19 Extracranial Lateral Cranial Base Vascular Tumor Surgery

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 classification¹⁵ is based on the extent of the tumor alone. The De La Cruz classification system¹⁶ makes a broad attempt to devise surgical approaches but lacks the description of finer details of tumor extension. The Ugo Fisch classification¹⁷ categorizes the tumor according to its extension and location based on the computed tomography (CT) examination. Modification of Fisch classification by Sanna et al¹⁸ 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 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).

Table 19.1 Modified Fisch classification system for temporal bone paragangliomas

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 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.

Related posts:

Bypass in the Treatment of Skull Base Tumors Endovascular Options to Treat Iatrogenic Vascular Injury and Tumor Involvement of the Skull Base Posterior Fossa During Open Skull Base Surgery Simulation and Training—Preparing for Vascular Injury Perforator Injury During Endoscopic Endonasal Skull Base Surgery Extracranial Anterior Cranial Base Surgery for Vascular Tumors

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