Splenic Infection and Abscess

Published on 20/07/2015 by admin

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Last modified 22/04/2025

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 Low-attenuation complex fluid collection ± air-fluid levels

image Internal gas bubbles, which although uncommon, are very specific for splenic abscess
image Multiloculated appearance seen with liver abscesses possible, but less common with splenic abscess
image May extend to subcapsular location and may rarely cause splenic rupture with generalized peritonitis
• Fungal microabscesses on CECT

image Multiple small hypodense lesions measuring a few mm
image Multiple punctate splenic calcifications after treatment
• Echinococcal (hydatid) cyst on CECT

image Complex cyst with multiple low density “daughter” cysts and thick, enhancing wall (“cyst within a cyst”)
image Serpiginous, linear densities within cyst due to collapsed parasitic membranes (water lily sign)
image May demonstrate thick peripheral calcification or internal wavy, curvilinear calcification in chronic setting

TOP DIFFERENTIAL DIAGNOSES

• Splenic infarct
• Splenic tumor
• Splenic trauma
• Infiltrating disorders

PATHOLOGY

• Multiple different causes for splenic pyogenic abscesses

image Generalized septicemia, septic emboli (usually in setting of endocarditis with mitral &/or aortic valve vegetations), or secondary infection of traumatic splenic hematoma or infarct
image Other predisposing risk factors: Recent surgery, other abdominal infections, intravenous drug abuse, immunodeficiency, malignancy or hematologic disorders, trauma, diabetes, and pancreatitis
• Most fungal microabscesses occur in setting of immunosuppression, HIV/AIDS, or hematologic disorders
• Echinococcal infections occur due to infection with tapeworm (Echinococcus granulosus)
image
(Left) Axial CECT shows a multiloculated mass image within the spleen that proved to be a pyogenic abscess. Such large abscesses are unusual in the spleen, especially in the absence of prior splenic infarction.

image
(Right) Axial CECT in a patient with a recent history of traumatic injury to the spleen and a new fever image demonstrates a rim-enhancing fluid collection with an air-fluid level image, consistent with a splenic abscess. The patient was treated with percutaneous drainage and antibiotics.
image
(Left) Axial CECT in a patient with HIV/AIDS who was admitted with fever and weight loss demonstrates microabscesses image throughout the spleen. The patient deteriorated rapidly, and multiple tuberculous abscesses were identified at autopsy.

image
(Right) Axial CECT shows a splenic hydatid cyst image with additional similar lesions in the liver and peritoneal cavity image, many of which have calcified walls. This patient had a prior rupture of a hepatic hydatid cyst with diffuse spread throughout the abdomen.

TERMINOLOGY

Definitions

• Splenic abscess: Collection of liquefied pus within splenic parenchyma

IMAGING

General Features

• Best diagnostic clue

image Rounded low-attenuation complex fluid collection with mass effect
• Location

image Variable: May be located anywhere within splenic parenchyma
• Size

image Variable: Typically 3-5 cm for pyogenic abscesses; < 1.5 cm for microabscesses (often fungal)
• Morphology

image Rounded cystic mass with irregular borders

– May have multiple locules similar to cluster sign of hepatic pyogenic abscess
– Internal septations common
– Exerts mass effect on splenic capsule

Radiographic Findings

• Radiography

image Very rarely gas bubbles within abscess may be visualized on radiographs
image Often associated with left lower lobe atelectasis and left pleural effusion on chest radiograph

CT Findings

• Pyogenic abscess

image Low-attenuation (20-40 HU) complex fluid collection ± air-fluid levels

– May have an enhancing peripheral rim, but not as conspicuous as generally seen with liver abscesses
– May have internal gas bubbles, which although uncommon, are very specific for splenic abscess
– May have multiloculated appearance seen with liver abscesses, but less common with splenic abscess
image May extend to subcapsular location and may rarely cause splenic rupture with generalized peritonitis
• Fungal microabscesses

image Often multiple, small, hypodense lesions measuring just a few mm
image Can be very difficult to diagnose on NECT
image May manifest as multiple punctate splenic calcifications after treatment
• Echinococcal (hydatid) cyst

image Complex cyst with multiple low density “daughter” cysts and thick, enhancing wall composed of fibrous tissue (“cyst within a cyst” appearance)
image Serpiginous, linear hypodense bands within cyst due to collapsed parasitic membranes (water lily sign)
image May demonstrate thick peripheral calcification or internal wavy, curvilinear calcification in chronic setting
image Similar lesions may be seen in liver or peritoneum

MR Findings

• Fluid signal at center of lesion (hyperintense on T2WI and hypointense on T1WI) with peripheral enhancement on T1WI C+ images
• Old healed/treated fungal microabscesses may show blooming artifact on GRE sequences due to calcification

