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Preoperative embolization of vascular tumors of the head, neck, and spine is considered an important adjunct to the surgical treatment of these lesions, primarily by minimizing the operative blood loss. In this article, the authors outline the fundamentals of preoperative embolization for highly vascularized tumors of head, neck, and spine. The authors discuss the indications, anatomical and physiological considerations, and illustrate technical details concerning the various embolic agents used to treat these complex lesions.
• Preoperative embolization is used for select cases of highly vascularized head, neck, and spinal tumors in order to minimize blood loss during surgery.
• The primary route for tumor embolization is transarterial; direct percutaneous puncture is an alternative for select cases.
• Commonly used materials available for embolization include n-butyl cyanoacrylate, ethylene vinyl alcohol, polyvinyl alcohol, and detachable coils.
• Preoperative embolization can be effective in reducing intraoperative blood loss by devascularizing hypervascular head, neck, and spinal tumors.
The term “embole” historically has had multiple connotations (31). In 1849, Virchow coined the use of “embolus” for the dislodgment of fragments of venous clots into the circulation generating arterial obstruction (31). Currently, the word “embolus” represents a liquid, solid, or gaseous body of matter that migrates intravascularly and might occlude the distal arterial bed or capillaries.
Tumor embolization refers to the mechanical blockage of the vascular supply of a lesion by injecting liquid or particulate agents either through a catheter-based endovascular intra-arterial approach or direct percutaneous puncture (30). The first descriptions of preoperative embolization of head and neck tumors were in the early 1970s for the treatment of juvenile nasal angiofibroma and glomus jugulare tumors (30; 17). Since then, preoperative embolization has become an important adjunct in the management of hypervascularized tumors and is standard practice at the authors’ institution.
The preoperative angiographic evaluation must be comprehensive to delineate all possible arterial feeders and relevant anastomoses. It might include a carotid balloon test occlusion or other provocative testing in cases of branches originating from the internal carotid artery. Collateral flow patterns are determined and the safety of carotid occlusion should be known because clamping or sacrifice may be necessary during surgery.
The goal is to attempt superselective mechanical blockage of the tumor vasculature. Ideally, intratumoral vessel devascularization is achieved at the arteriolar or capillary level (01; 15; 14; 07). Embolization of the tumor parenchyma with preservation of the parent artery is desirable to preserve surrounding tissues and avoid inadvertent ischemia. If the embolization is too proximal, the feeder may develop collaterals that will cause bleeding at surgery. Moreover, this blocks access to the tumor for subsequent embolization (15). A careful and slow injection of embolic material is performed under constant fluoroscopic guidance, mainly looking for potential embolic agent reflux proximally around the catheter tip. Once the capillaries are saturated, the other feeding pedicles are cannulated.
Direct tumor puncture was originally described for juvenile nasopharyngeal angiofibromas in 1994 (04; 28). Initially, direct tumor puncture was used in cases where the transarterial route was technically challenging because of small feeder size or in cases where there was involvement of direct branches of the internal carotid artery or vertebral arteries (when reflux of embolization material could occur and directly damage the intracranial circulation or the retina). A tumorgram is obtained through an intratumoral contrast injection for determination of blood supply and venous drainage. An advantage to this approach is that arterial tortuosity and vasospasm are not applicable because the needle is inserted directly into the tumor (14).
The timing of embolization is an important consideration, although evidence to support the optimal delay before surgery is unknown and should be individualized. Ideally, embolization should be performed up to 72 hours prior to the surgical resection. This time-frame allows maximal thrombosis over the occluded arteries, minimizes recanalization of the embolized arteries, and avoids formation of neovascularization and development of collateral channels (14). However, cases have been reported, particularly with intracranial meningiomas, requiring emergency decompression from increased mass effect and edema after embolization. At the same time, some studies have demonstrated optimal softening of the tumor after several days. This must also be balanced against the risk of dissipation of the embolic agent, which restores blood flow to the tumor parenchyma (32). Dissipation of the embolic agent is more applicable to the use of particles in contrast with n-butyl cyanoacrylate or ethylene vinyl alcohol, which provide a permanent occlusion of vessels.
A variety of agents with different basic physical properties are available for injection, each with individual specific handling characteristics, technique for delivery, and side effect profiles.
