Advances in surgical techniques have reduced the mortality associated with the resection of specific brain, head, and neck tumors. Complete tumor resection requires a multidisciplinary approach involving techniques from multiple specialties, including vascular and endovascular, otolaryngology, and neurosurgery. Ideally, patients with vascular tumors in the head and neck should be evaluated through a multidisciplinary team approach for optimal staging and therapeutic planning.

Tumor embolization refers to any percutaneous procedure, either through direct puncture of the tumor or via an endovascular approach in which particles, liquid embolic agents, coils, gel foam, or other materials are injected to reduce tumor vascularization. The direct puncture technique for preoperative embolization of hypervascular head and neck tumors has traditionally been performed with gel foam, fibrin glue polyvinyl alcohol, or permanent materials such as ethanol or N-butyl-cyanoacrylate [26]. It is a viable alternative to transarterial embolization, offering improved tumor penetration and potentially fewer arterial complications. While direct puncture embolization is safe and effective for hypervascular head and neck tumors, its use in intracranial pathologies requires caution due to the potential risk of venous complications [13].

The key recommendation for successful embolization is that the procedure be performed by a physician experienced in neuroendovascular techniques, angiographic image interpretation and with in-depth knowledge of relevant vascular and surgical anatomy (venous flow patterns, involvement of dural sinuses, anatomical variations, and regional anastomoses) [28].

The primary objective of tumor embolization is to facilitate the successful surgical resection of the lesion. Controlling bleeding during surgery can be challenging, particularly in highly vascularized tumors. In certain cases, embolization may be employed as a palliative treatment to reduce tumor size and alleviate pain in patients with tumors deemed inoperable [1]. Examples of tumors (brain, head, neck, and spine) typically characterized by significant vascularization include hemangioblastomas, meningiomas, juvenile nasoangiofibromas, aneurysmal bone cysts, paragangliomas (carotid body, glomus vagale, glomus jugulare), solitary fibrous tumors, and vascular metastases from renal cell carcinoma, thyroid cancer, and choriocarcinoma [30].

Table 1 summarizes the specific tumors commonly treated with adjuvant embolization prior to surgical resection. This list may exclude other tumor types where embolization could be indicated based on the tumor’s vascularity. It is recommended that the indication for tumor embolization be clearly defined before the procedure.

In the brain, meningiomas fulfill most of the objectives of preoperative embolization as they are hypervascular and primarily supplied by dural feeding vessels. While most convexity meningiomas do not require embolization, even if highly vascular, those located at the skull base or in the posterior fossa can present significant differences. (Fig. 1) [2,5]

Digital subtraction angiography provides additional information to complement clinical evaluation and findings from computed tomography or magnetic resonance imaging studies. Angiography enables the identification of feeding vessels supplying the tumor, facilitating their localization and ligation during surgery. Other critical information includes the extent of tumor growth around vessels (e.g., the internal carotid artery) and collateral flow distal to the affected vessel. Combined with a balloon occlusion test, angiography can assist in determining the feasibility of carotid artery sacrifice during surgery, if necessary [5].

The blood supply to a tumor can be predicted based on its location, extent, and type. For instance, paragangliomas are almost universally supplied by branches of the ascending pharyngeal artery. In the case of nasoangiofibromas, the vascular supply primarily arises from the distal branches of the internal maxillary artery, particularly the sphenopalatine, descending palatine, and posterior superior alveolar branches [22,35]. Therefore, selective catheterization of the external and internal carotid artery branches is required to delineate the blood supply properly. Additionally, super-selective catheterization of external carotid artery branches may reveal dangerous intracranial anastomoses, necessitating caution during embolization.

An evaluation of the contralateral carotid artery branches should be performed to rule out their contribution to the tumor, particularly in cases where the tumor has crossed the midline. Intracranial tumors, particularly those located in the posterior fossa, may require additional imaging of the posterior circulation (Fig. 2). It is important to note that anastomoses may exist between the external carotid artery branches (particularly the occipital artery) and the posterior circulation. These vascular connections can pose potential risks during embolization if they are not documented and thoroughly understood [12].

