Sandbox:splenic abscess

Overview

Splenic abscess is an uncommon and lifethreatening condition. Clinical presentation, etiological factors, natural history, treatment and prognosis depends on whether the abscess was solitary or multiple. It is always fatal if left untreated. Most commonly associate with immunodeficient patients especially, hematological disorders such as leukemia, sickle cell disease etc.

Definition

Splenic abscess is defined as any infectious suppurative process involving identifiable macroscopic filling defects either in the parenchyma of the spleen or the subcapsular space.

Historical Perspective

• Since the times of Hippocrates, splenic abscess has been reported several times and he described the natural history and prognosis of splenic abscess.
• In the early days of 20th century, splenic abscess most commonly caused by typhoid and then followed by malaria.
• Ooi et al. described significant etiological differences such increase in the percentage of abscess cases due to aenarobics as compared to aerobics (7 vs 18-28%), fungi (1 vs 18-41%) as well as Mycobacterium tuberculosis (0.8 vs. 14%) in the second half of 20th century.

Classification

Classification by Pathogenesis

Splenic abscess is classified traditionally based on the pathogenesis as follows:

• Hematogenous or Metastatic infection: Seen in endocarditis
• Embolic phenomenon: splenic abscess developed as consequence of cellular embolism in hemoglobinopathies such as sickle cell anemia or disease
• Contagious infection: Splenic abscesses can develop through continuity of infection from primary sources which are anatomically close eg. subphrenical abscesses
• Splenic trauma: secondary infections may developed due to splenic trauma
• Depressed immune defenses: chemotherapy-induced abscesses developed particularily in leucemias

Classification by Etiology

Classification of splenic abscesses based on the etiological factors is as follows:

• Mono-microbial abscess
• Poly-microbial abscess
• Sterile abscess

• Unilocular abscess
• Bilocular abscess

• Solitary abscess
• Multiple abscesses: More common in HIV patients.

Pathophysiology

Splenic abscess can result from various sources such as:

• Splenic trauma or splenic laceration
• Hematogenous spread of bacteria
• Contiguous spread of bacteria

Pathogenic Mechanism	Discription
Hematogenous Dissemination	Hematogenous Dissemination or arterial dissemination is the most common mode of infection that results in splenic abscess. It is a metastatic infection through hematologic seeding from distant infections such as endocarditis Often results in multiple abscesses
Embolic phenomenon	Embolic non-infectious events due to red cell abnormalities such as hemolytic and sickle cell anemia causes ischemia followed by superinfection of emboli which tend to obstruct free blood flow and oxygen delivery to the spleen on the microscopic level.
Contiguous spread of bacteria	It is a mode of infection spread to the spleen from anatomically neighboring structures. Can cause either solitory or multiple abscesses
Trauma	secondary infections may developed due to splenic trauma
Immunodeficiency	chemotherapy-induced abscesses developed particularily in leucemias

Casuses

Spleenic abscess is caused mostly by monomicrobial but some times it can be caused by polymicrobial agents. Bacteria is more common than other microbial agents such as fungi, protozoa which can cause splenic abscess in immunocompromised patients.

• Primary diseases of spleen
• Hemoglobinopathies

Common causes

Common causes of splenic abscess includes:
Aerobes
Aerobes are the most predominant organisms causing splenic abscess in 50% of cases.

• Staphylococcus species
• Streptococcus species
• Salmonella species
• Escherichia coli
• Klebsiella pneumoniae
• Pseudomonas aeruginosa
• Enterococcus species
• Mycobacterium

Anaerobes

• Bacteroides
• Actinomyces
• Propionobacteriums pecies
• Clostridium
• Fusobacterium

Fungal infection

• Candida albicans
• Candida troplcalis
• Aspergllus

Other causes include:

• Streptococcus pyogenes
• Streptococcus pneumonia
• Klebsiella pneumonia
• Pseudomonas aeruginosa
• Proteus mirabilis
• Bacillus cereus
• Malaria
• Schistosomiasis
• Staphylococcus epidermidis
• Enterobacter
• Shigella
• Diphtheroides
• Nocardia
• Brucella
• Citrobacter freundii
• Vibrio cholerae

Monomicrobial Most common causes

Risk Factors

Spleen abscess often co-exists with several risk factors, but the major one is the patient’s immunodeficiency. Common risk factors of splenic abscess include:

• Diabetes mellitus
• Immunocompromised conditions such as AIDS
• Intensive care unit patients
• Pulmonary tuberculosis
• Concomitant parenchymal liver disease such as cirrhosis
• Malignancies
• Trauma

Differentiating splenic abscess from other diseases

Splenic abscess should be differented from other causes of left upper quadrent pain causes:

• Splenic cysts
• Splenic hematomas
• Peri splenic abscess

Difference between Solitary abscess and Multiple septic abscesses

Characteristic	Solitary abscess	Multiple septic abscesses
Presentation	Common presentation is fever, abdominal pain, nausea and vomiting with signs of left upper abdominal quadrant tenderness, splenomegaly, left pleural effusion, and leukocytosis.	Most commonly present with generalized sepsis because of an ineradicable septic focus remote from the spleen
Caueses	Intravenous drug abuse Iatrogenic operative trauma to the spleen Direct extension from an extrasplenic focus Bacterialendocarditis Mastoiditis	Bacteroides Pseudomonas Serratia Enterobacter Klebsiella Escherichia coli Staphylococcus aureus Streptococcus viridans
Pathological findings	Gross findings: Enlarged spleen with due to large solitary abscesses with thick wall around the abscess to prevent dissemination Microscopic findings: Microscopically the abscess consist of necrotic tissue with a fibrous wall surrounded by inflammatory cell infiltration.	Gross findings: At the time of autopsy, spleen present as large and soft, and pus extruded organ from the cut surface. Microscopic findings: Multiple microscopically visible foci of infection riddled homogeneously throughout the spleen Abscesses are filled with polymorphonuclear leukocytes which were scattered throughout the parenchyma, intermixed with other foci of microinfarction and coagulation necrosis.
Complications		Pulmonary infection and abscess Uncontrolled nonsplenic abdominal suppuration Bacterial endocarditis Disseminated neoplasia with septicemia Immunosuppression with septicemia Meningoencephalitis
Treatment of choice	Best initial treatment is percutaneous drainage. If recurrent or not responding to combination of microbial therapy and drainage, then most appropriate treatment is splenectomy.	Splenectomy
Outcome		Most of the patient died of sepsis even though splenic infection had been eliminated

Difference between Bacterial abscess and Fungal abscess of spleen

Characteristic	Bacterial Cause	Fungal Cause
Presentation	Common presentation is fever, abdominal pain, nausea and vomiting. Signs of sepsis is common bacterial cause.	Similar presentation but signs of sepsis is rare
Treatment	Antimicrobial therapy ± Percutaneous drainage or Splenectomy	Antifunal therapy ± Percutaneous drainage or Splenectomy

Epidemiology and Demographics

Incidence

Indceidence of spelenic abscess varies between 0.1% to 0.7% based on population based autopsy studies. Incidence of splenic abscess due to hematogenous spread is gradually declining due to increased antibiotic use, but incidence due to fungal infection is increasing due to aggressive chemotherapeutic methods.

Prevalence

Prevalence of splenic abscess is increasing gradually due to increased risk factors and increased imaging modalities that can diagnose more accurately.

Case Fatality Rate

Splenic abscesses are associate with increased morbidity and mortality. If left untreated, mortality is definite (100%).

Natural History, Complications and Prognosis

Splenic abscess is a rare cause of abdominal abscesss, but life-threatening. Because of it's rarity, splenic abscess usually diagnosed at the late stages or after the onset of complications. Early diagnosis, prompt treatment can prevent complications. Mortality rate is very high if left untreated.

Demographics

Age

Splenic abscess shows bimodal distribution in age of the patients, with peak incidence seen in thirties and sixties.

Gender

Splenic abscess is more predominant in male compared to female (~2 folds).

Developing Countries

In Africa, splenic abscess is more common in hemoglobinopathies such as sickle cell disease [heterozygous (SA or SC) > homogygous(SS)].

Complications

Common complicaiton include:

• Bacterial sepsis or septicemia
• Respiratory complications such as post operative pneumonia
• Splenic rupture

Other complications include:

• Wound infection
• Paralytic ileus
• Deep vein thrombosis
• Meningitis

Prognosis

Prognosis of splenic abscess depends on the time of diagnosis and treatment. Delay in the management can lead to splenic rupture followed by spilling into peritoneal cavity or an adjacent organ which can lead to septicemia and death in severe cases.

Association

Splenic abscess is commonly associate with:

• Paranchymal liver disease
• Pancreatitis
• Pleural effusion
• Renal cysts
• Ovarian cysts
• Abdominal lymphadenopathy

Diagnosis

Splenic abscess commonly present with a triad of symptoms include fever, nausea, vomiting and abdominal pain along with palpable spleen on examination. Early diagnosis with imaging studies and prompt drainage is required to reduce morbidity and mortality. Presence of fever, left upper abdominal pain, leukocytosis and radiologic evidence shows pathology in the left chest X-ray especially in immunocompromised patients are the indications for high suspicion of splenic abscess.

History and Symptoms

Common symptoms of splenic abscess include:

• Fever
• Abdominal pain localized in the left upper quadrant or mesogastrium
• Nausea and vomiting
• Constitutional symptoms such as fatigue, loss of body weight, sweat and chills

Other symptoms include:

• Referred pain in the left shoulder
• Confusion
• Pain in the lower half of the chest
• Cough

Appearance

Patient with splenic abscess appear ill appearing and diaphoretic.