Liquid embolics. Liquid embolics can penetrate in the capillary bed of the tumor, but may generate angionecrosis, injury to normal structures, or cytotoxic edema (15). This class includes n-butylcyanoacrylate, ethylene vinyl alcohol, and ethanol.
N-butyl cyanoacrylic acid (NBCA) is an acrylic adhesive agent, commonly referred to as glue. N-butyl cyanoacrylic acid is mixed ethiodized oil in order to increase the polymerization time and with a powder to confer radiopacity. This process must be performed without contamination from ionic solutions (blood, contrast, or saline) to avoid inadvertent polymerization. The microcatheter is first flushed with 5% dextrose in water, followed by the N-butyl cyanoacrylic acid mixture injection (19). Once in contact with blood, N-butyl cyanoacrylic acid polymerizes, becomes adhesive, and forms an acrylic cast. Prolonged injections are not possible, and occasionally only a small portion of the nidus can be occluded with a single injection (20). At the end of the injection, the microcatheter is briskly withdrawn (19). N-butyl cyanoacrylic acid is thought to be one of the most permanent embolic agents (20). Catheter adhesion is a potential risk and careful retraction is recommended.
Ethylene vinyl alcohol copolymer (Onyx) is a mechanically occlusive agent that is nonadhesive to the arterial wall. It is dissolved in dimethyl sulfoxide and polymerizes by desiccation once dimethyl sulfoxide diffuses out of the compound. There are 2 concentrations available, 6% or 8%. Increasing concentration yields a higher viscosity (20). A lower viscosity is desirable when there is a slow flow pattern or if distal penetration into a vascular bed is desired. Onyx permits a single, prolonged, theoretically precise, and controlled injection with reduced risks of early polymerization and venous occlusion (20; 19). Catheter retention is also a risk and slow retraction is recommended. During injection, reflux of embolic material (retrograde embolic material flow around the catheter tip) is typically observed; a 1- to 2- minute pause should be taken to allow the agent to solidify, after which the injection is resumed. The reflux around the microcatheter generates a plug that allows the agent to take the path of least resistance, penetrating the nonembolized portions of the tumor (14). The fact that Onyx advances in a single column reduces the risks of dislodgement of part of the material distal to the tumor.
Absolute ethyl alcohol (Alcohol, Ethanol) has an extremely low viscosity, which allows deep penetration. Ethanol is highly cytotoxic, generating endothelial injury and necrosis with consequent tumor blockage by thrombosis; the obliteration is considered permanent. The main risk relates to the development of cardiopulmonary collapse from pulmonary precapillary spasm (06; 19).
Particulates. Compared to liquid agents, particulates are less likely to penetrate the tumor capillary bed and thus have an advantage in protecting normal parenchyma and cranial nerves and vasa nervorum. However, the embolization is considered temporary because the peri-particulate thrombus is reabsorbed and the particles dissipate over time (19; 11). Therefore, these agents are best suited when early surgery is planned. This category encompasses polyvinyl alcohol, microspheres, Gelfoam (gelatin sponge), and microfibrillar collagen.
Polyvinyl alcohol is composed of uneven surfaced micro-particles that are mixed with contrast and injected through a microcatheter in a pulsatile manner. The choice of size (45 to1180 m) will depend on the targeted vessels. These particles are adhesive to the endothelium and generate necrosis once accumulate within the tumor vasculature. However, the particles might aggregate and form a larger mass that might unintentionally occlude proximal vessels or clog the microcatheter.
Microspheres might be composed of gelatin, dextran, or poly copolymer. They are precisely calibrated, with consistent shape and size, which translates to reliability in the caliber of the vessels to be blocked. Because they do not aggregate, there is better tumor penetration and smaller chances of catheter clumping (19).
Detachable coils. Detachable coils might be used to sacrifice feeding arterial pedicles on termination of liquid or particulate embolization. The goal is to eliminate the feeding pedicle perfusion pressure, which could lead to recanalization (15). Coils may also be utilized to occlude a critical anastomosis that might be observed during the procedure, allowing for a safer continuation of the injection with less chances of embolizing normal tissue (15; 14). Fibered coils are useful due to dense polyester fibers that attach to the platinum coil, increasing thrombogenicity and occlusive potential (19).
The tumors most commonly presurgically embolized are the meningiomas, paragangliomas, and juvenile nasopharyngeal angiofibromas. Other tumors that might benefit from this treatment include hemangioblastomas, hemangiopericytomas, schwannomas, hemangiomas, and extracranial and intracranial metastases (15; 07).
