Splenic Abscess

Background

Abscesses of the spleen have been reported periodically since the time of Hippocrates, who postulated that the condition would take one of the following three courses^[1] :

• The patient might die
• The abscess might heal
• The abscess might become chronic, and the patient might live with the disease

Splenic abscess is a rare entity, with a reported frequency of 0.05-0.7%.^{[2, 3, 4]} Its reported mortality is still high, up to 47%, and has the potential to reach 100% among patients who do not receive antibiotic treatment.^[5] Appropriate management can lower mortality to less than 10%.^[6]

Timely and widespread use of imaging methods (eg, computed tomography [CT] and ultrasonography [US]) facilitates early diagnosis and guides treatment, thereby improving the prognosis.^[7]

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Anatomy

The normal adult spleen weighs up to 150 g, measures 4 × 7 × 11 cm, and represents the largest single accumulation of lymphoid tissue in the body. The spleen lies beneath the left hemidiaphragm and is attached to the stomach, left kidney, and diaphragm by the gastrosplenic, lienorenal, and phrenolienal ligaments. The gastrosplenic ligament contains the short gastric vessels, which can easily be injured during interventions in the area.

Anomalies of the spleen must always be considered, including wandering spleen, polysplenia, asplenia, or accessory spleen. Accessory spleen is the most common of the splenic anomalies (>1% of all patients). Solitary or multiple accessory spleens can be found in the splenic hilum, pancreas, lesser sac, retroperitoneum, liver, or gut mesentery.

The size and location of a splenic abscess determines its relations to the surrounding organs and the possible routes for extension or fistulization. Small solitary or multiple abscesses tend to remain contained by the splenic capsule. Advanced abscesses in the spleen's upper pole can fistulize into the pleura. Abscesses originating from the lower pole can involve the splenic flexure and communicate with the colonic lumen. The stomach and pancreas can be affected in an analogous way.^[8]

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Pathophysiology

Splenic abscesses occur in a variety of clinical scenarios. Published studies suggest that preexisting splenic tissue injury and bacteremia are required to form a basis for an abscess.^{[2, 9]} Published scenarios include the following:

• Hematogenous embolization to a previously normal spleen - Typical examples include patients with septic endocarditis who have abused intravenous (IV) drugs and patients undergoing chemotherapy who develop fungemia, resulting in a splenic abscess; generally, such patients either are immunosuppressed or have an overwhelming bacteremia, and it is expected that this patient group will expand to include analogous groups from the domains of transplantation and HIV/AIDS
• Hematogenous spread in the presence of previously altered splenic architecture - This group includes patients with single splenic infarcts (from trauma) or multiple splenic infarcts (from sickle cell disease or vasculitis); bacteremia from an intercurrent infection (eg, pneumonia, cholecystitis, or central line sepsis) can colonize a splenic avascular area and form an abscess (see the images below)
• Contiguous spread - This includes direct involvement from a pancreatic abscess, gastric or colonic perforations, or subphrenic abscesses

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This patient has splenic abscess due to pneumococcal bacteremia. Note that massively enlarged spleen is readily visible, with minimal retraction in le....

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Resected spleen (same as in above image) with abscesses caused by pneumococcal bacteremia. Note discrete abscesses adjacent to normal parenchyma.

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Etiology

Splenic abscesses have diverse etiologies.^[10] The most common is hematogenous spread originating from an infective focus (most commonly involving aerobes) elsewhere in the body. Infective endocarditis, a condition associated with systemic embolization in 22-50% of cases, has a 10-20% incidence of associated splenic abscess.^[11] Other infective sources include typhoid, paratyphoid, malaria, urinary tract infection, pneumonias, osteomyelitis, otitis, mastoiditis, and pelvic infections.

