The chapter deals with the pathophysology, anatomy, diagnostic workup, and intraoperative management of the extracranial vascular lesions of the lateral skull base. It focuses on the preoperative assessment of these tumors particularly involving the petrous internal carotid artery and makes an effort in providing valuable inputs to the reader in this regard.
Key wordsVascular lesions of the head and neck – extracranial skull base vascular tumors – paragangliomas of the skull base
19 Extracranial Lateral Cranial Base Vascular Tumor Surgery
19.1 Key Learning Points
Vascular lesions of the skull base, both benign and malignant need a thorough preoperative evaluation and meticulous workup.
Paragangliomas are the most common extracranial skull base vascular tumors.
Preoperative and intraoperative management of the petrous internal carotid artery is crucial in surgical excision of these tumors.
A methodical classification of these tumors based on their extent and their relation to the adjacent anatomical structures is quintessential for surgical intervention of these tumors.
Vascular tumors of the lateral skull base practically are divided into benign and malignant vascular tumors. Benign tumors include the more common paragangliomas and less common hemangiomas occurring in and around the temporal bone. The malignant group of vascular tumors in these areas are further grouped according to their malignant potential. Kaposi’s sarcoma and hemangioendothelioma are of intermediate malignant potential, while angiosarcoma and hemangiopericytoma are more malignant variants. The paragangliomas (of the head and neck), the most common of vascular tumors involving the lateral skull base area, shall be discussed in greater detail than the other lesions mentioned above, which will be touched upon in brief.
19.3 Paragangliomas of the Head and Neck
Paragangliomas are predominantly nonsecreting tumors arising within the head and neck from aggregates of paraganglionic tissue, which are derivatives of the neural crest. The largest aggregation of this tissue in the head and neck is concentrated in the carotid body on the medial aspect of the carotid bifurcation. The remaining is within the confines of the temporal bone, approximately more than half of which is distributed in the adventitia of the jugular bulb, around the Jacobson’s nerve, within the inferior tympanic canaliculus and over the promontory. The rest of this tissue is spread along the course of the Arnold’s nerve and around the mastoid segment of the facial nerve on some occasions.
Clinically, head and neck paragangliomas are broadly classified as temporal bone paragangliomas and cervico-carotid paragangliomas. The former includes the tympanomastoid and the tympanojugular proper paragangliomas, the most common tumors of the middle ear and temporal bone, respectively. The cervico-carotid paragangliomas encompass carotid body paragangliomas and vagal paragangliomas. Paragangliomas of the head and neck make up about 3% of all paragangliomas occurring in the body with carotid body tumors accounting for 60% and their vagal counterpart less than 5% of them. 1 , 2 , 3 , 4 , 5 , 6 , 7 Paragangliomas have been reported to be both sporadic and familial and a germline defect in the succinate dehydrogenase complex has been implicated in a considerable proportion of these tumors. 8 , 9 , 10 Multicentricity has been reported to occur in about 5 to 20% of sporadic cases and as high as 80% in familial cases, with the most common being bilateral carotid body tumors followed by carotid and vagal paraganglioma. 8
Despite being very slow growing tumors, skull base paragangliomas are aggressive with propensity to invade adjacent critical neurovascular structures and their slow growth rate often makes these tumors virtually impossible to detect early in their course. However, tympanomastoid paragangliomas present at an early stage with hearing impairment and/or pulsatile tinnitus. Tympanojugular paragangliomas, on the other hand, are not detected until they attain considerable size and quite often follow the path of least resistance into the middle ear cleft and other compartments of the temporal bone through the air cell tracts to involve the mastoid and petrous bone and not uncommonly, the cervico-petrous internal carotid artery (ICA), internal jugular vein (IJV), and in later stages, extend intracranially. Intracranial invasion of the paraganglioma occurs through the medial wall of the jugular foramen and in time along the inferior petrosal sinus. The involvement of the lower cranial nerves usually occurs at a very late stage after the tumor invades the medial wall of the jugular foramen, which acts as a barrier between the two and it is not very uncommon to come across cases with extensive tumors without lower cranial nerve palsy. 2 , 4 , 11 , 12 , 13 , 14 Characteristic bone erosion from ischemic necrosis is often extensive and underestimated. The cancellous portions of the temporal bone are extensively infiltrated, but the dense lamellar bone of the labyrinth is more likely to be spared.
