You are in: eMedicine Specialties > Radiology > BRAIN/SPINE Brain, HerniationArticle Last Updated: Sep 28, 2007AUTHOR AND EDITOR INFORMATIONSection 1 of 10
  Author: Margaret Loh, MD, Staff Physician, Department of Radiology, Santa Clara Valley Medical Center Margaret Loh-Lee is a member of the following medical societies: Radiological Society of North America Coauthor(s): Mahesh R Patel, MD, Chief of MRI, Department of Radiology, Santa Clara Valley Medical Center Editors: Chi-Shing Zee, MD, Chief of Neuroradiology, Professor, Departments of Radiology and Neurosurgery, University of Southern California School of Medicine; Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand; Robert L DeLaPaz, MD, Director, Professor, Department of Radiology, Division of Neuroradiology, Columbia University; Robert M Krasny, MD, Consulting Staff, Department of Radiology, The Angeles Clinic and Research Institute; L Gill Naul, MD, Professor and Head, Department of Radiology, Texas A&M University College of Medicine; Chair, Department of Radiology, Chief, Section of Magnetic Resonance Imaging, Scott and White Memorial Hospital and Clinic Author and Editor Disclosure Synonyms and related keywords: brain displacement, mass effect, transtentorial herniation, subfalcine/cingulate herniation, subfalcial herniation, foramen magnum/tonsillar herniation, sphenoid/alar herniation, extracranial herniation, uncal herniation INTRODUCTIONSection 2 of 10
  BackgroundThe brain is an organ of immense complexity and importance to life. 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. Herniations of the brain are divided into 5 major categories, as follows:
Each category of herniation is associated with a specific neurologic syndrome. PathophysiologyTranstentorial herniation Transtentorial herniation is a downward or an upward displacement of the brain through the tentorium at the level of the incisura. A descending transtentorial herniation occurs when the supratentorial brain herniates downward through the incisura. Conversely, an ascending transtentorial herniation occurs when the infratentorial brain herniates upward through the incisura. Descending transtentorial herniation occurs more often than ascending herniations and includes the subcategory of uncal herniation. Mass effect in the cerebrum pushes the supratentorial brain through the incisura; this displacement may lead to a host of neurologic symptoms, as discussed below in Clinical Details. Ascending transtentorial herniation is usually caused by a posterior fossa tumor with mass effect that 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. Extra-axial and intra-axial hematomas of the posterior fossa are less common causes. [see the eMedicine article Posterior Fossa Tumors.] Subfalcine/cingulate herniation Subfalcine herniation occurs when the supratentorial brain is displaced underneath the falx secondary to mass effect. Foramen magnum/tonsillar herniation Foramen magnum herniation occurs when the infratentorial brain is displaced through the foramen magnum secondary to mass effect. Sphenoid/alar herniation Sphenoid/alar herniation results from the supratentorial brain sliding 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 Extracranial herniation occurs with displacement of brain through a cranial defect. FrequencyUnited StatesVarious causes of brain herniation have been identified; the frequency of occurrence largely depends on the particular etiology. InternationalVarious causes of brain herniation have been identified; the frequency of occurrence largely depends on the particular etiology. Mortality/MorbidityMortality and morbidity vary with the causes and treatments of brain herniation. Clinical DetailsDescending transtentorial herniation can cause various symptoms. Compression of ipsilateral cranial nerve III may lead to ipsilateral dilatation of the pupil and abnormal extraocular movements. Compression of the ipsilateral corticospinal tracts in the brainstem may cause contralateral hemiparesis because these tracts decussate at the level of the medulla. Ipsilateral hemiparesis also can occur if there is sufficient mass effect to cause the contralateral cerebral peduncle (Kernohan notch) to be compressed against the adjacent incisura. Other complications include unilateral or bilateral occipital lobe infarction from compression of the posterior cerebral artery. Brainstem hemorrhages are another complication caused by compression or kinking of pontine perforating vessels. Compression on the midbrain may cause hydrocephalus. Ascending transtentorial herniation Ascending transtentorial herniation causing brainstem compression can cause nausea and vomiting, which may progress rapidly to