Frequency of Necrotizing Picture in Post-HSV Inflammatory Encephalitis
Necrotizing changes are a characteristic pathological feature of HSV encephalitis, occurring in the majority of cases, particularly affecting the temporal and frontal lobes with edema, hemorrhage, and necrotic changes in the brain parenchyma. 1
Imaging Manifestations of Necrotizing Disease
Early MRI changes demonstrate necrotizing inflammation beginning in the cingulate gyrus and medial temporal lobes, showing gyral edema on T1-weighted images and high signal intensity on T2-weighted and FLAIR sequences, with approximately 90% sensitivity within 48 hours of hospital admission. 2
Diffusion-weighted MRI is especially sensitive for detecting early necrotizing changes in HSE, demonstrating higher sensitivity compared to CT scanning, which has only 25% sensitivity for initial diagnosis. 2, 3
The necrotizing process characteristically involves bilateral temporal lobes, which is nearly pathognomonic for HSV encephalitis and helps distinguish it from other viral encephalitides. 3
Pathological Characteristics
HSV encephalitis always impacts the temporal and frontal lobes or limbic system, leading to edema, hemorrhage, and necrotic changes in the brain parenchyma as part of its fundamental pathophysiology. 1
The hemorrhagic nature of HSE is evident in approximately 50% of cases, with elevated CSF red cell counts reflecting the hemorrhagic and necrotizing pathology. 4
Autopsy studies reveal extensive hippocampal disease with viral protein in astrocytes and neurons, demonstrating the necrotizing involvement of specific anatomical structures including the entorhinal cortex and amygdala. 2
Clinical Implications of Necrotizing Disease
The necrotizing pathology results in severe long-term sequelae, with 20-60% of survivors developing memory deficits and neuropsychiatric complications reflecting permanent damage to hippocampal and limbic structures. 2
Even with appropriate aciclovir treatment, mortality remains 25-28% at 18 months, underscoring the devastating nature of the necrotizing inflammatory process. 2
Intracranial hemorrhage as a complication of the necrotizing process is rare (2.7%), but when it occurs, it significantly worsens prognosis despite appropriate antiviral therapy. 5
Diagnostic Approach to Necrotizing Features
Follow-up MRI is recommended to evaluate evolving necrosis or demyelination and to assess treatment response, as the necrotizing process can progress despite antiviral therapy. 3
Histopathologic examination demonstrates chronic encephalitic processes with late secondary parenchymal changes, though specific viral cytopathic findings may not always be present in necrotizing tissue. 6
Common Pitfalls
The "classical" necrotizing picture of HSV encephalitis in children is now considered outdated, as non-specific initial presentations are the most common reason for failure to diagnose HSV encephalitis, despite the underlying necrotizing pathology. 4
CT scanning should not be relied upon to detect necrotizing changes, as it has poor sensitivity for early HSE and may miss significant necrotizing inflammation visible on MRI. 3