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Cavernous Malformations

Histopathology | Radiologic studies | Natural history | Treatment
Management
| Figures | Other sources of information

Vascular malformations of the brain and spinal cord have typically been classified into four major types. Telangiectasias are typically small (0.3-1.0 cm) lesions composed of capillary type vessels separated from each other by more or less normal-appearing neural parenchyma. Cavernous malformations (cavernous angiomas, cavernomas, cavernous hemangiomas) are well-defined, grossly visible lesions that may reach a significant size. They are composed of a compact mass of sinusoidal-type vessels immediately in apposition to each other without any recognizable intervening neural parenchyma. Venous anomalies (venous angiomas) are composed of anomalous veins with no recognizable direct arterial input. The veins within these anomalies are separated by normal neural parenchyma. True arteriovenous malformations (AVMs) are high flow shunts of blood which are often thought to be the most clinically significant type of malformation.

Cavernous malformations account for some 8-15% of all intracranial and spinal vascular malformations. Including all four types of malformations, the incidence in the general population is on the order of 3-7%. However, many of these are clinically insignificant and are often only radiographic observations. The true incidence of cavernous malformations is difficult to estimate because these lesions may be mixed with other forms of vascular malformations. Cavernous malformations can occur anywhere in the intracranial parenchyma, as well as in the spinal cord or on cranial or spinal nerve roots. Cavernous malformations may be seen as an incidental finding on MRI studies, or they may present with symptoms. Supratentorial lesions typically present with seizures or hemorrhage and focal mass effects. Symptomatic lesions have been described in all age groups. The peak incidence of presentation is usually in the third to fourth decades without a sex predominance.

Cavernous malformations typically hemorrhage in small amounts with bleeding episodes separated by months or years. Therefore a hemorrhage may occur with exacerbation of symptoms followed by gradual improvement in symptoms as the blood is partially absorbed. Prior to MRI and CT scans, this clinical pattern was often misdiagnosed as a demyelinating process. In fact since the advent of CT and MRI studies, some patients who had carried the diagnosis of multiple sclerosis have subsequently been scanned and found to have cavernous malformations as the etiology of their episodic neurologic dysfunction. Although small, repeated hemorrhage is common, some cavernous malformations can present with a significant hematoma and severe neurologic deficit.

Histopathology

Grossly, cavernous malformations are well-circumscribed, lobulated, red to purple, raspberry-like lesions. They vary in size from punctate to several centimeters. On microscopic examination, cavernous malformations are shown to be composed of dilated, thin-walled capillaries that have one layer of endothelial lining and a variable layer of fibrous adventitia. Elastic fibers are absent in the walls of these vascular caverns. There is usually evidence of previous hemorrhage on pathological examination. Thrombosis may be present within some of the lumens.

At times, cavernous malformations may be associated with venous malformations. It is increasingly frequent to recognize a venous anomaly adjacent to a cavernous malformation. When these patients present with hemorrhage, it is often the cavernous malformation that has bled and not the venous anomaly. In fact, it is exceedingly rare for a venous anomaly alone to hemorrhage.

Radiologic studies

Given the fact that cavernous malformations are vascular malformations with low flow, they are "occult" to angiography. On CT scan one may see evidence of hemorrhage of various ages and with contrast administration the lesion itself may enhance.

MRI offers the most sensitive means of suspecting a diagnosis of cavernous malformation. Blood products of varying ages may be present throughout the lesion. This is usually mixed with the small 'caverns' of blood vessels themselves. Often the lesion can be distinguished from adjacent hemorrhage (Figure 1). It is now thought that hemorrhage can occur within the lesion or into surrounding brain parenchyma. Certain individuals may have multiple lesions and careful inspection of the MRI study must be performed to rule out the possibility of small lesions that have not yet hemorrhaged. In addition, families have been noted with a history of cavernous malformation, and multiple lesions are often present in family members. Alternatively, sporadic instances of patients with multiple lesions can occur.

