Teaching Case

Patient hospitalised due to recurrent febrile episodes each lasting 6-8 days (body temperature up to 39-40°C) during the past three months.
His previous medical history recorded acute myocardial infarction 5 years earlier, aorto-coronary bypass plus aortic valve replacement with biological prosthesis two years earlier.

At admission, conventional chest radiographs (not shown) were unremarkable. Laboratory tests disclosed mild leukocytosis (11.000/mmc WBC with 73% neutrophils), raised C-reactive protein levels (64). Initially, haemocultures were persistently negative due to previous empiric antibiotic therapies.
Trans-thoracic and trans-oesophageal echocardiography failed to visualise suspected endocarditic vegetations.
Routine abdominal ultrasound detected, as the sole abnormality, a roundish hypo-anechoic splenic lesion, measuring nearly 6 cm in its maximum diameter, internally inhomogeneous with some mobile echoes; the size of the spleen was within upper normal limits.
MRI, requested to further investigate this uncommon finding, confirmed the presence of a solitary ovoidal splenic lesion with well-defined margins, homogeneously T1-hyperintense due to a probable proteinaceous content, structurally mixed on T2-weighted sequences with portions of fluid-like signal intensity; after intravenous gadolinium contrast, no internal enhancement was present but a thin peripheral rim enhancement was appreciable.
Worsening of the patient’s clinical conditions led to his transfer to the Intensive Care unit: repeated haemocultures indicated sepsis due to Enterococcus avium infection, while unenhanced body CT confirmed stable hypodense splenic lesion. Intensive support and protracted multiple antibiotic therapy were insufficient to battle sepsis with multiorgan failure.

Purulent infections involving the spleen are uncommonly encountered thanks of the rich reticulo-endothelial splenic system. Most cases of splenic abscesses result from haematogenous seeding of infection from septic foci such as during endocarditis or in haemodialysis patients.
Presentation classically includes fever, chills, left upper quadrant pain and tenderness along with acute inflammation laboratory markers, but clinical manifestations are often unspecific. As confirmed with the presented case, splenic abscesses are associated with a high mortality rate even if promptly recognised and treated. Appropriate, intensive antibiotic therapy should be combined with splenectomy to remove the source of sepsis in refractory patients, and with subsequent valve replacement surgery (when indicated) to prevent re-infection of the valvular prosthesis.
Ultrasound has value as a screening modality for assessing the spleen, since it may detect splenic lesions with fair sensitivity but limited specificity; abscess lesions are visualised as poorly defined hypo- or anechoic areas. CT represents the mainstay imaging modality for diagnosing splenic abscess lesions, particularly in the acute setting. At CT splenic infectious lesions typically appear more well-defined than with ultrasound.
A large variety of congenital, infectious and inflammatory, vascular, haematologic, benign and malignant diseases involve the spleen and may show a cystic-like appearance at cross sectional imaging.
Despite its well-known limitations in acutely ill patients, thanks to its high contrast resolution and limited biological invasiveness MRI is an excellent tool for diagnosing pathologic conditions of the spleen, as it allows confident characterisation of most splenic lesions. Therefore, MRI including dynamic contrast-enhanced acquisitions can be proposed as a useful problem-solving imaging modality.
Some reports in literature have addressed MRI features of splenic abscesses, usually displaying low T1 and high T2 signal intensity, with some peripheral enhancement corresponding to the development of a capsule or to hyperaemic inflamed surrounding splenic parenchyma. Bacterial abscesses associated with endocarditis tend to be fairly large, whereas mycotic ones occurring in immunocompromised patients are usually smaller and multiple.
In this case report, clinical data combined with MRI features with peripheral enhancement allowed diagnosis of splenic abscess and differentiation from other cystic-appearing splenic lesions.