The blood contained within them is under very little pressure and they do not attract a very large blood supply themselves. In life their appearence has been compared by authors to rasberries, blackberries or mulberries. They range in size form millimetres to several centimetres. They are occasionally associated with malformations of the veins in the brain where they are located. These malformations are called Deep Venous Anomalies (DVA). DVAs are considered normal variants and they drain blood from the brain to the normal circulation. DVAs are carefully preserved when removing a cavernoma to prevent stroke in the surrounding brain.
With the increased availability of MR scanning it has been recognised that cavernomas are relatively common being found in between 1 in 200 and 1 in 600 MR scans. It has also been recognised that cavernomas may develop de-novo and that they become visible on MR images when blood leaks from them staining the brain or spinal cord.
The majority of cavernomas are isolated lesions. On occasion the cavernoma is the result of a gene mutation. In these cases multiple cavernomas are usually present. Three gene mutations have been identified: CCM1(KRT1), CCM2 and CCM3(PDCD10) but there are cases of inherited cavernoma within families where none of these mutations can be identified suggesting that other mutations remain to be dicovered. Cavernoma has been described in the wake of radiotherapy to the brain although there is no evidence these malformations behave in a more aggressive way.
Cavernoma are best seen on MR scans. Certain specialised MR scan sequences (Gradient echo imaging, T2*-Susceptibility weighted imaging) which are particularly sensitive for blood-breakdown products in the brain increase the chances of detecting small cavernomas. Cavernomas which have not bled overtly may appear as relatively high density lesions on CT scan. Sometimes calcification can be detected within them. They are not visible on angiography although assosciated deep venous anomalies may be demonstrated.
It is possible that the many cavernomas go undetected and do not cause any symptoms. For some they are a source of significant disability. When symptoms occur the type and severity are determined by the location of the cavernoma, whether there has been overt bleeding and how great the volume of the bleeding has been. When cavernomas cause symptoms it is usually because one of the following occur:
Epilepsy: Seizure is the commonest presenting neurological problem with cavernoma. Most cavernomas assosciated with epilepsy are located in the cerebral hemispheres. it is however possible for a cavernoma to co-exist with a seizure disorder while not being causative. This is perhaps why according to the medical literature only 75% of patients achieve seizure freedom in the wake of successful surgical removal of the cavernoma. Most seizures will be manageable with medication as with any other type of epilepsy. If surgical removal of cavernoma is being entertained as a way to improve seizure control, specialist investigation is important to try and demonstrate a causative link betwen seizures and cavernoma and also to determine what type of surgery would be necessary to give the best chance of seizure control. This may require a specialist team of neurologist, neurophysiologist, neuropsychiatrist and neurosurgeons. Investigations such as video-telemetry and sleep EEG my be recommended.
Brain haemorrhage: Bleeding is part of the growing process for cavernomas. small amounts of blood leech from them staining the surrounding brain tissue. There may be evidence on MR scan of bleeding without any symptoms. The significance of such bleeding, if no harm results, is questionable and it should perhaps be distinguished from symptomatic bleeding events translating into symptoms or disability:
Sudden onset of severe headache assosciated with nausea or vomitting
Loss of function e.g. weakness or paralysis of a limb, visual loss
Seizures triggered by the bleeding
Progressive disability: If a cavernoma is situated in a highly eloquent part of the brain (for eample in the brainstem) a small, "covert" haemorrhage, that would be asymptomatic in another location, may translate into progressively worsening disability. It is not inevitable that every cavernoma will behave in that way. The hazards of treating cavernoma in such locations may make it wise to wait on events to see definitely progressive problems before intervening. The decision to act is a nuanced one and the decision is properly shared between patient and clinician.
The risks of removing a cavernoma vary greatly depending on its location and so will be as individual as the patient harbouring the cavernoma.
There is a good deal of uncertainty as to whether aggressive removal of cavernomas, ones that have not bled overtly, provides the patient with any long term health benefits. The patient is however exposed to the short-term risks of the procedure whatever those might be.
Surgery to control seizures is addressed above so this section will concentrate on treatment designed to remove the risk of bleeding in the future.
What happens if a cavernous malformation is left untreated- its natural history- is not well understood at present. Studies estimate that the annual risk of bleeding from a caveroma which has not previously bled may be as low as 0.5% (1 in 200 patients) each year. The risk of having a second haemorrhage after the first one seems considerably higher- perhaps 20% within two years.
It would therefore be logical to offer treatment after a single haemorrhage? Unfortunately it is still not simple. The consequences of such a haemorrhage may not be as severe as a the consequences of a surgical complication. This seems particularly true of the superficially located cavernomas most amenable to removal. In other words the cavernomas most in need if removal to prevent future disability are those most difficult to treat.
Another consideration is the psychological impact of discovering that one harbours a cavernoma. The uncertainty over how it might behave can be very difficult to live with. Therefore each case for treatment needs to be assessed on its own merits. The risks of intervening should be weighted carefully against the estimated risks from the lesion itself. There is seldom pressure of time to arrive at a decision.
If decided that a cavernoma will be best treated, microsurgical removal is the mainstay of therapy.
As referred to above the potential risks are a function of where the cavernoma is located. A brainstem cavernoma will carry considerably more surgical risk than one located in the superficial cortex of the frontal lobe. Image guided surgery (described here) allows cavernomas to be approached with the minimum of disturbance to surrounding brain.
Endovascular treatment is not used for cavernoma as there are only very tiny blood vessels supplying them. They are usually invisible on angiography although an associated deep venous anomaly may be seen.
Stereotactic radiosurgery (SRS) has been used to treat cavernoma. In our practice it is presently reserved only for very symptomatic lesions which are inoperable. There remains uncertainty about its efficacy in altering the natural history of the cavernoma over the long term. Furthermore SRS is not a risk-free undertaking.
Future research is necessary to define the optimal mangement for patient with cavernomas and identify high-risk subgroups. There need to be long term, prospective studies of radiosurgery matched against conservatively and surgically treated groups so that its place can be clarified.