What is the sensitivity of head computed tomography (CT) for cytomegalovirus (CMV) ventriculoencephalitis?

Sensitivity of Head CT for CMV Ventriculoencephalitis

Head CT has poor sensitivity (approximately 20%) for detecting CMV ventriculoencephalitis, with MRI being the significantly superior imaging modality for this condition. 1, 2

Imaging Findings in CMV Ventriculoencephalitis

CT Limitations

• In a study of 10 AIDS patients with autopsy-confirmed CMV CNS infection, CT showed positive findings attributable to CMV in only 3 patients (30%) 2
• Even in symptomatic cases, CT significantly underestimated the degree of CNS involvement 2
• CT may only show non-specific findings such as:
  • Cortical atrophy
  • Mild hydrocephalus ex vacuo
  • Periventricular enhancement (detected in only 1 of 5 patients) 1

MRI Superiority

• MRI is significantly more sensitive than CT in detecting early cerebral changes of viral encephalitis 3
• Periventricular enhancement, a key feature of CMV ventriculoencephalitis, is more reliably detected by MRI (seen in 2 of 3 patients) compared to CT (seen in only 1 of 5 patients) 1
• Diffusion-weighted MRI may be especially sensitive for early changes in viral encephalitis 3

Diagnostic Approach for Suspected CMV Ventriculoencephalitis

Clinical Context

• CMV ventriculoencephalitis typically presents with:
  • Altered mental status
  • Focal neurologic signs (including cranial nerve palsies or nystagmus)
  • Rapid progression if untreated 3
• Most common in severely immunocompromised patients, particularly those with AIDS 3
• May be associated with CMV retinitis or other manifestations of disseminated CMV 1

Recommended Imaging Algorithm

1. MRI with contrast (including diffusion-weighted imaging) is the preferred initial imaging modality 3

   • Should be performed within 24-48 hours of admission for suspected viral encephalitis
   • Look for periventricular enhancement and ependymal necrosis

2. CT scan should only be used when:

   • MRI is contraindicated or unavailable
   • Patient is too unstable for MRI
   • Urgent evaluation for increased intracranial pressure is needed 3

3. CSF analysis is essential for definitive diagnosis:

   • Typically shows neutrophilic pleocytosis (100-200 neutrophils/μL)
   • Hypoglycorrhachia (low CSF glucose)
   • Elevated protein levels 3

Key Pitfalls to Avoid

• Relying solely on CT imaging can lead to missed diagnoses of CMV ventriculoencephalitis due to its poor sensitivity 2
• Delaying treatment while waiting for imaging results can be fatal, as untreated CMV neurologic disease progresses rapidly 3
• Overlooking CMV in differential diagnosis of encephalitis in immunocompromised patients, especially those with AIDS 3
• Misinterpreting normal CT findings as ruling out CMV ventriculoencephalitis 2

In conclusion, while head CT may be more readily available in emergency settings, its sensitivity for CMV ventriculoencephalitis is poor. MRI with contrast should be the imaging modality of choice whenever possible for suspected cases.