giovedì 21 settembre 2006

Pyogenic cerebral abscess


There is a well-defined, smoothly marginated, thinly rim-enhancing intraaxial mass (Figure 4) with surrounding edema (Figure 3) and mass effect centered in the right deep gray matter. The rim is essentially isointense to white matter on the T1-weighted image (Figure 1), hypointense on the T2-weighted image (Figure 2), and there is homogeneously increased signal intensity of the mass on the diffusion-weighted image (Figure 5).

Diagnosis: Pyogenic cerebral abscess

Most pyogenic cerebral abscesses are located supratentorially at the gray - white junction, secondary to hematogenous spread, and within the frontal and parietal lobes (middle cerebral artery distribution). Size is variable and may range from a few millimeters to many centimeters.

The characteristic imaging findings are illustrated in this case, but the pathogenesis and assoiciated imaging findings have been divided into four stages, which have been extensively published and are as follows:
- early cerebritis
- late cerebritis
- early capsule formation
- late capsule formation

Although hematogenous dissemination from an extracranial infection is the most common source, other potential etiologies to consider include: hematogenous spread from any right-to-left shunt, penetrating trauma, postoperative, and direct extension from a paranasal sinus, meningeal, calvarial, or otic infection.

These relatively uncommon lesions are potentially fatal but treatable, with treatment (often depending of the size of the lesion) typically ranging between systemic antibiotics alone and stereotactic aspiration or drainage. Reports of mortality vary, with published numbers between 0% and 30%. It is important to be aware of the complications of incompletely or inadequately treated abscesses and to look for them on MR.

These include:
- Intraventricular rupture with ventriculitis
- Meningitis with satellite abscess development
- Hydrocephalus
- Local mass effect or herniation.

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