Splenic abscess

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Venkata Sivakrishna Kumar Pulivarthi M.B.B.S [2]

Synonyms and keywords:Abscess of spleen

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

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 infective endocarditis, purulent teeth-related infections and urinary tract infections Most common organism involved is Staphylococcs aureus Often results in multiple abscesses Sources of pathogen Intra-abdominal sepsis especially after bowel surgery Chest infection Osteomyelitis Infected vascular access sites Infected ventriculo peritoneal shunts Skin lesions Tooth extraction
Secondary infection of splenic infarction	Embolic or thrombotic 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. Sources of emboli: Cardiac arrhythmia Bacterial endocarditis Lipid embolization with Weber-Christian disease Iatrogenic splenic artery embolization for the treatment of autoimmune hemolytic anemia Source of thrombus formation in splenic artery Sickle cell disease Hemoglobinopathies such as thalassemia Unexplained thrombocytosis After pancreatitis
Contiguous spread of bacteria	It is a mode of infection spread to the spleen from anatomically neighboring structures such as stomach or large bowel perforation, infected pancreatic cyst, perisplenic or subpleuric abscess. Can cause either solitory or multiple abscesses
Trauma	secondary infections may developed due to splenic trauma during any intra-abdominal procedures. Iatrogenic causes of splenic truma Gastric surgery Distal pancreatectomy Endoscopic retrograde cholangio pancreatography Percutaneous nephrostomy Therapeutic splenic arterial embolization for autoimmune hemolytic anemia and hypersplenism During splenic conservative techniques such as exploration only, mesh splenorraphy
Immunodeficiency	It is major factor involved in the course of splenic abscess especially if the causative organism is fungi or any other atypical organism. Common immunodeficient states associate with splenic absecess Systemic lupus erythematosus Felty’s syndrome End-stage renal disease Infectious mononucleosis Cancers like multiple myeloma and leukemia chemotherapy-induced abscesses developed particularily in leukemias Immunosuppressive therapy with renal transplantation

Causes

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 are the most predominant organisms causing splenic abscess in 50% of cases.

Aerobes	Anaerobes	Fungal
Staphylococcus species Streptococcus species Salmonella species Escherichia coli Klebsiella pneumoniae Pseudomonas aeruginosa Enterococcus species Mycobacterium	Bacteroides Actinomyces Propionobacteriums pecies Clostridium Fusobacterium	Fungal infection Candida albicans Candida troplcalis Aspergllus

Less common causes

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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
• Pre-existing splenic pathology such as splenic cysts, hemangiomas.