Connective-tissue diseases, arteriosclerosis and hypertension, alone or in combination, lead to various degrees of dilatory arteriopathy that may lead to massive vascular changes.
The most frequent of these are large fusiform aneurysms—i.e., long, spindle-shaped dilation of the basal cranial arteries. The basilar artery is often affected (megadolichobasilar artery), or more rarely the internal carotid artery or middle cerebral artery (Fig. 1.3-6). These changes usually become apparent clinically as a result of thromboembolic ischemia or neurological deficits due to local pressure damage, or rarely through rupture and intracranial bleeding. Treatment therefore usually consists of drug-based secondary prophylaxis. Surgical and endovascular treatment approaches are associated with a high level of procedural risk. They are usually attempted if local pressure damage has led to disability. Recently, flow diverters—extremely closely-woven stents—have been used in these conditions in order to modulate flow in the diseased vessel and eventually seal off the aneurysm.
The old term “mycotic aneurysms” (Fig. 1.3-7) covers aneurysms with an infectious and embolic pathogenesis. These are usually located on peripheral branches of the intracranial arteries and may be either saccular or fusiform. Treatment is indicated in order to prevent intracranial bleeding. If selective occlusion of the aneurysm is not possible, the affected vessel has to be occluded endovascularly or surgically together with the aneurysm.
Dissecting aneurysms occur intracranially only rarely. Due to the narrow vascular caliber, dissection as the cause of this type of aneurysm can usually not be confirmed on MRI and it can only be postulated. Here again, the location and shape of the aneurysm suggest the diagnosis. Morphologically, these aneurysms tend to be fusiform rather than saccular. The last segment of the vertebral artery (V4) is frequently affected. In this location, endovascular occlusion is the treatment of choice if the contralateral vertebral artery is adequate. In other cases (Fig. 1.3-8), treatment with a flow diverter or stent may be considered.
Traumatic intracranial aneurysms are also rare. The “trauma” usually involves iatrogenic injury to the internal carotid artery near the base of the skull, or more rarely a skull base fracture (Fig. 1.3-9). As these aneurysms may cause life-threatening bleeding intracranially or into the nasopharynx, they should be identified and treated at an early stage. Due to their position inside the skull base, surgical treatment is not usually possible and an endovascular approach is preferable. Here again, vascular occlusion is the treatment of choice when there is an adequate collateral supply, especially if endovascular reconstruction of the vascular lumen is not possible. As mentioned above, high-density and conventional neurostents are available for the purpose. This group of aneurysms also includes aneurysms of the internal carotid artery that rupture into the cavernous sinus, as well as iatrogenic vascular injuries—e.g., during pituitary surgery.
Fig. 1.3–6a-e A fusiform aneurysm in the basilar artery on digital subtraction angiography (a, b) and on a magnetization-prepared rapid gradientecho (MP-RAGE) sequence after intravenous contrast administration, in three spatial directions (c-e).
Fig. 1.3–7a, b “Mycotic aneurysm.” Peripheral fusiform aneurysm in the left middle cerebral artery; a “mycotic aneurysm” may have this appearance.
Fig. 1.3–8a-f Dissection-related aneurysm. (a) Digital subtraction angiography (DSA) of the left vertebral artery after subarachnoid bleeding, with evidence of slight wall irregularities. (b) At the follow-up examination, magnetic resonance angiography reveals dissection of the left vertebral artery. (c, d) A fusiform aneurysm at the level of the dissection, on DSA with 3D reconstruction and subtraction. (e, f) Findings after implantation of a flow diverter (f); 3D reconstruction of the check-up DSA (e).
1.3.2 Arteriovenous malformations and dural fistulas
1.3.2.1 Clinical picture in AVM
Vascular malformations in the brain and meninges are pathological shunts between the afferent arteries to the brain or dura and the efferent veins or venous sinuses.
AVMs are located in the cerebral parenchyma and are primarily supplied by afferent cerebral vessels; dural vessels may be recruited secondarily via transdural anastomoses. Drainage into the large venous sinuses takes place via parenchymal veins. The shunt (nidus) is located in the brain parenchyma and may have a plexiform, fistulous, or mixed structure. In the fistulous type, a very strong afferent artery opens directly into a vein without an intermediate vascular plexus. AVMs occur much more rarely than aneurysms. They are congenital vascular malformations with a tendency to grow larger during the course of life. They can occur in any location in the brain. They are usually classified using the criteria included in the Spetzler and Martin score, which was developed in order to assess operability, with the risk being classified relative to the size, location and type of venous drainage (Table 1.3-3).
Fig. 1.3–9a, b Traumatic (false) aneurysm. (a) Fractures in the middle and anterior cranial fossa (arrowheads) were diagnosed on the right side on a CT 6 months previously. (b) Due to recurrent epistaxis, a “false” aneurysm on the right internal carotid artery was in the meantime occluded with coils. One month later, massive bleeding from the nasopharynx occurred. The DSA shows the aneurysm, with extravasation into the sphenoid sinus (black arrow). The coils can be seen at the lower edge (white arrow). The internal carotid artery was occluded with additional coils.
Table 1.3–3 Spetzler-Martin grading of surgical risk in arteriovenous malformations (1 point = no risk, 5 points = high risk).
| Size Small | (< 3 cm) | 1 point |
| Medium (3–6 cm) | 2 points | |
| Large(> 6 cm) | 3 points | |
| Site | Not “eloquent” | 0 points |
| “Eloquent” | 1 point | |
| Venous drainage | Superficial veins | 0 points |
| Deep cerebral veins | 1 point |
1.3.2.2