This chapter focusses on temporal bone paragangliomas (tympanomastoid and tympanojugular proper paragangliomas) in greater detail from a surgical perspective and the carotid body tumor and vagal paraganglioma to a brief extent.
Classification: Tympanojugular paragangliomas, understood as tympanojugular proper and tympanomastoid categories, have been subjected to classification systems by several authors for better characterization of these tumors. Nonetheless, most of these classifications lacked a comprehensive understanding of these tumors from the surgical management standpoint. Glasscock and Jackson’s classification 15 is based on the extent of the tumor alone. The De La Cruz classification system 16 makes a broad attempt to devise surgical approaches but lacks the description of finer details of tumor extension. The Ugo Fisch classification 17 categorizes the tumor according to its extension and location based on the computed tomography (CT) examination. Modification of Fisch classification by Sanna et al 18 provides further insight on temporal bone paragangliomas and allows precise surgical planning. Authors of this chapter adopt the modified Fisch classification system for all practical purposes.
Class A tumors are those which arise from the tympanic plexus over the promontory and are limited to the tympanic cavity without any extension into the hypotympanum. Modified Fisch classification further classifies these tumors into A1 and A2 based on their extent within the tympanic cavity. Class A1 tumors are small, well-defined tumors within the confinements of the mesotympanum, with all the tumor margins visible on otoscopy. Class A2 tumors are those which are confined to the tympanomastoid compartment of the temporal bone, completely involving the mesotympanum and the ossicles, and show a certain degree of extension beyond the tympanic annulus. The margins of A2 tumors are not entirely visible on otoscopy. Class A2 tumors may extend anteriorly into the eustachian tube or into the posterior mesotympanum and should always be thoroughly examined by imaging preoperatively considering the fact that their margins are obscured on otoscopy so as to differentiate them from tympanojugular proper tumors.
Class B tympanojugular paragangliomas limit themselves to the tympanomastoid compartment of the temporal bone, and do not breach the bony dome of the jugular bulb. They are categorized further by modified Fisch classification system into three types: Class B1 tumors are those which encroach the hypotympanum; Class B2 tumors involve the hypotympanum and the mastoid compartment of the temporal bone; Class B3 tympanomastoid paraganglioma is any tumor which involves the tympanomastoid compartment with erosion of the carotid canal. The more extensive B2 and B3 tumors show considerable encroachment into the external auditory canal and give a clinical picture of a polyp arising from the middle ear and taking a biopsy is never advised.
Class C tympanojugular paragangliomas are extensive tumors with involvement of the cervico-petrous ICA. This class of tumors arises from the paraganglionic tissue concentrated over the jugular bulb or within the inferior tympanic or mastoid canaliculi. Because of their location, this class of tumors poses a unique challenge in their management. Class C1 tumors destroy the anatomical integrity of the jugular bulb with limited involvement of the vertical portion of the carotid canal and rarely infiltrates the ICA. Class C2 tumors show a greater degree of destruction by invading the vertical portion of the carotid canal. Class C3 tumors invade the horizontal portion of the cervico-petrous carotid, and C4 paragangliomas reach up to the anterior foramen lacerum. All the class C tympanojugular paragangliomas, more so particularly C2 through C4, have the propensity of encasing the cervico-petrous carotid, a crucial aspect in surgical planning. Class C tumors also show varied degree of intracranial extension. The tympanojugular proper subset of paragangliomas spread to various adjacent compartments: intradural when the spread of the tumor is more medial; into the petrous compartment and the infratemporal fossa regions of the skull base when the tumor spread is anterior; into the upper cervical compartments along the course of the lower cranial nerves when they spread inferiorly; posteriorly along the sigmoid sinus and toward the occipital condyle and the vertebral artery when they spread posteroinferiorly. Class C tumors show varied degree of intracranial extension and are described accordingly along with Class D as described in the (▶ Table 19.1).
19.4 Tympanomastoid Paragangliomas
The tympanomastoid paragangliomas, which correspond to the Fisch type A and type B classification, are tumors arising within the tympanomastoid compartment; they are relatively less common when compared to their tympanojugular proper counterparts. These tumors present typically with conductive hearing loss due to disruption of the middle ear conductive mechanism and are accompanied by pulsatile tinnitus. Clinically, the otoscopic findings are a red retrotympanic mass which blanches on pneumatic otoscopy (Brown’s sign) at times, with perceivable pulsations. 19 , 20 , 21 , 22 Tympanomastoid paragangliomas are less aggressive than their counterparts arising within the jugular foramen. Seldomly, they present as a mass in the external auditory canal mimicking a polyp arising from the middle ear. Their extensions are often into the eustachian tube and though not common, direct involvement of the carotid can occur when the tumor extension is inferior toward the jugular bulb.
