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Middle Ear and Skull Base Glomus Tumors: Tympanic and Tympanojugular Paragangliomas

MARIO SANNA, GIUSEPPE DE DONATO, ALESSANDRA RUSSO, AND TAREK H. KHRAIS

Paragangliomas are tumors that originate from the paraganglion system, mainly from type I stem cells that originate from the neural crest and belong to the diffuse neuroendocrine system (DNES).^{1, 2} The term glomus tumor is a misnomer, and was given to these tumors when it was believed that they originate from specialized pericytes of blood vessels. However, because paraganglion cells originate from neural crests and are unrelated to arteriovenous malformations, this theory has now been shelved.³ The term chemodectoma may only be used for tumors originating from the carotid or aortic bodies, which act as chemoreceptors.⁴ Currently, paragangliomas are also labeled by their anatomical site of origin (e.g., carotid paraganglioma, vagal paraganglioma, tympanic paraganglioma, jugular paraganglioma, and so forth).⁵

■ Symptoms—Diagnosis^{6, 7}

Diagnosis of paragangliomas is frequently made clinically (history and otoscopic findings). In the majority of cases, primary symptoms are hearing loss (conductive, sensorineural, or mixed) and pulsatile tinnitus synchronous with pulse. The tumor can erode into the labyrinth, causing vertigo of peripheral origin, toward the jugular foramen, leading to deficits of one or more of the lower cranial nerves (IX–XI), or toward the occipital condyle, leading to hypoglossal nerve paralysis.

The tumor can also extend into the petrous apex, leading to paralysis of the abducent nerve and trigeminal neuralgia; it can invade the mastoid, resulting in facial nerve paralysis; or it can further extend into the external auditory canal (EAC). Tumors occupying the EAC can lead to serous or purulent otorrhea due to the irritation of skin and the retention of squamous and epithelial debris. In spite of the fact that paragangliomas are highly vascular tumors, hemorrhagic discharge rarely occurs.

On otoscopy, a retrotympanic pulsatile mass is usually seen in the inferior quadrant of the tympanic membrane (TM). The color of the mass is generally red or purplish red, but when the mass blocks the eustachian tube, causing middle ear effusion, a reddish blue color may be seen. When the tumor erodes through the canal floor or the TM, a polyp may be seen in the EAC.

■ Radiological Workup^{6, 7}

A complete radiological workup in the form of high-resolution computed tomography (HRCT) with bone windows, magnetic resonance imaging (MRI) with gadolinium, and angiography is required for the confirmation of the clinical diagnosis and for the accurate definition of tumor extension. Radiology aids in differentiating paragangliomas from the anatomical variants that have similar presentation, such as an aberrant carotid artery and high jugular bulb. In addition, cholesterol granuloma, facial nerve neurinoma, or meningioma extending into the middle ear can be excluded.

The tumor classification system based on location and extension seen on HRCT scans proposed by Fisch and Mattox8 is useful in deciding which surgical intervention is most appropriate.

Class A: According to Fisch’s classification of temporal bone paragangliomas, glomus tympanicum corresponds to class A tumors. This class includes very small tumors (limited to the promontory), together with the tumors filling the middle ear cleft completely. We have further subdivided these tumors depending upon the degree of visualization on otoscopic examination into classes A1 and A2. Class A1 tumors are completely visible on otoscopic examination, whereas otoscopy fails to reveal the entire tumor in A2. This classification helps in formulating a surgical plan. A simple transcanal tympanotomy provides adequate exposure for total tumor removal in class A1. The comparatively extensive class A2 tumors necessitate a wider exposure (see section: Surgery for Class A Paragangliomas).

Class B: These tumors are limited to the tympanomastoid compartment of the temporal bone. We have further subdivided this class in two subclasses: B1 and B2. Tumors confined to the tympanomastoid compartment belong in subclass B1, whereas tumors extending from the tympanomastoid compartment toward the hypotympanum belong in subclass B2. This subclassification implies a different surgical strategy (see section: Surgery for Class B Paragangliomas).

Class C: These tumors originate in the dome of the jugular bulb and involve the infralabyrinthine compartment. They may spread in the following directions: inferiorly along the internal jugular vein and cranial nerves IX to XII, superiorly toward the otic capsule and the internal auditory canal, posteriorly into the sigmoid sinus, anteriorly toward the ICA, medially involving the petrous apex and the cavernous sinus, and laterally filling the hypotympanum and middle ear. Class C tumors are further subdivided according to the level of erosion of the carotid canal. C1 tumors erode the carotid foramen without involvement of the carotid artery, C2 tumors erode the vertical carotid canal up to the carotid genu, C3 tumors involve the horizontal segment of the carotid, and C4 tumors reach the anterior foramen lacerum extending to the cavernous sinus.

Class D: Tumors with intracranial extension are included in this class. These tumors are further subdivided into two groups, depending on whether they have an intradural extension. De-1 tumors have an intracranial extradural extension less than 2 cm in diameter, De-2 tumors have an intracranial extradural extension more than 2 cm in diameter. Di-1 tumors have an intracranial intradural extension of less than 2 cm, and Di-2 tumors have an intracranial intradural extension of more than 2 cm.

■ Surgical Management

Surgical management of middle ear and skull base glomus tumors is a complex endeavor. Table 22–1 summarizes some guidelines in diagnosing and managing these tumors. Resection of class A and class B tumors is within the competence of most middle ear surgeons. In contrast, because of the complex extensions of class C and D tumors and the fact that they involve important structures like the jugular bulb, the carotid artery, and rarely the vertebral artery, management of these structures requires considerable experience and should be reserved only to specialized and highly skilled skull base surgeons.

■ Surgery for Class A Paragangliomas9, 10

Surgical Steps

Class A1 tumors affect mainly the mesotympanum and may involve the ossicular chain. A transcanal approach is performed as in stapes surgery. The tympanomeatal flap is elevated and reflected anteriorly. Tumor removal involves both bipolar coagulation and blunt dissection. With bipolar coagulation the tumor size is reduced; thereafter the coagulated part can be removed easily without bleeding (Fig. 22–1). When the stapes is involved, the incudostapedial joint is disarticulated before tumor removal.

Class A2 tumors require a conventional retroauricular incision. The superficial layer of the temporalis fascia is harvested as grafting material. The skin of the posterior EAC is elevated as Korner’s flap and reflected away from the operative field with a self-retaining mastoid retractor to adequately expose the EAC and TM. The remaining skin of the EAC is incised at the level of the osseocartilagenous junction, and the meatal skin is elevated from lateral to medial. Any bony prominence in the EAC is drilled away to visualize the fibrous annulus in its entirety. The fibrous annulus is separated from the underlying bone all around its circumference. The TM is separated from the handle of the malleus by incising the periosteum along the long axis of the manubrium using a Beaver knife. In the majority of class A cases a good plan of cleavage can be found between the TM and the tumor, enabling the preservation of the integrity of the TM. In the rare cases where the tumor infiltrates the TM, the part infiltrated should be sacrificed. The end result of the aforementioned steps is a free tympanomeatal flap, which includes a major part of the meatal skin, the fibrous tympanic annulus, and the entire TM (Fig. 22–2). This glove finger flap

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