Brain Imaging in Cavernous Angiomas

Updated: Jan 07, 2016
  • Author: James C Jacobsen, MD; Chief Editor: James G Smirniotopoulos, MD  more...
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Overview

Overview

Cavernous angiomas belong to a group of intracranial vascular malformations that are developmental malformations of the vascular bed. These congenital, abnormal vascular connections frequently enlarge over time. The lesions can occur on a familial basis. Patients may be asymptomatic, although they often present with headaches, seizures, or small parenchymal hemorrhages. [1] Cavernous angiomas appear in the images below.

Large, right frontal and left occipital cavernous Large, right frontal and left occipital cavernous angiomas. Axial nonenhanced CT image demonstrates a large heterogeneous-appearing lesion in the right frontal region. The lesion is primarily hyperattenuating in its central region, with a more diffuse, peripheral area of increased density resulting from calcification and small areas of hemorrhage.
Large right frontal and left occipital cavernous a Large right frontal and left occipital cavernous angiomas. Nonenhanced axial CT image demonstrates findings of a large primarily hyperattenuating mass in the left occipital region. Note the relative lack of mass effect on the surrounding parenchyma here and on the MRI scans presented in this article.
Large, right frontal and left occipital cavernous Large, right frontal and left occipital cavernous angiomas on a T1-weighted axial MRI. These 2 heterogeneous masses have a reticulated core of high and low signal intensities surrounded by a hypointense rim of hemosiderin.
Gradient-echo axial MRI demonstrates increased con Gradient-echo axial MRI demonstrates increased conspicuity in large right frontal and left occipital cavernous angiomas. The hemosiderin rim demonstrates a blooming artifact as a result of its increased magnetic susceptibility effects.

Types of vascular malformations are differentiated from one another on the basis of their gross and histopathologic characteristics. Traditionally, intracranial vascular malformations are grouped into the following 4 types:

  • Capillary malformations (or telangiectasias)
  • Cavernous malformations ( cavernous angiomas/hemangiomas)
  • Venous malformations
  • Arteriovenous shunting malformations

Newer schemes add the following 2 classifications: arterial malformations (no arteriovenous shunting) and mixed malformations.

Cavernous angiomas can be found in any part of the brain, because they can occur at any location along the vascular bed. Intracranial, extracerebral cavernous angiomas also occur, but these are less common. Cavernous angiomas also can occur in the spinal cord, where they frequently coexist with multiple brain lesions.

Although most cavernous hemangiomas can simply be followed up over time, surgical removal is an option in lesions causing significant morbidity. Because cavernomas are well circumscribed and surrounded by a gliotic rim, surgical removal is relatively simple. Control of hemorrhage is relatively easier because of the flow of blood through the lesions is slower than that expected in more highly vascularized lesions with higher flow rates.

Preferred examination

Although cavernous angiomas may be apparent and although they can be diagnosed by using computed tomography (CT) scans, CT scanning is not the imaging modality of choice. CT scan findings are compatible not only with cavernous angiomas but also with low-grade tumors, among other entities.

The sensitivity of magnetic resonance imaging (MRI) to flowing blood and blood products of varying ages, as well as the greater contrast resolution of MRIs, greatly increases the specificity of MRI compared with that of CT scanning. Combining multiple MRI sequences has largely eliminated misdiagnosis of cavernous angiomas, because they have relatively specific signal characteristics. Additionally, gradient-echo imaging, with its increased sensitivity to susceptibility artifact, is useful in the detection of smaller and concomitant lesions, which may not be detected with traditional sequences. [2, 3, 4]

CT scanning and MRI can be used in the follow-up monitoring of patients with known cavernous angiomas, particularly when hemorrhagic events are suspected. Although the MRI appearance of cavernous angiomas is not helpful in predicting future bleeds, MRI is the method of choice for the long-term follow-up of patients with cavernous angiomas and for the assessment of family members in whom similar lesions are suspected. In addition, MRI is extremely helpful in presurgical planning to assess the extent of the lesion, define borders, and plan the surgical approach and exposure.

