From the Guidelines
Subdural empyema is best characterized by MRI findings, which demonstrate low signal intensity on T1-weighted images, high signal intensity on T2-weighted images, and restricted diffusion on diffusion-weighted imaging (DWI), with enhancement of the peripheral capsule and adjacent dura on post-contrast images. The imaging characteristics of subdural empyema are crucial for its diagnosis and management. On MRI, subdural empyema typically appears as a collection of pus between the dura mater and the arachnoid mater, with signal intensities that help differentiate it from other conditions 1.
Key Imaging Features
- Low signal intensity on T1-weighted images
- High signal intensity on T2-weighted images
- Restricted diffusion on DWI, which helps differentiate it from sterile effusions
- Enhancement of the peripheral capsule and adjacent dura on post-contrast images
- The empyema typically follows the contour of the brain without crossing dural attachments like the falx cerebri, unlike epidural collections
Importance of Early Imaging
Early imaging is crucial as subdural empyema represents a neurosurgical emergency requiring prompt diagnosis and treatment, typically involving surgical drainage and appropriate antibiotic therapy 1. Follow-up imaging is important to monitor treatment response and detect potential complications such as venous thrombosis, cerebritis, or abscess formation.
Role of MRI
MRI is the preferred imaging modality due to its superior sensitivity and ability to distinguish between different types of fluid, especially with the use of diffusion-weighted imaging 1. The use of IV contrast helps to identify abnormal epidural fluid collections, define their size and extent, and determine the presence of spinal cord and/or cauda equina compression. However, the provided evidence on spine infection 1 is not directly relevant to the imaging characteristics of subdural empyema, and therefore, it does not influence the recommendation.
Clinical Implications
The imaging characteristics of subdural empyema have significant clinical implications, as prompt diagnosis and treatment are essential to prevent morbidity and mortality. The most recent and highest quality study 1 supports the use of MRI as the preferred imaging modality for diagnosing subdural empyema, and its findings should guide clinical decision-making.
From the Research
Imaging Characteristics of Subdural Empyema
The imaging characteristics of subdural empyema can be identified through various diagnostic procedures, including:
- Contrast-enhanced brain MRI, which is crucial for diagnosis and shows features distinct from subdural hematoma or hygroma 2
- CT scans, which may miss intracranial subdural empyemas detectable by MRI, but can be used to detect concurrent paranasal or mastoid infections 3, 4
- CT myelography, which can be used to detect spinal subdural empyemas when MRI is negative 3
- Cranio-spinal contrast-enhanced MRI scans, which can be used to diagnose massive involvement of the entire CNS with multiple localizations, both intracranial and spinal 5
Key Findings
Key findings on imaging studies may include:
- Convexity low-density collections on CT scans 4
- Multilocalized pus collections on CT scans 4
- Loculated infection between the dura and the arachnoid on MRI scans 3, 5
- Midline shift on CT scans, which can resolve with treatment 2
Importance of Prompt Diagnosis and Treatment
Prompt diagnosis and treatment of subdural empyema are crucial to improve outcomes, as morbidity and mortality relate directly to the delay in institution of therapy 3, 5, 6