Ultrasonographic Findings

• Grayscale ultrasound

image 90% sensitivity for pyogenic abscess
image Pyogenic abscess

– Hypoechoic or anechoic mass with internal septations and low-level echoes representing pus or debris

image Rarely, atypical splenic abscess appears echogenic
– May have variable degrees of posterior acoustic enhancement, depending on cyst contents
– “Dirty” shadowing and ring-down artifact suggest presence of gas within collection

image US is much less sensitive for ectopic gas than CT
image Fungal microabscesses

– “Target” or bull’s-eye appearance similar to hepatic microabscesses
• Color Doppler

image Pyogenic and fungal abscesses typically show no internal color flow vascularity

Nuclear Medicine Findings

• PET

image Increased isotope uptake from hypermetabolic focus
• WBC scan: Increased isotope uptake

Imaging Recommendations

• Best imaging tool

image CECT
• Protocol advice

image  

DIFFERENTIAL DIAGNOSIS

Splenic Infarct

• Wedge-shaped area of low attenuation at periphery of spleen

image Very rarely rounded in configuration and in central spleen (potentially mimicking abscess or neoplasm)
• No enhancement on contrast-enhanced images

Splenic Tumor

• May be single or multiple discrete masses
• Most common solid malignancies include lymphoma, melanoma, and other metastases

image Melanoma and some cystic/necrotic metastases (ovarian cancer, sarcomas, germ cell tumors) can appear low density and cystic, mimicking abscess or fluid collection
image Lymphoma can present with innumerable tiny hypodense nodules in spleen mimicking microabscesses
• Most common benign lesions are lymphangioma and hemangioma

image Variable appearance; both lesions can appear low density and mimic abscess or fluid collection
image Hemangioma may appear hypervascular on arterial phase CECT and lymphangioma may show internal loculations and septations

Splenic Trauma

• History of recent blunt injury
• Linear low density, nonenhancing laceration almost always associated with perisplenic hematoma and hemoperitoneum
• ± active arterial extravasation

Infiltrating Disorders

• Sarcoid (and less commonly, Gaucher disease) can commonly present with multiple low-attenuation lesions
• Indistinguishable from microabscesses without history
• Sarcoid may be associated with similar lesions in liver, hepatosplenomegaly, and thoracic/upper abdominal lymphadenopathy

PATHOLOGY

General Features

• Etiology

image Multiple different causes for splenic pyogenic abscesses

– Generalized septicemia (most splenic abscesses arise due to hematogenous spread of infection)
– Septic emboli (usually in setting of endocarditis with mitral/aortic valve vegetations)
– Secondary infection of traumatic splenic hematoma or infarct
– Other predisposing risk factors: Recent surgery, other abdominal infections, intravenous drug abuse, immunodeficiency, malignancy or hematologic disorders, trauma, diabetes, and pancreatitis
image Most fungal microabscesses occur in setting of immunosuppression, HIV/AIDS, or hematologic disorders
image Echinococcal infections occur due to infection with tapeworm (Echinococcus granulosus)

– Most commonly occur in areas with sheep (transmission often via dogs who eat viscera of slaughtered animals)
– Most common in South America, Middle East, Eastern Mediterranean, and parts of Africa
• Genetics

image Hemoglobinopathies (sickle cell) predispose to pyogenic abscess

Staging, Grading, & Classification

• Pyogenic

image Unilocular (65%); multilocular or multiple (20%)
image Gram-negative organisms in 55%:  Klebsiella pneumoniae most common pathogen
• Fungal

image Typically microabscesses measuring < 1.5 cm (25%)
image Most often Candida (most common), Aspergillus, and Cryptococcus
image Tuberculosis (TB) and Mycobacterium avium-intracellulare (MAI) in AIDS patients
• Parasitic

image Echinococcus granulosus

Gross Pathologic & Surgical Features

• Necrotic areas of liquefied pus

Microscopic Features

• Liquefactive necrosis
• Pus with leukocyte debris
• Gram stain for pyogenic abscess

image 57% aerobic

– Staphylococcus
– Streptococcus
– Escherichia coli
• Fungal stain for mycotic organism

image Candida most common
image Aspergillus and Cryptococcus
image Tuberculosis (TB) and M yc obacterium avium-intracellulare (MAI) in AIDS patients
• TB stains for tuberculous abscesses

CLINICAL ISSUES

Presentation

• Most common signs/symptoms

image Pyogenic abscess

– Fever (92%), chills, LUQ pain (77%), splenomegaly
– May mimic symptoms of pneumonia, ulcer disease, or pancreatitis
– Lab data: Leukocytosis (66%), positive blood cultures
image Echinococcal cyst

– Many patients are asymptomatic and may remain without symptoms for years
– Symptoms depend on site of infection and size of cyst
– Lab data: Eosinophilia in only small minority of patients (< 15%)
• Other signs/symptoms

image Liquefied pus

Demographics

• Age

image Usually adult patients with predisposing factors (although any age group can be affected)
• Gender

image M = F
• Ethnicity

image No known predilection
• Epidemiology

image Rare: 0.2% of reported autopsies
image 25% of patients with splenic abscesses are immunocompromised patients