Organisms associated with splenic abscess include the following^[6] :

• Aerobes (in most published cases) - Gram-positive cocci (Streptococcus,^[12] Staphylococcus, and Enterococcus [predominant in most reports]); gram-negative bacilli (Escherichia coli, Klebsiella pneumoniae, Proteus,Pseudomonas, and Salmonella [occasionally predominant])
• Anaerobes - Peptostreptococcus, Bacteroides, Fusobacterium,Clostridium, and Propionibacterium acnes
• Polymicrobial (up to 50% of cases)
• Fungi - Candida
• Unusual flora - Burkholderia pseudomallei (occasionally reported in melioidosis); actinomycetes and mycobacteria (most typically seen in immunosuppressed patients)

Pancreatic, other retroperitoneal, and subphrenic abscesses, as well as diverticulitis, may contiguously involve the spleen. Splenic trauma is another well-recognized etiologic factor. Splenic infarction resulting from systemic disorders (see the image below), such as hemoglobinopathies (especially sickle cell disease), leukemia, polycythemia, or vasculitis, can become infected and evolve into splenic abscesses.^{[2, 5, 13, 14, 15, 16, 17, 18]}

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Splenic infarct. Selective splenic arteriogram showing extravasation of contrast from splenic artery at splenic hilum prior to angioembolization.

Alcoholics, diabetics, and patients who are immunosuppressed are among the most susceptible to splenic abscesses.^{[7, 16]} . Rarely, splenic abscess can be caused by a parasitic infection such as brucellosis^[19] or umbilical catheterization in the newborn.^[20]  A case of chronic splenic abscess occurring as the initial manifestation of pancreatic tail carcinoma has been reported.^[21]  Splenic abscess has been reported as a rare complication of sleeve gastrectomy.^{[22, 23]}

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Epidemiology

Published autopsy statistics suggest that splenic abscess is rare (0.05-0.7%); the incidence may depend on the study population.^{[2, 3]} For example, the incidence of splenic abscesses in Denmark was 0.056% per 1000 somatic hospital discharges per year or 0.0049% per year of all hospital deaths.^[3]

The literature suggests wide variability with regard to causative pathogens, demography, and clinical material.^[2]

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Prognosis

The natural history of untreated splenic abscess has not been studied prospectively. Data from prospective randomized studies are not available to determine the most effective treatment for splenic abscess. The lack of randomized studies does not provide a conclusive clinical algorithm for the condition.^[24] The published literature suggests that early diagnosis, individualized management, and increased experience with minimally invasive methods carry a potential for lower morbidity and mortality. The diversity of the patient population suggests the importance of patient selection to improve outcome.

Percutaneous CT-guided drainage is a safe, minimally invasive, and successful treatment option that should be used as a spleen-conserving alternative to surgery in suitable patients.^[25]

Available results from the use of laparoscopic splenectomy for splenic abscess have been promising, suggesting that there is significant opportunity for further development of this method.^[26] Surgical splenectomy must currently be considered the most reliable treatment for this condition and must be considered if the available less-invasive treatment methods fail.

In a study aimed at assessing means of predicting outcomes for 114 adult splenic abscess patients in the emergency department (ED), Hung et al comparison of the Mortality in ED Sepsis Score (MEDS), the Modified Early Warning Score (MEWS), the Rapid Emergency Medicine Score (REMS), and the Rapid Acute Physiology Score (RAPS).^[27] ​ They found MEDS to be superior to MEWS, REMS, and RAPS for this purpose, with a sensitivity of 92.86%, a specificity of 88.00%, and an accuracy of 88.60%.

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History

The history and physical examination are not sufficiently reliable to make the diagnosis of splenic abscess. However, information derived from the history and physical examination can suggest this diagnosis. Therefore, the clinician must maintain a high index of suspicion, particularly in higher-risk clinical scenarios and patient groups.^[28]

Although the signs and symptoms of splenic abscess have been well described, they are not very specific. Therefore, splenic abscess remains a substantial diagnostic challenge. The classical triad of fever, left-upper-quadrant pain, and splenomegaly is seen in only about one third of patients.