The tympanojugular proper paragangliomas, the class C tumors, present much later in their course, with the tumor having extended into the middle ear cleft after eroding the floor of the hypotympanum. Such clinical presentation in very advanced stages is attributed to their site of origin. They most commonly present with hearing impairment which is conductive type due to impingement of the tumor on the middle ear ossicles and with pulsatile tinnitus. 6 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 Though not very common, sensorineural type of hearing loss and vestibular symptoms depend on the extension of the tumor into the inner ear, internal auditory meatus, and the cerebellopontine angle. Lower cranial neuropathies develop very late in the course of the disease, as the extremely slow growth rate of the tumor allows progressive compensation, but when manifested denote the involvement of the medial wall of the jugular foramen, which essentially acts as an anatomical barrier between the tumor and these nerves. Glossopharyngeal and vagal palsies are more common followed by those of spinal accessory and the hypoglossal nerves and it is prudent to consider jugular foramen pathology when encountered with a compound lower cranial nerve palsy. 33 , 34 , 35 , 36 The facial nerve is by far the most common cranial nerve to be involved in extensive tympanojugular paragangliomas.
19.4.1 Preoperative Assessment
A comprehensive preoperative radiological assessment complemented with a well-planned surgery plays the most crucial role in effective management of these tumors. This includes high-resolution CT (HRCT) with reconstructions in the axial and coronal planes. In suspected cases with extension into the hypotympanum and in revision cases, T1- and T2-weighted images along with T1-weighted gadolinium-enhanced sequences with axial, coronal, and sagittal plane reconstruction are desired. Magnetic resonance angiography (MRA) and MR venography are additionally required to assess involvement of major vessels. 37 A thorough preoperative radiological evaluation not only gives insight of the extension and the size of the tumor, but also elucidates the intricacies of temporal bone invasion.
Class A tumors, as described earlier, arise from the tympanic plexus over the promontory and are limited to the tympanic cavity without any extension into the hypotympanum. Modified Fisch classification further classifies these tumors into A1 and A2 based on their extent within the tympanic cavity. Class A1 tumors are small, well-defined tumors confined to the mesotympanum, with all its margins visible on otoscopy. Class A2 tumors are those which are confined to the tympanomastoid compartment of the temporal bone, completely involving the mesotympanum, the ossicles, and show a certain degree of extension beyond the tympanic annulus; thus, the margins of the tumor not entirely visible on otoscopy. Class A2 tumors may extend anteriorly into the eustachian tube or into the posterior mesotympanum. These tumors should always be thoroughly examined by imaging preoperatively considering the fact that their margins are obscured on otoscopy so as to differentiate them from glomus jugulare tumors. Class A tumors on HRCT typically appear as small masses over the promontory without significant extension into the hypotympanum.
Class B tumors are those set of tumors which limit themselves to the confines of tympanomastoid compartment of temporal bone, but essentially do not breach the bony dome of the jugular bulb. They are categorized further by modified Fisch classification system into three types: Class B1 tumors are those which encroach upon the hypotympanum. Class B2 tumors involve the hypotympanum and the mastoid compartment of the temporal bone. Class B3 is any tumor involving the tympanomastoid compartment with erosion of the carotid canal. The more extensive B2 and B3 tumors show considerable extension into the external auditory canal and give a clinical picture of a polyp arising from the middle ear and any attempt of biopsy is not advised. 38 HRCT confirms the findings of the tumor extension and no other imaging is mandatory once the integrity of the bone over the jugular bulb is confirmed. Nevertheless, it is essential to assess the extension of the tumor within the confinements of the temporal bone. Magnetic resonance imaging (MRI) differentiates the tumor from the middle ear effusions.
The degree of bone extension is crucial, particularly around the vital structures like the facial nerve, and oval and round windows. The degree of involvement is sometimes difficult to assess on HRCT; in a poorly pneumatized temporal bone with disease extending into its petrous apex, these areas of the skull base are often filled with marrow. MRI in such cases offers information regarding the bone marrow spaces in these areas and is very helpful in differentiating tumor from middle ear and mastoid effusions. Angiography is required for revision surgeries and extensive cases of class B tumors, B3 in particular which erode the carotid canal. In cases with suspected involvement of the sigmoid sinus, MR venogram offers vital information.
