68 Intracranial Vascular Tumors
Abstract
Intracranial vascular tumors are lesions that have a vascular origin or those that have a rich vascular supply. These include hemangioblastoma, hemangiopericytoma, meningioma, choroid plexus tumors, and several metastatic lesions. Given their vascularity, these tumors require additional diagnostic and interventional considerations. Properly identifying them on preoperative imaging studies is critical to determining the need for angiography and planning the appropriate surgical approach, as these tumors have a propensity for high blood loss during surgical resection. Angiograms are often important prior to surgery to identify the vascular supply of these lesions and in some cases to embolize these vessels to mitigate blood loss. Careful selection of patients for embolization is imperative, as there is significant risk of stroke from these procedures. In our experience, very large tumors, those with difficult to access blood supplies, and those with multidirectional blood supplies are the most ideal candidates. More so than in other tumor operations, the surgeon must identify and coagulate the blood supply early in the sequence of the operation to avoid high blood loss. Correctly determining which vessels are supplying the tumor and which vessels are “en passage” is critical to avoiding strokes. Similar to other tumors, postoperative follow-up in these patients is dependent on the pathology.
Intracranial vascular tumors encompass both tumors of vascular origin and those that tend to have an extensive vascular supply. Both will be discussed in this chapter with respect to the workup, treatment, outcomes, and follow-up. An evidence-based approach to their surgical and endovascular management will be the focus.
Major controversies in decision making addressed in this chapter include:
Whether or not treatment is indicated.
Indications for diagnostic cerebral angiography.
Case selection for preoperative endovascular embolization and adequate timing for surgery after embolization.
Potential complications of endovascular embolization and technical nuances.
Hemangioblastoma
Introduction
Hemangioblastomas are benign, highly vascular neoplasms that account for 3% of all central nervous system (CNS) tumors, and 7.5% of posterior fossa tumors (▶ Fig. 68.1 ). These lesions are more commonly sporadic (75%), but are also heavily associated with von Hippel-Lindau (VHL) disease. They produce symptoms through local mass effect, obstruction of the ventricular system, or hemorrhage ( 1 –3 in algorithm ). The mainstay of treatment is surgical resection, with angiographic embolization and radiosurgery serving as adjuvant therapies ( 4 in algorithm ).
Whether to Treat
Symptomatic lesions amenable to surgery should be intervened on, with the goal of gross total resection. The cystic component of cystic hemangioblastomas typically will enlarge over time, leading some others to suggest resection of asymptomatic lesions that have shown radiographic progression.
Anatomical Considerations
The most common place for intracranial hemangioblastomas to occur in both sporadic and VHL cases is the posterior fossa, specifically the cerebellar hemispheres. Other locations such as the brainstem, spine, and cerebral hemispheres are less common.
Pathophysiology/Classification
A mutation of the VHL tumor suppressor gene on chromosome 3p is present in both VHL and sporadic hemangioblastoma. The mutation in VHL occurs in a germ line cell, leading to tumors of many types throughout the body including renal carcinoma, pheochromocytoma, and endolymphatic sac tumors. VHL disease is inherited in an autosomal-dominant fashion, with a high degree of penetrance.
Workup
Clinical Evaluation
The mean age at presentation for sporadic and VHL lesions are the fifth and fourth decades of life, respectively. The most common presenting signs and symptoms of hemangioblastomas correspond to their most common location being in the posterior fossa, including headache, gait disturbances, dysmetria, nausea, vomiting, nystagmus, dysarthria, and dysphagia. Lesions of other places in the CNS will present with deficits corresponding to the functions of these areas.
The majority of patients with VHL will initially present with brain or retinal hemangioblastomas. The diagnosis of VHL in a patient with a family history of the disease is confirmed with the diagnosis of any one of the previously mentioned lesions including CNS or retinal hemangio-blastoma, pheochromocytomas, or clear cell renal carcinoma. At risk or individuals with suspected VHL should be evaluated by an ophthalmologist, and also undergo computed tomography (CT) or ultrasound of the abdomen in addition to full CNS imaging.
Sporadic VHL makes up to 20% of diagnosed cases of VHL and is diagnosed in patients with two or more CNS hemangioblastomas or one of these lesions and one of the above neoplasms. The diagnosis can be confirmed with DNA testing.
Imaging
On contrast-enhanced, T1-weighted magnetic resonance imaging (MRI), hemangioblastomas have a very typical appearance: a homogenously enhancing, well-circumscribed nodule with an associated cyst (▶ Fig. 68.1a ). T2-weighted and FLAIR MRI better characterizes the hyperintense, cystic portion, and will also show mild to moderate peritumoral edema. Given that the retinal and CNS manifestations of the VHL are the typical presenting pathology, MRI of the entire neuroaxis and CT or ultrasound imaging of the abdomen is suggested if a hemangioblastoma is suspected in a patient without history of the disease.
