gms | German Medical Science

Treatment of skull base tumours especially those of larger extend and hypervascularization requires interdisciplinary management including neurosurgery, ENT surgery, maxillofacial surgery, ophthalmology, and radiooncology. For treatment decisions an optimized diagnostic workflow helps to select patients suitable for different treatment options and to decide whether a single or combined approach is necessary. Besides the clinical data mainly neuroradiological imaging, both CT and MRI including different MR-angiography techniques are very sensitive to almost any pathology in the skull base. The neuroradiologist uses anatomic location and imaging characteristics to arrive at a best approximation of the diagnosis preoperatively. Dynamic MR angiography or digital subtraction MR angiography is a time-resolved MR imaging technique using the injection of a contrast agent bolus and allows to observe the dynamics of its propagation [Ref. 1], [Ref. 2]. This technique is advantageous especially for vascular malformations or tumours with high vascularization, because the hemodynamics of the pathologic process can be assessed [Ref. 3], [Ref. 4], [Ref. 5], [Ref. 6], [Ref. 7].

Preoperative embolizations of hypervascularized tumours of the skull base are commonly used and were mainly applied in paragangliomas (tympanic and jugular foramen glomus tumours), juvenile nasopharyngeal angiofibromas, seldom in skull base meningiomas because tumour supplying vessels mostly arise from ICA, and also seldom in carcinomas and metastases [Ref. 8], [Ref. 9], [Ref. 10], [Ref. 11]. For devascularization of tumour tissue different embolic materials, such as Gelfoam, lyophlized Dura, butyl-2-cyanoacrylate (NBCA), silastic spheres, polyvinyl alcohol (PVA) particles, Trisacryl Gelatin microspheres (Embospheres), and liquid embolic material have been used with varying results [Ref. 8], [Ref. 9], [Ref. 10], [Ref. 11], [Ref. 12], [Ref. 13], [Ref. 14]. To date, particle embolizations with PVA or embospheres are most common in the treatment of hypervascularized tumours.

Exemplary, we demonstrate two cases with non-target embolization which were treated with embospheres and discuss the natural history of the embolic event.

During more than 20 years of experience with embolization of hypervascularized tumours, we mainly use PVA or embosphere particles (40–300 microns) and in selected cases liquid agents such as Ethibloc or NBCA in different concentrations. Before embolization a thorough analysis of the complete angioarchtecture of the tumour vessels, the feeding arteries, especially of collaterals and the draining type is mandatory. There exist many anastomoses between the external carotid artery (ECA) and the internal carotid artery (ICA) as well as between the ECA and the vertebral artery (Table 1 [Tab. 1]). All these anastomoses should be detected angiographically before embolization starts.

We present a 42-year-old female with petroclival meningioma and tumour related occlusion of the ipsilateral ICA. After thorough analysis of the angiogram, we detected an anastomosis between the middle meningeal and ophthalmic artery. Although incomplete embolization was done to prevent non-target embolization into the ophthalmic artery, MR showed infarcts in the ipsilateral MCA territory as well as in the posterior circulation with vermian infarct. We used embospheres with a size of 40–120 micron. The patient recovered and was treated by surgery two months later.

The second patient was a 78-year-old male with histological proven thyroid gland carcinoma of the paranasal sinuses. The reason for embolization was recurrent epistaxis with relevant haemoglobin decrease. The patient was embolized with embospheres (40–300 micron). During embolization an anastomosis was recognized between the left meningohypophyseal trunk and the ascending pharyngeal artery. Therefore embolization was stopped. During follow-up the patient did not wake up adequately from ITN. MR showed multiple embolic infarcts in all vascular territories although embolization of branches of both ICA and ECA and not of vertebral artery took place. The patient died a few days later.

To avoid false embolization into non-tumourous vessels all anatomical details have to be considered to find the right superselective position of the microcatheter, since proximal locations have a higher risk of embolization into existing but not visible extra-intracranial anastomoses. The identification of these collaterals close to the tumour site which can be called as “dangerous vessels” is absolutely necessary to avoid a non-target embolization. Moreover one has to be aware, that collaterals even can only become visible during embolization which requires the application of a mixture of contrast medium and particles and a permanent angiographic control with high pressure contrast injection in several steps during embolization.

The reason for non target embolization in the reported two illustrative cases can be explained with the experience provided by an animal model where embospheres of different size were used for embolization of the rete mirabile of the swine. In this model antegrade and retrograde non target embolization could be detected. These spherical, compressible and smooth Gelatine covered particles can even pass through small vessels such as in the rete mirabile into the anterior circulation of the brain inducing large infarcts. Another mechanism of false embolization is possible, when particles accumulate retrograde and pass via the occipital artery of the swine into the basilar territory inducing cerebellar infarcts. This effect could be detected in the specimen and was wondering because there was a reduced but constant antegrade contrast flow during fluoroscopically controlled embolization procedure [Ref. 15].

In consequence, Embospheres should not be used in tumours if we do not have a microcatheter position close to the tumour site being sure that the tumour supplied vessel is a terminal vessel. Our experience with two complications and the animal study indicates that embospheres should not be used especially for central skull base tumours because of a high risk of non-target embolization.

For embolization of skull base tumours which were mainly indicated as preoperative embolization, irregulary shaped PVA particles are recommended. These particles intend a more proximal vessel occlusion because they clump. However, PVA particles have the disadvantage of early recanalisation within 6 weeks [Ref. 16] and therefore surgery should be done a few days after embolization. The reported results of PVA particle in embolization of intracranial menigiomas were shown to be effective to reduce intraoperative blood loss [Ref. 8], [Ref. 9], [Ref. 10].