Most cavernous malformations are angiographically occult, and when they are evident on angiograms, the findings are nonspecific. When the lesions occur in combination with other vascular malformations, as they do in as many as 30% of patients with venous malformations, MRI characteristics become more complicated and less specific. In these patients, angiography can be helpful in further defining the lesions.

Limitations of techniques

CT scanning has only a limited role in the diagnosis of cavernous angiomas, largely because of its relative lack of specificity. CT scan findings are compatible with low-grade gliomas, hematomas, granulomas, and inflammatory conditions such as tuberculomas and sarcoidomas. When calcified and located near the dura, cavernous angiomas can even resemble meningiomas. CT images also cause small lesions to be missed altogether, and cavernomas, when they present as acute intracerebral hematomas, may not be detected by using nonenhanced CT scanning.

MRI may cause small lesions to be missed if T2-weighted pulse sequences, such as T2-weighted fast spin-echo sequences, are used because these can be less sensitive to chronic hemorrhage. Additionally, even standard T1- and T2-weighted images can fail to depict minute concomitant lesions. Therefore, T2-weighted gradient-echo sequences, with their increased magnetic susceptibility effects, always should be performed during an evaluation for smaller or multiple lesions that may not be visible on standard spin-echo images.

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Computed Tomography

With all relative imaging methods, dividing cavernomas into 3 components is helpful. These include (1) the peripheral pseudocapsule composed of gliotic hemosiderin-laden tissue, (2) the irregular intersecting connective tissue septa separating the sinusoidal spaces, and (3) the central vascular area composed of slow-flowing sinusoidal spaces.

Nonenhanced CT scans demonstrate cavernomas as focal oval or nodular-appearing lesions that demonstrate mild-to-moderate increased attenuation, without mass effect on the surrounding brain parenchyma. Areas of calcification and hemosiderin deposits in the walls of the fibrous septa, combined with the increased blood pool within the lesion, are responsible for hyperattenuation on nonenhanced images. CT scans demonstrate calcifications in as many as 33% of cavernomas. If the lesions are older, they can contain central hypoattenuating nonenhancing areas, which correspond to cystic cavities from resorbed hematomas.

Contrast enhancement can vary from minimal to striking, although 70-94% of cavernous malformations demonstrate mild-to-moderate enhancement after the intravenous administration of contrast agent. In large part, this enhancement results from the increased blood pool within the vascular component. The slightly heterogeneous and mottled enhancement results from the fibrous intravascular septa, and the peripheral rim of decreased attenuation results from the pseudocapsule of gliotic tissue surrounding the lesion.

Mass effect is not common unless the lesion is associated with recent hemorrhage. Cavernomas may not be detected when they present as acute intracerebral hematomas on nonenhanced CT images. After the administration of contrast material, cavernomas may be identified as areas of nodular enhancement adjacent to the hematoma.

Any hemorrhage found on CT scans in a relatively young patient should be characterized further, and cavernous angioma must be considered a possible etiology. In the workup of a patient with a seizure disorder, cavernous angioma must be considered the underlying etiology, especially if the patient is aged 20-40 years.

Calvernous malformations detecting by using CT include other occult vascular malformation (thrombosed AVM, capillary telangiectasia), glioma (low-grade astrocytoma or oligodendroglioma), and metastatic melanoma. (See the images below.)

Large, right frontal and left occipital cavernous Large, right frontal and left occipital cavernous angiomas. Axial nonenhanced CT image demonstrates a large heterogeneous-appearing lesion in the right frontal region. The lesion is primarily hyperattenuating in its central region, with a more diffuse, peripheral area of increased density resulting from calcification and small areas of hemorrhage.
Large right frontal and left occipital cavernous a Large right frontal and left occipital cavernous angiomas. Nonenhanced axial CT image demonstrates findings of a large primarily hyperattenuating mass in the left occipital region. Note the relative lack of mass effect on the surrounding parenchyma here and on the MRI scans presented in this article.
Typical nonspecific appearance of a left frontal-l Typical nonspecific appearance of a left frontal-lobe cavernous angioma on a nonenhanced CT scan in this young adult who presented with new-onset seizures. Note the lack of mass effect or surrounding vasogenic edema.