When angiography is performed for further investigation and potential embolization, a typical tumor blush from the solid portion of the mass will be present. Large feeding arteries and draining veins are not uncommon. An avascular region of the mass may be seen, which represents the cystic portion of the tumor (▶ Fig. 68.1b ).
Differential Diagnosis
For a cerebellar hemangioblastoma in an adult, the radiographic differential diagnosis includes the most common lesions of the posterior fossa: metastatic lesions such as breast and lung cancer. Metastatic disease is more common, and would generally be favored as the diagnosis except in patients with a family history or known VHL disease and the typical imaging characteristics of hemangioblastomas. The time at presentation for these lesions is typically less than metastatic disease (45 years for sporadic lesions and 36 years for VHL-associated lesions), so a heightened suspicion for the diagnosis should be maintained in younger patients.
Treatment
Conservative Management
Hemangiopericytomas are rare, highly vascular neoplasms with unpredictable malignant potential. These tumors originate from capillary pericytes, which surround endothelial cells and regulate the luminal diameter of the vessel. They make up less than 1% of all intracranial tumors and are commonly found attached to a dural surface. These tumors are challenging neoplasms to treat, given their high vascularity, tendency to recur, and ability metastasize outside of the CNS. Given these characteristics and a mortality rate of over 30% even with aggressive management, all suspected hemangiopericytomas should be treated.
Cerebrovascular Management—Operative Nuances
Surgery is the primary treatment option for symptomatic lesions of the cerebellar hemispheres and vermis, as well as superficial lesion of the cerebral cortex. Deep-seated lesions within the cortex and those within the brainstem, which do not come to a pial surface, are generally considered less favorable for surgical intervention. Given the vascularity of these tumors and the potential for heavy bleeding if the capsule is entered, en bloc resection is the typical approach. The tumor capsule is identified at the pial surface or after a corticectomy and then feeding arteries are coagulated at the tumor–cerebral interface. This is carried out circumferentially, and the tumor will generally soften after a sufficient amount of the vascular supply and the capsule is coagulated, which aids in removal. If there is a large associated cyst, drainage of this portion of the mass can also assist in creating space to mobilize the tumor. The cyst wall should be inspected for additional nodular components and these parts removed.
Preoperative embolization of hemangioblastomas remains a controversial topic, as it is with most intracranial tumors. Serious complications related to infarction of critical structures and large hemorrhages believed to be related to venous outflow obstruction have been reported. Liquid embolization agents rather than small particles are preferably used (▶ Fig. 68.1b,c ). Embolization with liquid agents requires experience and technical expertise and should be performed with caution. Anastomoses between the vessels to be embolized and nearby vasculature need to be heavily scrutinized to avoid unintended passage of embolization agents into these vessels. Given the chance for serious complications, and the fact that most series report favorable surgical results without the use of preoperative embolization, it is difficult to suggest employing embolization as a routine part of the management of these patients. For large lesions with vascular supplies that may not be easily accessible early on during the surgical approach, embolization becomes a more important part of the treatment scheme (▶ Fig. 68.1c,d ).
For small lesions deep within the cerebral cortex, radiosurgery is an alternative option as primary treatment, having been shown to halt progression of tumor growth and also improve symptoms. The reported durability of such treatments for small (<3 cm) lesions has been reported as high as 84 to 96% at 1 to 2 years, with long-term control at 5 years reported to be between 71 and 81% (supports algorithm step 8).
Clinical and Radiographic Follow-up
Special follow-up is required for patients with VHL syndrome. In one study with long-term follow-up of a group of 15 VHL patients presenting with hemangioblastomas, 67% developed additional CNS lesions of the brain and spinal cord. This occurred at a rate of approximately 1.5 to 2 years. Given the high rate and frequency of new lesion formation in this patient population, biannual or annual MRI of the entire neuroaxis is suggested.
Hemangiopericytoma
Introduction and Whether to Treat
Conservative management is an option in small, asymptomatic lesions, but a short-interval (6 months to 1 year) follow-up MRI is suggested to monitor for progression ( 6, 8 in algorithm ). The cystic portion can enlarge over this time period; therefore, resection or radiosurgery at that time even with the absence of symptoms has been suggested.
Anatomical Considerations, Imaging, and Differential Diagnosis
Meningeal hemangiopericytomas most commonly occur at the skull base and along the convexity in close proximity to the dural venous sinuses. The main consideration with respect to the differential diagnosis is a meningioma, but several imaging characteristics can aid in distinguishing the two lesions. On contrast-enhanced, T1-weighted MRI, these neoplasms are durally based, heterogeneously enhance, and can be seen invading the adjacent bone. The dural attachment tends to be less broad than a meningioma, with less of a tendency to have a dural tail. Hemangiopericytomas do not contain calcifications like meningiomas.
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