coma if rapid changes occur in the intracranial anatomy. A slow-growing mass in the posterior fossa results in slow changes in the intracranial anatomy; these do not often present as an acute emergency. Subfalcine/cingulate herniation Subfalcine herniation does not necessarily indicate severe clinical symptoms. This type of herniation may lead to the clinical findings of headache, and symptoms may progress to contralateral leg weakness or ipsilateral frontal lobe infarction secondary to compression of the anterior cerebral artery. Foramen magnum/tonsillar herniation Acute compression of the brainstem may result in obtundation and death. However, patients with an Arnold-Chiari I malformation may present with a paucity of symptoms, or they may present with dysesthesia in the extremities with cervical flexion. This is referred to as Lhermitte phenomenon. (See the eMedicine article Chiari I Malformation.) Sphenoid/alar herniation Associated clinical symptoms are usually minimal, although sphenoid herniations are often associated with other types of herniations. Extracranial herniation This finding usually results from a traumatic or surgical cause. The herniated region of the brain may become ischemic, leading to infarction. Preferred ExaminationFor 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. For extracranial herniation, CT scanning or MRI is useful for evaluation. RADIOGRAPHSection 3 of 10
FindingsRadiography is not useful for the diagnosis of brain herniation. CT SCANSection 4 of 10
FindingsWith a descending transtentorial herniation, mass effect in the cerebrum pushes the supratentorial brain through the incisura (see Images 1-2). With ascending transtentorial herniation, 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. With subfalcine/cingulate herniation, the supratentorial brain is displaced underneath the anterior falx (see Image 3). 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 (see Image 6). Degree of ConfidenceCross-sectional imaging provides a high degree of confidence. MRISection 5 of 10
FindingsWith descending transtentorial herniation, mass effect in the cerebrum pushes the supratentorial brain through the incisura. In ascending transtentorial herniation, 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 noted frequently (see Images 4-5). 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 Images 7-8). 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 (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], gadoteridol [ProHance]) have recently been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see the eMedicine topic Nephrogenic Fibrosing Dermopathy. 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. As of late December 2006, the Food and Drug Administration had received reports of 90 such cases. Worldwide, over 200 cases have been reported, according to the FDA. NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. For more information, see the FDA Public Health Advisory or Medscape. Degree of ConfidenceCross-sectional imaging provides a high degree of confidence. ULTRASOUNDSection 6 of 10
FindingsNeonatal intracranial ultrasonography may have a limited role. ANGIOGRAPHYSection 7 of 10
FindingsVascular 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. Degree of ConfidenceThe degree of confidence is high when classic displacement of the deep venous structures is seen. INTERVENTIONSection 8 of 10
The following treatments are used to decrease intracranial pressure, which can prevent or decrease brain herniation: hyperventilation, mannitol therapy, steroid treatment, barbiturate coma, hypothermia, and surgical intervention. In patients with obstructing hydrocephalus, ventriculostomy is appropriate for relieving some symptoms Hyperventilation Drug therapy Steroid treatment has been known to decrease cerebral swelling by decreasing the cell metabolism in the brain, allowing for healing.4 Dexamethasone 12-20 mg/d is given intravenously or orally, depending on the patient's condition. The mechanism of action of barbiturates reflects their ability to depress metabolic function; by decreasing cerebral blood flow, they bring about a reduction of intracranial pressure. As the induction of a barbiturate coma may result in systemic hypotension, it should not be routinely administered to patients in unstable condition. Hypothermia Surgery In cases of descending transtentorial herniation of the brain caused by a large subdural hematoma, emergency surgical decompression is required to prevent irreversible and catastrophic injury to the brainstem, as well as to other areas of the brain. MULTIMEDIASection 9 of 10
REFERENCESSection 10 of 10
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