Natural History & Prognosis

• Variable
• Excellent prognosis for pyogenic abscesses in immunocompetent patient
• Guarded prognosis in immunocompromised patients with fungal microabscesses
• Echinococcal disease can recur many years after treatment and should be monitored periodically for recurrence

Treatment

• Splenic pyogenic abscess

image Traditional treatment is splenectomy with broad-spectrum antibiotics

– Still standard treatment in setting of multiple pyogenic abscesses or abscess rupture
– Mortality postsplenectomy: 6%
image Spleen-conserving treatment increasingly being utilized

– Antibiotics alone may be curative in 75% of small pyogenic abscesses (< 4 cm)
– Percutaneous drainage may be utilized for unilocular unruptured abscesses with high reported success rates
• Fungal microabscesses

image Treatment with antifungal medications
• Echinococcal cyst

image Treatment options include surgical resection (especially in setting of ruptured cysts or other complications), percutaneous drainage (± introduction of scolicidal agent), drug therapy (e.g., albendazole), or observation

DIAGNOSTIC CHECKLIST

Consider

• Differentiate splenic abscesses from mimics, including lymphoma, low-density metastases, or splenic infarcts

Image Interpretation Pearls

• Splenic abscesses appear as solitary or multiple low-attenuation cystic lesions in febrile patient

image May or may not have the typical multiloculated, well-defined appearance traditionally associated with liver abscesses
image
(Left) Color Doppler image shows a well-defined solitary splenic abscess with a hypoechoic necrotic center image and a thick irregular wall image. The adjacent splenic parenchyma image appears normal. Note the typical avascular nature of the abscess.

image
(Right) Axial T1 C+ MR in a patient with LUQ pain and a fever illustrates the characteristic multiseptate appearance of a splenic abscess image. Blood cultures identified Staphylococcus and the patient recovered with antibiotics.
image
(Left) Axial CECT in a 29-year-old intravenous drug abuser with a 3-day history of fever and LUQ pain shows a focal hypodense lesion image in the periphery of the spleen’s midportion; findings that are consistent with an abscess.

image
(Right) Axial CECT in the same patient reveals lateral perisplenic inflammatory changes image, suggesting a possible abscess rupture. An echocardiogram showed multiple vegetations in both the aortic and mitral valves, suggesting that this abscess is due to underlying endocarditis.
image
(Left) Axial CECT in a 29-year-old known intravenous drug abuser who presented with multiple skin abscesses as well as abdominal pain and fever demonstrates a low-attenuation splenic abscess image.

image
(Right) Axial CECT in the same patient demonstrates multiple hepatic abscesses image as well. The patient underwent an echocardiogram, which additionally revealed aortic valve vegetations from endocarditis (not shown).
image
Axial CECT in a 25-year-old female presenting with fever and malaise demonstrates microabscesses within the spleen image and fewer, similar lesions in the liver image.

image
Axial CECT in the same patient demonstrates porta hepatis lymphadenopathy image. Liver biopsy and blood cultures confirmed a systemic infection with histoplasmosis.
image
Axial gadolinium-enhanced T1 C+ MR in a patient with pyogenic splenic abscess. Early-phase MR reveals rim enhancement around the low-signal abscess image.
image
Axial CECT of a patient with AML and splenic microabscesses from Candida shows innumerable low-attenuation lesions image.
image
Axial CECT shows a pyogenic splenic abscess. Note the low-attenuation abscess bulging the splenic parenchyma image.
image
Axial CECT shows fungal microabscesses. Note the numerous hypodense lesions; cultures grew Candida.
image
Axial CECT demonstrates splenic microabscesses. Note the small 1-cm lesions diffusely throughout the spleen.
image
Transverse sonogram shows a gas-forming splenic pyogenic abscess. Note the linear high amplitude echoes representing gas image.
image
Transverse sonogram shows a gas-forming splenic pyogenic abscess. Note the ring-down artifacts from gas bubbles image.
image
Transverse sonogram shows a splenic pyogenic abscess. Note the hypoechoic abscess image with little distal acoustic enhancement.
image
Transverse sonogram shows multiple splenic pyogenic abscess. Note the multiple hypoechoic round lesions image.
image
Transverse ultrasound in a 37-year-old female with fever, chills, and LUQ pain after a dental procedure shows a discrete hypoechoic lesion image in the midportion of the spleen, findings consistent with an abscess.
image
Transverse color Doppler ultrasound in the same patient demonstrates no internal flow in the lesion image, which excludes a solid lesion such as lymphoma or metastasis. Blood cultures were positive for anaerobic Streptococcus, and the lesion resolved with antibiotic therapy.

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