The symptoms of splenic abscess can be variable and depend on the location, size, and progression of the process. They can also be acute, subacute, or chronic. Deep-seated, small abscesses can be painless and accompanied by septic symptoms.^[29]  The following may be noted:

• Fever (>90%) can be moderate, continuous, intermittent, or even absent
• Abdominal pain (>60%) typically occurs suddenly, with a punctum maximum in the left hypochondrium (>39%); pain usually signifies perisplenitis^[30]
• Involvement of the diaphragmatic pleura can cause shoulder pain; the associated eponym is the Kehr sign, though there is no clear demonstration that Kehr either described it or suffered from it
• Pleuritic chest pain around the left lung base (>15%) is aggravated by coughing or forced expiration
• General malaise and other constitutional and dyspeptic symptoms can be included, all of which can also be seen in a variety of other septic conditions

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Physical Examination

Abdominal tenderness (>50% of cases) may or may not be accompanied by muscle guarding in the left upper quadrant. There may be edema of the soft tissues overlying the spleen. Costovertebral tenderness may also be noted.

Splenomegaly (< 50%) is less frequently observed, probably because of early diagnosis resulting from the widespread use of imaging methods.

Chest findings are nonspecific and reportedly include dullness at the left lung base (>30%), left basilar rales (>21%), or elevation of the left hemidiaphragm (>15%).

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Laboratory Studies

A complete blood count (CBC) demonstrates leukocytosis (white blood cell [WBC] count, >20,000/μL) with a left shift in most patients. Patients who are immunologically compromised may deviate from this rule.

Recurrent positive blood cultures can further suggest the diagnosis.

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Imaging Studies

Radiography

A chest radiograph is typically the first step in the preoperative evaluation, though it will reveal nonspecific changes typical of a septic process in the region rather than changes diagnostic of a splenic abscess in particular. The following may be noted:

• Abnormal chest radiograph findings (most patients)
• Elevated left hemidiaphragm (>30%)
• Pleural effusion (>20%)

Plain radiographic films of the abdomen are notoriously nonspecific in patients with a splenic abscess. Findings on abdominal radiographic films can include abnormal soft-tissue density or a gas collection in the left upper quadrant.

Nuclear studies

Radioisotope scanning is of little value, because most tests require more than 24 hours to perform and interpret.

Ultrasonography

Ultrasonography (US) is cost-effective, noninvasive, and readily available at the bedside around the clock.^[31]  However, US evaluation has the drawbacks of being nonspecific and operator-dependent.

Computed tomography

Computed tomography (CT) is presently the criterion standard in helping to establish the diagnosis of splenic abscess. The reported sensitivity of CT for this purpose typically approaches 100%. The characteristic image of splenic abscess reveals low-density lesions that fail to enhance after intravenous (IV) administration of contrast. CT best delineates the size, topography, and access routes to the spleen and surrounding structures. CT-guided drainage can be performed during the examination.

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Procedures

Diagnostic percutaneous aspiration guided by US or CT is useful in helping to confirm the diagnosis of splenic abscess and in providing a specimen for bacteriology.

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Approach Considerations

Once the diagnosis of a splenic abscess has been made, the patient must be admitted to the hospital and treated. Treatment depends on the patient's overall condition, comorbidities, and primary disorder (if any), as well as on the size and topography of the abscess.^[25]

Empiric broad-spectrum antibiotic therapy has a primary role in the initial management of splenic abscesses.^[4] The success of antibiotic therapy is not affected by the presence of multiple abscesses or by a polymicrobial flora. The choice of antibiotics is tailored to the culture results. Many splenic abscesses can be treated adequately without splenectomy.^[32]

Percutaneous drainage has gained acceptance as an effective and less invasive treatment method than surgical intervention in selected patients. The reported success rate of percutaneous drainage ranges from 67% to 100%. Such drainage preserves the spleen and avoids the risk of overwhelming postsplenectomy sepsis (OPSS). Percutaneous drainage can also be used as a bridge to elective surgery in patients who are clinically unstable or in patients who have multiple comorbidities.

