Deep cavernomas are considered to be those occurring in the brainstem (midbrain, pons or medulla), cerebellar nuclei, thalamus and basal ganglia. A typical MRI appearance can be seen in the adjacent image.
What are the chances of recovery from a bleeding deep cavernoma?
In a large study reported in the Journal of Neurosurgery in 1997 (Porter et al vol 87, page 190) 37% of patients fully recovered all function following a stroke from a deep cavernoma, 36% had partial recovery and 27% had no recovery of function. This is similar to the experience at the Sydney Aneurysm and AVM Neurosurgical Centre. Whilst it is usual for superficial cavernoma bleeds to fully recover this is not the experience with the deeper cavernomas.
What are the chances of a deep cavernoma bleeding?
From the time a cavernoma is diagnosed the chances of being unaffected by bleeding over the next 5 years is 57%, over the next 10 years is 33%, over the next 20 years is 11% and over the next 25 years is 6% (Porter et al, J Neurosurg 87:190, 1997). Although some studies have suggested that the risk of bleeding is not influenced by mode of presentation it is likely that if a large number of deep cavernomas could be followed that those with a history of having bled in the past are more likely to bleed in the future.
What can be affected when a deep cavernoma bleeds?
The brainstem, thalamus, and deep cerebellar nuclei are very important regions of the brain. The brainstem is that part of the brain that conducts all the nervous impulses from the body to the brain (and vice-versa). It occupies a very small volume and is no more than an inch in cross section or length in much of its length. A small bleed into this tissue from cavernoma can lead to almost any part of the body being affected in strength, co-ordination (including walking, swallowing, vision and breathing) and sensation (all modalities including pain, temperature, touch, knowledge of the position in space, hearing and taste). The brainstem also contains a very important centre for keeping a person awake and damage to this centre can lead to coma. The thalamus is a little higher than the brainstem and connects to both the cerebrum and the brainstem. This area of the brain acts as a relay and process centre for nervous impulses coming from the body (and other regions below the cerebrum) that are entering the cerebrum. It is important for sensation (including pain, temperature, touch, knowledge of the position in space and vision).
How are brainstem, deep cerebellar, thalamic or basal ganglia cavernomas treated?
Watch and wait.
It is difficult to know what the risk of bleeding is from a cavernoma that has remained silent. The serendipitous discovery of a cavernoma does occur and can create a significant dilemma as to recommended treatment. However, for those brainstem (and other deep) cavernomas that have been diagnosed after a bleed the chances of being unaffected by bleeding over the next 5 years is 57%, over the next 10 years is 33%, over the next 20 years is 11% and over the next 25 years is 6%. If bleeding occur ). Full recovery can be expected in 37% of following a stroke, 36% have partial recovery and 27% will have no recovery of function lost. What function that can be lost is dependent on the brain tissue damage but may include a loss of function of arms, legs, face, swallowing, or speech as well as a loss of feeling on many parts of the body. Double vision and loss of balance are also common.
Microsurgery involves removing a part of the skull overlying the cavernoma (to be replaced at the end of surgery) and computerised guidance to where the cavernoma is located. When this has been found, with the aid of a microscope for vision, the cavernoma is separated and then removed from the surrounding brain tissue. Although the margin of error is very low for such surgery there is a small rim of non-functioning brain surrounding the cavernoma and the cavernoma itself can be readily identified and separated from the brain. The surgery for brainstem cavernomas, in my experience of just over 50 of such cases, has a low risk of death (no patient as of October 20, 2003) and a risk of permanent new deficits of approximately 25% (almost always associated with a loss of function that does not cause a loss of independence). I believe the risk of surgery is like having another bleed but it will be most likely the last bleed that occurs. However, 10% of patients will develop a new cavernoma in the surgical bed. The reason for this is not certain. It may be because of residual cavernoma that could not be seen at the original surgery, it may be because in the region of brain tissue cavernomas are prone to form or it may be due to the fact that the underlying reason for the cavernoma development cannot be treated (such as high pressure in the veins). Although an MRI can easily diagnose a cavernoma before surgery it is more difficult following surgery because of the previous effects of the bleeding. When a cavernoma bleeds, the red blood cells eventually breakdown. This leaves iron that remains in scavenger cells around the cavernoma. It is this iron that gives much of the characteristics of a cavernoma identifiable on the MRI. When we operate it is imperative not to remove the surrounding brain and therefore some of the iron remains. This will be detected on the post-operative MRI scan. This makes confirmation of complete resection difficult. Despite the limitations of scanning confirmation we do know that only 10% of cases are likely to bleed at any time after surgery. This is approximately the risk of one year without treatment.
This is no longer recommended in most cases because it may not alter the risk of bleeding from a cavernoma (Karlsson et al, J Neuroosurg 88:293, 1998) and the risk of radiation damage to the brainstem may be as high as 41% (Pollock et al, J Neurosurg 93:987, 2000). This can be more disabling than the effects of the cavernoma bleeding.