19.4.2 Surgical Approach
The management of the temporal bone paragangliomas continues to be a challenge despite several radiological and surgical advancements. Although paragangliomas are histologically benign, they are locally aggressive with extensive invasion of the bone and the soft tissue. With an initial innocuous growth pattern, their early diagnosis is often missed. The literature has rather little to offer regarding the fundamental aspects of these tumors such as their classification and protocols for surgical approaches. Thus, it really does not come as a surprise that the treatment of skull base paragangliomas in particular is yet to be standardized and there is still ambiguity on whether surgery, radiation, or simply observation is the best approach.
Nevertheless, surgical excision of the tumor offers a better treatment modality than radiotherapy. It is now well accepted that radiotherapy is not recommended at least for the cure of paragangliomas limited to the tympanomastoid compartment (classes A and B) but only in cases of recurrence and as a second option to the patient. 19 , 39 The selection of the optimal surgical approach mainly depends on the location, extension of the tumor, and the neurovascular structures involved by the tumor. The primary goals of surgery for class A and B tumors are complete disease clearance and hearing preservation. It was rather impractical in the past to achieve this twin objective and it was either a radical surgery for complete disease clearance or radiotherapy to preserve hearing, but with the latest advances in imaging and surgical equipment, it is now practically possible to preserve serviceable hearing while completely clearing the disease. It is now apparent, with substantial clinical evidence, that all tumors from classes A1 to B2 show good audiometric improvements in air conduction, the air-bone gap, and bone conduction postoperatively when a proper surgical technique is employed, the results which cannot be mimicked by radiotherapy. 40 Class B3 tumors, considering their extensiveness, require a more radical approach. This chapter unveils our perspective in managing these tumors from a surgical point of view.
19.4.3 Class A Tumors
Class A1 Tumors
For class A1 tumors which are very limited, with clear margins, and confined to the promontory, the approach is ideally transmeatal as for a stapes surgery. An aural speculum of optimal size is inserted into the external auditory canal and a tympanomeatal flap is raised as crafted for a stapes surgery. Canalplasty is done if deemed necessary. The tumor removal is essentially by coagulating its surface with bipolar electrocautery followed by blunt dissection using Surgicel (Johnson & Johnson, New Brunswick, NJ). The dissection ideally begins from the anterior margin of the tumor, away from more critical structures like the incudostapedial joint and round window area. It is recommended to flush the surgical field over the promontory periodically with cool saline to avoid thermal insult to the cochlea. The main feeding vessel of the tumor, the inferior tympanic artery from within the inferior tympanic canaliculus, is cauterized and the remaining tumor is dissected. The middle ear space is packed with Gelfoam (Pfizer, New York, NY) or with an adequately sized silastic sheet to prevent adhesions between the raw middle ear surface and the tympanic membrane.
Class A2 Tumors
For class A2 tumors, whose margins extend beyond the tympanic annulus, it is vital to preoperatively assess the inferior extent of the tumor in the hypotympanum radiologically and to be certain about the integrity of the dome of the jugular bulb, thereby ruling out the possibility of a tympanojugular paraganglioma. Of course, it is important to assess the integrity of other key middle ear structures like the facial nerve canal, petrous carotid canal, the ossicular chain, and the round window region. The approach for class A2 tumors is a retroauricular transmeatal approach (Fig. 19.1). Optimal field visualization mandates a wide canalplasty along with widening of the tympanic annulus. This is facilitated by elevating the tympanomeatal flap along with the tympanic membrane in a glove finger fashion. The ossicular chain is invariably involved in class A2 tumors; if it is not disrupted, salvaging the middle ear hearing mechanism becomes a priority. Extreme care is taken to dissect the tumor around the ossicles. Addressing the superior extent of the tumor warrants caution to watch for a dehiscence in the facial nerve canal. Class A2 tumors bleed considerably; hence, the dissection ideally begins from the anterior margins of the tumor as described for class A1 tumor. Cauterizing the main feeding vessel, the inferior tympanic artery at its canaliculus, reduces the bleeding from the remaining tumor which eases the dissection at the more critical regions. The superior limit of those tumors which extend into the epitympanum can be accessed with a transmeatal epitympanotomy. Efforts are directed to maintain the integrity of the ossicular chain but should it be disrupted owing to the disease, ossiculoplasty is done either as a part of the same procedure or in a staged manner.
