69 Skull Base Vascular Tumors
Abstract
Complex skull base vascular tumors are an enigmatic challenge for head and neck surgeons because of their close proximity to vital neurovascular structures. The decision-making process and management principles for skull base tumors have evolved gradually over the past century as our understanding of surgical anatomy, diagnostic imaging, and therapeutic intervention (including radiosurgery and medical therapy) has improved and technological innovations have been implemented. Technological advances in surgery have dramatically improved management as well. The paradigm in skull base surgery of radical resection with high functional morbidity has shifted to encourage tailored resection under neuromonitoring to allow optimal functional outcome while supplementing treatment of residual disease using adjuvant treatment modalities such as stereotactic radiosurgery and chemotherapy/radiotherapy. In this chapter, we discuss the major controversies in decision making and evaluate current treatment outcomes associated with management of complex skull base tumors including commonly encountered benign (i.e., meningioma, hemangiopericytoma, cavernous sinus hemangioma, paraganglioma, and juvenile nasopharyngeal angiofibroma) and malignant (i.e., esthesioneuroblastoma and dural metastasis) tumors. Relevant technical pearls and complication avoidance techniques pertaining to operative nuances, revascularization strategies, and skull base reconstructive measures will also be dealt with in brief.
Introduction
Until the late 20th century, many lesions located in the skull base were considered inoperable, but the introduction of microsurgical techniques, the development of better imaging modalities, and advances in neuroanesthetic techniques, neuronavigation, endoscopy, high-speed drills, and hemostatic agents have dramatically improved surgical management of these tumors. In addition, recent advances in the field of preoperative embolization and stereotactic radiosurgery (SRS) have greatly added to the surgeon′s ability to provide safe surgical resection and better functional outcome in patients with complex highly vascular skull base tumors. In this chapter, we discuss the decision making associated with treatment of complex skull base tumors including commonly encountered benign (i.e., meningioma, hemangiopericytoma [HPC], cavernous sinus hemangioma [CSH], paraganglioma, and juvenile nasopharyngeal angiofibroma [JNA]) and malignant (i.e., esthesioneuroblastoma and dural metastasis) tumors. We will discuss role of high-flow carotid artery bypass, preoperative tumor embolization, and skull base reconstruction.
Major controversies in decision making addressed in this chapter include:
The management of incidentally diagnosed tumors.
Evolving management paradigm for aggressive skull base tumors.
Role of preoperative embolization in vascular skull base tumors.
Indications of cerebral revascularization in surgical management of aggressive skull base tumors.
Skull base reconstruction after surgical resection.
Whether to Treat
Treatment algorithm for skull base vascular tumors is primarily driven by their symptomatology ( 1 in algorithm ). The majority of clinically symptomatic skull base vascular tumors will require treatment with either surgery or radiotherapy (RT) depending on the patient′s age, functional status, preference, and the site and size of the tumor ( 2 in algorithm ). Patients planned for surgical resection might require preoperative embolization, simultaneous cerebrovascular bypass, or adjuvant chemotherapy/RT depending on histological diagnosis, staging of disease process, and aggressivity of surgical resection ( 4 in algorithm ). On the contrary, only a fraction of asymptomatic/incidental lesions will require treatment ( 3 in algorithm ). These are identified by the patient′s age, the site and size of the lesion, suspicious radiological findings for malignancy, close proximity to vital neurovascular structures with impending involvement, and patient preference ( 5, 6 in algorithm ). For instance, a small cavernous sinus lesion with atypical radiological features in a young patient is likely to be treated earlier than a corresponding larger lateral sphenoid wing lesion with typical benign imaging features in an elderly patient ( 3 in algorithm ).
Conservative Management
Conservative management is typically advocated for incidental, presumably benign appearing, small skull base lesions located at distance from vital neurovascular structures in middle aged or elderly patients ( 5 in algorithm ). Serial imaging and observation are used to assess tumor growth potential and natural history of these lesions. The initial follow-up serial image (usually magnetic resonance imaging [MRI] with and without gadolinium contrast) is performed at 3 to 4 months to rule out a fast-growing lesion. If the lesion shows no growth, then a 1-year follow-up image is planned. A growing lesion in a short interval is an indication for treatment. Using these findings, a case-by-case decision is made in consultation with the individual patient who has been advised of the pros and cons of available options ( 5 in algorithm ).
Anatomical Considerations
Meningioma is the most common primary intracranial extra-axial dural-based hypervascular skull base tumor. These lesions arise from remnant arachnoid cap cells along the inner surface of the skull base dura mater. These tumors derive blood supply from dural arterial feeders from both the internal carotid artery (ICA) and the external carotid artery (▶ Fig. 69.1 ). Invasive meningiomas also derive blood supply from the pial vessels (▶ Fig. 69.2 ). They can arise from any part of skull base and are named accordingly.
HPCs are rare, aggressive, mesenchymal, nonmeningothelial dural-based tumors arising from Zimmermann pericytes, which are contractile, spindle cells surrounding the capillaries and postcapillary venules. They comprise < 1% of all intracranial tumors and ~2 to 4% of all dural-based lesions. A majority are present as solitary supratentorial dural-based lesions (62%) in falcine and parasagittal regions.
