Tympanic Tumor

Tympanic tumors arise from the glomus body of the promontory along Jacobson’s nerve. The tumor is confined entirely to the mesotympanum, and all of its borders can be seen with routine otoscopy. This small tumor could not arise from the jugular bulb, or it would extend beyond the inferior margins of the tympanic annulus. Although no additional studies are necessary to define the extent of the tumor, any vascular tumor of the middle ear must be differentiated from an aberrant carotid artery or a dehiscent jugular bulb. An aberrant carotid artery lies more anteriorly and is paler than the glomus tumor. The jugular bulb lies more posteriorly and is darker blue. If there is any question about the existence of either of these lesions, cranial computed tomography (CT) must be done to exclude them.

Tympanomastoid Tumor

Similar to tympanic tumors, tympanomastoid tumors arise from the glomus body on the promontory. It extends beyond the tympanic annulus, however, inferiorly or posteriorly. Because there is no way clinically to delineate the tumor’s extent, any patient with a tumor that extends beyond the tympanic annulus must have a thorough radiographic evaluation. The key feature of this tumor category is that studies show the lesion does not involve the jugular bulb itself. Tympanomastoid tumors may extend into the mastoid and into the retrofacial air cells.

Jugular Bulb Tumor

Jugular bulb tumors arise from the glomus body of the dome of the jugular bulb. Lesions may extend into the middle ear and into the bulb itself. This lesion is limited to involvement of the middle ear, mastoid, and jugular bulb. By definition, it does not extend onto the carotid artery or medially into the skull base or intracranially.

Carotid Artery Glomus Tumor

Carotid artery glomus tumors arise from the jugular bulb, but extend beyond the confines of the jugular bulb and vein and contact the carotid artery. Small tumors of this category may involve only the carotid artery at the skull base, whereas larger tumors may extend far medially, and may involve the horizontal portion of the internal carotid artery (ICA) and the petrous apex.

Transdural Tumor

Transdural tumors arise from the jugular bulb and extend not only to the ICA, but also through the jugular foramen intracranially.

Glomus Vagale Tumor

Glomus vagale tumors arise from the glomus body along the vagus nerve at the base of the skull. Because glomus vagale tumors do not begin within the temporal bone, they are often larger than glomus tumors of the temporal bone itself because they later produce symptoms of pulsatile tinnitus and hearing loss. Clinically, these lesions produce vocal cord paralysis before the onset of hearing loss or tinnitus or the appearance of a vascular middle ear mass. In contrast, glomus tumors of the temporal bone produce otologic symptoms before the onset of vocal cord paralysis.⁶

Jugular Foramen Schwannoma

Although schwannomas are the second most frequently occurring tumor of the jugular foramen, they still are extremely rare. They arise from the Schwann cells of CN IX, X, and XI. The most common cranial nerve to be affected is the vagus nerve.^7,8 The clinical distinction between glomus vagale tumors and vagale schwannomas is that glomus vagale tumors develop vocal cord paralysis early in their course.⁹

Presentation of a jugular foramen schwannoma depends on the growth pattern. Kaye and colleagues¹⁰ categorized three different patterns: A, B, and C. Type A tumors occur primarily in the posterior fossa. Type A tumors with intracranial extension may manifest with CN IX, X, or XI palsies. Similar to most cerebellopontine angle tumors, hearing loss or imbalance or both may be the only significant presenting symptoms. Type B tumors remain confined to the skull base with extension often into the clivus. Type C tumors begin in the jugular foramen and extend inferiorly into the neck. Type B and C tumors manifest more frequently with lower cranial neuropathies than type A tumors.¹⁰

Radiologic assessment is performed with magnetic resonance imaging (MRI) and CT. MRI of the jugular foramen schwannoma shows a smooth contoured mass isodense on T1-weighted images, high signal intensity is usually noted on T2-weighted images, and significant enhancement occurs on T1-weighted gadolinium scans. CT is helpful in differentiating schwannoma from glomus jugulare tumors. Schwannomas tend to produce smooth erosion of the jugular foramen. Glomus tumors tend to show an irregular bone margin at the jugular foramen. The third most common lesions in this area are meningiomas of the jugular foramen. These lesions may be difficult to distinguish from schwannomas preoperatively. An enhancing dural tail on MRI is helpful. They also tend to infiltrate the bone around the jugular foramen, rather than smoothly enlarge it.

Routine Hearing Tests

Air, bone, and speech audiometry are performed to assess the degree of conductive and sensorineural hearing impairments.

Cranial Computed Tomography

The mainstay of assessment of glomus tumors of the temporal bone is thin-section (1.5 mm thick) cranial CT using the bone algorithm. Tumors confined to the middle ear and mastoids are distinguished from tumors that involve the jugular bulb. Extensive lesions that extend onto or medial to the ICA and lesions that extend transdurally are also defined by this technique. In many cases, cranial CT is the only examination necessary for planning treatment. Because the jugular bulb is the major consideration in preoperative planning, cranial CT has supplanted retrograde jugular venography in assessing involvement of the jugular bulb.

