervention. The goal is to control the sepsis with adequate drainage while allowing the fistula to heal. This often involves a multidisciplinary discussion with colorectal surgery. The drain will need to remain in place for a much longer period, and surgical revision may ultimately be necessary if the fistula does not close.

If the Collection Remains Complex or Fails to Resolve:
If upsizing alone is insufficient due to extensive loculations or extremely viscous pus, the next step may involve placing a second drain into a separate pocket or initiating intracavitary thrombolytic therapy. If multiple percutaneous attempts fail to control the sepsis, escalation to laparoscopic or open surgical drainage becomes necessary.

Pitfalls to Avoid (and When to Get Help)

In managing a failing abscess drain, several common pitfalls can delay recovery. First, avoid the pitfall of “watchful waiting” in a symptomatic patient. Fever and pain with a non-resolving collection on CT are clear signs of inadequate source control that antibiotics alone cannot fix. Second, do not simply flush a poorly draining catheter without a proper diagnostic evaluation; this rarely solves an underlying mechanical issue like malposition or occlusion from viscous pus. Third, be wary of prematurely removing a drain. The decision should be based on a combination of minimal output, clinical resolution, and imaging confirmation, not just the number of days it has been in place.

If the patient develops signs of septic shock, worsening peritonitis, or if an enteric fistula is confirmed, immediate escalation and consultation with both Interventional Radiology and Surgery is critical.

Related ACR Topics and Tools

This article covers one specific scenario in depth. For a broader view of all clinical variants and imaging modalities covered by the American College of Radiology for this topic, please see our parent guide. For additional resources on imaging selection, protocols, and radiation safety, the following GigHz tools are available.

Frequently Asked Questions

Why not just pull the drain and replace it at the bedside?

Blind bedside replacement is not recommended. The procedure should be performed under image guidance (fluoroscopy or CT) to ensure the new, larger catheter is correctly positioned within the abscess cavity. Image guidance also allows for a diagnostic abscessogram to assess for complexity or fistulas, which is a critical step that cannot be done at the bedside.

How long should we wait to see if the upsized catheter is working?

Clinical improvement should be evident within 24-48 hours. This includes reduction in fever, improvement in abdominal pain, and a decrease in white blood cell count. Drain output should also increase significantly if the problem was a blockage or a catheter that was too small. If there is no improvement in this timeframe, further investigation is warranted.

What if the CT report says the drain tip is outside the collection?

If the drain is clearly malpositioned on CT, the procedure is technically a catheter repositioning or replacement, not just an upsizing. However, the workflow is similar. The interventional radiologist will use image guidance to manipulate the existing drain or place a new one in the correct location to ensure effective drainage.

Is there a role for MRI in this specific scenario?

MRI is generally not used for evaluating a failing abscess drain. CT with intravenous contrast provides excellent anatomical detail, is fast, and is ideal for guiding percutaneous procedures. An abscessogram performed under fluoroscopy during the catheter exchange is the most direct way to evaluate the drain, the cavity, and potential fistulas.

What if the patient is too unstable to transport to Interventional Radiology?

In a hemodynamically unstable patient with uncontrolled sepsis from an abdominal source, the primary goal is rapid source control. This may necessitate an emergency open surgical washout and drainage in the operating room, as it can be performed more quickly than mobilizing an IR suite for a complex procedure. This decision requires urgent consultation between the primary team, surgery, and critical care.

Reviewed by Pouyan Golshani, MD, Interventional Radiologist — May 21, 2026