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

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

## Less common causes
- 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
- Cryptococcus neoformans
- Aureobasidium pullulans
Monomicrobial
Most common causes

# Risk Factors
Spleen abscess often co-exists with several risk factors, but the major one is the patients 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.

# Differentiating splenic abscess from other diseases
Splenic abscess should be differented from other causes of left upper quadrent pain causes:
- Splenic cysts
- Splenic infarct
- Splenic hematomas
- Peri splenic abscess

# 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%). Mortality rate also varies with treatment of choice such as splenectomy, percutaneous drainage, anti microbial therapy carries 8%, 29%, 20% of mortality rate respectively.

## 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 .

# Natural History, Complications and Prognosis

## Natural History
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.

## Complications
Life threatening complications:
- Septic shock
- Death
Common complications:
- Bacterial sepsis or septicemia
- Respiratory complications such as post operative pneumonia
- Splenic rupture and peritonitis
- Fistula formation with abscess
Less common complications:
- 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

## Physical Examination Findings

## 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
InspectionPalpation
- Tender splenomegaly
- Palpable spleen orabdominal mass
Auscultation
- Friction rub over the spleen

## Laboratory Tests

## 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)
- Microbiological tests: 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.
Gram stain
Bacterial culture
- Gram stain
- Bacterial culture
- Mycological tests

## 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.

## Diagnostic Evaluation of Splenic abscess

# Treatment
Treatment of splenic abscess depends on etiology. In bacterial abscesses, splenectomy combined with post-operative antibiotic therapy is the most appropriate treatment of choice with least mortality rate when compared to percutaneous drainage or antimicrobial therapy.

## Antimicrobial Regimen

# 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