Continuing Education Activity

Abdominal abscesses contain cellular debris, enzymes, and liquid from an infectious or non-infectious source. They are a common and serious condition and can develop almost anywhere in the abdomen. However, most are confined to some part of the peritoneal cavity. To avoid the high morbidity and mortality associated with this condition, it must be promptly diagnosed and treated. This activity reviews the evaluation and treatment of abdominal abscesses and the importance of the interprofessional team in recognizing and treating this condition.

Objectives:

• Identify the clues for an abdominal abscess.
• Review the most definitive imaging test for an abdominal abscess and describe what this imaging might show in a patient with an abdominal abscess.
• Describe the treatment strategy for an abdominal abscess.
• Explain how careful patient monitoring and strong communication amongst the interprofessional team will improve patient outcomes in those with abdominal abscesses.

Introduction

Abdominal cavity infections commonly arise following the inflammation or disruption of the gastrointestinal tract. Less frequently, they might originate from the gynecologic or urinary tract. Abdominal infections are typically polymicrobial and result in either an intra-abdominal abscess and phlegmon in more localized cases or secondary peritonitis in more diffuse conditions.[1]

An abdominal abscess is a collection of cellular debris, enzymes, and liquefied remains from an infection or non-infectious source. An intra-abdominal abscess usually signals that something serious is happening to the patient. In many cases, the omentum, viscera, or mesentery may wall off an intraabdominal abscess. An abdominal abscess is quite common and is a serious condition. To avoid high morbidity and mortality, the condition must be promptly diagnosed and treated. In general, sepsis that occurs after perforation in the upper gastrointestinal (GI) tract or leak is often associated with less morbidity and mortality compared to leaks that result from a colonic perforation or injury.[2][3][4]

Etiology

Intra-abdominal infections usually occur following the breach in the mucosal defense barrier that would cause the normal bowel flora to inoculate the abdominal cavity. The microbiological spectrum depends on the specific gastrointestinal source, including the small versus large intestine.[5]

Four to six main colonic flora are generally common in intra-abdominal abscesses and infections, reflecting the frequency of associated diseases originating from this anatomic site, including, but not limited to acute appendicitis, complicated diverticulitis, colon malignancies, inflammatory bowel disease, and former colon surgeries. Accordingly, the predominant organism involved in such infections is coliforms bacteria (including Escherichia coli, Klebsiella spp, Proteus spp, and Enterobacter spp), streptococci, enterococci, and the spectrum of anaerobic bacteria.[6] However, Bacteroides fragilis and E. coli are the two major organisms isolated from abdominal cavity infections and abscess formations.[7]  B. fragilis, as an obligate anaerobic gram-negative bacillus, is a highly invasive anaerobic pathogen in abdominal infections.[8] 

Considering the phases of the early abdominal sepsis and intra-abdominal abscess, coliform bacteria mainly contribute to early sepsis and anaerobes implicated in the late sequelae and complications with abscess formation.[9] 

Perforation of the proximal intestines and peptic ulcer results in ubiquitous infections with aerobic and anaerobic gram-positive bacteria or Candida spp.[10] Several critical points in the past medical history review enable the diagnosis of the possible culprit. Accordingly, the history of former antimicrobial therapy and exposures are associated with microbiologic alterations in the gut flora. Therefore, intra-abdominal infections in such settings are more likely nosocomial pathogens, including Pseudomonas aeruginosa and other drug-resistant organisms.[11] Specific organisms, including Enterococci, are more likely to be found in hospital-acquired settings than in community-acquired infections.[12]

Moreover, candida infections have been reported in both the small and large intestines-originated infections, particularly in the following patient groups; 1. history of antibiotic therapy, 2. immunocompromised patients, and 3. history of recurrent infection.[13]