Meningiomas. Meningiomas are the most common benign brain neoplasm (36). They often occur between the ages of 30 and 70 and can be related to radiation exposure, genetic syndromes, or hormonal factors.
Meningiomas are graded as benign, atypical, and malignant based on histological features such as mitotic activity and infiltration of underlying brain (23).
The diagnosis may be suggested by progressive neurologic symptoms and signs but is often found incidentally. Noninvasive imaging with CT or MRI reveals homogeneous enhancement due to high vascularity. Digital subtraction angiogram may show a characteristic delayed tumor blush.
Arising from the meninges, these tumors are usually fed by dural arteries, which originate primarily from the external carotid artery (middle meningeal artery, accessory meningeal artery, ascending pharyngeal artery, or occipital transmastoid perforating branches). Meningiomas of the tentorium and posterior fossa may be fed by dural branches from the internal carotid artery (tentorial arteries and the inferolateral trunk) or the vertebral artery (posterior meningeal branch), respectively. Indications for treatment include progressive symptomatology such as headache, seizure, or neurologic deficit due to expansion, infiltration, or cerebral edema from mass effect.
Although the vascular supply for commonly occurring convexity meningiomas, where the dural feeders are encountered on opening, is easily accessible, the blood loss can be significant before it is controlled. Meningiomas also may have a fibrous or calcified consistency that hinders resection. Embolization facilitates resection by causing necrosis, leading to a softening of the tumor, in addition to decreased blood loss. Complications have been reported, however, and embolization is generally reserved for selected cases (32).
Paragangliomas. Paragangliomas, also known as glomus tumors, are benign tumors that develop from neuroendocrine cells of the autonomic neural system in the paravertebral sympathetic and parasympathetic chains. These extremely vascular tumors will rarely undergo malignant transformation. Paragangliomas are typically sporadic; they tend to affect adult individuals and to present as with a palpable mass or cranial nerve palsy from mass effect. The clinical manifestations will depend on the location, size, and neuroendocrine function.
The origin of these neck tumors gives rise to the nomenclature. Carotid body paragangliomas (glomus caroticum) are the most common type and often present as a painless mass in the carotid bifurcation. Tympanic paragangliomas (glomus tympanicum) develop in the middle ear, along the temporal bone involving the tympanic nerve, and may cause hearing loss, pulsatile tinnitus, and a retro tympanic vascular mass. Glomus jugulare tumors may present with hoarseness due to lower cranial nerve palsy related to the tumor presence in the jugular fossa. Vagal paragangliomas are often diagnosed as a mass at the angle of the mandible that grows near the vagus nerve, causing vagal and hypoglossal nerve dysfunction.
As with meningiomas, the vascularity of paragangliomas makes them readily apparent on CT or MRI with homogeneous contrast enhancement. Uptake of radio-labeled octreotide corroborates the diagnosis preoperatively. Angiography frequently demonstrates enlarged arterial feeders with intense tumor blush, and rapid venous drainage. Mass effect is apparent on angiography with large tumors. Characteristically, carotid body tumors will splay the external and internal carotid arteries further apart. In contrast, glomus vagale tumors will displace internal and external carotid artery anteriorly and the internal jugular vein posteriorly (14).The ascending pharyngeal artery is the usual feeding branch; however, other external or internal carotid artery branches might be involved--especially in larger lesions--and anastomoses to the vascular supply of critical structures must be respected. Preoperative embolization should be considered for paragangliomas due to their potential for surgical blood loss, particularly in lesions larger than 3 cm (35).
Juvenile nasopharyngeal angiofibroma. Juvenile nasopharyngeal angiofibroma is the most common tumor of the nasopharynx. It usually affects male patients during adolescence, manifesting as nasal obstruction and recurrent epistaxis. According to the tumor size and to the direction of growth, patients might develop sinusitis, facial swelling, and proptosis. On endoscopic examination, a reddish-gray sessile, lobulated, and encapsulated mass might be observed. Juvenile nasopharyngeal angiofibromas are benign tumors that might be locally aggressive, with rare malignant conversion or spontaneous remissions.