A comprehensive understanding of extracranial-to-intracranial arterial anastomoses is vital for minimizing complications during neuroendovascular procedures. Among the most clinically relevant pathways is the connection between the facial artery or the internal maxillary artery (IMAX) and the ophthalmic artery (OA), which arises from the internal carotid artery (ICA). The facial artery, via its terminal angular branch, forms anastomoses with the supratrochlear and supraorbital arteries-distal branches of the OA. This vascular linkage creates a potential conduit for unintentional embolic material to reach the intracranial anterior circulation, including the retinal territory, particularly during embolization of nasal or facial vascular lesions [15]. Similarly, the IMAX establishes communications with the OA through orbital branches such as the zygomaticotemporal artery, presenting additional risk during procedures involving the maxillofacial region [15].

Another important anatomical connection involves the middle meningeal artery (MMA), a branch of the IMAX, which communicates with branches of the meningohypophyseal trunk (MHT) of the ICA. Notably, the marginal tentorial artery may anastomose with the petrosquamosal branch of the MMA [17,29]. This pathway poses a considerable risk for retrograde embolization into the intracranial circulation, especially when liquid embolic agents are employed for treating dural arteriovenous fistulas or meningeal tumors [15]. Such events may result in significant neurological deficits.

A third noteworthy route is established via the vidian artery, which links the IMAX to the petrous segment of the ICA. This artery may originate from the IMAX as part of the pterygoid canal vasculature and anastomose with a corresponding branch from the ICA. This pathway is particularly relevant in the context of nasopharyngeal tumors such as juvenile angiofibromas, where these arteries are often hypertrophied [24]. Failure to identify these anastomoses during embolization can lead to the inadvertent delivery of embolic agents into critical intracranial structures.

Finally, the occipital artery (OccA) forms frequent and robust connections with the vertebral artery (VA) through radicular and muscular branches at the C1 and C2 levels. These segmental anastomoses are capable of providing collateral flow to the vertebrobasilar system in cases of proximal vertebral artery occlusion (15). Additionally, the stylomastoid branch of the OccA may communicate with the posterior meningeal artery, itself a branch of the VA. These connections pose a potential risk for embolization into the posterior fossa or brainstem, necessitating careful consideration during interventions in the upper cervical spine or posterior skull base.

Though often not visible on conventional angiography, these anastomoses can become functionally significant in altered hemodynamic states, such as elevated intraluminal pressure or downstream vascular occlusion. Consequently, meticulous knowledge of these arterial pathways is essential to safely navigate neurointerventional procedures and avoid inadvertent intracranial complications [15,21].

There are three main embolization techniques: the transarterial approach, direct puncture, and a combination of both. Any of these methods is feasible, and there are no established guidelines regarding the preferred route [2]. However, advancements in endovascular therapy, particularly in embolic materials and microcatheter technology, have expanded the window of opportunity for adjuvant treatment of challenging-to-resect neoplasms [1].

Traditionally, embolization is performed through the transarterial route using super-selective catheterization and embolization of the feeding vessels via microcatheter-guided injection of one or more agents. Additionally, occlusion of the main tumor-feeding vessel with coils is also a viable option [10,30] (Figs. 3, 4). This method can be challenging when the vascular anatomy involves tortuous or small-caliber vessels, which may hinder attempts to achieve the necessary microcatheter positioning. The presence of local collaterals also poses a risk of material migration into adjacent normal branches. Moreover, injection into a single feeding vessel may be insufficient to achieve complete tumor devascularization, often needing additional selective catheterizations. These challenges prolong the total procedure time and increase the risk of unintended arterial embolization.

Direct puncture embolization has been proposed as an alternative to address these challenges and can also be used as a complement to the transarterial method. Using an 18-25 Fr gauge needle, a liquid embolic agent is directly injected into the tumor bed under fluoroscopic guidance. While this approach achieves a higher concentration of the embolic agent within the tumor and eliminates the need for endovascular catheterization, it carries a higher likelihood of inadvertent trans-tumoral embolization of venous structures due to the shorter distance to the venous system. Additionally, direct tumor injection poses the risk of unintended migration to surrounding normal structures [14]. Generally, the method choice is determined by factors such as tumor location, the number of arterial feeding vessels, vascular access, vascular anatomy, individual tumor characteristics, presenting symptoms, the patient’s age, and clinical condition.