Collectively, the most common organisms cultured from an abdominal abscess includes aerobic and anaerobic bacteria originating from the gastrointestinal tract.[14] Most intra-abdominal abscess formations result from perforations in the GI tract, including complicated peptic ulcer disease, appendicitis, and diverticulitis, or chronic complications related to pancreatic necrosis, ischemic bowel disease, and anastomotic leaks. Moreover, penetrating abdominal trauma, including stab wounds, gun-shot wounds, post-operative surgical complications with anastomotic leaks, sigmoid and less-commonly cecal volvulus, intussusception, retained cholelithiasis, and fistula formations due to gallstone ileus might cause an abdominal abscess. However, rarely do injections result in abdominal sterile abscess formation.[15] Therefore, organisms involved in an abdominal abscess could be summarized as the following: 1. Escherichia coli, 2. Bacteroides, 3. Neisseria, 4. Chlamydia, and 5. Candida.[16]

Epidemiology

In most cases, intra-abdominal abscesses derive from an intra-abdominal organ and often develop after operative procedures. It is estimated that about 70% are postsurgical and that 6% of patients undergoing colorectal surgery may develop a postoperative abscess. Hepatic abscesses account for 13% of all intra-abdominal abscesses. Most hepatic abscesses involve the right lobe, probably due to the larger size and greater blood supply.[17] Complicated intra-abdominal infections (cIAIs) originate from the three most frequent organ-specific reasons for patients admitted with septic shock, with mortality rates of up to 40%.[17] 

Pathophysiology

An intra-abdominal abscess may be confined or generalized within the peritoneal cavity. Localized collections of pus may have a barrier that may include adhesions, omentum, or other adjacent viscera. In almost all cases, abdominal abscesses contain a polymicrobial collection of both aerobic and anaerobic organisms from the GI tract. The bacteria usually incite an inflammatory reaction that often results in a hypertonic environment that continues to expand as an abscess cavity. If left untreated, an abdominal abscess can lead to septic shock.[18][19]

Anaerobic infections originate from the leakage of endogenous bacteria into the affected cavity. However, disturbed host defense mechanisms would allow the anaerobic organism to be displaced.

History and Physical

Patients with an intra-abdominal abscess may present with abdominal pain, fever, anorexia, tachycardia, or prolonged ileus. The presence of a palpable mass may or may not be present. If the presentation is delayed, some individuals may appear in septic shock.

If the abscess is retroperitoneal or located deep in the pelvis, there may be no clinical signs. In such cases, the only suspicion may be a fever, mild liver dysfunction, or prolonged ileus.[20]

In post-surgery patients, the diagnosis of an abdominal abscess is difficult because of analgesia and antibiotics, which often mask the signs of an infection.

A subphrenic abscess may present with shoulder tip pain, hiccups, or atelectasis.[21]

Most patients with an abdominal abscess will show signs of dehydration, oliguria, tachycardia, tachypnea, and respiratory alkalosis.

The following clues imply that anaerobic infections are the leading cause of abdominal abscess formations; 1. putrid odor, 2. gas formation with the crepitus sensation in palpation and the vascular structure, including the hepatic-portal venous gas formation, 3. gram staining of the aspirate, indicating a polymicrobial flora, or anaerobes, 3. classic presentations of clostridial syndromes, including but not limited to necrotizing enteritis.[22]

Evaluation

Blood work is not specific for an intra-abdominal abscess but may reveal leukocytosis, abnormal liver function, anemia, or thrombocytopenia. These are features that signal an infection. Blood cultures are often negative but, when positive, may reveal predominantly anaerobic organisms, the most common being Bacteroides fragilis.

Plain abdominal x-rays are not sensitive for identifying an intraabdominal abscess; hence a CT scan is required and is considered the most definitive test to rule out an intra-abdominal abscess. A CT scan can reveal the location, size, and presence of bowel thickening, thumbprinting, and ileus. Intra-abdominal abscess almost always requires intravenous (IV) antibiotics. If the abscess is localized, CT-guided aspiration can be performed to drain the abscess. CT scan has the advantage that it avoids general anesthesia and wound complications. It also prevents contamination of other parts of the abdominal cavity.[23][24][25]

In some patients, ultrasound may help identify abdominal abscesses.