Histologically, these tumors are mainly formed of a thin-walled vascular tissue with fibrous stroma and scant muscular fibers. Juvenile nasopharyngeal angiofibromas might spread extensively along tissue planes. Grading is based on anatomic extent on CT or MRI. Lower grade tumors are confined to the nasopharynx, with higher grades assigned on extension into the sinuses, pterygopalatine fossa, infratemporal fossa, and intracranial skull base (12; 29). Although bone invasion does not occur, remodeling and erosion are common.
Diagnostic angiography usually demonstrates an early and intense blush that persists until the venous phase. Distal branches of the internal maxillary artery feed these tumors. As the tumor enlarges, other vascular territories may be recruited, such as the ophthalmic artery branches (14). Their blood supply can be bilateral, thus, it is important to perform angiograms of both carotids. Preoperative embolization might be useful in larger tumors and in the ones that extend intracranially. Their location in the nasopharynx makes them suitable for embolization by direct puncture as an alternative to transarterial therapy. These lesions can be punctured with a spinal needle under direct visualization using an endoscope. This route is best suited for use with liquid embolics and has been associated with decreased radiation exposure to the patient and greater degree of devascularization (10).
Hypervascular spinal tumors. Vertebral metastases are relatively common in patients with breast, lung, prostate, and kidney cancer. Although less frequently, the vertebrae also might be affected by benign vascular spinal tumors such as hemangiomas. These lesions cause pain or other symptoms such as compression to nerve roots or spinal cord. The diagnosis is often suspected after CT or MRI with contrast reveals an extramedullary enhancing mass. Blood loss for vascularized tumors in the spine can be extremely high; therefore, preoperative angiogram may be used to characterize vascularity and plan embolization if indicated. Spinal angiography must confirm prior to embolization that the procedure will not compromise major medullary branches to the anterior spinal artery.
Head and neck tumors can be embolized with particles (such as polyvinyl alcohol, embolic spheres, and Gelfoam) or liquid agents (such as N-butyl cyanoacrylic acid and Onyx – the latter more recently described) (08; 11; 09; 02). The capillary bed of head and neck tumors is roughly 200 µ, therefore, 150- to 250 µ particles are appropriate (15). Small-sized particles with diameters below 150 µ should be avoided because they can penetrate distal to tumor microvasculature and cause injury to the normal parenchyma or obstruct draining veins of normal tissue.
In regard to spinal lesions, angiography and embolization can be performed in any segment of the spine (cervical, thoracic, lumbar, and sacral) (16). For the spinal cord, particles are typically used, and sizes below 150 µ should also be avoided (03; 16). Liquid agents as ethanol, N-butyl cyanoacrylic acid, and Onyx might be used by experienced operators--considering the high diffusibility and potential for complications (34; 18; 22). Thus operator experience, tumor characteristics, and the properties of the agent must be considered when choosing the particular agent used. An advantage to particles is that they can be used in patients under conscious sedation, which facilitates intraoperative neurologic examination. The use of solvent DMSO used with Onyx and the use of n-butyl cyanoacrylic acid may cause significant pain, and some operators advocate the administration of steroids and/or utilization of general anesthesia.
Preoperative embolization therapy is technically successful in the vast majority of cases. Generally there is prominent decrement of tumor blush by angiography. The majority of the series report nonmatched samples, making it difficult to quantify the clinical magnitude of the benefit. A comparison between embolized and nonembolized patients with meningioma has been reported to reduce surgical blood loss (533 versus 836 cc) and the need for postoperative blood transfusion (0.39 versus 1.56 units), with statistically higher means in the nonembolized group. Presurgical embolization was found safe, and trends towards cost-effectiveness, surgical resection time, and length of hospitalization were observed (05). In a study of 59 patients with benign and malignant vertebral tumors treated prior to corporectomy, efficacy of polyvinyl alcohol embolization was demonstrated with a median perioperative blood loss of 1850 mL in the embolized sample versus 4350 mL in controls. In a series of metastatic spinal tumors, the mean intraoperative blood loss was 1,900 ml in patients with complete devascularization, whereas it was 5,500 ml in only 2 patients where embolization was not possible (16).
Direct tumor puncture might be used as an alternative to the transarterial route for treatment of paragangliomas and juvenile nasopharyngeal angiofibromas. A review of the series comparing these 2 techniques revealed similar safety and efficacy (09).