19.4.4 Class B Tumors
Class B paragangliomas are extensive but are limited to the confines of the temporal bone. Approach to class B1 and B2 tumors is quite similar. They both require a retroauricular transcortical approach. These procedures are ideally individualized for each case based on the extent of the disease.
Class B1 Tumors
Class B1 tumors are those which involve the hypotympanum, the facial recess and the tympanic sinus. The initial steps are similar to those of any retroauricular approach. It is recommended to create large posteroinferiorly based and small anteriorly based soft tissue flaps over the mastoid region. The tympanomeatal flap is either elevated in a glove finger fashion or just as done for a routine middle ear surgery if the anterior extent of the disease in the tympanic cavity is limited. But it is not uncommon that some of these tumors show an outward growth into the external auditory canal involving the meatal skin, in which case, the tympanomeatal flap needs to be crafted accordingly. Canalplasty to the extent possible optimizes the transmeatal surgical field. Canal wall up mastoidectomy is performed. The amount of bleeding can be significant in these cases owing to the high vascularity of the tumor and impeded drainage of the mastoid air cells system due to the disease. For class B1 tumors, an extended posterior tympanotomy is performed to access the facial recess area and the hypotympanum. Combined transmeatal and transcortical access provides optimal control over the tumor aiding in its total resection. A transcortical epitympanotomy is performed as needed to clear the disease from the epitympanum. The middle ear conduction mechanism in these cases is compromised more often than not and the reconstruction of the ossicular chain is either done as part of the procedure or in a staged manner.
Class B2 Tumors
The initial surgical strategy for class B2 tumors is no different from the one which is employed for class B1 tumors. For class B2 tumors, which have significant extension into the mastoid cavity, it is ideal to expose all margins before the tumor resection begins. Class B2 tumors are any paraganglioma confined to the tympanomastoid compartment of the temporal bone without breach of the petrous carotid canal. The elements which dictate the later course of the surgery for this class of the tumors are the breach in the tegmen with intracranial extension of the tumor, erosion of the sigmoid sinus plate with its possible involvement, and intraoperative finding of involvement of the jugular bulb. The extended posterior tympanotomy along with transmeatal access gives good control of the tumors in the mastoid and hypotympanum. The tumor which is further inferior in the hypotympanum and the deep tympanic sinus are accessed by a subfacial tympanotomy. Drilling out the presigmoid and postsigmoid bone over the posterior fossa dura facilitates the collapse of the posterior fossa dura along with the sigmoid sinus, thus giving extra working space to accommodate the instrumentation to drill the bone medial to the mastoid segment of the facial nerve and above the jugular bulb. Extreme care has to be taken while drilling the bone around this area to avoid injury to the facial nerve and the jugular bulb. A thin layer of bone is always left out around the mastoid segment of the facial nerve, particularly on its medial side. Learning the involvement of the jugular bulb intraoperatively is always a challenging scenario. The resection around this area proceeds with caution. Finding the plane between the tumor and the jugular bulb holds the key. It is wise to abandon the procedure if the plane is not achievable and prepare for a more comprehensive infratemporal fossa approach later.
Class B3 Tumors
Class B3 tumors are differentiated from other tympanomastoid paragangliomas by their involvement of the carotid canal with or without involving the carotid artery. These tumors are extensive involving the external auditory meatus (Fig. 19.2a), mastoid cavity, facial recess, sinus tympani, eustachian tube, and hypotympanum. Tumors with such extensiveness derive their blood supply from a lot of feeding vessels and the possibility of torrential bleed intraoperatively from the tumor as well as the possibility of bleeding from the internal carotid and the jugular bulb are to be anticipated. The prospect of postoperative serviceable hearing in these cases is encouraging with intact preoperative bone conduction and every effort has to be made to preserve it. 41 Hence, an ideal approach would be a subtotal petrosectomy (Fig. 19.2b) aiming for a near-total disease clearance and a blind sac closure of the middle ear cleft. It does not require special mention that such large tumors often involve the facial nerve in which case, the nerve is transected for tumor access and a nerve grafting is done later. In cases where the facial nerve can be preserved despite the magnitude of the tumor, the nerve is anteriorly rerouted.