Vital signs

• High-grade fever
• Hyperthermia
• Tachycardia

If patient present with sepsis:

• Hypotension
• Tachycardia
• Increased capillary refill time

Signs of sepsis indicate that splenic abscess is most likely due to bacterial cause than fungal source.

Heart

• New onset murmur may be present

Abdomen

Inspection
Palpation

• Tender splenomegaly
• Palpable spleen orabdominal mass

Auscultation

• Friction rub over the spleen

Blood Tests

Blood tests such leukocytosis are increased but not significant in the diagnosis of splenic abscess because these tests may not be appropriate in immunocompromised patients.

• CBC with differential
• Erythrocyte sedimentation ratio (ESR)
• Blood culture: In solitary abscesses blood culture is not sensitive in the initial stages when as in multiple abscesses it is helpful in prompt diagnosis and early treatment.

Imaging

As the clinical features of splenic absecess are non specific and vague such as abdominal pain, fever and vomiting, that makes diagnosis is challenging and relied on imaging modalities. Imaging studies such as ultrasound, computerized tomography made the diagnosis early and more accurate that reduces morbidity and mortality. Common imaging findings includes:

• Elevated and immobile left diaphragm
• Ipsilateral pleural effusion
• Displacement of the stomach and splenic flexure of the colon

Ultrasound

Advantages

• Emergency radiography with high sensitivity (75-100%)
• Non invasive
• Cost effective

Computerised Tomography

Computerised tomography with contrast is both diagnostic and therapeutic test of choice for splenic abscess.
Advantages

• High sensitivity (88-100%)
• Can differentiate unolocular and multilocular abscesses
• Can identify the contents of abscess
• Can differentiate splenic abscess from splenic cysts and splenic hematomas
• More precise and accurate than ultrasonography, in identifying the location of abscess in relation to other internal organs during per-cutaneous drainage.
• It is superior to all other diagnostic tests for splenic abscess.

Scintigraphic Studies

Scintigraphic studies include technetium-99m liver and spleen scans, gallium scans, and indium scans. Splenic scan is diagnostic modality to identify abscesses which relies upon splenic uptake of the radionuclide 99m technetium which shows abscess as a negative or filling defect.

Advantages

• High specificity: If patient showing high suspicion of splenic abscess and scan supports the diagnosis, then splenectomy can be performed.

Disadvantages:

• Scan can not identifie or visualize incurable small abscesses.
• Less sensitive: If the scan shows negative or equivocal results for splenci abscess but clinical suspicion remains, an arteriogram should be ordered.

Arteriography

Arteriography is the technique that involves injection of contrast material through a catheter passed retrograde into the splenic artery followed by rapid exposure of sequential x-ray films which shows abscesses as filling defects in the spleen.

Advantages:

More reliable and precise than splenic scan in diagnosing small abscesses.

Disadvantages:

• Invasive technique

Treatment

Percutaneous Drainage

Percutaneous drainage is the primary mode of tretament for splenic abscess, even though splenectomy is the definitive treatment because of increased risk of infections in splenectomised patient. It is genereally done under the guidance of imaging studies such as ultrasound or computerised tomography.

• First line of treatment for splenic abscess
• Safe and effective than surgery in both unilocular and bilocular abscesses, especially in peripherally located abscesses.
• Preferred in critically ill patient and patients unfit for general anesthesia

Advantages

• Preserves spleen
• No abdominal spillage of abscess contents
• Less expensive, high acceptance rate and less operative risk

Complications

• Splenic haemorrhage
• Injury to other abdominal organs
• Septicemia
• Empyema
• Pneumothorax
• Fistula formation
• Deep vein thrombosis

Contraindications

• Multiple or septated abscesses
• Anatomically inaccessible for drainage
• Coagulopathies
• Ascites

Splenectomy

Splenectomy is the most effective and definitive treatment of choice for splenic abscess.
Advantages

• Definitive treatment for splenic abscess
• Treatment of choice if more than 2 abscesses are present
• Patients with failed percutaneous drainage
• Patient with recurrent abscesses

Disadvantages

• Splenecetomisesd patients are more prone to infections especially catalase positive bacteria such as staphylococcus aureus.
• Mortality rate varies between 0-20%
• Longer duration of hospital stay than percutaneous drainage procedure

Complications such as

• Lung infection
• Wound infection
• Septicemia
• Paralytic ileus
• Deep vein thrombosis

Prevention

Primary Prevention

Primary prevention for splenic abscess can prevent in specific cases especially patients who are at high risk such as immunocompromised patients (e.g. recipients of renal transplants or patients on immunosuppressive drugs for other reasons).

• In transplant patients best way to prevent splenic abscess is by splenectomy, where as in patients with other immunocompromised states it can be achieved by proper care, early detection and aggressive treatment of minor infections.
• Avoid intravenous drug abuse