B Battal MD; M Kocaoglu MD; V Akgun MD; N Bulakbasi MD; C Tayfun MD.
Corpus callosum: Normal imaging appearance, variants and pathologic conditions
Article first published online: 28 DEC 2010
© 2010 The Authors. Journal of Medical Imaging and Radiation Oncology © 2010 The Royal Australian and New Zealand College of Radiologists
Journal of Medical Imaging and Radiation Oncology
Volume 54, Issue 6, pages 541–549, December 2010
How to Cite
Battal, B., Kocaoglu, M., Akgun, V., Bulakbasi, N. and Tayfun, C. (2010), Corpus callosum: Normal imaging appearance, variants and pathologic conditions. Journal of Medical Imaging and Radiation Oncology, 54: 541–549. doi: 10.1111/j.1754-9485.2010.02218.x
Conflict of interest: None of the authors has any conflict of interest, financial or otherwise.
- Issue published online: 28 DEC 2010
- Article first published online: 28 DEC 2010
- Submitted 30 June 2010; accepted 8 September 2010.
- corpus callosum;
- corpus callosum agenesis, magnetic resonance imaging (MRI);
Various types of lesions can occur within the corpus callosum (CC) which is a white matter tract communicating corresponding regions of the cerebral hemispheres. Magnetic resonance imaging is the modality of choice for the evaluation of the CC. In addition, diffusion weighted imaging and diffusion tensor imaging can provide additional information about the CC. The aim of this study is to illustrate the imaging features of the corpus callosum and its pathologies.
The corpus callosum (CC) is the largest white matter tract that crosses the two cerebral hemispheres.1–3 Various types of lesions can occur within this structure such as congenital anomalies with or without various associated abnormalities, toxic and metabolic diseases, ischemic-hypoxic disease, demyelinating diseases, tumours, trauma and transient signal changes.1–14 Ultrasonography (US), computed tomography (CT) and magnetic resonance imaging (MRI) can be used in the assessment of CC. However, MRI is the modality of choice for the evaluation of this structure.1,2,6,7
The aims of this article are to discuss the role of state-of-the-art imaging tools and techniques in the imaging evaluation of CC, to describe the classification of CC pathologies and to recognize the patterns and imaging features of diseases that may involve the CC.
Normal imaging appearance
The CC is divided into four sections: the rostrum, genu, body and splenium. Magnetic resonance images in the three planes (especially in sagittal plane) can be used in detecting normal appearance and developmental and acquired lesions of the CC (Fig. 1).
Lesions of the CC
Agenesis of the CC is one of the common central nervous system malformations. This condition may be encountered as an isolated lesion or, more commonly, in association with a wide variety of other malformations of the central nervous system or other organ systems. The main feature of this entity is the lack of commissural fibers crossing the midline. These fibers instead migrate ipsilaterally and course along the superomedial region of the lateral ventricles and form a structure known as Probst bundles (Fig. 2).1,2
Growth of the CC is primarily from anterior to posterior with the genu forming first, then the anterior body, posterior body and splenium. The exception to this orderly anterior–posterior development is the rostrum. As a consequence of the order of formation, in dysgenesis, the splenium and rostrum are always missing (Fig. 3).1–3
Interhemispheric cysts occur in fewer than 7% of the patients with agenesis of the CC. The Barkovich classification divides cases of interhemispheric cysts associated with agenesis of the CC into two groups. The type 1 cysts are diverticula of the lateral or third ventricles, unilocular and isointense to cerebrospinal fluid (CSF). The type 2 cysts do not communicate with the ventricular system and have four subgroups (2a–d). Type 2a, 2b and 2c cysts are multilocular, whereas type 2d cysts are unilocular. When compared to CSF, type 2b cysts are hyperintense on the T1-weighted images, whereas other three subgroups are isointense (Fig. 4).4
Approximately one-third of all intracranial lipomas arise in the pericallosal region. Depending on their size, either partial or complete agenesis of the CC is present in over 50% of cases with pericallosal lipoma.5 Lipomas of the CC are classically seen as well-marginated masses showing same signal intensities with fat tissue in all MR sequences (Fig. 5).
In Dandy–Walker complex, associated supratentorial anomalies such as callosal dysgenesis and neuronal migration anomalies may be present.6
Syntelencephaly, also known as middle interhemispheric holoprosencephaly, was originally thought to be a semilobar holoprosencephaly type. However, it has been determined to be a unique malformation characterized by failure of cleavage of the dorsal regions of the brain. MRI reveals fusion of cerebral hemispheres in the dorsal region of the brain along with various degree of partial agenesis of the CC (Fig. 6).
