Cavernomas are malformations of blood vessels formed from thin-walled, venous caverns. There is no arterial supply; cavernomas are characterised haemodynamically by slow venous blood flow with partial thrombosis.
Due to the presence of blood clots of different ages, the morphology of cavernomas is diverse, with the resorption process often leading to the deposition of haemosiderin in and around the lesion. In many cases, an enlarged vein (DVA; deep venous anomaly) is seen in association with the lesion.
The size of cavernomas varies from a few millimetres to several centimetres and, intraoperatively, typically shows a mulberry-like appearance with lobulated, dark red caverns.
Since the advent of MRI, cerebral cavernomas are diagnosed with increasing frequency. They have a prevalence of between 0.4 and 0.5% in the general popualtion and occur both sporadically and occasionally as a hereditary phenomenon.
On MRI, cavernomas appear as well-defined, round structures, often demonstrating a central area with mixed signal on T2-weighted images representing the products of bleeding at different time points and surrounded by a ring of reduced intensity (haemosiderin deposition). On computer tomography, cavernomas often appear as patchy areas of increased density with variable, weak contrast uptake. Occasionally points or larger clumps of calcification are seen.
Symptoms of cavernomas in the brain are highly dependent on the position of the lesion and whether it has bled. The spectrum thus extends from an entirely asymptomatic course to epileptic seizures or severe focal deficits (e.g. paralysis or speech disorders) following a bleed in an eloquent area.
Due to their position amongst neuronal pathways and nuclei, cavernomas in the brainstem often result in a rapid onset of neurological symptoms. When multiple, small bleeds occur within the lesion, the cavernoma may increase in size like a balloon and compress the surrounding structures. Pressure on the small arteries in the brainstem increases the risk of regional blood flow disturbance and stroke.
The risk of bleeding from a cavernoma has been the subject of many studies. With respect to cavernomas in the cerebrum, the risk appears to be between 0.25 and 2.6% per year. In contrast, cavernomas in the brainstem are associated with an increased risk of up to 7% per year in the case of symptomatic lesions.
The therapeutic management of cavernomas is determined by many factors. In general, asymptomatic cavernomas, which are discovered incidentally need no therapy and may be observed in regular intervals with MRI scans. In the case of symptomatic cavernomas, a surgical excision of the lesion should be considered, taking into account the position of the cavernoma and the risk of the operation. In each case the individual risk constellation must be determined and weighed up.
In brainstem cavernomas the appraisal of the risk and benefit associated with an operation is especially important. In principle, every cavernoma that shows evidence of bleeding or becomes symptomatic represents a risk and, as a result of the statistically increased probability of further bleeding, microsurgical resection should be considered as a therapeutic option. This is particularly true in the context of recurrent bleeding and neurological deterioration. The spatial relationship of the cavernoma to the surface of the brainstem and the position of the cranial nerves and neuronal pathways is directly related to the feasibility of surgery, the choice of surgical approach and the individual risk profile of an operation. In this exquisitely sensitive region, precise planning prior to the operation is of utmost importance.
With high resolution MRI and DTI tractography, the important pathways of the brainstem can be visualised (the corticospinal tract, the medial lemniscus and the cranial nerve nuclei). With this information, the most minimally invasive approach to the cavernoma can be defined.
The operation itself is performed under constant microelectrical neuromonitoring, similar to a radar directed from the operative field into the deep structures, which alerts the operator to the presence of sensitive structures. With this approach, it is usually possible to carefully dissect along the surface of the cavernoma and to remove it without injury to surrounding structures.