From the Guidelines
Knife edge atrophy in brain MRI is a specific pattern of brain tissue loss characterized by sharp, thin edges of the cerebral cortex, most commonly associated with cerebral atrophy in conditions like Alzheimer's disease, frontotemporal dementia, and other neurodegenerative disorders, as well as chronic traumatic encephalopathy 1.
Definition and Characteristics
Knife edge atrophy refers to the appearance of the cerebral cortex when it undergoes significant atrophy, resulting in sharp, thin edges that resemble the blade of a knife. This pattern is due to the narrowing of the gyri and the widening of the sulci as a result of brain tissue loss. The frontal and temporal lobes are particularly affected, showing significant neuronal loss and correlation with cognitive decline and neurological symptoms.
Clinical Significance
The presence of knife edge atrophy in brain MRI is indicative of irreversible brain tissue loss and is associated with the progression of neurodegenerative diseases. It is essential for radiologists to identify this pattern during MRI interpretation to aid in differential diagnosis and assess the extent of neurodegeneration. The severity of knife edge atrophy generally correlates with the progression of the underlying disease, making it a crucial finding for managing and predicting patient outcomes.
Associated Conditions
Knife edge atrophy is not only associated with neurodegenerative disorders like Alzheimer's disease and frontotemporal dementia but also with chronic traumatic encephalopathy, a condition resulting from repetitive traumatic brain injuries, as discussed in the context of chronic TBI 1. The underlying biologic mechanism of chronic traumatic encephalopathy involves aggregation of hyperphosphorylated tau and neurofibrillary tangles, along with diffuse axonal disruption and loss, similar to other neurodegenerative conditions.
Imaging and Diagnosis
Imaging techniques such as three-dimensional isotropic short echo time spoiled gradient-recalled echo and magnetization-prepared rapid gradient-echo sequences are used to assess TBI-associated brain atrophy, including knife edge atrophy 1. These sequences help in characterizing injuries, understanding persistent symptoms, prognosticating, and improving functional outcomes in patients with chronic TBI. However, the literature on the long-term neurocognitive outcomes in patients with mild TBI imaged using conventional MRI sequences in the subacute to chronic stages after injury is limited, highlighting the need for further research.
From the Research
Definition of Knife Edge Atrophy
- Knife edge atrophy refers to a specific pattern of brain atrophy that can be observed on magnetic resonance imaging (MRI) scans, particularly in patients with frontotemporal lobar degeneration (FTLD) [ 2 ].
- This type of atrophy is characterized by a narrow, knife-like appearance of the affected brain region, typically in the frontal and temporal lobes.
Association with Frontotemporal Lobar Degeneration
- Knife edge atrophy is often seen in patients with Pick disease, a subtype of FTLD, and is considered a characteristic feature of this condition [ 2 ].
- The atrophy is usually visible at a relatively early stage of the disease and can be detected on routine MRI scans, although more advanced imaging techniques such as voxel-based morphometry may be more sensitive [ 2 ].
Distinction from Other Neurodegenerative Disorders
- While knife edge atrophy is a distinctive feature of FTLD, other neurodegenerative disorders such as Alzheimer's disease, chronic traumatic encephalopathy, and amyotrophic lateral sclerosis may also exhibit brain atrophy on MRI scans [ 3, 4, 5, 6 ].
- However, the specific pattern and location of atrophy can help distinguish between these conditions and FTLD.