Brain Herniation Imaging - Medscape Reference

Although CT is the mainstay of imaging for acute traumatic brain injury, MRI is more sensitive for the detection of certain intracranial injuries (eg, axonal injuries) and blood products 24-48 hours after injury. However, MRI does have limitations in terms of speed, accessibility, sensitivity to motion, and cost. Evidence primarily supports the use of MRI when CT findings are normal or when there are persistent and unexplained neurologic findings. [10, 4, 13, 5]

With descending transtentorial herniation, mass effect in the cerebrum pushes the supratentorial brain through the incisura. In ascending transtentorial herniation (seen in the images below), mass effect from the posterior fossa pushes the infratentorial brain through the incisura. This results in the distortion of the midbrain, flattening of the posterior quadrigeminal plate, and narrowing of the bilateral ambient cisterns. Hydrocephalus is frequently noted. [1, 4, 18, 12, 13, 5, 2, 6]

Right parasagittal gadolinium-enhanced T1-weighted magnetic resonance image in a 9-year-old girl with a history of right cerebellar astrocytoma who presented with headaches and vomiting. Heterogeneously enhancing mass is demonstrated in the right cerebellum, with compression of the adjacent brainstem and fourth ventricle. Ascending transtentorial herniation of the cerebellum is demonstrated through the incisura. Descending tonsillar herniation also is present. View Media Gallery Axial gadolinium-enhanced T1-weighted magnetic resonance image obtained at the level of the midbrain in the same patient as in the previous image. A heterogeneously enhancing mass is seen in the right medial anterior cerebellum, with mass effect on the right posterior lateral midbrain and fourth ventricle. The image shows enlargement of the temporal horns of both lateral ventricles as a result of obstruction by the cerebellar mass at the level of the fourth ventricle. View Media Gallery

Subfalcine/cingulate herniation causes the supratentorial brain to be displaced underneath the anterior falx.

In foramen magnum/tonsillar herniation, the infratentorial brain is displaced through the foramen magnum (see the images below).

T1-weighted sagittal magnetic resonance image through the cervical spine in a child with a history of an Arnold-Chiari I malformation. Image shows tonsillar herniation with compression of the central canal at the craniocervical junction and resultant syringohydromyelia in the visualized portion of the cervical spinal cord. View Media Gallery T2-weighted sagittal magnetic resonance image through the cervical spine was obtained in the same patient as in the previous image. The cerebellar tonsils are projecting inferiorly below the level of the opisthion, with compression of the central canal at the craniocervical junction. Hyperintense syringohydromyelia in the visualized portion of the cervical spinal cord is demonstrated. View Media Gallery

With sphenoid/alar herniations, the supratentorial brain slides either anteriorly or posteriorly over the wing of the sphenoid bone. An anterior herniation occurs when the temporal lobe herniates anteriorly and superiorly over the sphenoid bone. Conversely, a posterior herniation occurs when the frontal lobe herniates posteriorly and inferiorly over the sphenoid bone.

Extracranial herniation causes the brain to be displaced through a cranial defect.

Gadolinium-based contrast agents have been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or magnetic resonance angiography (MRA) scans.

Cross-sectional imaging provides a high degree of confidence.