The use of Onyx was described in a series comparing direct tumor puncture versus transarterial embolization in 43 patients with head, neck, and spinal tumors. Although the intraparenchymal penetration of embolic material was greater in the tumor puncture versus the transarterial embolization cases, the mean percentage of tumor devascularization (as estimated by tumor blush) was similar. However, the mean intraoperative blood loss was lower in tumors with intraparenchymal penetration (459 ml) than without (2689 ml) (11). Another study compared tumor puncture and transarterial embolization in a homogeneous sample that only included juvenile nasopharyngeal angiofibromas (5 patients treated by each modality). All individuals treated with tumor puncture had intraparenchymal penetration (mean tumor devascularization of 93%) versus none treated with transarterial embolization (mean devascularization of 77%). The operative estimated blood loss was 412 ml in the tumor puncture and 862 ml in the transarterial embolization cases. The volume of Onyx injected was more than 10 times higher in the tumor puncture patients, which might indicate tumor puncture as a higher cost approach (09).
The choice of embolic agent profile (liquid viscosity or particle size) is an extremely important step; the multiple potential anastomotic arterial connections and tumor-specific pathology should be considered. Smaller particles and less viscous liquid agents might migrate during the tumor embolization procedure from the external carotid artery towards the internal carotid artery or the vertebral arteries.
This could generate inadvertent infarcts in the retina (through the ophthalmic artery), in cranial nerves (through embolization of the vasa nervorum) or in the brain parenchyma. The embolization of external carotid artery branches might lead to mucosal and tongue necrosis as well as damage to the larynx (14). A recent series of preoperative embolization of glomus jugulare tumors with Onyx found an 18% incidence of permanent cranial neuropathy (13). In the cases with cranial neuropathy, nontarget embolization was not observed, which highlights the importance of patient and embolic agent selection for each individual lesion.
In spinal cases, particles may dislodge through intersegmental anastomoses and generate spinal cord ischemia. Therefore, small-sized particles are avoided because they may block the arterial input to the spinal cord at levels with inadequate or absent collateral supply. Likewise, embolization in cervical tumors requires additional attention due to potential anastomoses between the carotid, vertebral, and subclavian arteries. In this setting, direct tumor puncture for cervical vertebral body lesions may be considered if feeders are too small for safe catheterization.
The tumor-feeding pedicles might be tested for supply to eloquent neurologic structures (such as cranial nerves in head and neck tumors and spinal cord and nerves on spinal embolizations) prior to embolization. This can be done through a lidocaine provocative test, where a 3 ml lidocaine injection is done in the feeding pedicle, and the patient is examined for deficits. An important limitation is that the lidocaine test cannot predict the sudden opening of collateral branches during embolization; therefore, repeated clinical and angiographic monitoring during embolization is imperative to avoid unintentional injury of normal tissue (03).
Presurgical embolization is reportedly safe for the treatment of head, neck, and spine tumors. In a series of 47 patients with paragangliomas treated with polyvinyl alcohol, Gelfoam, and N-butyl cyanoacrylic acid, 4 patients (8%) developed permanent postembolization complications. One developed permanent facial nerve palsy, and the remaining 3 had tumors that originally encapsulated the affected nerves (26). In a series involving 14 patients with glomus tumors treated with Onyx through transarterial embolization and tumor puncture routes, no neurologic complication or inadvertent embolization of parent arteries were observed (11).
In a recent review, treatment of juvenile nasopharyngeal angiofibroma patients with diverse embolic agents was demonstrated to be safe, with an overall 3% chance of complications. Two of 56 patients treated with tumor puncture had adverse events (embolizations to the ophthalmic and to middle cerebral arteries) versus 3 of 79 patients treated transarterially (1 central artery embolism, 1 transient jaw weakness, and 1 transient ischemic attack) (09).
A report of preoperative embolization of meningiomas described complication rates of 3.6% (4 patients of 111) related to cranial nerve injury or monocular blindness (the latter related to smaller particulate sizes of < 150 µ) (15). The use of Onyx in meningiomas has been described, but the literature regarding this liquid embolic agent is scarce (33).
In relation to the treatment of spinal tumors, a study that included 59 patients embolized prior to corporectomy for metastatic vertebral tumors and other benign tumors (plasmocytomas, hemangiomas, giant cell tumors, and aneurysmal bone cyst) reported no neurologic complications (03). Another series of 24 patients with extradural hypervascular metastatic spinal lesions described no permanent neurologic deficits and no skin or muscle necrosis (16).
