Brain Herniation Imaging
- Author: Margaret Loh-Lee, MD; Chief Editor: L Gill Naul, MD more...
The brain is an organ of immense complexity. In the cranium, dural reflections and bony landmarks divide the brain into anatomic regions. Brain herniation represents mechanical displacement of normal brain relative to another anatomic region secondary to mass effect from traumatic, neoplastic, ischemic, or infectious etiologies. See the images below.
Herniations of the brain are divided into 5 major categories, as follows:
Transtentorial herniation 
Foramen magnum/tonsillar herniation (seen in patients with Arnold-Chiari malformation, as demonstrated in the images below) [2, 3, 4, 5]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.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.
Each category of herniation is associated with a specific neurologic syndrome.
For transtentorial herniation, computed tomography (CT) scanning or magnetic resonance imaging (MRI) is useful for evaluation. MRI can provide axial, as well as sagittal and coronal, views.
For subfalcine/cingulate herniation, CT scanning or MRI is again useful for evaluation, with MRI able to provide axial, sagittal, and coronal views.
For foramen magnum/tonsillar herniation, MRI provides the best visualization on sagittal and coronal views. However, because patients with this type of herniation often present acutely, axial CT scanning enables visualization of this condition.
For sphenoid/alar herniation, MRI provides the best visualization on parasagittal images. However, axial CT scanning or MRI can demonstrate anterior displacement of the ipsilateral middle cerebral artery, which is an indirect sign of sphenoid herniation.[6, 7]
For extracranial herniation, CT scanning or MRI is useful for evaluation.
A study by Probst et al found that among 161 patients with frank brain herniation diagnosed by CT scan, 3 (1.9%) had no neurologic deficit. The authors sought to determine if some patients with brain herniation or significant brain shift diagnosed by cranial CT might have a normal neurologic examination. Using cranial CT scan radiology reports, CT scans were classified into 3 categories: frank herniation, significant shift without frank herniation, and minimal or no shift. The investigators also found that of 91 patients with significant brain shift but no herniation, 4 (4.4%) had no neurologic deficit.
With a descending transtentorial herniation, mass effect in the cerebrum pushes the supratentorial brain through the incisura.
With ascending transtentorial herniation, mass effect from the posterior fossa pushes the infratentorial brain through the incisura (as seen below). 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.
With subfalcine/cingulate herniation (seen below), the supratentorial brain is displaced underneath the anterior falx.
With foramen magnum/tonsillar herniation, the infratentorial brain is displaced through the foramen magnum.
With sphenoid/alar herniations, the supratentorial brain is sliding 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.
With extracranial herniation, the brain is displaced through a cranial defect, as in the image below.
Cross-sectional imaging provides a high degree of confidence.
Magnetic Resonance Imaging
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.
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, as demonstrated below.
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). For more information, see the eMedicine topic Nephrogenic Systemic Fibrosis. 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. For more information, see Medscape.
Cross-sectional imaging provides a high degree of confidence.
Neonatal intracranial ultrasonography may have a limited role.
Vascular displacement from mass effect associated with herniation can be seen on cerebral angiograms. Specifically, deep venous anatomic distortion aids in identifying these entities, although CT scanning and MRI are the currently favored diagnostic modalities.
The degree of confidence is high when classic displacement of the deep venous structures is seen.
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