The initial steps of retroauricular soft tissue dissection, elevation of soft tissue flaps, and canal wall down mastoidectomy remain the same as executed for class B2 tumors. After transecting the meatal skin leaving a healthy margin from the tumor, the canal is closed in a blind sac fashion, which we usually prefer to execute at the beginning of the procedure. To achieve optimal exposure of the carotid for tumor resection and for gaining good control of the vessel in case of an injury, the tympanic bone is to be completely removed. Drilling the inferior portion of the tympanic bone exposes the vertical portion of the petrous carotid and removing the anterior wall of the tympanic bone gives unimpeded access to the horizontal segment of the carotid. After complete tumor resection, the rest of the procedure includes obliteration of the eustachian tube with pieces of periosteum and bone wax, obliteration of the cavity with the abdominal fat harvest, and closure of the wound in layers.
19.5 Tympanojugular Paragangliomas
Paragangliomas arising from the jugular foramen are more aggressive, in the sense that these tumors are often diagnosed very late in their course of evolution. Their slow growing nature often accommodates neural compensation of the lower cranial nerves, thereby going unnoticed. With the propensity of tumor spreading to various adjacent anatomical compartments, as described earlier, their surgical management depends on proper preoperative assessment of their extent, involvement of surrounding neurovascular architecture, and devising a surgical approach accordingly.
19.5.1 Preoperative Assessment
Tympanojugular paragangliomas (classes C3 and C4) invariably involve the ICA and the management of these tumors begins with a thorough preoperative radiological assessment of their size, their relation to the ICA and the surrounding other important vessels, and the extent of involvement of these vessels.
Indications for preoperative intervention for managing the ICA are based on tumor extension, related angiographic findings, and related patient characteristics:
The competency of the collateral circulation in maintaining the perfusion of the areas that would be affected by manipulation or sacrifice of the involved vessel. The investigations available to achieve this aim include four-vessel angiography with manual cross-compression test for functional evaluation of the circle of Willis, xenon-enhanced CT of cerebral blood flow, single photon emission computed tomography, and carotid stump pressure management.
The degree and extent to which the tumor has involved the ICA. The investigations available for this purpose include CT, MRI, MRA and digital subtraction angiography.
Circumferential encasement of the distal cervical and petrous segment of the internal carotid (vertical and horizontal) by more than 180 degrees as evident on CT and MRI in the axial planes.
Evidence of stenosis and irregularities of the arterial lumen on angiography of the distal cervical and the petrous carotid on angiography.
Extensive feeders to the tumor from the internal carotid as evident on angiography.
Classes C3 and C4 tympanojugular paragangliomas, vagal paragangliomas, and carotid body tumors.
Previous radiotherapy or manipulation of the internal carotid in a previous surgery.
The modalities available for managing the ICA preoperatively in these scenarios include permanent balloon occlusion (PBO), cervical-to-petrous ICA saphenous vein bypass grafting, and intravascular reinforcement with stenting.
The intraoperative management of the ICA is by: (a) decompression with or without partial mobilization of the artery, (b) subperiosteal dissection, (c) subadventitial dissection, (d) subadventitial dissection with stent coverage, and (e) arterial resection (after preoperative PBO).
19.5.2 Permanent Balloon Occlusion (PBO)
Pretherapeutic knowledge of carotid artery dependence is essential in patients undergoing ICA sacrifice as vascular bypass or alternative interventional approaches may be necessary in those unable to tolerate ICA sacrifice. PBO involves a preprocedure balloon occlusion test (BOT), an angiographic test to assess ischemic tolerance after permanent occlusion of the ICA by assessing if there is a good cross-filling from at least one of the two communicating systems and also to study the circle of Willis.
Angiography is performed in two phases:
To ascertain the patency of the anterior communicating system, the contralateral ICA is injected and the diseased carotid is manually compressed (Mata’s test). Rapid and complete filling of the anterior and middle cerebral arteries indicate a patent anterior communicating system.
Assessment of the posterior communicating system involves injecting the dominant vertebral artery while the ipsilateral common carotid artery is compressed (Allcock’s test). Rapid and complete filling of the middle cerebral artery on the compressed side indicates a competent posterior communicating system.