Case 1. A 67-year-old female with neurofibromatosis type 2, bilateral acoustic schwannomas, and multiple meningiomas was found to have a rapidly enlarging right parietal meningioma causing mass effect.
The meningioma was targeted for presurgical embolization.
Under general anesthesia, a load of intravenous heparin was given and ACT checked hourly to levels between 250 to 300 seconds. A 6F Envoy catheter was navigated over a 0.038-inch glidewire across the aortic arch and maneuvered in to the RICA artery. Under magnified roadmap guidance, a Marathon microcatheter was advanced over a shaped Mirage microwire into the right middle carotid artery. A moderate tumor blush from the distal parietal middle carotid artery branches was observed.
The microcatheter was then carefully navigated distally into each of the 2 feeding pedicles, one at a time.
After a microinjection through the microcatheter, DMSO was infused at a rate of 0.1cc/ min (0.3cc total) through the microcatheter in each pedicle, which were then embolized with Onyx-18 until there was reflux back toward the catheter (0.2cc). The microcatheter was removed, and final AP/lateral angiograms were obtained, demonstrating substantial decrement in the tumoral capillary blush.
Case 2. A 61-year-old male with hepatocellular carcinoma developed cord compression and progressive lower extremity weakness related to metastatic disease to the spine. Because a previous resection attempt had been aborted due to excessive tumor bleeding, presurgical embolization was performed.
A 5-French Cobra catheter was advanced over a 0.038 inch Glidewire, and a selective segmental artery angiogram was done from T5 to T12 bilaterally, revealing tumor blush from the right T9, T10, T11, and left T9 and T10 radicular arteries. An Echelon 14 microcatheter was advanced over a shaped Synchro micro-wire into the radicular branch of right T9 where a microangiogram was performed. Concentric microspheres of 100 to 300 µ were prepared in a contrast-saline mixture and titrated to a uniform and diffuse suspension. They were then injected under subtracted roadmap guidance until stagnation was seen in the radicular artery. The Echelon catheter was removed, and a Prowler select catheter was navigated over the microwire into the radicular branch and flushed with 5% dextrose solution; nBCA glue (proportion of 3:1) was injected to occlude the proximal radicular artery and branches.
Of note, the dilution ratio of Ethiodol to N-butyl cyanoacrylic acid determines the depth to which penetration of glue is desired. A ratio of one part Ethiodol to one part NBCA (1:1) polymerizes very rapidly after entering in contact with blood, whereas a ratio of (3:1) allows more penetration. The same process was done at the level of right T10 and left T9.
The right T11 was only injected with nBCA.
Although tumor blush was observed during left T10 radicular artery injection, embolization was not performed as this branch also gave rise to the artery of Adamkiewicz. After treatment, no tumor blush could be appreciated.
Preoperative embolization of hypervascularized tumors, such as paragangliomas, juvenile nasopharyngeal angiofibromas, and meningiomas, has been shown to reduce intraoperative blood loss and operative time (37; 25; 21). Catastrophic hemorrhage of up to 10 liters during a high-grade tumor surgery has been reported, thus, the main objective of the preoperative embolization of such tumors is to block capillaries through arterial feeders that may be difficult to access at surgery (24). Advantages to preoperative embolization include decreased blood loss, reduced operative time, improved visualization of the surgical field, reduced risk of injury to healthy surrounding tissue, and increasing the chances of complete resection (07).
The goal of embolization is to aid in the surgical resection; however, this approach may also be used as primary treatment for palliation of unresectable tumors. It might also be used as a direct route for chemotherapeutic agent delivery (01; 27).
Diogo C Haussen MD
Dr. Haussen of University of Miami Miller School of Medicine - Jackson Memorial Hospital has no relevant financial relationships to disclose.See Profile
Brandon G Gaynor MD
Dr. Gaynor of University of Miami Miller School of Medicine - Jackson Memorial Hospital has no relevant financial relationships to disclose.See Profile
Dileep R Yavagal MD
Dr. Yavagal of University of Miami Miller School of Medicine received consultation fees from Stryker, Aldagen/Cytomedix, and Covidien/EV3.See Profile
Edward J Dropcho MD
Dr. Dropcho of Indiana University Medical Center has no relevant financial relationships to disclose.See Profile
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