Nuclear scans are rarely used today to detect abscesses because the technique is time-consuming and has a high rate of false positives.[26]

Treatment / Management

Broad-spectrum antibiotics and hydration are essential. Once cultures become available, one can use specific antibiotics, as noted by their sensitivity. Intravenous hydration is required. A nasogastric tube may help decompress the bowel and lower the emesis.[27][28][29]

Percutaneous CT-guided drainage is widely used to drain abdominal abscesses. The procedure can be done under local anesthesia and decreases the duration of hospitalization. In most patients, improvement occurs within 48 hours after drainage. In localized abscesses, CT-guided drainage has a success rate of over 90%.

Percutaneous abscess drainage (PAD) has been a widely approved treatment modality for accessible postoperative intra-abdominal abscesses.[30] Percutaneous drainage in managing inta-abdominal abscesses (IAA) was first introduced in the 1970s. The preliminary outcomes showed a success rate of up to 86%.[31] The contributing factors in the success rate of percutaneous drainage in managing IAA have not been well established yet. However, according to some research on adult patients with a single appendicular abscess, the success rate was higher than those with multiple abscesses.[30] On the other hand, the favorable results of the non-operative management of appendicular abscesses in the pediatric population have been well-documented.[32] It should be noted that the major factor affecting the success rate in the pediatric population is the abscess size of less than 4 cm.[33]

The threshold for percutaneous drainage interventions in IAA differs according to the abscess origin, and an abscess size of 3 to 6 cm is generally accepted as a cutoff for diverticular abscess treatments.[33]

If the patients fail to improve within 24 to 48 hours, surgical consultation is required. Both laparoscopic, interventional radiology and open procedures can be used to evacuate the abdominal abscess. However, if surgery is required, the necrotic tissue will be removed, and all adhesions can be lysed. Most of these patients require monitoring in the intensive care unit (ICU) and need aggressive resuscitation with fluids. If the abscess is localized and promptly treated, the prognosis is good.

A pelvic abscess may be drained transrectally or transvaginally. Pelvic abscesses present a serious and challenging management problem. Endoscopic ultrasound (EUS)-guided drainage provides a safe and effective minimally invasive treatment option. The likelihood of a successful outcome is dependent on appropriate patient selection, drainage technique, and postoperative management.[34] 

Open surgery for an abdominal abscess is a difficult undertaking and can be difficult because of adhesions and the lack of proper anatomical pathways to separate the bowel.

As with most abscesses and contained infected spaces, drainage is the definitive treatment of a subdiaphragmatic abscess. It prevents progressive sepsis. It can be accomplished either by percutaneous or surgical drainage. Percutaneous drainage is the least invasive and just as effective as surgical drainage and is currently the standard of care. CT-guided drainage with interventional radiology is highly effective and can prevent the morbidity and mortality associated with surgical drainage.[35]

Percutaneous computed tomography (CT)-guided drainage is considered the gold standard in management and has a very high success rate. The advantages include that it avoids general anesthesia, especially in the elderly with multiple comorbidities, prevents complications of the surgical wound, and reduces the length of hospitalization. Percutaneous drainage can be used as both a diagnostic and therapeutic modality. Especially in critically ill patients, it can be used to control sepsis and improve the general condition of the patient before definitive surgical treatment. Persistent drainage usually suggests the presence of an enteric fistula, which can be diagnosed with a contrast CT. Complications include bleeding, injury to nearby visceral organs, pleural effusion, pneumothorax, and mediastinitis. Hence, transmural drainage has been developed using endoscopic ultrasound (EUS-TD). It is beneficial due to real-time visualization of the abscess cavity, a doppler to avoid major vessels, and a high success rate.[36] Trans-esophageal and trans-gastric approaches have been tried to drain the subphrenic abscess.[36]

If percutaneous or endoscopic drainage fails, then surgical drainage, either by an open or laparoscopic method, is indicated. Laparoscopic drainage is minimally invasive and permits exploration of the abdominal cavity without the use of a wide incision, and hence purulent exudate can be aspirated under direct vision. If the patient does not improve with the laparoscopic technique, an open surgical technique should be considered. The open approach may be difficult due to adhered bowel, loss of anatomic delineation, and fragile viscera. Of late, there has been increased use of open abdomen therapy (OAT), mainly in managing abdominal compartment syndrome and trauma patients. The concept of damage control surgery is being used. The use of a vacuum dressing to close the abdomen is preferred.[37]