BOT and PBO are performed under local anesthesia with mild sedation and systemic heparinization with anesthesiologist monitoring. Three balloons are usually placed, first one at the cavernous segment just proximal to the origin of the ophthalmic artery, the second in the petrous segment of the vessel at the level of the carotid canal, and the third in the cervical segment of the internal carotid just distal to the bifurcation of the common carotid. The angiographic studies during the Matas and Allcock maneuvers are evaluated for visualization of the anterior cerebral artery and middle cerebral artery on the tested side. The angiographic anatomy of the circle of Willis is studied according to the presence or absence of an anterior communication between the two ICAs via anterior communicating artery and the posterior communication of the tested ICA with the basilar artery system via posterior communicating artery. The neurological evaluation and electroencephalography (EEG) monitoring are carried out to detect ischemia during the procedure. Any signs suggesting intolerance to the procedure, which is quite apparent immediately after the occlusion, warrants deflation of the balloon and abandoning the procedure followed by planning for an alternative procedure. 42 After a successful PBO, the tumor resection is planned 3 to 4 weeks later.
19.5.3 Intraluminal Stenting of the Internal Carotid Artery
The intra-luminal reinforcement of the cervico-petrous carotid (Fig. 19.3) is done when the tumor extent is significant and significant manipulation of the vessel intraoperatively is anticipated. 43 , 44 , 45 , 46 The number of stents required is based on the length of the vessel segment to be stented and the technical features of the stent. Occasionally two or even three stents are used. Ideally about 10 mm of tumor-free portion of the vessel is advised to be stented both proximal and distal to the limit of the tumor to avoid the possibility of accidental injury of ICA at the vessel–tumor interface and facilitate a radical tumor excision. The nature of the stent used for reinforcement is based on diameter (ideally 4 or 5 mm), length, flexibility (during endovascular deployment and positioning especially at the posterior loop of the ICA), and resilience of the stent to withstand manipulation during the surgery. 47 , 48 Occasionally, stenting is not technically possible when the ICA is significantly tortuous, in which case an alternative procedure is employed. A variety of intraluminal self-expanding nitinol stents are available which include Xpert Stent System (Abbott Laboratories Vascular Enterprises, Dublin, Ireland) and Astron (Biotronik SE, Berlin, Germany).
19.5.4 Facial and Hearing Rehabilitation
Facial and hearing rehabilitation is an integral part of the management of tympanojugular paragangliomas. In facial paralysis of less than 1-year duration, efforts are made to salvage the nerve intraoperatively. However, should the nerve be resected due to tumor infiltration, a sural nerve cable grafting is performed in such cases in the same sitting. Facial nerve palsy of greater than 1-year duration is ideally rehabilitated by reanimation procedures which include ipsilateral eyelid implant and facial–hypoglossal or facial–trigeminal nerve anastomosis. Hearing rehabilitation is best done by using a bone anchored hearing implant (BAHI). We routinely perform a simultaneous ipsilateral BAHI procedure along with facial nerve rehabilitation procedures as a part of the surgical treatment.
19.5.5 Surgical Approach
Class C tympanojugular paragangliomas, as described earlier, essentially arise from the jugular foramen area and hence are considered as tympanojugular proper paragangliomas. These tumors present very late in their course of evolution with significant extensions into the surrounding anatomical compartments of the skull base: medially to become intracranial or intradural, anteriorly into the infratemporal fossa and to the petrous compartment of the temporal bone, posteriorly into the sigmoid sinus, posteroinferiorly to involve the occipital condyle and the vertebral artery, and inferiorly into the upper cervical spaces. Class C tumors often present with varied degree of intracranial involvement with or without intradural involvement. The fundamental surgical principle of management of class C tumors is gaining access to the jugular foramen portion of the skull base. Despite the latest advances in preoperative imaging and in surgical equipment, these procedures are fraught with complications and anticipating them and managing these complications postoperatively are an integral part of the treatment of these difficult lesions.
Adequate exposure of the jugular foramen while minimizing associated morbidity with adequate proximal and distal exposure of the major vessels are the basic principles to be followed while operating in this region. The major impediments in achieving these objectives are management of the facial neve and salvaging the middle ear. Transposition with rerouting of the facial nerve gives uncompromised access to the petrous segment of the internal carotid, which invariably shows a certain degree of tumor encasement in all class C tumors.