Early diagnosis and percutaneous drainage can increase the chance to preserve the spleen and, hence, its immunologic function.^[33]

Percutaneous drainage is likely to be useful in patients who have unilocular or bilocular collections and if the character of the abscess content permits minimally invasive drainage. Multilocular abscesses, ill-defined cavities, septations, and necrotic debris typically do not respond to percutaneous drainage.

Surgery is reserved for patients who are stable and not amenable to percutaneous drainage. Depending on available expertise, laparoscopic or open procedures can be considered.

Contraindications for percutaneous drainage include the following^{[7, 15, 25]} :

• Multiloculated or debris-filled abscess
• Multiple small abscesses
• Uncontrollable coagulopathy
• Poorly defined abscess on computed tomography (CT) or ultrasonography (US)
• Diffuse ascites
• No safe route for drainage

Relative contraindications for percutaneous drainage include the following:

• Splenic abscesses secondary to spread from a contiguous process, such as other large primary abscesses (eg, pancreatitis, perforated colon cancer) that cannot be eradicated by this method
• Abscess rupture
• A phlegmonous or poorly characterized lesion on CT or US

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Medical Therapy

Early supportive care and parenteral broad-spectrum antibiotics are of paramount importance while further diagnostic and therapeutic arrangements are made.^[2] Antibiotic coverage should target the presumed bacterial strains. Medical management as the only treatment of selected splenic abscesses has been advocated in several studies but remains controversial. The published literature suggests that most patients in this category have contiguous infections in the abdomen; the mortality in this group has been reported to be approximately 50%.^[15]

Besides the more common organisms isolated from splenic abscesses, mycobacteria, Candida, and Aspergillus should also be considered; these organisms account for a small but significant number of splenic abscesses in patients who are immunocompromised. Fungal abscesses are known to respond more favorably to antifungal treatment, because they result more often from a disseminated infection.^{[3, 9, 29]}

A retrospective multicenter French study of 10 pediatric and adult patients investigated the effect of corticosteroid therapy on individuals with symptomatic chronic disseminated candidiasis that persisted despite the administration of antifungal treatment.^[34] In addition to finding evidence that corticosteroid therapy can effectively resolve the symptoms and inflammatory response associated with the infection, the study's authors also reported that hepatosplenic microabscesses in the patients decreased or disappeared.

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Surgical Therapy

Surgical options

Invasive treatment of splenic abscess includes the following three options:

• Percutaneous drainage
• Open or laparoscopic splenectomy
• Open drainage

Percutaneous drainage

Percutaneous drainage is indicated for easily accessible uniloculated or biloculated abscesses with otherwise favorable features, as described previously, and also for surgical patients at very high risk who cannot tolerate general anesthesia or surgery.^{[35, 36]}  The procedure includes a risk of iatrogenic injury of the spleen, colon (splenic flexure), stomach, left kidney, and diaphragm.^[25]

Calcified walls of the abscess, the presence of other intra-abdominal cysts with intraluminal daughter cysts, and an origin from endemic areas (eg, the Mediterranean basin or Eastern Europe) should raise suspicion of Echinococcus granulosus.^[8] Percutaneous drainage of such suppurative cysts increases the risk of hydatid seeding and anaphylaxis and is therefore contraindicated.

Other iatrogenic complications resulting from percutaneous drainage include hemorrhage, pleural empyema, pneumothorax, and enteric fistula.^{[7, 37]}

Splenectomy

Splenectomy has long been considered the standard treatment of splenic abscess. Depending on the patient population, open splenectomy has a mortality of 0-17% and a morbidity of 28-43%.^[38]  The procedure removes the septic source and the diseased organ. The surgeon can explore and manage coexisting septic collections.

Laparoscopic splenectomy is safe and effective in selected patients. It can be performed with no morbidity or mortality, and patients who have undergone the procedure reportedly have a shorter hospital stay.^[26]

Very infrequently, the perisplenic adhesions are so severe that safe dissection between the spleen and the surrounding structures is impossible. The only choice in this scenario is to perform an open splenotomy and drain the collection.