In rare cases where vascular anatomy or pathology complicates endovascular access, direct puncture embolization may be the only option for preoperative embolization. While there are no systematic comparisons of the two techniques, some authors have suggested that direct puncture allows for better tumor penetration, thereby reducing intraoperative blood loss when liquid embolic agents are used. Additionally, it may facilitate resection by delineating the tumor from surrounding tissue [12,28]. However, this technique also includes significant complications. Further comparisons between these techniques are needed before definitive recommendations regarding their relative merits can be made.

Tumor embolization can be performed under either general or local anesthesia. Local anesthesia with conscious sedation allows for neurological examination during provocation maneuvers and avoids potential complications associated with intubation and exposure to general anesthetic agents. General anesthesia, on the other hand, eliminates risks related to patient agitation and movement during the procedure, which could be hazardous during critical phases of the embolization [5,12,16]. In general, embolization can be safely performed using either method; therefore, the choice of anesthesia should be guided by the patient’s specific characteristics, such as the presence of airway obstruction caused by the tumor or coexisting medical conditions, at the discretion of the endovascular operator.

As previously mentioned, the goal of tumor embolization is to reduce its vascularization to facilitate surgical resection or provide palliation. However, some authors have questioned the utility of preoperative embolization [5,6]. The literature supports the efficacy of tumor embolization in reducing intraoperative blood loss, surgical times, and recurrence rates [20,23,33]. Despite the additional resources required for embolization procedures compared to resection alone, the benefits of embolization are promising. However, conclusive randomized studies are still needed. It is clear that, while feasible and beneficial, embolization may not be necessary in all cases. The decision should be individualized based on various factors, as previously mentioned.

When reporting efficacy, the amount of tumor “blush” is used as a radiographic measure of vascularization. The goal of embolization should be to reduce tumor blush by 80% or more [28,33]. Digital subtraction angiography (DSA) images should be reviewed after completing embolization, and the percentage of reduction should be quantified. Magnetic resonance angiography (MRA) images (indicating lack of contrast uptake or diffusion restriction) or intraoperative computed tomography (CT) have also been employed to quantify the extent of vascularization following embolization. Intraoperative parameters such as blood loss, transfusion requirements, and surgical duration are additional quantitative measures that should be evaluated. For embolization procedures performed with palliative intent, the presenting symptoms and their subsequent regression or improvement have been reported as efficacy measures [2,12].

Tumor embolization is optimally performed 1 to 7 days before surgery. This timing facilitates 1) maximum thrombosis of the embolized vessels, 2) ideal tumor necrosis, and 3) tumor softening [7,18]. If delayed beyond this time frame, tumor inflammation and neovascularization may occur.

The radiographic and clinical effects of embolization can be transient or permanent, depending on the embolic material used. Therefore, the timing of the embolization of surgery is crucial. Very early tumor resection (<24 hours) after embolization may negate the benefits of embolization by not allowing sufficient time for devascularization and tumor necrosis to occur, leading to increased surgical blood loss [3,9]. Histological examination of tumors embolized with particles reveals thrombus formation and multinucleated giant cell reactions within 7 days post-embolization. Subsequently, partial recanalization and revascularization can be observed in approximately 30% of the embolized vessels [25].

It has been demonstrated that the change in tumor consistency and ease of resection are maximized 7-9 days following embolization of meningiomas [9,34]. Therefore, surgical resection should be performed 1 to 8 days after embolization to maximize the benefits of the latter procedure. Steroids should be administered for large tumors at risk of post-embolization edema, such as meningiomas, particularly if surgery is delayed. Transarterial embolization for meningiomas and other vascular tumors of the skull base may lead to infarction, inflammation, and even brain herniation. In such cases, embolization immediately before surgery should be seriously considered [18].

Complications can be classified as either procedure-related or non-procedure-related. The most common complications associated with tumor embolization are outlined in Table 2 and include cranial nerve paralysis, skin or mucosal necrosis, and unintended vascular occlusions [2,28]. Procedure-related complications can be further subclassified based on their clinical relevance and impact into minor or major complications.