E2090. Taking It to the Next Level: Understanding Fluid-Fluid Levels in the CNS
  1. Matthew Braiman; Donald and Barbara Zucker School of Medicine at Hofstra/Northwell
  2. Faizullah Mashriqi; Donald and Barbara Zucker School of Medicine at Hofstra/Northwell
  3. Rona Woldenberg; Donald and Barbara Zucker School of Medicine at Hofstra/Northwell
Fluid-fluid levels are a finding visible on a variety of imaging modalities, and may indicate an array of pathologies in the central nervous system (CNS). Fluid-fluid levels can arise from traumatic, vascular, neoplastic, iatrogenic, and infectious causes. Fluid-fluid levels often aid the radiologist in generating an accurate differential diagnosis.

Educational Goals / Teaching Points
This educational exhibit aims to identify some common etiologies of fluid-fluid levels in the CNS in the intracranial, spinal, and head and neck regions.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
A fluid level occurs when a substance containing materials of different densities (air, fat, hemorrhage, or fluid, etc.) is allowed to settle over time. The level is readily visible when perpendicular to the imaging plane. A leading cause of fluid-fluid levels in the CNS is intracerebral hemorrhage (ICH), often exacerbated by the use of anticoagulants. A recent study among patients with CT-confirmed acute ICH found that fluid-fluid levels, though minimally sensitive for detection of intracerebral hemorrhage (4.2%), were 99.4% specific for oral anticoagulant-associated ICH. This finding underscores the importance for identification of fluid-fluid levels by the radiologist in determining an underlying cause of hemorrhagic stroke. Other disease processes where hemorrhagic-fluid levels are seen include arterial and venous infarctions and hypertensive hemorrhages. Fluid-fluid levels may also be seen in neoplasms of the brain, including glioblastomas, astrocytomas, and metastases. Multiple fluid-fluid levels therefore should raise concern in the radiologist for possible metastases or diseases associated with high tumor burden, such as Von Hippel-Lindau syndrome. Another important differential for fluid-fluid levels is infection - case series have demonstrated fluid-fluid levels in cases of bacterial ventriculitis. Fluid-fluid levels within the ventricles in a toxic patient should raise the index of suspicion for possible CNS infection.

Fluid-fluid levels are common in the CNS, but are nonspecific. Having an understanding of the appearance of fluid-fluid levels, as well as an appreciation of the variety of differential diagnoses that may lead to their occurrence, is valuable to the diagnostic radiologist in confirming a diagnosis and influencing management decisions.