Given the vascular nature of the tumor, its presentation in a very advanced stage, and its propensity to involve complicated anatomical domains in the vicinity of its origin, a wide and uncompromising exposure of the tumor is required, which optimally can be achieved by the infratemporal fossa approach type A (ITFA-A) allowing a safe and yet radical surgery. Although the ITFA-A is associated with a certain degree of morbidity, namely, conductive hearing loss, facial nerve dysfunction, and short-term masticatory difficulties, it nevertheless provides uncompromised access to the infralabyrinthine compartment, the jugular foramen and jugular bulb area, the cervico-petrous segment of the ICA, the upper cervical carotid artery, and poststyloid parapharyngeal spaces. Primarily designed for large extradural lesions of these areas, the ITFA-A can be utilized in combination with other skull base approaches. 49 , 50 , 51
Several arguments against ITFA-A for these tumors do exist. Hypotympanic access to the jugular foramen area by partial petrosectomy and infralabyrinthectomy without facial nerve rerouting for limited C1 tumors is achievable, but only at the expense of limited carotid exposure and compromised control of the proximal and distal jugulosigmoid system.
Infratemporal Fossa Approach Type A
The ITFA-A has been a workhorse in surgical management of tympanojugular paragangliomas since it was described by Fisch and Pillsbury in 1979. 52 This is an extralabyrinthine approach passing below the otic capsule and is mainly designed for extensive extradural lesions involving the jugular foramen area, infralabyrinthine, and apical compartments of the petrous bone with anterior rerouting of the facial nerve as its key feature. Primarily designed as a cranio-temporo-cervical approach, gaining a wide access to the jugular bulb, jugular foramen, and the petrous apex of the temporal bone along with the mandibular fossa and posterior portion of the infratemporal fossa is the prime objective of ITFA-A.
A wide postaural cranio-temporo-cervical incision is applied that extends down to the neck. An anteriorly based subcutaneous flap is crafted followed by an inferiorly based musculoperiosteal flap. The inferiorly based musculoperiosteal flap is elevated in continuum with the sternocleidomastoid muscle up to splenius capitis. A posterior meatotomy is done and the external auditory meatal skin is transected. The meatal skin cuff is dissected and elevated from the surrounding tissue and delivered externally with the help of tissue hooks and sutured with an absorbable suture material. The conchal cartilage (within the pinna) and the tragal cartilage are released from their surrounding soft tissue and are sutured together creating a scaffold for blind sac closure to avoid iatrogenic fistula. The posterior belly of the digastric muscle is divided at its origin; the occipital artery encountered underneath the digastric is ligated. The glossopharyngeal nerve is identified traversing the ICA anteriorly. The vagus is identified coursing between the IJV and the ICA and the hypoglossal is seen crossing the ICA anteriorly toward the tongue. The spinal accessory nerve is identified lateral to the IJV (in majority of cases) and passing anterolateral to the transverse process of C1 vertebra. The condylar emissary vein which lies in close proximity to the CN XI is cauterized when needed. The great vessels are marked with vessel loops. The dissection so far exposes the lateral surface of the temporal bone from the root of zygoma anteriorly to the occipito-mastoid synchondrosis posteriorly along with its squamous and tympanic parts.
After cortical mastoidectomy, the canal wall down mastoidectomy is then performed; the tip of the mastoid is removed taking care to leave behind a cuff of soft tissue around the facial nerve at the stylomastoid foramen area. The tympanic bone is drilled and removed in toto. A neo bony canal is created at the root of the zygoma; the facial nerve is decompressed from the geniculate ganglion up to the stylomastoid foramen releasing the nerve from the fallopian canal. The dissection of the facial nerve (in its extra-tympanic segment) is carried within the parotid, thereby creating a soft tissue tunnel, which reduces the stretch injury of the nerve after its rerouting. The nerve is then positioned in the neo canal and secured with tissue glue. Now that the tympanic bone is excised and the facial nerve rerouted anteriorly, the jugular foramen is freely accessed after completion of subtotal petrosectomy. The sigmoid sinus is skeletonized and decompressed leaving behind a ledge of bone at its superior aspect under which Surgicel is packed, thereby compressing it extraluminally. Further compression is achieved by intraluminal packing of the sinus with Surgicel, completely ceasing the venous backflow from the transverse and the sigmoid sinuses.
After clipping the IJV in the neck with multiple Ligaclips (Johnson & Johnson, New Brunswick, NJ), the ligated portion of the IJV is then reflected superiorly. The lower cranial nerves are preserved by sparing the medial wall of the bulb and the upper portion of the IJV. Addressing the intradural extension of the tumors requires a thorough preoperative evaluation and needs to be done only after identifying and separating the anterior inferior cerebellar and anterior-inferior and posterior-inferior cerebellar arteries. The intradural component of the tumor is dealt with either in continuum with the extradural tumor resection or executed in a staged manner.