Magnetic Resonance Imaging

Because bone involvement by tumor is not clearly shown on MRI, this technique provides only adjunctive information regarding the extent of tumor involvement. If the diagnosis is in question, MRI combined with CT provides exquisite preoperative guidance in the differential diagnosis of petrous apex lesions.¹¹ MRI can indicate occlusion of the jugular bulb and vein because the normal flow signals are altered. In intradural tumors, MRI can delineate more clearly the tumor-brain interface and the relationship of the lesion to the intradural structures. MRI must be interpreted cautiously because T1 images of glomus tumors may overestimate the degree of tumor involvement. Marrow-containing bone of the petrous apex is hyperintense and indistinguishable from enhancing tumor in the petrous apex. Magnetic resonance angiography and MR venography offer another diagnostic tool in evaluating glomus tumors. In their present form, however, MR angiography techniques cannot provide adequate imaging resolution to define feeding vessels to the tumor. CT angiography is another promising technology in evaluating vascular temporal bone lesions¹²; however, the role of these techniques in the preoperative assessment of glomus tumors has not been fully clarified.^13,14

Arteriography

Four-vessel angiography is necessary when cranial CT shows a glomus tumor involving the jugular bulb, carotid artery, or intradural structures. The principal indication for angiography is to assess the involvement of the ICA by tumor. In addition, this technique ensures preoperative identification of additional glomus lesions, if present. Although estimates vary, paragangliomas are multicentric in approximately 10% of nonfamilial cases and 33% of familial cases.

Brain Perfusion and Flow Studies

For tumors that abut the ICA, it is necessary to assess the adequacy of the cerebral cross-perfusion from the contralateral ICA. Cross-compression angiography, stump pressure measurements, and clinical evaluation during test occlusion of the involved carotid are basic guides to the risk of stroke in the event that the affected carotid artery must be sacrificed. Xenon blood flow and radioisotope studies offer much more precise quantification of the risk of stroke and the possible need for surgical replacement of the ICA.¹⁵ In certain cases with extensive invasion of the carotid artery and acceptable results on the perfusion studies of the contralateral artery, the involved carotid artery may be permanently occluded with a detachable balloon. We generally do not recommend carotid sacrifice. Despite excellent advances in diagnostic flow studies, an appreciable risk (about 5%) of stroke exists with carotid artery sacrifice even in cases with favorable functional and perfusion characteristics or test occlusion studies. If possible, repair or graft replacement of the carotid is recommended if the carotid is injured during tumor removal.

Embolization

Large glomus tumors may result in significant intraoperative blood loss. We have found that preoperative embolization of feeding vessels can significantly reduce such loss.¹⁶ The embolization is usually performed with polyvinyl alcohol (Ivalon) and is performed at the time of angiography 1 or 2 days before surgery. A longer interval between embolization and surgery may result in collateral blood flow to the tumor, which may paradoxically increase tumor perfusion and intraoperative blood loss.

Biopsy

Biopsy of vascular middle ear masses is not recommended. The clinical and radiographic appearance of glomus tumors is characteristic enough to permit definitive management without a tissue diagnosis. Efforts at obtaining a tissue diagnosis before completion of the radiologic evaluation can result in injury to an aberrant carotid artery or a high jugular bulb, and significant bleeding from the tumor itself.

Transcanal Approach

The transcanal approach is used for small glomus tympanicum tumors that are limited to the mesotympanum. Because the entire circumference of the tumor is visible within the middle ear, preoperative imaging studies are unnecessary. If there is any doubt of the possibility of an aberrant ICA, however, preoperative CT scanning should be obtained to exclude this possibility. The tympanomeatal flap is modified with the inferior incision extending more anteriorly so that the inferior aspect of the tympanic membrane can be elevated. The tumor is identified on the promontory (Fig. 46-1).

FIGURE 46-1 Transcanal exposure of glomus tympanicum tumor limited to promontory.

The inferior tympanic branch of the ascending pharyngeal artery supplies the glomus tympanicum tumor. The vessel may be controlled with bipolar cautery or a small piece of absorbable knitted fabric (Surgicel) to occlude the bony canaliculus from which the vessel arises. It is crucial to avoid unipolar cautery on the tympanic promontory because this may severely injure the cochlea.

The tumor is removed with cup forceps. The brisk bleeding from the distal end of the artery anterior to the stapes (near the cochleariform process) is difficult to control directly; however, it usually clots readily. Small pledgets of Surgicel assist in hemostasis; the tympanomeatal flap is replaced, and the ear canal is packed. No specific dressing is necessary, and the patient is ready for hospital discharge the following day. Accurate preoperative assessment is crucial for success with the transcanal approach for glomus tympanicum tumors. If the entire circumference of the lesion is not visible through the meatus, the hypotympanotomy or mastoid–extended facial recess approach should be considered.

Tumors with limited hypotympanic extension without posterior involvement on CT scan may be removed by a modified transcanal (hypotympanic) approach.¹⁷

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