Toxic and metabolic diseases
Adrenoleukodystrophy is a sex-linked metabolic encephalopathy of the childhood in which the basic defect is an impaired capacity to degrade very long chain fatty acids, caused by a peroxisomal enzyme defect in beta-oxidation, leading to the demyelination of the central nervous system. Involvement of the peritrigonal white matter and white matter tracts follows the involvement of the splenium of the CC which is usually the first affected site. Enhancing peritrigonal demyelination is the most important imaging feature (Fig. 7).7
The mucopolysaccharidoses lead to the accumulation of glycosaminoglycans in many tissues, such as brain parenchyma. Enlarged perivascular spaces can be prominent in healthy individuals. However, during the natural course of mucopolysaccharidoses, the formation of the enlarged perivascular spaces is usually followed by white matter changes and atrophy (Fig. 8).8
Ischemic-hypoxic disease (periventricular leukomalacia)
Periventricular leukomalacia (PVL) is the most common ischemic brain injury in premature infants. The ischemia occurs in the border zone of the arterial territories. This process typically involves the white matter surrounding the lateral ventricles. Direct corpus callosal involvement in PVL is extremely rare. However, atrophied and irregular CC may be seen in advanced PVL (Fig. 9).9
Multiple sclerosis is a demyelinating disease that commonly affects young women. Although plaques can be found anywhere in the white matter, lesions of the multiple sclerosis characteristically involve the periventricular white matter, internal capsule, CC and pons. The CC lesions that occur along the ventricular margin and callosal-septal interface are considered to be very sensitive and specific for multiple sclerosis (Fig. 10).1
Acute disseminated encephalomyelitis
Acute disseminated encephalomyelitis (ADEM) is an uncommon immune-mediated inflammatory demyelinating disease of the central nervous system. Usually, it is a monophasic illness, which may occur after viral infection or vaccination, in association with rheumatic fever, or without any recognized antecedent disease. Patients with ADEM and multiple sclerosis have a similar pattern of abnormalities on conventional MR images (Fig. 11).10
The most common primary tumour of the CC is glioma. Since the dense compact nature of the white matter tracts in CC makes a barrier to the flow of interstitial oedema and tumour spread, only aggressive tumours, such as glioblastoma multiforme and lymphoma typically cross or involve the CC. The diagnosis of callosal tumours can be made on MRI findings (Fig. 12).1
CC may be traumatised by surgical procedures such as tumour surgery or therapeutic callosotomy. In some cases, seizures may spread from one hemisphere to the other through the CC. Corpus callosotomy may be performed in patients with generalized seizures resistant to multiple seizure medications.11 MRI is an effective method for evaluating callosal surgery and postsurgical changes such as oedema, haemorrhage, infarction and gliosis.
Diffuse axonal injury
Diffuse axonal injury (DAI) is a frequent cause of impaired clinical outcome in patients with traumatic brain injury. The location and severity of traumatic axonal injury is related to various factors, and one of the most common sites of DAI is the CC.12 In the acute and subacute phases, T1 or T2-weighted MR images can be used for detecting hemorrhagic lesions as foci of high signal intensity. On the other hand, T2-weighted images are more sensitive than T1-weighted images in detecting non-haemorrhagic DAI lesions. The use of fluid-attenuated inversion recovery (FLAIR) sequences to show acute non-hemorrhagic DAI and gradient echo sequences to show chronic haemorrhagic DAI lesions are helpful in diagnosis (Fig. 13).13
Transient signal changes
Transient lesions of the CC are significant but non-specific findings. They are probably associated with oedematous and/or inflammatory changes of the CC. Acute withdrawal of the Carbamazepine or various infectious agents such as influenza, rotavirus, Escherichia coli, mumps and adenovirus are reported to be related with this entity. MRI usually reveals an oval-shaped lesion in the splenium of the CC that shows low signal intensity on T1-weighted images and apparent diffusion coefficient (ADC) maps, and high signal intensity on T2-weighted, FLAIR- and diffusion-weighted images. These lesions usually disappear within a few weeks following adequate therapy (Fig. 14).14
Vascular malformations such as cavernomas and arteriovenous malformation (AVMs) may also involve the CC and have the same appearance with the ones located in any part of the central nervous system other than CC (Fig. 15).
MRI findings of the CC may provide clues for understanding the patterns and extent of disease processes and to facilitate diagnosis, staging and in determining prognosis. Diffusion-weighted and diffusion tensor imaging of the CC may be useful especially for the disease processes that are less obvious on conventional sequences such as transient lesions of the CC. CT and US are less accurate imaging modalities for depiction of the CC. However, head US is useful in the newborn period.