Most patients with a timely intervention will recover with supportive care like intravenous hydration. Patients who worsen and develop septic shock will need admission to the intensive care unit. Need for multiorgan support like mechanical ventilation, vasopressors, and dialysis will be needed in patients with significant organ failures.[38]

Differential Diagnosis

• Prolonged ileus
• Fever of unknown origin
• Crohn disease
• Ulcerative colitis[39]
• Complicated perianal infection[40]
• Perforated colon cancer[41]
• Diverticular abscess[42][41]

Prognosis

The prognosis of patients with an abdominal abscess before the era of the CT scan was very high. Today, with the availability of CT scans, the diagnosis is made much earlier, and, in many cases, CT-guided drainage has helped lower morbidity. However, if an abdominal abscess is misdiagnosed and not treated, the mortality is very high. Risk factors that increase mortality and morbidity include the following:

• Advanced age 
• Multi-organ failure
• Multiple recent surgeries
• Complex abscess
• Delay in diagnosis[17]

Complications

An abdominal abscess can lead to the following complications:

• Multiorgan failure
• Formation of fistula
• Septic shock
• Both CT-guided drainage and surgery can lead to bowel perforation
• Death
• Deep vein thrombosis
• Malnutrition

Postoperative and Rehabilitation Care

Patients with an abdominal abscess usually require a stay in the hospital. Repeat imaging is often done to ensure that there is no more residual abscess after treatment.

Depending on the complexity of the abscess, some patients may require total parenteral nutrition.

Because the patients are often frail, physical therapy is recommended to help recover muscle strength and flexibility.

Consultations

Once a diagnosis of an abdominal abscess is done, a general surgeon and a radiologist should be consulted.

Pearls and Other Issues

Those with gross contamination of the abdominal cavity can develop multiorgan failure and consequently have a high mortality rate.

Today with the availability of CT scans, diagnosis and drainage can be accomplished with very low morbidity.

A complex abscess may require a laparoscopic or an open approach.

Enhancing Healthcare Team Outcomes

An abdominal abscess is not an uncommon presentation on the general surgery ward or in the emergency department. Because of its vague clinical presentation, the disorder is best managed by an interprofessional group of health professionals that includes a surgeon, dietitian, pharmacist, radiologist, gastroenterologist, and a wound care nurse. An abdominal abscess has significant morbidity and can rapidly become fatal if left untreated. To improve outcomes, communication between the interprofessional team is highly recommended.

While initial antibiotics are broad-spectrum, the pharmacist and clinicians need to watch the blood cultures to determine the type of organisms growing and their sensitivity. In many cases, patients with an abdominal abscess may not be able to eat and may require peripheral or central parenteral nutrition hence, a dietary consult should be involved. While there are no universal guidelines on the management of an abdominal abscess, the current consensus indicates that percutaneous drainage by a radiologist has low morbidity compared to an open procedure.

All patients with an abdominal abscess need close monitoring as they can quickly become septic. The nursing responsibility lies in measuring vital signs, urine output, pressure sore prevention, DVT prophylaxis, ambulation, and timely antibiotics. Any change in the patient's clinical status should be immediately communicated to the clinician.

There should not be any delay in consulting with the surgeon, as delay can lead to adverse outcomes and significant healthcare costs. Many of these patients also develop wound infections that do not heal. Hence a consult with a wound care nurse for daily dressings is necessary.

The progress and monitoring of patients with an abdominal abscess are made by regular physical exams, vital signs, and imaging tests. Often these patients have drainage devices that also need to be monitored for the type and amount of fluid discharge. Only through a systematic clinical interprofessional team approach can the morbidity and mortality of an abdominal abscess be lowered.[43][44](Level III)

Outcomes

The outcomes after an abdominal abscess depend on patient morbidity, the cause, extent of contamination, and age. When multiple organs are involved and the patient is septic, the outcomes are poor. However, for localized abscesses from a rupture of an appendix or sigmoid diverticulitis, the outcomes are good. Many of these patients have significant comorbidity which affects their long-term survival. The key to improving mortality is an interprofessional approach with prompt diagnosis, close monitoring, and early treatment. [Level 5}  [45][15] (Level V)