Subphrenic Abscess

Etiology

The formation of the subphrenic abscess occurs after bowel content and gut bacteria contaminate the peritoneal cavity. A retrospective review of 52 patients between 1974 and 1988 showed most infections to be polymicrobial, with predominantly aerobic isolates with Escherichia coli, Enterococcus spp, Enterobacter, and Staphylococcus aureus. The most common anaerobes are Peptostreptococcus, Bacteroides fragilis, Clostridium spp, and Prevotella.[3] Staphylococcus aureus is the most common isolate after gastric surgery, and Bacteroides fragilis and Clostridium spp are the most common after colon surgery or appendicitis. Enterococcus group D predominates after biliary surgery, and Fusobacterium and Prevotella species are the cause following gastric or duodenal surgery. Risk factors include previous abdominal surgery that involved significant contamination from the gastrointestinal tract, such as perforated appendicitis, gastric ulcer or diverticulitis, gastric and intestinal perforation, mesenteric ischemia, appendicitis, trauma, empyema, and sepsis.

Epidemiology

Recent advances in early diagnosis and non-operative management of subphrenic abscesses have decreased the incidence and improved the outcomes. A primary subphrenic abscess is an abscess that develops in the intraabdominal space without introducing bacteria from outside. The actual frequency of primary subphrenic abscesses is unknown and is considered very rare. It constituted 13% in 1 case series.[4] Most subphrenic abscesses are caused by introducing bacteria into the subphrenic space. Among secondary subphrenic abscesses, gastric and biliary tree surgery constitutes 52% of abscesses. Appendicitis contributes to 8%, while colonic surgery and trauma comprise 19% and 8%, respectively. Left-sided abscesses occur in 40%, and multiple space abscesses in 20% of patients.[5]

Pathophysiology

The diaphragm, an intrathoracic organ, separates the thoracic and abdominal cavities and is covered by pleura and peritoneum, as it is both extrapleural and extraperitoneal. The subphrenic space is divided by the falciform ligament.

1. The subphrenic space is divided into 5 regions: The intraperitoneal space above the liver, limited medially by the falciform ligament, is a common location for pyogenic and amebic abscess; appendicitis or pelvic infections can localize here, ascending through the paracolic gutter.
2. The intraperitoneal space below the liver (Rutherford Morison’s kidney pouch) communicates with the right gutter. It is home to infections from stomach duodenal perforations and gallbladder empyema.
3. Above the liver, the intraperitoneal perisplenic space may become infected from stomach perforation, cancer, splenectomy, or colon resection.
4. The lesser peritoneal sac behind the pancreas and the left kidney is limited below the transverse colon. Infection in this area is usually caused by perforation on the posterior wall of the stomach.
5. Above the liver space, the “bare area” is bounded above and behind by the diaphragm. It is affected by extraperitoneal infections like retrocecal or retroperitoneal appendicitis, kidney abscesses, or the retroperitoneal portion of the duodenum.[6]

History and Physical

The clinical presentation varies with the anatomic location of the subphrenic abscess. However, fever, upper quadrant pain, costal margin tenderness, shoulder pain, abdominal tenderness, and dyspnea may be present. It may also be a hiccup, cough, or unexplained pulmonary manifestations like pneumonia, pleural effusion, and basal atelectasis. Pyrexia of unknown origin is not uncommon. The majority of the patients who are not treated immediately progress to have a systemic inflammatory response syndrome and develop tachycardia, hypotension, and low urine output, eventually leading to multiorgan failure and death.