 

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Magnetic Resonance Imaging

Cavernous angiomas represent approximately 1% of intracranial vascular lesions and 15% of cerebrovascular malformations. With the advent of MRI, cavernous angiomas are currently the most commonly identified brain vascular malformations. In early studies of major autopsy reports, the calculated prevalence was 0.02-0.53%. MRI of lesions with the appearance of cavernous hemangiomas provided information that led to a prevalence of 0.39-0.9%. The detection of previously unidentified asymptomatic lesions by using MRIs has been raised the estimated overall prevalence to 0.45-0.9%.

MRI findings of parenchymal cavernous angiomas demonstrate typical, popcornlike, smoothly circumscribed, well-delineated complex lesions. The core is formed by multiple foci of mixed signal intensities, which represents hemorrhage in various stages of evolution. [5, 6, 7, 8, 9]

Acute hematoma containing deoxyhemoglobin is isointense on T1-weighted images and markedly hypointense on T2-weighted images. Subacute hematoma, which contains extracellular methemoglobin, displays hyperintensity on both T1- and T2-weighted images because of the paramagnetic effect of the methemoglobin.

The interspersed fibrous-containing elements demonstrate mild hypointensity on T1- and T2-weighted images because they contain a combination of calcification and hemosiderin. The heterogeneous core typically is surrounded completely by a low-signal-intensity hemosiderin rim on T1-weighted images. The hypointensity of this rim becomes more prominent, or blooms, on T2-weighted and gradient-refocused images because of the magnetic susceptibility effects.

Smaller cavernomas may appear as focal hypointense nodules with T1- and T2-weighted sequences. The small lesions are depicted more clearly and are more numerous on gradient-echo images because of the increased susceptibility effects of the sequences. Sequential gradient-echo images also have been shown to define these punctate lesions further when the echo time is lengthened; this finding suggests that such lesions contain paramagnetic substances.

When imaged with time-of-flight techniques, the methemoglobin in the central core of a cavernous malformation may mimic flowing blood. However, a subsequent phase-contrast magnetic resonance angiogram obtained with low-velocity encoding (10-20 cm/s) should not demonstrate flow or abnormal vascularity; this finding helps exclude a vascular lesion.

Typically, cavernous angiomas are not associated with mass effect or edema and do not demonstrate a feeding artery or draining vein, except when associated with other vascular malformations with similar features. Cavernous angiomas are reported to be associated with venous malformations, which typically demonstrate a draining vein. Often, conventional angiography can be helpful for further characterization in these mixed cases.

Calvernous malformations detected by using MRI include other occult vascular malformation (thrombosed AVM/aneurysm, capillary telangiectasia), hemorrhagic primary or secondary neoplasm (metastatic melanoma, thyroid, renal cell, choriocarcinoma), amyloid angiopathy, treated or prior infection (toxoplasmosis, cysticercosis), nultiple hemorrhages associated with blood dyscrasia (disseminated intravascular coagulopathy, leukemia), and sequelae of diffuse axonal injury.