Natural history

When a cavernous malformation bleeds, this may occur as a minimal clinical event, a significant clinical event, or merely be observed as an increase in size of the lesion on MRI studies without any clinical sequelae. The exact incidence of these events remains uncertain. However, two recent studies where a large number of patients were followed for a relatively short interval of time suggested that the annual risk of hemorrhage was 0.7% in one study and 0.25% per lesion per year in another study. Regardless of this apparently small hemorrhage rate, certain patients present with hemorrhages which occur very close together in time. Stepwise neurologic deterioration can occur over several months with each deterioration representing a small hemorrhage.

While it has been stated by some that cavernous malformations in eloquent areas such as speech cortex, motor cortex, or the brainstem may hemorrhage with higher frequency, it may well be that this merely reflects the fact that each hemorrhage is a clinically significant event. The final decision as to whether or not to treat a cavernous malformation must be carefully balanced against the number of years the patient has at risk (i.e., their age) and the exact location of the lesion in terms of potential risk for neurologic deficit with treatment. Other studies have suggested that the actual rehemorrhage rate is higher, on the order of 2% per year which is similar to true arteriovenous malformations. Little information is available on the natural history of risk for patients who are asymptomatic.

Treatment

When patients present with recurrent hemorrhage, progressive neurologic deterioration, or intractable epilepsy, then treatment in the form of surgery should be considered. The decision to operate on a patient with a cavernous malformation must be made based on the exact location of the lesion and its surgical accessibility. By and large surgery offers an excellent option in terms of complete excision of lesion with stabilization of symptoms. Even seemingly deep- seated lesions can be reached using currently available stereotactic techniques. Thus, a relatively small lesion deep in the hemisphere can be reached through a small (1 cm or less) cortisectomy.

Another alternative is that of stereotactic radiosurgery. While this has been used for patients with cavernous angiomas thought to be inoperable and associated with progressive worsening of neurologic symptoms, the results are difficult to analyze. The endpoint of treatment is difficult to assess in that cavernous malformations that have hemorrhaged will decrease in size simply by reabsorption of the blood around the lesion. The only true test of whether radiosurgery (focused radiation) will offer protection from subsequent hemorrhage will be results obtained after following patients for long intervals of time. This type of follow-up is currently in process and hopefully will shed light on this very issue. The risks of focused radiation for cavernous malformations appears to be somewhat higher than true arteriovenous malformations of the same size. The exact reason for this difference in complication rate remains unknown but is thought to relate possibly to the lower flow present in cavernous malformations. In addition, as with large true AVMs, the risk of radiosurgery increases with larger lesions.

Management

As patients are encountered with cavernous malformations, the reason for the discovery of the lesion must be factored into the final decision as to

whether treatment should be offered. In older patients with lesions which are difficult to reach surgically, conservative management may be entirely appropriate. However, for younger patients with more accessible lesions, removal of lesions may help control epilepsy, reduce worsening of neurologic deficit or prevent any subsequent hemorrhage. For lesions in critical locations in the brain and brainstem, complications can occur with treatment, and the rate of these complications must be carefully balanced against the natural history of the lesion itself.

Figure 1. Small cavernous malformation in the left opercular region in a 38-year-old man who presented with mild speech abnormality. The MRI study demonstrates the small hemorrhage adjacent to the malformation (arrow).

Figure 2. MRI study on the same patient as shown in Figure 1 five years after the initial study. At the age of 43, he had his third episode of speech abnormality with an aphasia which required several weeks to clear. As can be seen, the T1 weighted MRI study demonstrates a cavernous malformation (arrow) as well as a fairly large areas of hematoma surrounding the lesion. The lesion was surgically excised with resultant transient right arm weakness which resolved completely over two weeks' time. The patient made a normal neurologic recovery.

Other Information sources on cavernous malformations

1. Robinson JR Jr, Awad IA, and Little JR. Natural history of the cavernous angioma. J Neurosurg 1991; 75:709-714.

2. Curling OD, Jr, Kelly DL Jr, Elster AD, et al. An analysis of the natural history of cavernous angiomas. J Neurosurg 1991; 75:702-708.

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