Evaluation

Leukocytosis with neutrophilia and an elevated sedimentation rate are common. A chest x-ray may show hemidiaphragm elevation, pleural effusion, and lung abnormalities. Blood cultures indicating polymicrobial bacteria are highly suggestive of a subphrenic abscess. Abdominal ultrasound is the gold standard for right-sided subphrenic abscesses, with high sensitivity for fluid collections. A computerized tomography (CT) scan seems better for detecting a left-sided subphrenic abscess. CT scan is the diagnostic imaging of any patient with suspected intraabdominal abscess.[7] Sagittal imaging on a CT scan is best for visualizing subdiaphragmatic abscesses. Abdominal magnetic resonance imaging (MRI) and an indium-111-labeled leukocyte scan may be helpful for hidden intraabdominal or subphrenic abscesses. MR enterography is the investigation of choice in patients with inflammatory bowel disease. Blood gas analysis may reveal respiratory alkalosis initially due to hyperventilation and may progress to metabolic acidosis if left untreated.

Treatment / Management

Management of subphrenic abscess includes antibiotics, drainage of the abscess, and general patient care. Broad-spectrum parenteral antibiotics should be initiated empirically at diagnosis, covering both aerobes and anaerobes. Later, the antibiotics can be modified as per culture and sensitivity. Early initiation of antibiotics improves outcomes. Combination therapy or a single broad-spectrum antibiotic can be initiated. Cephalosporins with metronidazole can be considered as the initial choice. In immunosuppressed patients, antifungals covering candida may be indicated. The antifungal of choice depends on the patient's general condition. Azoles are preferred if the patient is stable and cultures show sensitivity to azoles. In critically ill patients and non-albicans candida, echinocandins like anidulafungin are the drug of choice.[8] Antibiotic duration depends on the source control's etiology and extent. The Surgical Infection Society guidelines suggest 96 hours for well-controlled intrabdominal sepsis and 5-7 days for those without a definitive source control procedure.[9] Cultures should be obtained, and antibiotics should be tailored based on the speciation and sensitivity of those cultures. 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.[10](B2)

Percutaneous 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 surgical wound complications, and reduces hospitalization length. 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 patient's general condition 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 the real-time visualization of the abscess cavity, the use of Doppler to avoid major vessels, and the high success rate.[11] Trans-esophageal and trans-gastric approaches have been tried to drain the subphrenic abscess.[11] If percutaneous or endoscopic drainage fails, surgical drainage is indicated either by an open or laparoscopic method. Laparoscopic drainage is minimally invasive and permits exploration of the abdominal cavity without a wide incision; hence, purulent exudate can be aspirated under direct vision. An open surgical technique should be considered if the patient does not improve with the laparoscopic technique. 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 the management of abdominal compartment syndrome and trauma patients. The concept of damage control surgery is being used. A vacuum dressing to close the abdomen is preferred.[9] With timely intervention, most patients recover with supportive care, like intravenous hydration. Patients who worsen and develop septic shock need admission to the intensive care unit. Need for multiorgan support like mechanical ventilation, vasopressors, and dialysis are needed in patients with significant organ failures.[8](B3)

Differential Diagnosis

The differential diagnosis for subphrenic abscess include the following:

• Inflammatory bowel disease
• Prolonged ileus
• Unexplained postoperative fever

Surgical Oncology

In patients with gastric cancer who undergo gastrectomies, the complication of a subphrenic abscess can be as high as 4.0%. This usually happens after total gastrectomies and is thought to be caused secondary to leaks in the anastomoses. The treatment is the same for abscesses, including intraabdominal catheter drainage and intravenous antibiotics.[12]

Prognosis

Using computed tomography (CT) in diagnosis and drainage has drastically reduced morbidity and mortality. Multiorgan failure is the main cause of death. Early resuscitation and adequate source control have decreased the mortality due to severe sepsis from 40% to 60% to 18% to 30%.[13]

Complications

A subdiaphragmatic abscess can cause chest complications like pleurisy, pleural effusion, empyema, lung abscess, and bronchial fistula. It can also lead to intraabdominal complications like generalized peritonitis, pelvic abscess, and abscess in the right paracolic gutter. Additionally, it can lead to systemic complications like sepsis, septic shock, and multiorgan failure.