Open drainage

Open drainage is used when the abscess cannot be drained percutaneously. Depending on the location of the abscess, one of the following three access routes can be employed:

• Transpleural - This usually requires resection of the 12th rib in the posterior axillary line and drainage of the abscess through the diaphragm
• Abdominal extraperitoneal - This accesses the abscess through the lateral abdominal wall and between the peritoneum and the flat abdominal muscles
• Retroperitoneal - This is used when the abscess extends to the flank

Operative details

The difficult location of the spleen increases the risk of iatrogenic hemorrhage or hollow organ injury. Patients with splenic abscess must be typed and screened, and massive blood transfusion must be anticipated. Prophylactic broad-spectrum antibiotic coverage is essential. A nasogastric tube must be used to decompress the stomach. The risk of injury to the colon requires preoperative bowel preparation in nonemergency cases. Administration of polyvalent vaccines must be planned.

The operating room must be warm in order to decrease the risk of coagulopathy and wound infection. Blood products must be readily available.

A splenectomy can be performed through one of the following abdominal incisions:

• Midline incision - This is preferred in adult patients by most surgeons because it provides easy access to all four quadrants
• Left subcostal incision This spares the rectus abdominis (Singleton) and is preferred in pediatric patients
• Thoracoabdominal incision - Rarely, this is required in cases where massive pleural involvement by the abscess necessitates open thoracic access

Massive perisplenitis with adhesions carries a significant risk of iatrogenic splenic rupture. The spleen is mobilized carefully by dividing the ligamentous attachments. Special care must be taken to avoid injury to the pancreas and resulting pancreatic fistula.

In laparoscopic splenectomy, the spleen must be morcellated intra-abdominally to allow retrieval of the specimen through a limited incision. Prophylactic peritoneal drainage is at the discretion of the surgeon.

Because interventions for splenic abscess are potentially morbid, patients must be placed under close observation after the procedure, especially during the first 24 hours, when the risk of postoperative hemorrhage is high.

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Complications

Mortality in patients with untreated splenic abscess approaches 100%. The list of complications is long but most importantly includes free rupture into the peritoneal cavity with generalized peritonitis, rupture into the colon, erosion of the abscess through the diaphragm, or, more rarely, necessitation through the skin.

Complications of treated splenic abscesses depend on the topography and treatment method. They can include the following:

• Life-threatening hemorrhage from the splenic parenchyma or hilar vessels
• Pneumothorax
• Left-side pleural effusion
• Subphrenic abscess
• Perforation of the colon, stomach, or small intestine
• Pancreatic pseudocyst or fistula
• Postsplenectomy thrombocytosis
• OPSS
• Atelectasis or pneumonia

Knowledge of the anatomy, careful preoperative planning, optimal exposure, and attention to the details of the technique can substantially reduce the incidence of iatrogenic complications.^{[37, 25, 6]}

Respiratory complications are minimized or avoided by incentive spirometry and chest physical therapy.

Subphrenic abscess, though uncommon after splenic surgery, is a recognized consequence of pancreatic or hollow-organ injury. The condition requires prompt diagnosis and drainage.

In cases of splenectomy, thrombocytosis occurs in more than 50% of cases. A very high platelet count (>1,000,000/μL) necessitates intervention to minimize the incidence of thrombotic complications. Platelet apheresis or anticoagulants can be used in this regard.

OPSS carries a significant mortality risk, especially for young patients who have undergone splenectomy. Whenever splenectomy is considered, patients should undergo immunization against Streptococcus pneumoniae, Meningococcus, and Haemophilus influenzae type b. The administration of oral antibiotics to splenectomized individuals is the mainstay of prophylaxis (and initial therapy). Two complementary strategies are commonly used: daily antibiotic prophylaxis and empiric antibiotic therapy for fever.

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Long-Term Monitoring

Follow-up is an essential element of the management of patients undergoing treatment of splenic abscess. Patients must be screened for the following:

• Late iatrogenic complications, such as residual intra-abdominal abscesses, pancreatic or enteric collections, or fistulas
• Intestinal obstruction and ventral hernia
• Recurrent splenic abscess
• OPSS

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