Skull base or CSH is a rare (2–3% of all cavernous lesions) primary intracavernous, extra-axial neoplastic lesion that is highly vascular, benign, and well encapsulated and contains slow-flowing or stagnant blood. These tumors can extend medially into the sella or into contralateral cavernous sinus, superiorly into the suprasellar space, anteriorly into the orbital apex, and laterally into the temporal fossa.
Paraganglioma (previously called chemodectoma, glomus tumor, and nonchromaffin tumor) is a highly vascularized, histopathologically benign but locally aggressive tumor with possible invasion of bone, dura mater, vessels, and cranial nerves. The temporal bone, middle ear, jugular foramen, hypoglossal canal, and clivus are commonly involved. Less commonly, these lesions can extend to the cavernous sinus or sella or even metastasize to the lung or gastrointestinal tract.
JNA is a highly vascular, slow growing, locally aggressive, vasoformative, and benign neoplasm commonly seen in adolescent males. In these patients, tumor originates from the superior margin of the sphenopalatine foramen. Recognizing its point of origin and understanding the pattern of spread is relevant in surgical planning for these lesions. JNAs can extend laterally into the infratemporal fossa, posterosuperiorly into the inferior/superior oblique fissure, or inferiorly into the nasal cavity.
Esthesioneuroblastoma (or olfactory neuroblastoma) is a malignant tumor of neuroectodermal origin that presumably arises from the mitotically active basal layer of the olfactory epithelium. Tumor can extend to the skull base, paranasal sinuses, and orbits. Esthesioneuroblastoma is a rare sinonasal neoplasm with a bimodal age distribution. It comprises about 2 to 3% of all intranasal neoplasms across all age groups.
The incidence of skull base dural metastasis is 18/100,000 persons/year. It occurs in approximately 4% of all cancer patients. The most common sources of metastasis are breast, lung, renal, or prostate cancers. The anterior cranial fossa is most commonly affected (51.8%), followed by the middle cranial fossa.
Pathophysiology/Classification
Skull base tumors are broadly classified into two categories—benign and malignant. The World Health Organization (WHO) has classified meningioma into grade I (benign, 90%), II (atypical, 5%), and III (malignant, 5%), based on cell density, nuclear cytoplasmic ratio, growth pattern, proliferation rate, evidence of necrosis, and presence of brain invasion. Histologically, HPCs have spindle cells with a rich vascular network with dilated vascular “staghorn” channels. Similar to meningioma, HPC is classified by WHO into grade II/III depending on the presence of atypical or malignant features histologically.
Other commonly encountered benign lesions include CSH, paraganglioma, and JNA. Pathologically, CSHs are divided into sponge-like and mulberry-like types based on gross impression. Histologically, they have irregularly sized vessel cavities or dilated sinusoidal vascular spaces covered by a single layer of intima without neural tissue around intima. Paraganglioma has three types that involve the skull base: glomus jugulare, vagale, and tympanicum. They are supplied by arterial feeders from ascending pharyngeal, thyrocervical trunk, middle meningeal, and occipital arteries. ICA feeders also supply larger and intracranial tumors. Histologically, they have characteristic polygonal cells arranged in distinctive cell balls, called Zellballen. Paragangliomas are classified according to the Fisch′s classification system, based on the pattern and extent of tumor spread. With respect to JNA, Chmielik et al proposed a theory for the etiopathogenesis, which states that JNA is an angioma with fibrous component and that activation of the hypothalamic–pituitary–gonadal axis participates in the onset and progression of disease. In current opinion, JNA is considered a developmental anomaly affecting the embryonic vascular network surrounding the sphenoid bone. On the basis of the extent of disease, both of the classification systems for JNA, presented by Radkowski et al and Andrews et al, are commonly acceptable.
Esthesioneuroblastoma and dural metastasis from systemic disease are malignant skull base vascular tumors. Kadish′s tumor staging for esthesioneuroblastoma is done based on the extent of disease process.
Workup
Clinical Evaluation
Meningioma is most prevalent in middle-aged females in their third or fourth decade of life. Meningiomas generally grow at a rate of 0.02 to 0.24 cm/year. Older patients with small (< 2.5 cm) calcified meningioma are less likely to demonstrate progression. Anosmia, visual disturbance, endocrine dysfunction, and proptosis are the most common clinical presentations for anterior and middle cranial fossa lesions. Raised intracranial pressure and cranial nerve deficits are more common for posterior cranial fossa lesions.
In contrast with meningiomas, HPCs have a male predominance (2:1) and their incidence peak is in the fourth to fifth decades of life. Clinical, radiological, and gross characteristics render them indistinguishable from meningioma; however, over the long term, the biological and clinical behaviors of HPCs differ from that of meningiomas.
Middle-aged women are most commonly affected in CSH. Headache and visual impairment are the most common modes of clinical presentation, followed by hypoesthesia of the face and diplopia.
Paraganglioma also has a strong female predominance (6:1). Pulsatile tinnitus and hearing loss is the most common symptom complex associated with paragangliomas. Lower cranial nerve paresis is also present in more aggressive variants.
JNA is typically silent for years before presenting in the second decade of life and most commonly in males with epistaxis, nasal obstruction, facial numbness, ear popping, sinusitis, cheek swelling, visual changes, and occasionally headaches. Up to one-third of patients have orbital involvement with proptosis. Although JNA is the most common benign tumor of the nasopharynx, it is still a rare, sporadic tumor (0.5% of all head and neck tumors).
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