Cerebral Shear Injury

cerebral shear injury

This 20 year-old female patient had a follow-up MRI after head injury 4 months previously. The axial gradient-echo (FLASH) sequence shows punctate areas of signal loss at the grey-white interface in the frontal lobes. These are due to magnetic susceptibility artifact from haem degradation products (microhaemorrhages).

Gradient-echo MRI is capable of detecting millimeter-size paramagnetic blood products in brain parenchyma, and has a greater sensitivity than spin-echo sequences. Microhaemorrhages appear larger than they are due to the “blooming” effect (due to distortion of the local magnetic field). Microhaemorrhages are visible for many years because haemosiderin is stored in macrophages. Causes of microhaemorrhage other than trauma include: hypertensive vasculopathy; cerebral amylod angiopathy; cerebral cavernous malformations; cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL); and cerebral infarcts.

Shearing injury is an important cause of morbidity in head injury. Disruption of penetrating blood vessels at the corticomedullary junction, corpus callosum, internal capsule, deep grey matter and upper brainstem produce numerous small haemorrhagic foci. The lobar white matter, corpus callosum and dorsolateral brainstem are most commonly affected. Apart from microhaemorrhages, there may be white matter hyperintense lesions on T2-weighted sequences, and later there may be nonspecific atrophic changes.

References:
1. Viswanathan A, Chabriat H. Cerebral Microhaemorrhage. Stroke. 2006; 37: 550-555.
2. Osborn AG. Diagnostic Neuroradiology. 1st edition. Mosby 1994.

Credit: Dr Laughlin Dawes