Large, right frontal and left occipital cavernous Large, right frontal and left occipital cavernous angiomas on a T1-weighted axial MRI. These 2 heterogeneous masses have a reticulated core of high and low signal intensities surrounded by a hypointense rim of hemosiderin.
Gradient-echo axial MRI demonstrates increased con Gradient-echo axial MRI demonstrates increased conspicuity in large right frontal and left occipital cavernous angiomas. The hemosiderin rim demonstrates a blooming artifact as a result of its increased magnetic susceptibility effects.
This image demonstrates increased sensitivity of g This image demonstrates increased sensitivity of gradient-echo sequences compared with T1- and T2-weighted sequences in the detection of smaller lesions. This T1-weighted MRI fails to demonstrate the multiple, tiny cavernomas demonstrated on the gradient-echo image.
This T2-weighted axial MRI does not demonstrate we This T2-weighted axial MRI does not demonstrate well the multiple tiny cavernomas seen with a gradient-echo sequence.
Gradient-echo MRI demonstrates multiple, bilateral Gradient-echo MRI demonstrates multiple, bilateral punctate and rounded areas of hypointensity within the periventricular and subcortical white matter. The largest lesion in the periventricular frontal white matter just anterior to the frontal horn of the left lateral ventricle near the genu of the corpus callosum. Multiple smaller lesions are seen both anteriorly and posteriorly.
T1-weighted MRI demonstrates a small hyperintense T1-weighted MRI demonstrates a small hyperintense lesion in the left temporal cortex with a hypointense rim. This smaller lesion is demonstrated better and is more apparent on a T2-weighted image and on a gradient-echo image.
T2-weighted MRI demonstrates the hypointense bloom T2-weighted MRI demonstrates the hypointense blooming artifact within the lesion in the left temporal lobe, although the blooming is not nearly as marked as seen on a gradient-echo image.
The lesion becomes obvious on this gradient-echo i The lesion becomes obvious on this gradient-echo image. Even this relatively small temporal-lobe lesion is detected easily with this pulse sequence. Because cavernous angiomas are often multiple, a gradient-echo sequence should be performed in addition to standard T1- and T2-weighted sequences to carefully identify all concomitant lesions, as clinically indicated.
T1-weighted MRI demonstrates a pontine cavernous a T1-weighted MRI demonstrates a pontine cavernous angioma. Note the slightly hypointense lesion located centrally and to the right near the middle cerebellar peduncle. Given its location, a significant hemorrhage can have a clinically devastating result. This lesion demonstrates that location, more than size, is a critical factor in predicting outcome or sequelae of future hemorrhage.
T2-weighted MRI of a pontine cavernoma. T2-weighted MRI of a pontine cavernoma.
Minor amounts of hemosiderin can make smaller lesi Minor amounts of hemosiderin can make smaller lesions evident on gradient-echo MRIs, as seen in this pontine cavernoma.
T1-weighted MRI of the classic popcornlike appeara T1-weighted MRI of the classic popcornlike appearance of a large left-sided cavernous angioma, which primarily affects the temporal lobe.
T2-weighted MRI of a large cavernoma. Note the min T2-weighted MRI of a large cavernoma. Note the minimal mass effect of this large lesion.
Gradient-echo MRI demonstrates the large amount of Gradient-echo MRI demonstrates the large amount of blood-breakdown products within this large lesion. Repeated hemorrhage is believed to contribute to the slow growth of some cavernomas over time.
T2-weighted MRI of a left frontal cavernoma. T2-weighted MRI of a left frontal cavernoma.
On this T1-weighted MRI, the lesion begins to take On this T1-weighted MRI, the lesion begins to take on the more characteristic mixed-signal-intensity appearance of a cavernoma. Hyperintense bilateral arclike artifact from the patient's metallic dental braces is seen centrally over the basal ganglia and thalamic regions.

 

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Angiography

In general, cavernous malformations are considered angiographically occult, and when they are evident on angiographic studies, the findings are nonspecific. [10] MRI has largely replaced conventional angiography in the diagnosis of cavernomas. However, when the lesions occur in combination with other types of vascular malformations, as they do in as many as 30% of patients with venous angiomas, MRI characteristics become more complicated and less specific. In these patients, angiography can help to further define the lesions.

Most cavernous malformations (37-48%) correspond to avascular masses on conventional angiograms. Because of the extremely slow flow of blood through these lesions, cerebral arteriographic findings are often normal. If the lesions are large enough or associated with hematomas, mass effect on adjacent vessels can be appreciated. The avascular appearance is the result of compression or destruction of vascular channels by hemorrhage, thrombosis, and generalized slow flow because of the small size of the connecting sinusoidal vessels with the peripheral normal parenchymal vessels.

When lesions are smaller and not associated with hematomas, 20-27% of angiograms demonstrate normal findings. Capillary blush is demonstrated at 12-20%. The capillary blush may not be visualized during the first injection; if the injection is repeated a few minutes later with a larger volume and over a longer period, the blush can be demonstrated better. Capillary blush is by no means a specific finding, and it can be seen in a variety of other processes and entities.

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